# Finding a Good Coupler



## sifawangiaEV (Jan 1, 2021)

Hi everyone,

I'm in the process of choosing a coupler to mate my Warp9 DC motor with my Mini Cooper manual transmission and I've come across a couple of options. I'm browsing grainger.com and their Rigid Couplers here and I've come across a few coupling types that I think will work for my conversion. Here are the different types (on the grainger.com website):








I've heard that these types of couplings have been successful in EV conversions so I thought I might give one a try. I'm leaning towards using either the 1-piece clamp rigid shaft coupling with a 1.125 inch bore diameter:








Link (https://www.grainger.com/product/RULAND-MANUFACTURING-Rigid-Shaft-Coupling-1-1-8-2ALJ3?Pid=search)

Or using the 1-piece set screw rigid shaft coupling with a 1.125 inch bore diameter:








Link (Rigid Shaft Coupling: 1 1/8 in Bore Dia., Steel, 1 7/8 in Outside Dia.)

Are their any benefits/drawbacks to using one coupling over the other? I'm thinking of having a machine shop cut and weld my clutch plate onto the transmission side of the coupling. What does everyone think of this? What coupling do you recommend?


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## 57Chevy (Jan 31, 2020)

if you make it rigid then your alignment needs to be absolutely perfect and you need to 'clock' the shafts to each other first by putting a DTI on one shaft and rotating it around the other in several places to ensure it is both parallel and concentric. This is not an easy task if your coupling lives hidden inside a bellhousing and even harder if you don't have a shimming/adjustment system. The jaw couplings allow easy assembly plus have a stated acceptable misalignment amount. Any misalignment in the shaft that is forced into alignment by tightening a rigid coupling will cause extra stresses and lead to something failing.


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## sifawangiaEV (Jan 1, 2021)

57Chevy said:


> if you make it rigid then your alignment needs to be absolutely perfect and you need to 'clock' the shafts to each other first by putting a DTI on one shaft and rotating it around the other in several places to ensure it is both parallel and concentric. This is not an easy task if your coupling lives hidden inside a bellhousing and even harder if you don't have a shimming/adjustment system. The jaw couplings allow easy assembly plus have a stated acceptable misalignment amount. Any misalignment in the shaft that is forced into alignment by tightening a rigid coupling will cause extra stresses and lead to something failing.


What kind of coupler would you recommend?


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## 57Chevy (Jan 31, 2020)

I already sent you a link on the other thread


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## sifawangiaEV (Jan 1, 2021)

57Chevy said:


> I already sent you a link on the other thread


Yeah I commented on it but Pete didn't seem to think it would be reliable. Are you using it in your conversion? If so, how did it turn out?


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## 57Chevy (Jan 31, 2020)

I'm using direct drive so no. I have used couplings on large engine driven gas compressors and have seen a variety of failure modes due to the things I have tried to outline. Whatever coupling you choose will work as it was intended, if you use it as it was intended. If your guy just has a hunch that it won't work then ask him for evidence/why. Often people can't explain their 'engineering' assessments, sometimes they can and you learn something


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## sifawangiaEV (Jan 1, 2021)

Ok, I think I'll give it a shot based on what you've told me.








I will be purchasing the coupling that is specified in these stats (link) with a 1-1/8" bore diameter. Will I need to purchase two steel hubs to make a complete set (versus one) as well as the spider and the steel spider cover, totaling out to: 2(61.13) + 25.58 + 38.45 = $186.29?


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## sifawangiaEV (Jan 1, 2021)

I'm pretty set on buying this part but I would like if anyone could approve or disapprove buying this part so I could feel more confident of my purchase if you know what I mean


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## brian_ (Feb 7, 2017)

57Chevy said:


> if you make it rigid then your alignment needs to be absolutely perfect and you need to 'clock' the shafts to each other first by putting a DTI on one shaft and rotating it around the other in several places to ensure it is both parallel and concentric. This is not an easy task if your coupling lives hidden inside a bellhousing and even harder if you don't have a shimming/adjustment system.


As soon as you release the clutch pedal, a traditional clutch setup is also a rigid coupling. The alignment of the coupler is reset every time you push and release the pedal, and that's okay because the engine and transmission are properly aligned, and in a traditional setup the short transmission input shaft is supported and aligned on the engine end by a pilot bushing or bearing.


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## 57Chevy (Jan 31, 2020)

brian_ said:


> As soon as you release the clutch pedal, a traditional clutch setup is also a rigid coupling. The alignment of the coupler is reset every time you push and release the pedal, and that's okay because the engine and transmission are properly aligned, and in a traditional setup the short transmission input shaft is supported and aligned on the engine end by a pilot bushing or bearing.


Ah, didn't realise he was using a clutch too so yea, those little metal tabs on the periphery of the disc inside of the lining are the flexible coupling. In fact having a flex coupling and a disc would not be a good idea. Otoh, two separate items with average alignment ability joined by a rigid coupling ends in damage eventually.


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## sifawangiaEV (Jan 1, 2021)

57Chevy said:


> Ah, didn't realise he was using a clutch too so yea, those little metal tabs on the periphery of the disc inside of the lining are the flexible coupling. In fact having a flex coupling and a disc would not be a good idea. Otoh, two separate items with average alignment ability joined by a rigid coupling ends in damage eventually.





brian_ said:


> As soon as you release the clutch pedal, a traditional clutch setup is also a rigid coupling. The alignment of the coupler is reset every time you push and release the pedal, and that's okay because the engine and transmission are properly aligned, and in a traditional setup the short transmission input shaft is supported and aligned on the engine end by a pilot bushing or bearing.


Sorry if I didn't make this clear before but I'm going clutchless so I won't be using my clutch pedal or a clutch at all. I just want to connect the motor shaft to the transmission shaft with a coupling. Would the McMaster Carr coupling work fine for this application?


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## 57Chevy (Jan 31, 2020)

It is your project, ultimately you have to make the decision, otherwise you are outsourcing it to randoms on the internet. 

What are you using on the spline, are you going to weld the centre of a clutch onto a coupling or how are you doing that part? A solid coupling will be preferred but only if the shafts are in good alignment. Any misalignment in the housing that results in stressed applied to the shaft as it tries to rotate where it wants to go will end up breaking something eventually. Use a solid coupling but also know that it is suitable for a solid first.

This is why an automatic transmission uses a flex plate and why a manual trans uses a flex coupling in the friction disc. These are done by design for a very good reason- automotive parts aren't good enough tolerance in the worst case situation out of the factory to reliably use a solid coupling. Solution: chuck a flex in.


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## brian_ (Feb 7, 2017)

57Chevy said:


> Ah, didn't realise he was using a clutch too so yea, those little metal tabs on the periphery of the disc inside of the lining are the flexible coupling. In fact having a flex coupling and a disc would not be a good idea. Otoh, two separate items with average alignment ability joined by a rigid coupling ends in damage eventually.


Sorry that wasn't clear, I didn't mean that there's a clutch in the proposed coupling, only that a clutch obviously works and isn't compliant. Yes, the springs in the clutch disk allow torsional compliance, but shouldn't allow radial or angular compliance.

But speaking of how things move...
just as with a normal clutch setup, something needs to have a sliding fit and remain free to float axially to make assembly practical. That's normally a splined connection, and the transmission has a male splined shaft, so the coupler rationally should be clamped to the motor shaft and have a matching female spline to slip over the transmission input shaft, with a pilot bore for the transmission shaft end if that's what the original transmission installation does.


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## brian_ (Feb 7, 2017)

57Chevy said:


> This is why an automatic transmission uses a flex plate and why a manual trans uses a flex coupling in the friction disc. These are done by design for a very good reason- automotive parts aren't good enough tolerance in the worst case situation out of the factory to reliably use a solid coupling. Solution: chuck a flex in.


But every production EV in which the motor shaft is not also the transmission input shaft couples the motor to the transmission input (which is exactly what we're talking about here) with a splined shaft connection and nothing flexible.


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## 57Chevy (Jan 31, 2020)

brian_ said:


> But every production EV in which the motor shaft is not also the transmission input shaft couples the motor to the transmission input (which is exactly what we're talking about here) with a splined shaft connection and nothing flexible.


I don't know what the tolerance specs for an EV are but if that is their approach then I'd wager a buck that they don't use the same fit and tolerance bands as an ICE. Just don't assume that a DIY EV with unknown alignment has the same degree of accuracy as an EV OEM. 

Given that the input is splined, it kind of rules out a jaw coupling anyway. A solid coupling with a female spline and a mount that has known and predictable alignment would be the best situation. Just don't chuck one in, hope that it will be fine, and then be upset later when it fails


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## KiwiME (Apr 8, 2016)

brian_ said:


> But every production EV in which the motor shaft is not also the transmission input shaft couples the motor to the transmission input (which is exactly what we're talking about here) with a splined shaft connection and nothing flexible.


That's true for the Leaf and the legacy Hyundai/Kia family comprising the Kona/Niro/Soul and classic Ioniq. The splined coupling with adjacent radial locating diameter and closely-located bearings each side is clearly an over-constrained design but Nissan seems to have gotten away with it, presumably by precise production machining methods.

Hyundai/Kia on the other hand did not and there have been quite a few issues surrounding the spline, starting with a knocking noise. In many cases only the gearbox or motor are replaced under warranty and the noise returns. It seems that most successful fixes involve replacing both. This has been ongoing for 3 years now and they seem to be slowly addressing the problem. The motor costs around US$6.5k and the gearbox US$1.5k. I have a Kona from 2018 and am lucky, it's quiet.

The new E-GMP platform seems to have moved to the design tactic adopted by Tesla and no-doubt others where the spline provides support for one end of the pinion shaft, so three bearings in total across the motor and gearbox. The Bolt is even more simple, the pinion gear is simply cantilevered off the motor output shaft. This is not a mistake GM's experienced powertrain engineers would make and the entire gearbox design shows good attention to detail. The legacy H/K and Leaf to lesser extent look no more advanced than a 1950s BSA motorcycle.

Used oil analysis from Konas and Leafs show that the Kona has typically twice the contamination of the Leaf regarding iron and aluminium, and at half the distance driven.

It's fair to say that a gearbox to transfer case splined coupling on a typical 4x4 is not dissimilar in principle but generally one side will have a longer distance to the bearing such that a tiny amount of misalignment can be tolerated.

But there's another issue that legacy H/Kia seem to be weak on and that is draining shaft currents from the motor. There is a circular conductive brush at the motor output shaft but still the gear oil turns black in short order, under 10,000 km or miles. A small number of Ioniq and Kona owners have had unexplained bearing failures, tellingly one leaving no significant ferrous debris. The Leaf gearbox design uses a grounding brush assembly on the intermediate shaft but I'm not clear if there is also one on the motor output as well. Perhaps someone here can confirm that one way or the other? The problem I see with circular brushes is that a tiny amount of oil contamination can reduce the effectiveness. The Leaf's brush (pair) is contained in a dry, sealed cavity.








Note the shagged out spline on this example.









Kona/Niro gearbox showing proximity of pinion bearing to spline, upper-right.


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## taylor chamber (11 mo ago)

sifawangiaEV said:


> Ok, I think I'll give it a shot based on what you've told me.
> View attachment 127472
> 
> I will be purchasing the coupling that is specified in these stats (link) with a 1-1/8" bore diameter. Will I need to purchase two steel hubs to make a complete set (versus one) as well as the spider and the steel spider cover, totaling out to: 2(61.13) + 25.58 + 38.45 = $186.29?
> View attachment 127472


Thanks for your nice informative and necessary post.


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## sifawangiaEV (Jan 1, 2021)

Sorry everyone if I've been all over the place but I've decided to go with a rigid coupling because it would be the longest lasting for my conversion and I'm willing to do the extra tough work to make it work. I just dropped it off at the machine shop with my clutch plate to be welded together, when I realized something not so good...the torque of the rigid coupling wasn't as high as I thought it was. Here's the spec sheet:








I could've sworn that when I bought the item, it said that it had a torque rating of 2,400 in-lb. I'm thinking there might be a glitch on the website but I'm not certain because there is a chance that I somehow read it wrong. What do you all think? Does this rating look right for this coupling or does it seem like a glitch? Should I be considering a new coupling?


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## KiwiME (Apr 8, 2016)

I'll stick my nose in because this sort of thing was within my profession before I retired. Assuming the Mini gearbox has a conventional input shaft the first issue is that the pilot end of the input shaft _must_ be supported just like it had been by the crankshaft. Gearboxes normally rely on this, that's why they appear somewhat loose when you wiggle the input shaft on the bench. 

Then you have to transfer the torque off the keyed motor shaft to the spline without loading the spline unevenly. You rely on the involute teeth under torque for alignment.
A normal clutch disk of course is rattle-loose in the middle so that can happen freely (and cheaply).

A huge problem with a keyway-type coupling half is that the constant back and forth torque can shag out the key if the coupling is "hard", but allowing slight rotational flex will help that, which is what the rubber does, another requirement to add to the list. The clamp style coupling half (as used in the type you've identified) can help or at least delay the issue. But a far better design is what's called a taper-lock hub (see image) where there is a tapered sleeve between the motor shaft and coupling half that is drawn in by screws. These are really effective, far better than what you've chosen.

Generally engineers send the dimensional details of the two sides to the coupling manufacturer with the maximum torque and RPM and they determine the best product for the job. Hacking something together especially involving welding may work for a while but it's not a professional solution unfortunately.

One suitable design would be a rubber-based flexible coupling (see image) with both radial and bending flexibility that is configured with a taper-lock on one side and machined to match the spline on the other, allowing the pilot journal to poke through the center and locate into the end of the motor shaft - with a bushing as needed. Or the pilot support can be part of the motor side coupling half. It's only holding it centered just like a pilot bushing or bearing in a crankshaft. This would allow a radial misalignment error of perhaps 0.001 to 0.003" between the motor and gearbox, entirely practical.

If you want more assistance a useful photo would be of the two physical parts set to the locations you need.


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## sifawangiaEV (Jan 1, 2021)

KiwiME said:


> I'll stick my nose in because this sort of thing was within my profession before I retired. Assuming the Mini gearbox has a conventional input shaft the first issue is that the pilot end of the input shaft _must_ be supported just like it had been by the crankshaft. Gearboxes normally rely on this, that's why they appear somewhat loose when you wiggle the input shaft on the bench.
> 
> Then you have to transfer the torque off the keyed motor shaft to the spline without loading the spline unevenly. You rely on the involute teeth under torque for alignment.
> A normal clutch disk of course is rattle-loose in the middle so that can happen freely (and cheaply).
> ...


Thank you for your input. I may try looking into this but I have already sent both the coupling and the clutch plate to the machine shop to be welded together. I think that I might just try to align the couplings the best I can to ensure the most minimal misalignment and keep it on for maybe a year or 2 before changing it. 
I have pictures of the clutch plate and the rigid coupling above. Could you send links to the 2 different coupling that you recommended so I could look into it? Thanks!


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## sifawangiaEV (Jan 1, 2021)

sifawangiaEV said:


> Sorry everyone if I've been all over the place but I've decided to go with a rigid coupling because it would be the longest lasting for my conversion and I'm willing to do the extra tough work to make it work. I just dropped it off at the machine shop with my clutch plate to be welded together, when I realized something not so good...the torque of the rigid coupling wasn't as high as I thought it was. Here's the spec sheet:
> View attachment 127750
> 
> I could've sworn that when I bought the item, it said that it had a torque rating of 2,400 in-lb. I'm thinking there might be a glitch on the website but I'm not certain because there is a chance that I somehow read it wrong. What do you all think? Does this rating look right for this coupling or does it seem like a glitch? Should I be considering a new coupling?
> View attachment 127750


Update: there was an error on the website. The torque rating is actually 4,400 in-lb.


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## KiwiME (Apr 8, 2016)

Just send a dimensioned drawing to Rexnord and have them size and configure it for you.


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## sifawangiaEV (Jan 1, 2021)

The machine shop that I sent my rigid coupling and clutch plate to has finished welding the two parts together. Here's the picture that they sent me:








I'm going clutchless which is why I'm just using the hub and not the clutch plate. What does everyone think of the design? If aligned properly, will it hold? Are there any modifications they should make or is it good?


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## 57Chevy (Jan 31, 2020)

put it on your input spline and spin the gearbox over, does it wobble? Put it on your motor and spin that over, how much does the welded bit wobble? Put a DTI on it and work out how far out it is. It will be out of alignment to some degree, how much determines how long the spline and/or coupling will last

It looks like they bead blasted it, give it a thorough disassembly and clean with brake clean or similar first and then blow out with compressed air


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## KiwiME (Apr 8, 2016)

They did a nicer job than I expected but I'd be impressed if it lasts, even if the parts are concentric.
1) there is evidence of shrinkage along the middle of the weld.
2) the coupling split will cause a stress concentration where it intersects the weld. (just below the arrowhead)

I would have welded up the coupling split on the gearbox half to stop movement at the weld. At least shim the gap tight and install some screws to limit flexing of that half.

In your favour, the gearbox input shaft will have some some wiggle tolerance and it's unlikely anything expensive will be damaged if the coupling fails. Grease the splines lightly at installation and make sure that the key(s) are a tight fit in the keyways.


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## brian_ (Feb 7, 2017)

KiwiME said:


> Just send a dimensioned drawing to Rexnord and have them size and configure it for you.
> View attachment 127792


That looks like a really nice coupling line, although not fundamentally different from other rubber flex joints (or giubos).
The rubber is available in a range of hardness, but any of them will be torsionally much softer than required; maybe that's harmless.
It can handle some misalignment, but every rotation of the shaft is a cycle of distorting the rubber, by an amount dependent on misalignment. I don't know how big one of these things would need to be to withstand highway travel, but I didn't look at the specs in detail.

I'm inclined to like these just on a sentimental basis - my father once worked for Rexnord.


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## brian_ (Feb 7, 2017)

KiwiME said:


> ...
> 2) the coupling split will cause a stress concentration where it intersects the weld.
> 
> I would have welded up the coupling split on the gearbox half to stop movement at the weld. At least shim the gap tight and install some screws to limit flexing of that half...


This is an excellent observation.  The original coupler is designed to clamp to each shaft, but in this modification the transmission side uses a spline instead, so the clamping action won't be used at all... and is completely incompatible with the rigid splined insert welded all the way around.


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## KiwiME (Apr 8, 2016)

brian_ said:


> ... but every rotation of the shaft is a cycle of distorting the rubber, by an amount dependent on misalignment.


An industrial coupling is a professional solution for the very-common motor to gearbox application. Properly sized these would last a long time. There are other types of less-flexible material of course; I only posted that particular photo to show that a spline can be machined into one half. The other half would use a tapered lock sleeve around the keyed shaft. Decoupling motor interia from the gearbox is never a bad thing as long as resonances are avoided.
I worked as an engineer in the field of engine and powertrain test equipment for a few years in the UK, 1980s, Froude Engineering.


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## brian_ (Feb 7, 2017)

KiwiME said:


> An industrial coupling is a professional solution for the very-common motor to gearbox application. Properly sized these would last a long time.
> ...
> Decoupling motor interia from the gearbox is never a bad thing as long as resonances are avoided.


Sure, but no one is engineering this system of interacting inertial objects, so torsional compliance in the coupling could create resonant problems, rather than solve them... and no production EV designer finds a need to decouple the motor inertia from the transmission. At least the hysteresis of the rubber will tend to damp out problems, unlike the steel coil springs of a typical clutch hub.


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## DMPstar (Mar 2, 2016)

I'm adding my 2c not because I am an expert in this field, but because I made critical errors in this step of my conversion project. My transmission started leaking from the input shaft within a few blocks of the first test drive, and I drove the conversion less than 50 miles before scrapping the project due to lack of time, space, and money to redesign the adapter assembly.



57Chevy said:


> put it on your input spline and spin the gearbox over, does it wobble? Put it on your motor and spin that over, how much does the welded bit wobble? Put a DTI on it and work out how far out it is. It will be out of alignment to some degree, how much determines how long the spline and/or coupling will last


Agreed, use the dial indicator when the coupler is attached to the motor. Looking at wobble with the coupler slid onto the trans input shaft may be misleading and difficult depending on the transmission design, as well as the aforementioned clutch disc spline-slop factor. Also as mentioned earlier, transmissions that use a pilot bearing can be a bit wobbly at the input shaft when detached from the accompanying engine.

*sifawangiaEV: *Can you confirm if your crankshaft has a pilot bearing or not?

It appears your project may be moving faster than the advice can come in and be appreciated. The momentum of an exciting DIY build can be great, but can also corner you if something gets overlooked or compromised. You have been given some legitimate and free Mechanical Engineering advice in the above posts, so make sure you understand the concerns that have been raised. I ignored or glazed over some advice from experienced members here and got to see the results, even though myself and the machinist agreed on the feasibility of the adapter design.

Can you get the machinist to run the piece with a dial indicator, and show you how the parts were made centric for the welding? Did they put machine screws in the threads and torque them onto some properly sized rod for that portion? If you did not provide them with a runout spec or some measurable expectations then you probably cannot expect them to compensate you, but you may be able to save damage to your gearbox by stepping back and taking some time to confirm some things.


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## KiwiME (Apr 8, 2016)

brian_ said:


> Sure, but no one is engineering this system of interacting inertial objects,...


Perhaps they should.
Designed EVs have larger gears and splines than were seeing here. This is a fairly flimsy setup in comparison and I'd see softening shock loading as an advantage.


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## sifawangiaEV (Jan 1, 2021)

KiwiME said:


> 1) there is evidence of shrinkage along the middle of the weld.
> 2) the coupling split will cause a stress concentration where it intersects the weld. (just below the arrowhead)


That's a good point. I did notice that split and wondered if that would be an issue. What should I tell the machine shop to do to fix this issue? Should they just reweld it?


KiwiME said:


> I would have welded up the coupling split on the gearbox half to stop movement at the weld. At least shim the gap tight and install some screws to limit flexing of that half.


Are you saying that the clutch bit should be inserted deeper into the coupling? Because I believe that it partially is but I'll have to see it to find out. The person at the machine shop that I was talking to mentioned using screws and a key with the transmission side spline so that the coupler can work as intended but he later decided to have some of the clutch hub part in the coupler and weld it on.


brian_ said:


> The original coupler is designed to clamp to each shaft, but in this modification the transmission side uses a spline instead, so the clamping action won't be used at all... and is completely incompatible with the rigid splined insert welded all the way around.


Yes, the clamping wouldn't be used on the transmission side but it would be used on the motor side. I'll still be able to use a key and the screws and clamp down on the motor shaft.


DMPstar said:


> *@sifawangiaEV: *Can you confirm if your crankshaft has a pilot bearing or not?


I don't think that it has a pilot bearing. I attached a picture of the clutch disc in my starting post so you can see that too for confirmation.


DMPstar said:


> Can you get the machinist run the piece with a dial indicator, and show you how the parts were made centric for the welding? Did they put machine screws in the threads and torque them onto some properly sized rod for that portion? If you did not provide them with a runout spec or some measurable expectations then you probably cannot expect them to compensate you, but you may be able to save damage to your gearbox by stepping back and taking some time to confirm some things.


I believe that they did torque the screws to a rod, but I'll check in on Monday when the shop is open to find out what they did and if they can modify it if it needs fixing. If the part is determined to be concentric, and the split in the welding is fixed, am I in the clear?

Thanks everyone for the input. It is greatly appreciated, considered, and very very helpful.


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## 57Chevy (Jan 31, 2020)

If the weld cracked on the first go then a second go over the top isn't the solution. They need to find out why; is it incompatible materials, incompatible filler rod, contamination, technique... That crater in the end pool looks ominous, it likely has porosity right down to the root and could initiate a crack anyway, even if that line isn't a crack.

Welding axles is an age old practice that often results in failure. Some people have the knack of it, many don't. You are doing a very similar thing to welding an axle, just less torque.


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## sifawangiaEV (Jan 1, 2021)

57Chevy said:


> If the weld cracked on the first go then a second go over the top isn't the solution. They need to find out why; is it incompatible materials, incompatible filler rod, contamination, technique... That crater in the end pool looks ominous, it likely has porosity right down to the root and could initiate a crack anyway, even if that line isn't a crack.
> 
> Welding axles is an age old practice that often results in failure. Some people have the knack of it, many don't. You are doing a very similar thing to welding an axle, just less torque.


Ok, that makes a lot of sense. I'll talk to them about what the cause might be and if they can't fix it, I'll take it to a different machine shop and see if they can figure it out/do it right.

Also I cannot find the specs for this coupling that specify how much to torque the screws...Is there a general rating out there somewhere?


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## KiwiME (Apr 8, 2016)

Presumably they've machined the clutch hub end (the end not visible) to fit the coupling so that it's centered but now that it's welded there's no reason to allow that side of the coupling to flex.
I was suggesting welding it along the red line but you'd want to grind a "V" first so that the weld can take good hold of the parent steel.

But before spending the money, perhaps check runout first in case it's not concentric and needs to be redone. If the minor diameter of the spline and/or the outside diameter is more than 0.002" out radially I'd scrap it. Oh, and that's when clamped to the motor shaft as mentioned by others.

I'd sure like to see photos of the actual gearbox input shaft and motor output shaft. And some idea of the spacing between them you're expecting.

I'll just add that my recommendation remains to use an industrial flexible coupling. That still requires the two sides to be well-aligned, perhaps 2-3 thousandths TIR.


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## remy_martian (Feb 4, 2019)

You've shown that the upper half of the black coupler is useless and what he has is going to be an out of balance mess.

That weld is cold, almost looks like it was "aluminum welded" vs TiG welded using one of those special rods that works with MAPP gas. That weld makes that assembly a writeoff. Can't be fixed for service.

Next go...cut the black coupler in half to where only two cinch bolts are used and a sliver above the factory gap. 

Groove the spline piece and the new baby two bolt coupler for welding HALF way around, like its amputated friend was joined. 

Get it TiG welded, several passes, then chuck it in a lathe and fillet the weld so it's balanced and there are no stress points (sudden geometry changes...ridges, etc). You may need to take it to a machine shop and a competent welder vs guys who do joints on irrigation stuff.


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## DMPstar (Mar 2, 2016)

KiwiME said:


> If the minor diameter of the spline and/or the outside diameter is more than 0.002" out radially I'd scrap it.


👍 
A few thousandths is the actual tolerance here as I have learned.



KiwiME said:


> I'd sure like to see photos of the actual gearbox input shaft and motor output shaft. And some idea of the spacing between them you're expecting.


👍


sifawangiaEV said:


> I don't think that it has a pilot bearing. I attached a picture of the clutch disc in my starting post so you can see that too for confirmation.


It is hard to determine if your gearbox used a pilot bearing based on pictures of the clutch disc. Gotta have pics of those shafts as KiwiME said, short of us doing research into your car's design.



sifawangiaEV said:


> Also I cannot find the specs for this coupling that specify how much to torque the screws...Is there a general rating out there somewhere?


Specified screws on the product snip you posted were 1/4-28. You should be able to find a torque spec for that. Grade 8 would be a good estimate, you shouldn't break or strip them in that range.



remy_martian said:


> You may need to take it to a machine shop and a competent welder vs guys who do joints on irrigation stuff.


ohhh r_m, _sometimes_ getting to the point using restraint.


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## sifawangiaEV (Jan 1, 2021)

KiwiME said:


> I'd sure like to see photos of the actual gearbox input shaft and motor output shaft. And some idea of the spacing between them you're expecting.


The other end of the coupler that's hidden fits the motor shaft and part that's welded fits the transmission shaft. Here are the pictures:

























KiwiME said:


> I was suggesting welding it along the red line but you'd want to grind a "V" first so that the weld can take good hold of the parent steel.


I'm not a welder so I'm having trouble understanding what you mean. Are you saying that the coupling should fit in deeper? Or are you saying to weld through that gap for a better grip?


remy_martian said:


> Next go...cut the black coupler in half to where only two cinch bolts are used and a sliver above the factory gap.
> 
> Groove the spline piece and the new baby two bolt coupler for welding HALF way around, like its amputated friend was joined.
> 
> Get it TiG welded, several passes, then chuck it in a lathe and fillet the weld so it's balanced and there are no stress points (sudden geometry changes...ridges, etc). You may need to take it to a machine shop and a competent welder vs guys who do joints on irrigation stuff.


Sorry but I don't really understand what you're telling me to do. So I cut the coupler in half and then what do I do? How will this be different from what I have already? Is the only difference a different weld (TiG vs aluminum)?


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## 57Chevy (Jan 31, 2020)

Maybe it'd be a better shot welding the clutch spline to a stump of shaft the same diameter as the motor shaft, then tighten the coupler on both the motor and the stump shaft how it was intended to work

You can find generic torque specs for the fasteners online. They look about 1/4 unf


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## remy_martian (Feb 4, 2019)

^ This. My daughter called and interrupted me typing this very same suggestion up. 

The problem might be that there won't be enough meat over the splines to get to motor diameter, but that just means reaming half the coupler to a larger ID...but only if they don't already stock couplers in two different ID's.

No welding needed..


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## brian_ (Feb 7, 2017)

DMPstar said:


> ... transmissions that use a pilot bearing can be a bit wobbly at the input shaft when detached from the accompanying engine.
> 
> *sifawangiaEV: *Can you confirm if your crankshaft has a pilot bearing or not?





sifawangiaEV said:


> I don't think that it has a pilot bearing. I attached a picture of the clutch disc in my starting post so you can see that too for confirmation.





DMPstar said:


> It is hard to determine if your gearbox used a pilot bearing based on pictures of the clutch disc. Gotta have pics of those shafts as KiwiME said, short of us doing research into your car's design.


Rather than hard, it's impossible to tell if the transmission input shaft is supported by a pilot bearing (or bushing) in the crankshaft from looking at the clutch disk. Fortunately...



sifawangiaEV said:


> The other end of the coupler that's hidden fits the motor shaft and part that's welded fits the transmission shaft. Here are the pictures:
> View attachment 127822


... this image shows that the transmission input shaft is splined to the end, without a plain section to insert into a pilot bearing. A pilot bearing is normally needed in a traditional layshaft transmission, in which the input shaft is very short, carrying only a gear which transfers the drive to the layshaft and a coupling to the mainshaft for the direct "gear" (1:1 ratio). This Mini Cooper is typical of transverse transaxles which are all-indirect, meaning that the input shaft is long, carrying the input-side gear for every ratio; since the shaft is supported at two widely-separated bearings, the clutch disk can be safely cantilevered on the end so no pilot bearing is needed or used.

A 2006 Mini Cooper should be the last year of the first generation. If the Wikipedia article is correct, that means that - because it is the Cooper S version - it has a Getrag G285 6-speed transaxle (which was also used in the Ford Focus ST170 and SVT). It is a typical "3-shaft" transverse manual transaxle. This is a photo of the internals of a racing version (with straight-cut gears and dog ring shifting), showing that each of the three shafts (one input, two layshafts each driving the diff's ring gear) is supported by bearings are each extreme end:








The bearings visible (on top as it sits in this photo) are in the end opposite the engine, supported in the main case which has been removed; the bearings at the engine end (the bottom as it sits on the bench here) are in the engine-side case which is visible. The input shaft is the nearest one (without any shift elements on it); the differential housing area is just visible on the far side).

Edit note: replaced image with view from more useful perspective


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## sifawangiaEV (Jan 1, 2021)

57Chevy said:


> Maybe it'd be a better shot welding the clutch spline to a stump of shaft the same diameter as the motor shaft, then tighten the coupler on both the motor and the stump shaft how it was intended to work





remy_martian said:


> The problem might be that there won't be enough meat over the splines to get to motor diameter, but that just means reaming half the coupler to a larger ID...but only if they don't already stock couplers in two different ID's.
> 
> No welding needed..


So the problem with that I think is the fact that the coupler works with a key so if I used it as intended, I would need to make a keyway in the clutch hub and I don't know if that would be very reliable/practical. Is there a way where I can have the machine shop lathe the coupler to have a bigger diameter and weld the clutch hub so that it sits in there? Or would tightening the coupler around the clutch hub without a key be enough to keep it in place?
In response to remy, this coupler brand does not sell couplers with different IDs. Do you think that using this method but welding the clutch piece in instead would work fine?


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## remy_martian (Feb 4, 2019)

Why are you married to the coupler brand? Find one that works.

Making a keyway in a uniformly cylindrical (turned to same diameter full length) hub is trivial for a well equipped shop. Takes 10 minutes.


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## 57Chevy (Jan 31, 2020)

How much length do you have between the motor and spline, i.e. is there enough room to have a stump sticking out of the coupling with the spline inside? If so then you can get the spline EDM cut into a short section of turned bar and not worry about welding the clutch disc on, that way everything is as good as perfectly true to start with. Broaching or milling a keyway is no drama.


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## sifawangiaEV (Jan 1, 2021)

Considering all that you all have said, I have two options to present to the machine shop. I will be presenting one of these options to the machine shop on Monday and ensure that the parts are concentric. I'll have the machine shop torque the screw to the rated toque for 1/4-28 screws which is about 13 ft-lb. Here are my two options:

*Option 1:* Remove the clutch hub from the coupler and then lathe the bore of the coupler to make it larger and also make the clutch hub diameter as small as it can be (while still maintaining its integrity, of course). Then they'll broach or mill a keyway into the clutch hub and tighten it inside the coupling, torqued to 13 ft-lb.

I really like this option and the fact that I will be using the coupler how it was intended, but in the event that things don't work out the way that they are supposed to, I may go for option two:

*Option 2:* I'm going to talk to the machine shop about the split in the coupler and ask what could be the possible cause of it. In the event that they figure out what caused the split and know how to fix it, I'll see if they can weld the piece back on and make it concentric. If there are no splits and the part is concentric, will this method work fine?

I will use a DTI to make sure that the part is concentric for both options. Will both options work fine? Please let me know what you think of the options.


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## sifawangiaEV (Jan 1, 2021)

57Chevy said:


> How much length do you have between the motor and spline, i.e. is there enough room to have a stump sticking out of the coupling with the spline inside?


There is enough room for a stump to stick out of the coupler. I'll need an adapter plate that's about 1/2" thick.


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## KiwiME (Apr 8, 2016)

@sifawangiaEV, Thanks for posting the photos of the actual parts. Because it's now clear that the transmission input (clutch) shaft is already fully supported within the gearbox you *should* use a flexible coupling that can tolerate parallel misalignment. If you use a solid coupling your alignment must be perfect. That's a tall order and not something I'd recommend trying if any sort of reliability past a few weeks is your goal. So, when I say "should" I mean like an engineer speaking politely to his manager, I really mean "must". You're shooting yourself in the foot if you try to mickey-mouse this, which is regrettably the path you are already on.

There are a number of industrial coupling types that are suitable but you also have to ensure that the type chosen will be available with appropriate shaft options. Because of the frequent torque reversals I would stick to those that use clamping methods on the shaft(s), not just a split clamp but a proper taper-lock design. There may even be one for the spline according to the literature I'm referencing below. A small amount of torsional flexibility would not be a bad thing either, but not a lot.

Because the radial misalignment could be realistically kept to within 0.5mm TIR, one option that I found quickly is the Rexnord CentaFlex. It's quite complicated to navigate the engineering selection details but it's likely that their application department will do all that for you *if* you supply a fully-dimensioned drawing of both sides and max torque/RPM specs. You'll need to identify the spline dimensions as well and the desired gap between the shaft ends. When you get a recommendation from them you'll need to verify that it fits within the bellhousing.

There are many other coupling manufacturers but that's up to you to research. Following this advice will provide a reliable solution but I'm going to wish you the best of luck and leave the rest up to you, as I have to move on to other things.


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## sifawangiaEV (Jan 1, 2021)

KiwiME said:


> @sifawangiaEV, Thanks for posting the photos of the actual parts. Because it's now clear that the transmission input (clutch) shaft is already fully supported within the gearbox you *should* use a flexible coupling that can tolerate parallel misalignment. If you use a solid coupling your alignment must be perfect. That's a tall order and not something I'd recommend trying if any sort of reliability past a few weeks is your goal. So, when I say "should" I mean like an engineer speaking politely to his manager, I really mean "must". You're shooting yourself in the foot if you try to mickey-mouse this, which is regrettably the path you are already on.
> 
> There are a number of industrial coupling types that are suitable but you also have to ensure that the type chosen will be available with appropriate shaft options. Because of the frequent torque reversals I would stick to those that use clamping methods on the shaft(s), not just a split clamp but a proper taper-lock design. There may even be one for the spline according to the literature I'm referencing below. A small amount of torsional flexibility would not be a bad thing either, but not a lot.
> 
> ...


I called Rexnord and some of their distributors and they told me that they can’t make couplings with splines because of how precise that they have to be. So, sadly, I won’t be able to use a CentaFlex coupling for this application.
I was working with a local machine shop on making the coupling better and they were able to take off the weld and redo it. The weld that they used was TiG weld. And it has no streamline cracks. The only downside is the TIR rating of .006”. Thé machine shop said that they were getting different ratings based on where they were taking the measurements on the splined side of the coupling. They concluded that it’s most likely because the coupling is used (186 thousand miles in the car) and that it would most likely be fine since I’m putting it on the shaft that it came from and worked with. 








When I tried to put the coupling on the transmission, it wouldn’t slide on all of the way. It just stopped. So basically, the coupling and the splined part shrank due to heat when it was being welded. 








I decided to tap the coupling on the transmission shaft and pull it off until it was able to slide on and off easily. I’ve only gotten it to slide on a little bit more though. If this method fails, I will use a brake cylinder hone to shave down the inside diameter of the splined coupling just a little bit. I will also have to do this for the motor side because that side of the coupling shrunk as well.
My other option is to buy a new clutch plate and have the machine shop weld that clutch plate on my coupling instead (but not letting the coupling shrink). Please let me know what you all think.


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## 57Chevy (Jan 31, 2020)

I'm glad you are finding all these little things out early on, far better now than on the side of the road in six months with a thrashed gearbox spline. 0.006" is a lot of runout, you'll likely feel that binding as it rotates. Welding will always cause some amount of distortion, there isn't really any way around it other than old-man skill and knowledge of the welder. 

A better way would be to EDM the spline, that way you start with a single piece fully machined and so very little runout. 
[sound off]


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## KiwiME (Apr 8, 2016)

Yeah, 006" TIR is pretty horrific for the RPMs and physical scale of the system when using a rigid coupling. It will end in disaster. I'm not surprised that the splined hub warped during welding and that's an unfortunate compilation. But I'll repeat that using a rigid coupling is a bad idea anyway.

Almost all modular (meaning configurable) flexible couplings can be purchased with a blank end (with pilot hole only) and could be machined to suit your requirements. EDM would certainly be ideal, no-doubt pricey but you get what you pay for. I'm a bit surprised that in the US of A you can't get this sort of thing done easily? On a remote island in the South Pacific where I live I'd expect that.

I think your machine shop is leading you astray by telling you it will work. More research into flexible couplings is my recommendation. It would be useful if you can identify the spline size on the Mini gearbox. Additionally, creating a proper engineering drawing that you can send out for quote showing the two sides would make your search so much easier because application engineers can quickly interpret the requirements from that without any verbal or written explanation.


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## 57Chevy (Jan 31, 2020)

Kiwi, the problem with a jaw coupling is that the spline doesn't axially locate the gearbox half and it'll separate. The other issue is that a flex coupling needs both halves to be rigidly secured and the spline isn't very compatible with that. A lightly press-fitted spline in a blind cavity would work. A loose spline will hammer out with a flex coupling if there is any misalignment, so may be easier to use a solid and clock it up properly during install. Btw, I'm up the top end of the islands


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