# Flywheel 0.13mm off centre



## Woodsmith (Jun 5, 2008)

You could take it off and refit it to see if it moves.

Also get the assembly balanced.

My wrecked 12" motor had the coupler machined over 1mm off centre. It vibrated and moved about a bit but nothing scary. I didn't have a flywheel on it though.
It was wrecked by bad machining not the vibration.


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## O'Zeeke (Mar 9, 2008)

if my math is right that is a little over .005 inches which will be noticeable, also motor bearing wear, metal fatigue and coupler failure are issues you dont want to deal with later. Who made your adapter? 



sabahtom said:


> Just fitted the adapter and found that out. Plan to spin it up to 2800rpm using an electric drill (too much hassle to hook up battery pack).
> 
> 1. Will this harm the motor? Its an AC55
> 2. Is it worth the bother? Maybe someone can just tell me that it's going to jump all over the workshop.
> ...


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## Ellrot (May 17, 2010)

As a precision Engineer, I would agree with the other lads, 0.13mm isn't that much to worry about, if you really wanna be perfect, you could always take it to an engineering workshop and they should be able to take that out for you. With time to clock it and setting up properly it should take no longer than 10 minutes to do....


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## sabahtom (Mar 1, 2011)

Thanks for the quick replies! I've got Friday off work and the machinist is free so I'm hoping to have a solution ready for him. Part of the adapter was done in a manual shop, but the whole assembly is now in a cnc shop (they don't have a machine to do female splines).

This version was made by a local machine shop. They don't specialise in adapters. The female spline was done with a manual machine, then they reversed the piece so that they could drill in the holes for the flywheel bolts. I guess that's where the misalignment came in.

The splined section seems quite straight, but the hub for the flywheel bolts is off centre. 

I can bolt the splined adapter, adapter plate and flywheel all together and get it into a cnc lathe but if they balance out the flywheel, and the flywheel is bolted to a hub that is off centre, is it possible to fix it?


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## sabahtom (Mar 1, 2011)

Re the project management side of it:

Being an AC55 in a minivan this isn't going to rev past 2500 very often. It's going to be doing around 30km on an average day at average speed of 45km/h. 

So if .13mm off centre isn't going to noticeably damage anything before 10000km, I'd like to get the thing on the road. It's been dragging for a year already because I couldn't find anyone to do the machining. I've got all the other parts already. 

Advice? Should I wait for a better job (I can get a splined sleeve from Hub City for this motor, $120 total) or get it on the road?


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## Ellrot (May 17, 2010)

When dealing with Engineers it is good practice to specify a tolerance. A cnc and manual lathe the are still only as accurate as the guy setting the job up.


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## sabahtom (Mar 1, 2011)

Hi Ellrot

I'm in Borneo, so good machinists aren't common. For the splined adapter I did spec 5 micron. When I went to collect it I asked him for a demo. He used a piece of wire on a stand and touched the tip to the adapter. He says he doesn't normally do work that requires a needle gauge. The guy with the cnc does have a needle gauge so I trust him more


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## mizlplix (May 1, 2011)

We usually hold a flywheel to .0003" or less. so, yes, you will feel yours wobble.

Borneo, that is a lot tougher to get it repaired. 

Assemble it and if it gets annoying, remove it at that time for a touch-up. But My guess is yes, you will want to in the end.

Miz


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## sabahtom (Mar 1, 2011)

Thanks for the help everyone, I'll check with the shop tomorrow if they have time to balance it.

Could anyone confirm for me: since this is AC induction, its totally safe to spin the shaft up to 3000 rpm (below mechanical limit of course) without having it connected to a load? I understand that without permanent magnets or a source of PWM no current will be generated by spinning it.

My reason for asking is that there are some markings on the edge of the flywheel that seem to be for calibration or balancing, and they may be disturbing the needle gauge. So I thought I'd spin the adapter assembly with an electric drill and see if the motor jumps or not.


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## mizlplix (May 1, 2011)

I have seen 4000 RPMs or so on my AC50 unloaded...BUT, that was from just pecking the throttle pot. It would redline if I just pressed it for 1 full second.

It was possible to get it to just tick over, but you must use the smallest throttle input you can manage. The unloaded condition lets it rev up wildly fast. 

If you go into your controller and set the max rpms to what you want to test at, it would be good to go also.

The unloaded condition is not the motor killer, it is the wildness caused by no-load. Just be really careful and you can do a test.

Miz


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## sabahtom (Mar 1, 2011)

thanks mizlplix. Before I connect up all the batteries (which are sitting on the other side of town at the moment) I thought of putting a rubber wheel on the end of my electric drill and spinning the flywheel using friction between drill and flywheel. Can I do that without harming the motor?


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## DavidDymaxion (Dec 1, 2008)

If the bolt pattern allows it, try taking the flywheel off and bolting it back on at a new angle. Pick the angle that minimizes wobble. Then put on the pressure plate at different angles until vibration is minimized. Then you can do the John Wayland trick of adding washers to just 1 bolt (the closer to the edge of the flywheel the better) until vibration is minimized.

My flywheel wobble was about 0.002 inches, but vibrated more than I liked until I rotated the pressure plate 180 degrees. It was then smooth enough I didn't think I needed to balance the flywheel and pressure plate combo.


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## sabahtom (Mar 1, 2011)

Thanks David Dymaxion. I spun it up to 1000rpm with my drill. Slight vibration but the motor didn't jump off the bench  I tried undoing the flywheel, turning it 180 deg and bolting it on again. Exactly the same 0.13mm bump so I guess the flywheel itself is good but the hub is off centre.

I was wondering if this could be due to the weight of the flywheel pulling the spline down? Maybe it'll straighten up when the pressure plate is applied.

Seemed to be two bands where there was some harmonic and the loose tools on the bench started to rattle. Otherwise ok.

I got a fright at how much power it takes to spin that flywheel + motor! My drill is 650w and it took around 25 seconds to get to max. I'm guessing it'll use at least 4kw to spin the whole lot up to 2500 rpm in 5 seconds or so, as with normal driving.


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## MemphisPapa (Feb 16, 2012)

I went through some of this today when I tried to get my motor connected to an 020 VW transmission. I found that since I didn't have the tool to get the clutch plate exactly in the center between the pressure plate and the flywheel, the flywheel kept bumping the bell housing. I thought it might be a problem with my hub, but then took a closer look at my adapter plate. I found that when I got the whole thing bolted together, I couldn't spin the tail shaft with the trans in neutral. I added some shims between the motor and the adapter and am now sure that my hub it too long. Very careful clutch assembly with shims on the motor face allow enough to keep the flywheel clear. I'm figuring the motor spinning CCW with the right hand rule will keep everything pushed against the motor? I'll need to come up with a plan to get my hub fixed or add a quarter inch to the adapter plate.


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## Joey (Oct 12, 2007)

I had 0.38 mm of runout and 0.05 mm wobble on my hub adaptor, and the vibration with just the hub (4 kg) was too much for me at 2000 rpm. After a small touch up on the lathe, I measured 0.075 mm runout and 0.05 mm wobble, and the vibration was gone. Try to get the hub as true as possible. I would recommend <0.1 mm, but it does depend on rpm and spinning mass. I had the flywheel balanced at an automotive machine shop and adding the flywheel did not introduce any vibration.


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## sabahtom (Mar 1, 2011)

Thanks Joey. 

If the hub bolt holes are machined off centre then as far as I understand I can't fix it without getting a new hub made? The issue seems to be that the female spline (top of this photo, not quite visible) was machined straight, then the piece was removed from the jaw and turned around for the flywheel bolt holes to be drilled.

Other question I have is if I need Loctite or a grub screw on the two nuts to lock the thrust bearing against the back of the adapter plate? I think if I torque them down it'll be enough?

Cheers!


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