My 914 was converted to an electric vehicle; other than having an electric motor instead of a gasoline engine, the drivetrain is the same as you're familiar with. The electric motor has a hub adapter which matches the bolt pattern of the original flywheel. Then I'm using the orig flywheel, clutch, and transmission. The problem is that somewhere around 3000 RPM the car starts to vibrate (and gets worse with increasing RPMs).

Now at least two or maybe three other guys who did this same conversion had similar vibrations and all of them found that they had troubles with their transmissions. So I jumped to conclusions and thought the same. But I just discovered that I get the same vibration whether driving, sitting in neutral, or sitting with the clutch disengaged.

I have my own new theories now but want to hear what some of you other people think.

Thanks,
Dave

p.s. images of the car, including some parts such as the motor, flywheel, etc. can be found here: http://www.halestorm.us/evconstruction.htm

Dave,

I just sent you an email without reading this thread first. This is very unlikely to be a transmission problem if the vibration occurs while in neutral *and* not in motion.

Per my email, you need to check the pressure plate/flywheel/adapter both for alignment, proper assembly, and for balance as an assembly. Now that you have mostly ruled out the trans this should be a failrly easy problem for a machinist to diagnose. This is not something you can "eye ball" like some of those EV guys were talking about on the EV Google thread.

Yank the motor and take it to one of the guys on campus, Hollywood Machine in Pasadena, or my favorite - John Edwards at Costa Mesa R&D. Tell any of them Aaron sent you!

Are you sure the the flywheel is properly aligned? If that is off, it will cause vibration.

Zach

Car may have sat on tires for too long and you now have flat spots!

Ask me how I know!

It vibrates when sitting still, so flat spats probably are not the problem.
Has to be a rotating mass that keeps spinning when the car is not moving...

I'm guessing the flywheel is not centered, but my guess may be wrong too. I don't know if the flywheel is attached to the engine like on a gas motor, or some other configuration.

Zach

Your right, I originaly read it as rolling with the clutch in or in neutral!

No, I'm not sure (and that's one of my suspicions). Below you say "off-center" but centration didn't seem to have an adjustment. There could be wobble, however (ie. the plane of the flywheel may not be orthogonal to the axis of rotation).

As for how it connects to the motor, it uses the same 5 bolts as before. The only difference is it is bolting to a hub adapter. Here is a photo (not mine) of the electric motor showing the hub adapter:

hub adapter link

This photo is from another 914ev'ers blob, http://914ev.blogspot.com/search?q=hub (he has more pictures than I do).

And I suppose it is possible that the hub adapter went on incorrectly, too, though very unlikely.

I kept the original registration between the pressure plate and the clutch (but did not have anything checked or rebalanced).

Are you sure the pressure plate and the flywheel are balanced? The flywheel can be checked out of the car on the motor for trueness but the balance can't be. Just put a dial indicator on the back surface then on the od and turn it slowly to check for trueness. A flywheel shop can check the pressure plate and flywheel for balance, they should be balanced individually and checked together also then marked so they are a matched set.

The only thing spinning at the engine speed is the motor and flywheel and pressure plate in neutral setting still and the clutch pushed in. The clutch disk and input shaft will turn from some internal friction but probably not at the same speed. The bearings in the motor won't last long with a vibration.

Is there a input shaft bearing in the crank hub in the picture? If there is no bearing push the clutch in while spinning up to 3k and if it gets better the clutch disk may be floating around inbetween the pressure plate and the flywheel and not centered with the clutch out. You gotta have a input shaft bearing to support the input shaft on the clutch disk end. If all else fails check the trueness of the adapter.

The adaptor wouldn't be the first part made wrong or have a slightly less than perfect match with the motor shaft. Is the motor off the shelf? if so, the output shaft has a range of outer diameter tolerances that te motor factory uses and you have no control on what you get. Mate that shaft up to the adaptor, and depending on tolerances, you might have a problem.

I'd measure the crap out of that hub adaptor and the assembly of the hub adaptor with the flywheel. There are a lot of variables that can cause the problem. Look for simple stupid stuff too- burrs and the like can cause a small amount of cocking.

Balance is another factor. You have two planes to worry about.

Ken

UPDATE:

First, I properly calibrated by tach and the vibration is felt around 3800-4000 RPM (not 3k as I estimated earlier).

Second, I hated to take it apart but I removed the drivetrain. When off the car but still otherwise fully assembled, I took it up to 5k RPM. I dunno, it was louder, but it didn't really seem to vibrate. It's hard for me to estimate vibration with my hand. Yeah, it maybe vibrated a little but it didn't shake like the car did (when in the car you could REALLY feel it in the steering wheel and seats and your whole body). When it's not bolted to the car it doesn't sound or feel the same though. I then removed the transmission and took it up to about 6K RPM, motor+flywheel+pp only. It was quieter (but by this time my helper had gone to sleep so I couldn't both spin it and feel it at the same time). It didn't wobble away though. These "feel" tests aren't great tests I know, but just was curious.

Third, I made the following measurements.

FLYWHEEL, everything still assembled
runout 0.008'' measured through the hole in the top of the bell housing

FLYWHEEL, transmission removed
runout 0.008''
wobble 0.008'' measured on outer surface (just inside teeth ring)

FLYWHEEL, pressure plate removed
wobble 0.002'' measured on the inner polished surface where the clutch mates

HUB ADAPTER (flywheel removed)
runout 0.002''
wobble <=0.0005'' (that's about 1/2 mill or less)

Does it have the input shaft bearing for the front of the input shaft? If not the clutch will be floating around and clamped in a off center position when you let the clutch out. It sounds about as straight as it can be, It must be balance. You might want to take the flywheel and pressure plate in and have the balance individually checked.

You have many more measurements to do with the flywheel removed.

For example, did you measure the OD runout along the length of the adaptor????
If the center hole (in the adaptor) is drilled at an angle, one end will have more run out than another.

DId you measure the face of the adaptor (with the bolt hole pattern)?? Is it flat??? Is it machined at a right angle to the angle of rotation? Does the indicator move when reading that surface and rotating the adaptor on the motor??? A small error there magnifies as wobble of the flywheel.

Do your motor bearings deflect when putting a side load on the adaptor?

Did you measure the bolt hole pattern? If it's off center,, then that could account for the .008 runout is measured at the flywheel. Prolly need a deflecting arm indicator fixed relative to the motor and able to go into each hole as you rotate the adaptor.

With the adaptor removed, measure the runout of the motor shaft as it rotates to see if there is a slight bend to it.

We haven't even started on the flywheel. Porsche or aftermarket????

Ken

You could put some studs in the adapter and measure off of their sides rotating it slowly. .008 at the outside of the circumferance of the flywheel is not a lot. .002 on the clutch surface is as good as it will get.

You could do a little shade tree engineering and mount a 18 inch or two foot coat hanger on one of the motor mount holes and tape a washer on the end straight up and run the motor without the flywheel and with it, then add the pp and see what it does. The wire should show the vibration depending on the degree of the mounting of the motor assembly.

It does. I think I will take it in to have the balance checked.

Someone correct me if I'm wrong but if you place the trans in gear and depress the clutch doesn't that stop the trans main shaft from spinning ?
If so do it and see if your vibration is still there, if so that takes the trans out of the picture. IMO I"m looking at that big flywheel, heavy etc and the electric motor with only 2 bearings nothing like the support a crank shaft has.
I do love the set up you have !