source of vibration?, car vibrates at ~ 3k RPM Options

[astronomerdave]

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

[Katmanken]

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

[astronomerdave]

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)