Flywheel weight

#1

I’m probably several months away from doing this, but I started looking into how to swap my clutch. I came across this page (http://www.e30zone.net/e30zonewiki/index.php/M20#Flywheel) that has this line:

“Two weights of flywheel were fitted to M20 engines. The standard flywheel is 8.4kg, while cars fitted with air conditioning have a flywheel 1.3kg lighter.”

The rulebook states (Section 9.3.12.7):

“After balancing, the flywheel must be within factory dimensions for diameter, and weigh at least 17.5 pounds.”

17.5 pounds is 7.95kg. The e30 zone site says that the AC-fitted flywheels weigh 7.1kg.

e30 zone is a UK site – did this difference not exist in US models? Or is there a disconnect with the rules? Or are there multiple ways to weigh a flywheel?

Thanks,

Som

#2

There’s more flywheels that, at some point, were put on M20’s, then what you’ve found. But all our M20B25’s came with the same flywheel and you’ll find that it weighs 17.5lbs or slightly more. Use it as is, w/o any funny business in removing weight and you’ll be fine. It’s no more complicated then that.

#3

I stopped referring to that site after I found some errors. I don’t know if they are right or wrong on this but I wouldn’t go by that info alone.

#4

Thanks for the feedback, guys. It does seem weird that all the AC M20s would weigh 15.62lbs, as e30 zone states, since I would think most of these cars probably came with AC and this issue would have been brought up long ago.

So is the typical process here to remove the flywheel and take that to a shop to have the surface smoothed and then balanced along with the clutch/pressure plate?

Som

#5

Typically unless it is in really good shape a shop can’t do much with it. The spider cracks that develop prevent it from being resurfaced and many times it is worn past it’s minimum. Never hurts to check, but you proabaly have an anchor.

#6

So on a 200k mile car, do people just do a clutch swap without removing/resurfacing/balancing the flywheel? Or does everyone hunt for good condition flywheels when they swap their clutch?

Som

#7

You’re paying a lot more attention to this than I ever did. I’ve been thru many prob 3 flywheels and 5 clutches, as comedy came and went. I bolted that shit on and loaded the car on to the trailer.

Bolt that shit on and go. Race with your buddies, drink some beer, laugh a lot in the paddock, and after 4-5yrs, you feel compelled to obsess over minutia, then go right on ahead. But first spend those years racing with your buddies.

#8

I don’t plan to lose any racing time with my buddies over this, that’s for sure – pretty sure my kids will do enough of that by themselves. :slight_smile:

It would be good to know this stuff from a general “like to know about cars/E30s” perspective – not just strictly from a “I’m working on the race car” perspective. It sounds like I’ll probably just do the clutch and be done with it, but doesn’t mean I’m not curious.

Som

#9

I know this is a really old thread but the subject is close to a current question that I have and I’m sure there are plenty of E30 experts here. I have 2 single mass e30 flywheels and it appears both have been resurfaced at some point. Can anyone tell me the original specification for the height difference between the friction surface and the pressure plate mounting surface? The 2 examples that I have in hand measure somewhat different.