Flywheel

#1

I am interested in the spec e30 series and one question I have is if a lightweight flywheel can be used:

9.3.12.8. Balancing of the flywheel/clutch/pressure plate assembly is permitted. After
balancing, the flywheel must be within factory specifications.

Does that statement include weight? as long as the diameter and thickness are the same as stock and what if i do not balance the flywheel and just replace it? it does not state that a aftermarket flywheel is prohibited. Just looking for some clarification.

Thanks.

#2

BCStringfellow wrote:

[quote]I am interested in the spec e30 series and one question I have is if a lightweight flywheel can be used:

9.3.12.8. Balancing of the flywheel/clutch/pressure plate assembly is permitted. After
balancing, the flywheel must be within factory specifications.

Does that statement include weight?
[/quote]
Yes.

#3

9.3.12.6. Any clutch disc and pressure plate of original diameter may be used provided that
they bolt directly to an unmodified stock flywheel

#4

Yep gotta run the stock unmolested flywheel is the way I read it. I just had a shop resurface mine for my new clutch install and tranny swap.

#5

How many pounds did they have to grind off of it to get it smooth again. :wink:

#6

The flywheel has to be unmodified per 9.3.12.6 - it is illegal to resurface it. You can balance the assembly per 9.3.12.8, but evidently that only allows modification of clutch and pressure plate of “original diameter” since you can’t touch the flywheel.

I’m not saying the rule makes sense (given the gains you could have with trick unobtainium clutch/pp parts since the ONLY rule is diameter), but it is the rule.:huh:

Steve D.

#7

Isn’t resurfacing it balancing it. You are trying to get a level and balanced clutch grip section. I told the shop to only resurface it and nothing else. Seriously how do they expect you to change a clutch out and not resurface the flywheel properly?

#8

King Tut wrote:

I don’t disagree, but the rule states “unmodified.” I’m not sure how you resurface something without modifying it to some extent.

Don’t worry. It would be a weenie protest.

Steve D.

#9

King Tut wrote:

My experience in this is limited but:

  1. Resurfacing isn’t balancing.

  2. Resurfacing isn’t an automatic part of clutch replacement. If the flywheel’s surface isn’t beat up then just put the clutch in and drive on. If the flywheel’s surface is beat up you’ve got the option of finding a better one (there’s lots of them around), researching BMW’s official take on resurfacing, or just having a clutch shop take a couple mill off and be done with it.

I took my flywheel to a clutch shop when I swapped motors the other month. I wanted to know if it seemed ok or if I needed to do something. It seemed ok to me, but what do I know, I figured. I showed them the flywheel and they sat their beer down, spat in a nearby spitoon and told me that I didn’t need to bother resurfacing it. “Just put it in and it’ll be fine”.

9.3.12.6 does not preclude resurfacing. 12.6 is not even about the flywheel. It’s about the clutch disk and pressure plate. It is saying that the clutch disk and pressure plate have to be such that they can bolt to a stock flywheel. Dang guys, my HS English teacher was the god$#amned wrestling coach.

#10

Ranger wrote:

9.3.12.6. Any clutch disc and pressure plate of original diameter may be used provided that they bolt directly to an unmodified stock flywheel.

12.6 states that the disc and PP are required to bolt to “an unmodified stock flywheel.” That precludes resurfacing. It shouldn’t. Nobody should be deterred from resurfacing their flywheel.

My only point is that it is a slippery slope to read intent into the rules. But the annual rules editors seem to be satisfied with some of the internal inconsistencies in rules (e.g. 12.6 says “unmodified” and 12.8 says “After balancing, the flywheel must…”).

Steve D.

PS - That explains why you run like an English major. :stuck_out_tongue: :stuck_out_tongue:

#11

Steve D wrote:

[quote]Ranger wrote:

9.3.12.6. Any clutch disc and pressure plate of original diameter may be used provided that they bolt directly to an unmodified stock flywheel.

12.6 states that the disc and PP are required to bolt to “an unmodified stock flywheel.” That precludes resurfacing. It shouldn’t. Nobody should be deterred from resurfacing their flywheel.

My only point is that it is a slippery slope to read intent into the rules. But the annual rules editors seem to be satisfied with some of the internal inconsistencies in rules (e.g. 12.6 says “unmodified” and 12.8 says “After balancing, the flywheel must…”).

Steve D.

PS - That explains why you run like an English major. :stuck_out_tongue: :P[/quote]

I love ya man, but that doesn’t make you right. The subject of the applicable sentance is the clutch disk and the pressure plate. It’s the old “subject” and “predicate” thing. The reference to the flywheel is the predicate to the sentance. The predicate modifies or provides info on the subject.

I’m not attempting to read intent into the rules. I’m applying the rules of the English language as taught by that grizzled wrestling coach. Remember when the teacher made you parse the sentance apart and diagram it all out? Just because we forget how English works doesn’t mean we can explore new meanings to the rules.

That wrestling coach English teacher was a big scary dude and you either figured it out or became his practice dummy after school. I chose the former because the latter course sounded like it would hurt.

And, after 25yrs of triathlons, my running is pretty good. It’s my driving that is weak.

#12

ctbimmer wrote:

[quote]9.3.12.6. Any clutch disc and pressure plate of original diameter may be used provided that
they bolt directly to an unmodified stock flywheel[/quote]

That says that any clutch kit can be used and I take that as saying i can use any clutch kit i want as long as its the original diameter as stock and it can bolt to a stock flywheel. So i assume that a racing clutch could be used as long as its the same diameter and bolts to a stock unmodified flywheel.

This rule does not state that the flywheel has to be a stock unmodified one only that the clutch in question bolts to a stock flywheel and is the same diameter as the stock clutch.

As far as the original question of the flywheel the only clarification I needed was that weight was included in the statement about the original specs as stock i.e. diameter, thickness, and weight. If that is the case then the stock unmodded flywheel will have to be used and im fine with that. Due to the wording of the clutch rule I take that as the afformentioned meaning.

#13

If they wanted you to run an OEM clutch kit and flywheel they should of worded it like that.

#14

BC, my interpretation of the rule is we can use any clutch and pressure plate we want as long as it bolts up to a stock unmodified flywheel.

Mr. Mechanic, Isn’t “sentence” spelled sentence. :wink:

#15

Balancing a flywheel involved removing material from a section of the flywheel, not resurfacing it. Resurfacing is just to give the clutch discs a smooth surface to engage to, like a brake rotor. Here is a pic of a balanced flywheel, note circular sections removed to balance weight, like adding weight to a wheel/tire.

#16

BCStringfellow wrote:

I agree. It sounds like they don’t want you running some ultra small ultra lightweight Tilton clutch and flywheel that you had to modify to get it to fit on this application. I just want to run my Sachs OEM clutch kit and a properly surfaced OEM flywheel. A rule clarification for next season would be real nice.

#17

Ranger wrote:

So the interpretation is that the phrase “…provided that they bolt directly to an unmodified stock flywheel…” means that the C/PP must be ABLE to bolt to an unmodified flywheel, but the flywheel you ACTUALLY bolt the C/PP to can be resurfaced and/or balanced?

Believe it or not, I can buy that. I guess the adjective “unmodified” is there to clarify that the mounting points for the C/PP must be the stock holes…

Ranger wrote:

And that’s why I won’t challenge you to a pit bike duathlon. :laugh:

Steve D.

#18

King Tut wrote:

Actually, it is OK if you run an ultra lightweight clutch. It’s the ultra small part the rule forbids. :wink:

Steve D.

#19

Steve D wrote:

[quote]Ranger wrote:

So the interpretation is that the phrase “…provided that they bolt directly to an unmodified stock flywheel…” means that the C/PP must be ABLE to bolt to an unmodified flywheel, but the flywheel you ACTUALLY bolt the C/PP to can be resurfaced and/or balanced?

Believe it or not, I can buy that. I guess the adjective “unmodified” is there to clarify that the mounting points for the C/PP must be the stock holes…

Steve D.[/quote]

We’re saying the same thing pretty much. The only thing I differ about is “but the flywheel…can be resurfaced and/or balanced?”

The sentance doesn’t say anything “about” the flywheel one way or another. The sentance is only about the clutch/PP.

#20

Resurface, yes. Balancing without doing the whole rotating assembly NO!!! BMW got it right…any balancing done to the assembly leaves very little whittling. If you rebalance the flywheel you will screw up the primary balance from BMW. Leave well enough alone.

Now, if you are building a motor, give the following to the balancer: Crank, rods/piston/pin/clips/rings, damper from front of crank with pulley and bolts, flywheel/clutch/lock ring with all bolts. Do not send friction disk. In other words, the complete rotating assembly. Every motor I have had balanced has has very little removed from the crank, and less from the flywheel. Chuck