E28 flywheel interchange?

[Robert Bondi]

One of these questions that can really only be fielded by someone with multiple BMWs. Would an E28-era flywheel work with the E12? I'm guessing it might just have extra sensors. New availability of either looks iffy.

[Mike W.]

Yep, not a problem as long as it's a M30 one. I've got a lightweight 533/M5 flywheel in my E12 and it does spin up faster than stock E12 or the heavy 535i flywheel. But either will bolt up and is fine to use. Only compatibility factor I've found is you can't use a 3.5 clutch friction disc with an early pressure plate, it hits with the pedal on the floor.

[Robert Bondi]

Awesome. Thanks Mike.

[jkycia]

You wonder if the supply for a new flywheels is iffy.
I looked around and found a company, jbracing sells a single mass aluminum flywheel that weighs only 8 lbs. I don't know if that is a good thing or not. Is there a significant drawback to getting an light weight aluminum fly wheel? I think stock is 16 lbs and then I have seen dual mass.
Do you want the heavy flywheel when you are idling and you may have the
air conditioner kick on and would otherwise stall the car? Wouldn't the
idle control. What is the property of the m5 flywheel that is appealing?

[Mike W.]

Stock E12 is roughly 17 pounds. Not bad. 533i/M5 (E28) is roughly 14 pounds. Better, it revs up quicker. 8 pounds seems awfully light, maybe too light on a street car. E28 535s used ~22.5 and E34s dual mass was over 30 pounds I believe. A quicker reving engine won't accelerate any faster but it will feel sportier.

[onovakind67]

A quicker reving engine won't accelerate any faster but it will feel sportier.

It will accelerate faster, acceleration = power/mass. Mass accelerated directly by the engine is more influential than mass accelerated after the gearbox, and also after the differential. We switched from a 18# steel flywheel to an 9# aluminum one on our road racer and the difference in acceleration was noticeable. Another advantage of a lightweight flywheel is the reduced gyroscopic effect when turning the car, the same with lightweight wheels.
Here's a mathematical analysis of the increased acceleration provided by a lighter flywheel on a couple of BMWs:

http://www.uucmotorwerks.com/flywheel/h ... _works.htm

[Robert Bondi]

An update on M30 flywheel searching challenge:

E12(D=240 X 27), 11221270286 - P/N has come back NLA from 3 sources despite appearing available on Realoem. I'm pretty sure it's single mass, but Realoem says it's twin mass? For more confusion, Walloth & Nesch has 11221262617 M30 flywheels; Realoem cross references that to many M30-based vehicles, yet doesn't explicitly show that P/N on any parts diagram....I wonder if it's a newer redesign that is somewhat universal on M30s?
E28 533i and M5, 11221271463, Realoem says NLA
E28 535i, 11221289244, Realoem says NLA
E3 3.0Si(D=240 X 33), 11221706577 (also used in E32,E34,late E24)

It's also amazing, if true, that the later E32 and E34 actually appear to use the same flywheel as E3 and E9? That certainly supports vast interchange options. Anyone vouch for this?

Any have opinions on resurfacing? We were originally treating this like a brake rotor where you can only remove so much before you need a new one; however, Metric Mechanic is very convinced you can resurface a used one many times before you've removed too much. MM makes it sound like less of a thickness issue and more of a surface issue - heat treatment during manufacturing makes the "skin" a bit harder and more durable - you don't want to go through that surface layer.

[Mike W.]

Wow, you covered a lot there with relatively few words Robert!

The way I read it, Motronic flywheels with the tab are unavailable new. No biggie for the E12 crowd. The 617 appears to be a new P/N for an E12 flywheel, relatively lightweight and available. The 577 appears to be a heavy 22 pound flywheel that would work, much like an E28 535 flywheel, but without the motronic tab. It also appears to be single mass and note it only came on the smaller engine E34s, not the 535, and I would guess it would work on an E12 and other early M30s. Whatever Tischer is calling themselves these days shows it for $276, but that doesn't mean it's available. Schmiedmann also shows the 617 to be available. One odd quirk is the 617 show up as ~7 pounds from multiple sites when it should be about 17 pounds, a typo I assume, but a consistent one.

On surfacing, I've had it done and it's worked well. I don't think there is significant surface hardening. To me the biggest thing would be to make sure they machine the step in place where the pressure plate is actually 1MM or so recessed from the friction surface. Without that it's like your brand new clutch has 40K of wear on it.

[wkohler]

Resurfacing the old one should be okay. M30s really don't go through clutches so there arent a lot of them out there getting resurfaced constantly. The step is critical and I really think there is plenty of room in the thickness department. At some point, the 1/84 and later flywheels will be desired for the purposes of lightening. Prices are slightly on the rise.

[Robert Bondi]

Good discussion. Thanks for the feedback.

I think I'll shoot for a -617 or resurface a used E12 flywheel; at this point, whatever route is less time consuming. W&N pictures suggest the -617 looks a lot like the 533i flywheel with beefy circle cutouts spaced 90 degrees apart. This must be where most of the weight is shed. If I get the -617, I'll report back on its weight.

[Robert Bondi]

Part of the significance of the -617 flywheel is that it's for automatics, while the -286 is for manuals. Clearly, they aren't the same, but could they be interchanged? Optimistically, maybe the difference is only weight?

[CabbageFumes]

Part of the significance of the -617 flywheel is that it's for automatics, while the -286 is for manuals. Clearly, they aren't the same, but could they be interchanged?

No they cannot. The Auto FW is just a piece of stamped steel. No machined surface for a clutch.

[Lock]

Hey guys, reviving this thread because I have a similar question.

I'm going to put in a Getrag 260 from an e34 535i into my e12 528i. I also have the dual mass flywheel which is in serviceable condition.

The problem is on my bathroom scales the e34 flywheel alone weighs in at 30lbs exactly, whereas the stock flywheel is around ~15lbs from previous posts.

This first problem I know it's going to rev up slower, but secondly I'm wondering is this going to cause harmonic balance problems or other stress on the engine? I'm assuming the front damper/harmonic balancer is designed to work with the flywheel, and I'm about to double it's weight.

I don't plan to keep this flywheel forever, just to convert the car to manual, then upgrade to a single mass lighter flywheel later. Just wondering anyone knew if this would cause some kind of damage.

[wkohler]

No damage. The E34 had a lighter balancer than the E12 and everything is independently balanced anyway.

[CabbageFumes]

I don't know if you have other plans or just don't care, but you do realize that there is no speedo drive on the later trans, right?
Anyway, as Chris said, balance isn't affected with a different flywheel.
The added weight of the dual mass flywheel is a trade off for a more comfortable gear change. If it is a commuter car, I'd keep the dual mass.
I just happen to have a new Sachs clutch kit for your dual mass flywheel if you haven't sourced one yet if you're interested.