Dual mass Flywheel Resurfacing -Myth or Fact.

[GS535i]

Following a seperate post on a 'E28' to E34 M30 flywheel swap, I thought to share this tidbid from the Master Machinest of a reputed local facility. He asked me why I was thinking of dropping the dual mass unit: one of the 'facts' I quoted was that they could not be resurfaced if required.
With a knowing smile, he reassured me that he had resurfaced numerous BMW dual mass units.
He brass shims the inner 'mass' such that they can be clamped down in the same plane. Them, brass wedges are used to force the two discs concentric. The resurfacing grind then proceeds as for a normal flywheel .. "A breeze" he said, with excellent results!
Interresting, or so I thought: not bad for <$50 if one wants a dual mass unit restored. Yes, I know that a preferred route is to 'downgrade' to the E28 M30 assembly; however, that may not be the route for everyone - and this may be a viable option.

[pyro]

and good for those with the m50 and have no other flywheel to get

[bfd]

The E28 flywheel is lighter, produces faster revs, and less complex, what's not to like?

[Bellicose Right Winger]

Good info. The world is full of individuals performing tasks others deem impossible. This is an interesting approach. I've often thought you chuck the dual mass flywheel in a fashion that reached over the ring gear and grabbed the rim of the surface the disk rides on.

Paul Shovestul





Following a seperate post on a 'E28' to E34 M30 flywheel swap, I thought to share this tidbid from the Master Machinest of a reputed local facility. He asked me why I was thinking of dropping the dual mass unit: one of the 'facts' I quoted was that they could not be resurfaced if required.
With a knowing smile, he reassured me that he had resurfaced numerous BMW dual mass units.
He brass shims the inner 'mass' such that they can be clamped down in the same plane. Them, brass wedges are used to force the two discs concentric. The resurfacing grind then proceeds as for a normal flywheel .. "A breeze" he said, with excellent results!
Interresting, or so I thought: not bad for <$50 if one wants a dual mass unit restored. Yes, I know that a preferred route is to 'downgrade' to the E28 M30 assembly; however, that may not be the route for everyone - and this may be a viable option.

[Bill R.]

common reason is that its making noise rattling or the other frequently seen reason is they want a lighter flywheel. Bmw also doesn't state that you can't regrind it. They state that its not to be resurfaced. 2 entirely different statements. I don't know the reason why, a couple of ideas pop into mind. The flywheel not only acts as a kinetic energy storage device, I think it also acts as a thermal mass to help absorb and dissipate the heat generated by the clutch. If you look at the cross section of the dual mass flywheel i have to wonder if there's a reason why they don't want it machined. http://www.bimmernut.com/%7Ebillr/images/flywheel-3.jpg





Following a seperate post on a 'E28' to E34 M30 flywheel swap, I thought to share this tidbid from the Master Machinest of a reputed local facility. He asked me why I was thinking of dropping the dual mass unit: one of the 'facts' I quoted was that they could not be resurfaced if required.
With a knowing smile, he reassured me that he had resurfaced numerous BMW dual mass units.
He brass shims the inner 'mass' such that they can be clamped down in the same plane. Them, brass wedges are used to force the two discs concentric. The resurfacing grind then proceeds as for a normal flywheel .. "A breeze" he said, with excellent results!
Interresting, or so I thought: not bad for <$50 if one wants a dual mass unit restored. Yes, I know that a preferred route is to 'downgrade' to the E28 M30 assembly; however, that may not be the route for everyone - and this may be a viable option.

[Bellicose Right Winger]

Bill,
Seems to me resurfacing covers any operation to restore the wear surface including regrinding or cutting in a lathe. I don't think BMW wants you to regrind or resurface the dual mass flywheel. If either was OK they'd give some dimensions and surface finish criteria, like is available for their other flywheels. I can't help but suspect they're concerned someone will hold it by the ring gear and end up with the internal gears transmitting the cutting forces.

Paul Shovestul


.......Bmw also doesn't state that you can't regrind it. They state that its not to be resurfaced. 2 entirely different statements. I don't know the reason why, a couple of ideas pop into mind. The flywheel not only acts as a kinetic energy storage device, I think it also acts as a thermal mass to help absorb and dissipate the heat generated by the clutch. If you look at the cross section of the dual mass flywheel i have to wonder if there's a reason why they don't want it machined.

[GS535i]

The E28 flywheel is lighter, produces faster revs, and less complex, what's not to like?

There is lots to like .... ;), that's why I went to the Machinest with an E24 flywheel in hand. The implied context of 'downgrade' here was to indicate reaching back into the '84 - '87 parts bin to get a clutch assembly that would IMPROVE the E34 - as you have indicated.
However, I thought the ability to restore dual mass units worthy to some - especially if a single mass option ( like the E28) is not available. New prices are .. well, high!!.
Bill, a valid distinction made between 'not to be resurfaced' and regrinding point. The amount of material removed during a resurface has to be less than a small fraction of 1% of the ~32 pound mass: It is unlikely that the kinetic energy storage or heat rejection capacity is measurably compromised; however, BMW had some rational to have made that statement. As you, I do not know the answer. Regardless, from this Machine shop, they claim to have been successfully doing this dual mass fix for some years .... with happy customers ...

[genphreak]

Bill,
Seems to me resurfacing covers any operation to restore the wear surface including regrinding or cutting in a lathe. I don't think BMW wants you to regrind or resurface the dual mass flywheel. If either was OK they'd give some dimensions and surface finish criteria, like is available for their other flywheels. I can't help but suspect they're concerned someone will hold it by the ring gear and end up with the internal gears transmitting the cutting forces.

Paul ShovestulSounds pretty logical to me Paul, great thread fellows... I always liked a lightened clutch, but dual mass is always easy on the foot, and these engines are not the smoothest... just concerned about my passenger/s, as opposed to the rally driver up-front who can handle any noise or vibration resulting from performance enhancements, he does disliketheir accusations of driving 'too roughly'- perhaps dampening the odd vibration out of the drivetrain would lower their concern threshold to my erratic traffic-speeds. :D j/k- if they piss me off I usually just drive harder. :D

[Bill R.]

grinding or cutting in a lathe either one was ok... I'm saying that bmw never said its impossible,they just say it can't be done. As in its a no-no. Flywheel grinders lock down the flywheel off the center hole not off of the ring gear... They use about a 36 inch diameter rotating table and have a cupped wheel that comes down just like a blanchard...So all you have to do is to lock the flywheel which as the other machinist does with the shims and then grind it... the cupped wheel gives it that swirly finish also... But what i am saying is that bmw must have their own reasons for saying it can't be refinished, they don't mean its physically impossible they mean don't do it. So i'm guessing that they have other reasons for saying so. And i don't think its just to sell somebody another flywheel. I have also seen a magnetic chuck 36 inch diameter rotating table grinder that was used for flywheels as well which didn't need any hold downs at all but they still used a center bolt




Bill,
Seems to me resurfacing covers any operation to restore the wear surface including regrinding or cutting in a lathe. I don't think BMW wants you to regrind or resurface the dual mass flywheel. If either was OK they'd give some dimensions and surface finish criteria, like is available for their other flywheels. I can't help but suspect they're concerned someone will hold it by the ring gear and end up with the internal gears transmitting the cutting forces.

Paul Shovestul

[winfred]

it may be as simple as they don't want the spoil/coolent getting into the interior of the flywheel, or the fact that the two parts of the flywheel move independantly and may or may not stay square to the cutter as the wear part wiggles around on the ring gear part

[Bellicose Right Winger]

Ok, I see your point. I mentioned the ring gear to make a distinction between the two sides of the dual mass flywheel. If you're cutting a flywheel in a lathe it's more secure to hold it by it's outside diameter rather then the small center hole. Both the center hole and the ring gear holdown are ok for normal flywheels, but they are the wrong way to mount a dual mass flywheel for resurfacing, unless you can lock the two sides together using shims or clamps. The trans side of the dual mass flywheel must be secure in order to resurface and there are several ways to do this.

BMW has other odd recommended practices, like allowing machining of rotors on all but M series.

Paul Shovestul



......... Flywheel grinders lock down the flywheel off the center hole not off of the ring gear... They use about a 36 inch diameter rotating table and have a cupped wheel that comes down just like a blanchard...So all you have to do is to lock the flywheel which as the other machinist does with the shims and then grind it... the cupped wheel gives it that swirly finish also... But what i am saying is that bmw must have their own reasons for saying it can't be refinished, they don't mean its physically impossible they mean don't do it. So i'm guessing that they have other reasons for saying so. And i don't think its just to sell somebody another flywheel. I have also seen a magnetic chuck 36 inch diameter rotating table grinder that was used for flywheels as well which didn't need any hold downs at all but they still used a center bolt