lightweight flywheel?

Hello,

My 2003 R1150RT(ex-P) has 96,280 miles on the clock, of which 33,777 since I acquired it in May 2015. I commute daily year-round from San Jose to San Francisco, usually on I-280 but occasionally I take the scenic route to play in the twisties on CA-35 atop the Santa Cruz Mountains.

It's past time for my first spline inspect+lube, so I'm preparing by gathering parts and considering options and contingencies.

I'm making a list of all the things to check, and all the things to replace prophylactically, while I'm in there. (Is there a sticky here already, with such a list?)

I've studied various threads here with some great photos and advice, and I've watched Chris Harris' characteristically excellent and helpful

If the flywheel measures out too thin, the default action will be to replace it with the stock item, whether OE (BMW label) or OEM (Sachs).

When I've done similar work on my BMW automobiles, I have opted to instead install a mechanically compatible but lighter flywheel. For example, on my 1988 E28 535iS, I used the flywheel from an E28 M5.

(Why bother? The benefit I most enjoy of the reduced rotational inertia is quicker increasing revs when the clutch is disengaged, such as when "blipping" the throttle to match revs for smooth engagement in a lower gear. Precise matching avoids upsetting front-to-rear balance when downshifting to accelerate out of a corner. Yes, this makes a difference, even when driving a big heavy sedan instead of a race car, or when riding a big heavy touring bike instead of a Boxer Cup crotch rocket.)

It looks as though the same part was used on all the R1150s (GS, GSA, R, RT, RS, S) and some of the R850s and R1100s too. Its spec says 1.560 kg - pretty heavy.

A different part was used on other R850s and R1100s, but its spec says 1.739 kg - even heavier.

Are there any other mechanically compatible but lighter weight OE or OEM options? Any quality aftermarket options to consider?

Thanks for any suggestions!

Afternoon Bob

Your BMW boxer already has a fairly lightweight flywheel "or clutch housing" (actually fairly light entire clutch pack assembly) for a 2 cylinder engine with large offset pistons.

I haven't ever heard of trying to go lighter & some would like to go heavier.

If you want to spend money on that bike/engine then use it to have the clutch group assembly balanced.

I remember how shocked I was test riding an R1100RT for the first time after my R80RT. The airhead seemed to spin for days after closing the throttle, but close the throttle on the oilhead and the engine "instantly" died to idle. I thought dang this oilhead has NO flywheel! Hope you find a flywheel solution you like.

You mentioned the E28 flywheels -- Even just going back and forth from my E46 convertible to my E90 sedan N51 (manual trannies), their different flywheels take getting used to.

Considering that your "flywheel" is a stamped clutch housing and prone to being bent by ham-fisted mechanics, Going lighter would be ill-advised as well as next to impossible. Keep in mind that the clutch on your bike assembles opposite of what you are thinking of in automotive terms. The fixed clutch surface you associate with the flywheel is actually the the front / inner face of the clutch cover. The friction disk, pressure plate and diaphragm spring are sandwiched between the clutch cover and clutch housing.