Originally Posted By: BMWR1150GS
BMW boxer engines (the OILHEAD version) are merely glorified lawnmower engines resembling half of an old VW air cooled 4-cylinder engine but fitted with some rather interesting cylinder construction.
Yes, and with a redline of around 6.5K RPM, it's not unlike my flat-four car engine, except of course that your twin is air/oil cooled, and hence may benefit from the thermal stability of the synthetic you're using.
Originally Posted By: BMWR1150GS
The oilhead design also utilizes a separate gearbox that is lubed with GL-5 hypoid gear oil in its own reservoir. Finally, the clutch is an automotive design, again, much like the old VW 4-cylinder design and suffers only when the rear engine seal fails and wets the dry clutch, necessitating a change.
Well, that's what one would hope and expect, but I have direct experience with two cases in which the clutch catastrophically failed and the final drive failed on an R1150R and an R1150GS, respectively . There is an article regarding the latter in this month's Motorcycle Consumer News that's worth checking out.
Among the ten or so people with whom I regularly ride, these are the only two who own BMWs. Your engine may go 200K miles without any major work, but it seems that the drive train is the weak point of these bikes.
To make matters worse, both these failures occurred while these guys were away on long trips. On the R1150GS, there was considerable lateral play at the rear wheel of between 1/2" and 1". Luckily, the failure occurred under warranty, and the nearest BMW dealer replaced it with a new one from one of their showroom bikes.
My friend with the R1150R wasn't as fortunate as his failure occurred outside of warranty at 30K miles, and he had to tow his bike home in a Uhaul. I dropped the tranny and were shocked by what we found: the splines on the clutch disc were worn almost smooth, and when it finally gave out, the free wheeling clutch disc knurled up the input shaft splines on the tranny when he pulled in the clutch. Had he never disengaged the clutch, the input shaft wouldn't have needed replacement as it did not appear to have worn otherwise.
I'm guessing that either Sachs had a very bad run of clutch discs, with substandard metallurgy or slightly off tolerances. Otherwise, perhaps the clutch design on these bikes cannot withstand the stresses of the newer, relatively more powerful engines.
On automotive clutches, the tip of the input shaft slides into a pilot bearing that is pressed into the flywheel. This bearing minimizes torsional flex under load. It takes only a little bit of play, like a crack in [censored], for these high stress components to work themselves free until the last straw -- in this case, acceleration through an uphill turn -- breaks them. BTW, the old clutch disc looked otherwise new with plenty of friction material.
In any event, we got the tranny back from the dealer and put everything back together. We'll keep our fingers crossed.
Sorry to go off topic here.
