R60/6 Crankshaft fit

Hello all. It's been a while since I've posted here.

I have to replace the crank shaft in my 1976 R60/6 (Mfg. 10/75 - as stamped in the engine case). I seized a big end bearing on the rear (right) con rod. I've pulled the old one out, and can BARELY make out the three numbers on the bottom of one of the bob weights. It looks like something like "735" or close to that.

My question is, as I am looking for used crank shafts, will a crankshaft from a 1975 R60/6 fit this bike? My engine case number starts with 492... I've found a used one with 734 or the bob weight.

I can't find any information about LWB vs SWB or if this even matters (mine's a LWB). I know there was some issue with parts matching around 1976 R60s, but I don't know that it has to do with engine parts or if that was just related the Wheelbase parts.

Also, besides discoloration or galling on the journals, is there anything I should be looking for on a used replacement?

Thanks in advance for any guidance you can offer.

Well, it appears that the part numbers are different for the '75 and '76 crankshaft. Go to RealOEM and compare the numbers:

1975 - 11211338172 (the fiche lists M10x1...not sure what that means...size of flywheel bolts?, but it lists 11211338171 and M11x1.5 which is the same for the 1976?)
1976 - 11211338171

But the crankshaft for the R75/6 or R90/6 of the same year appears to be the same part number. So that will let you expand your search some.

Actually, take the 1976 part number, go to RealOEM and copy that into the Part Number Application Search box. You'll see that that crankshaft is used across many different models. What makes the engine size is the piston/cylinder on the other end.

Make sure you have 11mm Flywheel Bolts

gossamerjohn,

You cannot use any cranks from an earlier bmw on yours because the flywheel bolts were smaller, (they had problems with them shearing), however any 1976 on will work, with the one exception being the R65 models, stay away from all of them. All the later R75/ R80/100's /7's, RS, RT, T's & Std. models use the same crank along and the 11mm flywheel bolts as yours.
It does not matter if it is for a single or double row timing chain either. If I remember right, even the monoshock models still used the same crank.

Many years ago, about 1980, I installed a crank from a 1977 R75/7 in a pals 1976 R90/6. He had forgotten to tighten down the bolt on oil filter cover, engine became oil starved and burned up one of the rod bearings.

Good luck with your repair...........................George

Thanks for the responses.

I'm looking into a wider grouping of years for the crankshaft and rod.

I see entire short blocks for sale on eBay for around $400. I wonder how much of that I would be able to use with my R60 top end if I had to go that route.

Camshafts are different for the R60 series. So, if you're going to swap, you'll need to swap the whole bottom end. Also be aware that prior to the 1976 series, the engine case opening was 97mm, then it became 99mm. So, without some serious machine work, you can't swap top ends around.

Also, the clutch/transmission situation changed with the 1981 models, so that's a restriction on mating on the components together.

Thanks, Kurt.

I'm seeing a few blocks but they are 81s or later. So, I'll just keep looking for a decent crank. Meanwhile, I'll tear down my block and clear out the oil passages etc..