Boxerworks.com

1980 R100T

Last thread was a doozie, so I'm starting fresh.

All in all, we determined through much effort that the crankshaft in my r100t is needing to be replaced.

only one I can find is on eBay for $400, and I know that I've seen better prices. Is it just a waiting game? Are there other options in the states for sourcing a used part?

Which models can I use the crankshaft out of outside of another r100? I've heard there may be options between the r75/7 and maybe some r80's? is that true?

R50, R60, R75, R80, R90, and R100 all have the same 70.6mm stroke. They have different counterweights but that may not be critical.

melville wrote: ↑Tue Jul 26, 2022 4:10 pm R50, R60, R75, R80, R90, and R100 all have the same 70.6mm stroke. They have different counterweights but that may not be critical.

Wow. That’s quite the range. Good to know.

Would it were that simple...

In 1981 there are actually 8 part numbers for crankshafts. These fall into two groups... those used on engines up to 09/75 and those used after 09/75. The difference is the size of the flywheel mounting bolts (10x1 for the earlier crank, 11x1.5 for the later).

As you can see, there are four numbers for each of the early and later cranks and I have no information what the difference is between them, it may be different balance weight masses or something else. What is apparent from the parts lists is that it isn't engine size dependant. By 2001, only two cranks were offered as replacement by BMW. 11 21 1 338 172 is for early machines up to 09/75 and 11 21 1 338 171 is for machines after that date. The good news for you is that the same crank is listed for every long stroke engine up to fininsh of production in 1995.

In conclusion, you need to avoid a crank from a /5 or all except the last year of the /6 models. Anything from a bike after that should fit and work with your machine. Ideally, you can be pretty certain that a crank with the part number 11 21 1 338 171 will fit.

Please be aware that I am working from various BMW parts lists which can be confusing, contradictory and sometimes just plain wrong (how many times do you hear of parts being wrongly supplied by BMW... now you know why), however, they're the best indicator available for part use there is. and form the basis of the parts lists published by RealOEM and MaxBMW... which have the same failings.

Rob

Rob Frankham wrote: ↑Wed Jul 27, 2022 5:10 am In conclusion, you need to avoid a crank from a /5 or all except the last year of the /6 models. Anything from a bike after that should fit and work with your machine. Ideally, you can be pretty certain that a crank with the part number 11 21 1 338 171 will fit.

As young as possible with low kms from a working bike would be what I'd be after.

Be patient...ring around a few wreckers.

You could give Re-Pscyle bmw a call here in the states

Stoners Stash out in California. Airhead Salvage outside San Marcos Texas.

I don't want to add to your woes but, as you now have to do a complete stripdown, make sure you check the oil pump, the pressure relief valve and the oil filter bypass valve. Something caused that crank to fail in the first place and lubrication failure is a good possibility.

Rob

Rob Frankham wrote: ↑Thu Jul 28, 2022 6:09 am I don't want to add to your woes but, as you now have to do a complete stripdown, make sure you check the oil pump, the pressure relief valve and the oil filter bypass valve. Something caused that crank to fail in the first place and lubrication failure is a good possibility.

Rob

The problem, as far as I can tell from the various symptoms, was excessive oil loss caused by improper use of an extra gasket at the oil filter cover. Which prematurely drained the oil from the system (within 800 miles, max), ultimately causing me to spin a bearing when the oil ran out.

Kurt in S.A. wrote: ↑Wed Jul 27, 2022 4:32 pm Stoners Stash out in California. Airhead Salvage outside San Marcos Texas.

outerbanker wrote: ↑Wed Jul 27, 2022 2:10 pm You could give Re-Pscyle bmw a call here in the states

Sweet. I’ll give them both a call.