Flash (flash@bucolix.ncsu.edu) wrote:
: God I feel stupid.

And rightfully so.

: I don't know how I didn't notice. Two weeks ago, I : bought a 1971 R75/5 BMW. It had low miles and LOOKED to be in pristine : condition. I THOUGHT the price quite reasonable, though not a steal : (according to some friends). Now I'm kicking myself. Even though it : rides just fine, I think this bike has been wrecked, BAD. Yesterday, I : looked down and noticed that the right cylinder has been knocked back : about 2 inches behind where the left cylinder goes into the block.

Wow, this is bad news. It wasn't caused by a wreck though. For a couple of months in early '71, BMW lost the receipe for their cast aluminum alloys. Instead of the silicon alloy precipitation hardening with age, the alloys had the peculiar tendency to develop mass molecular repulsion (aided by some rare trace elements) linked closely to the rotating gravitational field generated by the steel crankshaft. In very simplistic terms, what you are witnessing is a miniature form of the plate tectonics that you seem so afraid of (for apparently good reasons).

: There doesn't seem to be any other damage. The only thing I can think : is that the previous owner hit a tree or something. What should I do?

If you look closely, you'll see that it isn't that the right cylinder is moved back 2 inches, it's that the left cylinder is moved forward 1 inch and the right cylinder is moved back 1 inch. The best fix for this problem is to rotate the engine in reverse for an equal number of miles to those on the bike now. This is best accomplished by removing the wheel and hooking your drill chuck to the driveshaft. I guess you're pretty lucky that the bike is low miles. It should only take a couple of weeks before you can start to see the cylinders drifting back into position. Watch closely.

The quick method to restore the cylinder position would be to get the jugs nice and hot (running the engine 2k past redline with no oil for several minutes is a good method), then tapping them back into position with a large mass of metal (a '68 Buick is effective).

: (It sure is great to have knowledgable friends on this Information : Highway.)

Thanks. You'll find the bill in the mail.

-Jeff Deeney- DoD#0498 NCTR FOLMA#2 '88 XR600-Shamu
jld@fc.hp.com AMA#540813 COHVCO '81 CB750F-Llamaha
"I will find humor in my everyday life by looking for people I can laugh at"
-Shanti Goldstein