How bad is this? Do I need to replace the crank? This is what is wrong with the engine that came free with the other parts I bought. (Well, low compression on one side but that is easy fix as I understand it: pistons & cylinder)

Maybe have a brass of copper plug machined up and inserted then weld it up and take the plug out, and machine the excess off.

What are we looking at here... is this the generator side?

If you're referring to the enlarged keyhole on the end of the crank? That's fixable, as described above. My only question would be if you need to pull the crank to do the repair... I'm not even sure that would be necessary if you're careful (use a MIG welder, surround the crank with wet rags, weld in bursts and monitor temp.)

I see a lot of flayed-off steel in the pic... that either came from the crank or what it was attached to I suppose. Only way to tell if it will still work is bolt everything back up and check clearances. If you're short material, you could make a spacer (basically a washer with two holes in it) to put it all right again.

Either way I don't see needing a new crank in this case... it looks salvageable.

No flayed off steel. You're seeing reflections of dust & stuff from the flash. Photo taken when VERY dark. In there it is pretty clean. No metal flakes. Just the hole is munched.

I would think the crank would have to come out but if your careful enough maybe

That damage looks to have been caused by someones pi**poor attempt to drill the pin out of the end of the balancer shaft for whatever reason  ....See how it appears to wander off to the lower right. Either that or the case hardening has failed in that area and a chip has come off.

I would go with the simple way stuff first......... Get a new pin and epoxy the fecker in  Turn the shaft through about 180degs so the pin rests aginst the good side of the hole and it will sit square.  The pin doesnt have to come out ever again so why worry. Iits there to index the advancer on the end of the balance shaft for timing purposes and to prevent the advancer slipping when subject to inertia and it sees negligable torque...... Get the advancer bolted up tight and I doubt you will have any problems.





Looks like the seal has failed too.

I'm with Sledge on this one. Did a PO try a diy ignition advance?

The PO is a real bike enthusiast. Saw his shop - must have been 30'x30'. Quite a few bikes. Seems engine just lost compression on one side then this. He put a 2004 engine into the 1991 bike (son's or cousins as he is tall and said he likes larger bikes). This guy was no BS'r and knew his stuff. Probably easier to use a spare GS motor he had than fix this one. He decided to clean out all his spare GS parts so that's how it was a steal. One man's junk is a parts whore gold! He has some really nice bikes. I got 2 sets of '04 pickips because he used the 91 pickup in the 04 engine when he swapped them. Also got the '04 carbs because he used the 91 carbs on the swap. He did weld on a bracket for the '04 oil cooler. Other than that, he said it was a real simple swap.

Nice to buy parts from someone who is not a duck and really knows bikes. I think I spend 2 hours listening to him and all his bikes and projects. Nice day!

He pointed out the cam end and said the engine was free if I wanted it (dumb question to a parts whore). Pointed out the cam and made sure it had all the shims and stuff in the head. Also mentioned oil test on the one bad cylinder.

But when he handed me the 89 clip ons and a perfect set of '04 forks - I nearly pooped my pants.

Consensus seems to be glue in the pin since there is no stress or force on the tiny rotor. That, thread lock and making sure it is on tight should do it. Just sold my extra old pickup. Since I got extra new pickups and a few sets of new carbs, maybe I'll put them on this old engine. Got a complete wiring harness with ignition and everything else in the deal. Probably a complete bike and more, minus the frame (of which I have 3 already). He put old carbs on new engine. No reason I can't put new carbs on an old engine. Carb to engine boots are the same.

I normally wouldn't trust it enough in normal internal fixes, but I think in this case I'd use a little jbweld on a new pin, then try to use a dremel/sandpaper to file it all back down nice and smooth. Sounds like a good plan to me.

What about a little copper tapered slug hammered into it? You could then sand it down and possibly glue it.

drill the hole larger and make a stepped plug .

Quote from: twinrat on January 15, 2012, 11:23:50 PM
drill the hole larger and make a stepped plug .

Now that is a good idea! 

Quote from: twinrat on January 15, 2012, 11:23:50 PM
drill the hole larger

Good luck on that one  ..... its made from case hardened steel same as the crank and cam is.

The case hardening is only about 0.050" thick and if you do actually manage to drill it oversize and get a good circle from it you will have broken through and removed the casing in that area with the risk of weakening it

Nice idea but nahhhh.......there are easier ways that that

+1 on jbweld, or weld, or completely tearing down teh engine and doing a BMW kinda rebuild.

me, jbweld. def.

Probably displaying my ignorance here, but what's a "BMW rebuild"?

ive drilled hardend gun actions for years .The secret is to drill very slowly using steady pressure and avoid letting the drill skid ,also use a good cutting compound .Also made firing pins for pistols from UMBRAKO allen keys MACHINED SLOWLY.