A friend of mine gave me a bike recently - it was her Uncle Ben's beloved 1977 BMW R100S. Unfortunately it had been in various storage locations since his passing over 12 years ago and it was in kinda rough shape. I wasn't really looking for a project, but what the hell...
My first priority is to determine if it's worth spending much money and time on. I wanted to have some fun with it, but not get sucked into to a long drawn out project. I also wanted to spend as little as possible. I figured I'd better determine if the motor was any good. If that needed a lot of attention, I'd stop right there. I wanted to get it running, so I'll need to rebuild the carbs, change fluids, filters, and figure out if the pistons,valves, rings are OK. Fortunately with Airheads the cylinders are very accessible, and the carbs had to come off anyway and the headers where rusted through, so in about 5 minutes... (I just sawed through the header pipes as they were frozen into the heads).
Left side head and piston:
I don't have a picture, but it looks like the bores are OK. The right is showing a bit more wear with a few lengthwise scratches, but nothing horrible. You can see the hone crosshatch pattern, albeit faintly in some areas, but it's there. I popped the valves out and found a bit of trouble there. The exhaust seats have seen better days (I think one had been sitting in the open position and got a bit of condensation/rust damage. The exhaust valves also have some pitting (maybe from oxidation or combustion??). My plan is to use lapping compound to see if I can clean up the seat faces enough. If not, then I have decide if its worth spending the money.
Heres a pic before and after glass beading and jugs:
The blue tape didn't do much, but I was primarily worried about blasting gasket surfaces and also embedding glass in internal areas due to the beads shattering on impact. I figured if it was just loose beads, I could wash em out with a bit of diligence. Sure looks much better!
There was a bit of damage to the exhaust port threads on the left head. I think it'll work, but they are only about 50-60% there.
So I'm willing to put this back together as is with the knowledge that the valves may not be so hot. If I really like the bike, I can always pull the heads and get em done right. That shouldn't be too hard.
My plan had been to tear things down enough to make sure the engine was OK, clean things up, and as a result of tearing down - replace most of the seals. My initial thinking was to get the cylinders off and check the rings and bore, thinking they would probably be the worst of it. Once I got them off however, I found the conn rods had a lot of slop and weren't spinning very freely (kinda notchy). So that meant pulling the rods, which meant ordering the conn rod bolt tool. Skip forward a week or so and the tool showed up. Pulled the caps and found:
I found the rest of the big end bearings in the oil filter pleats! This bike probably had quite a knock, maybe that's why it was off the road??? However, the crank looked perfect - I guess BMW journal hardening is very good (better than my old Norton!). New bearings and I think we're good.
The worst of the issues I've found so far have been these bearings being trashed and the valves (both guides and seats) looked a bit worn. I'm going to simply lap the valves and put in the new bearings then on to reassembly!