oilburner /2

[boxedbike]

I was shooting the breeze with a guy at work when he mentioned a oilburning problem on his r50/2 (i think thats what i was) he said it would start and run fine but about fifty miles into the ride the bike starts burning oil like crazy. he rebuilt the motor himself and after discovering the problem took the bike to a local bmw mechanic who couldnt figure out the problem. any ideas?

[flash412]

any ideas?Run a leak down test. Then pour a tablespoon of oil in each cylinder, spin the crank around a half dozen times and run the leakdown again. If the number comes up, it has bad rings. Otherwise, I would suspect valve seals (more likely anyway). I don't recall offhand if /2 even have valve seals. If they don't, then the guides were improperly reamed during the rebuild. They're supposed to be installed and THEN reamed. And then the seats are supposed to be cut after which, the valves are supposed to be lapped.

[pmdave]

Flash, do the slash 2s have a crankcase vent valve? If the rings are bad, wouldn't it burn oil just as much when first warmed up as at 50 mi.?

The slash 2 is lubricated by slingers, right? Is there some sort of oil feed to the valve rockers? Could there be some "pumping up" of the oil in the heads that causes oil to be sucked into the intake guides? How is the oil around the valve rockers supposed to drain back into the case? Is there a drain hole that got plugged up during the rebuild? Excess oil in the rocker box that takes about 50 miles to build up would explain why it only smokes later in the ride.

Just brainstorming.

pmdave

[DarrylRi]

The /2s have no valve seals.

There is a timed breather that runs off the front of the cam shaft, and exits directly to the outside world (the 50s and 60s were a much simpler time) via a short tube at the lower front left of the motor.

The /2 motor is lubricated through 4 or 5 (depending on the year) oil passages that lead to: the front main bearing, the rear main bearing, the timing gears, the right cylinder base and, in later models, the left cylinder base. Lubrication of the big end conrod bearings is accomplished with the oil that passes through the main bearings and into the slinger rings (http://darryl.crafty-fox.com/motorcycles/slingers.htm), and then is guided into the hollow crank pins, where it drains to the inside of the big end bearings. All other lubrication, including the cam shaft, followers, the entire valve train, and the piston pin is by splash.

There's a drain tube that leads from the head through the cylinder and back to the sump. This tube is small and can become plugged. Also, when people assemble the cylinders, they tend to want to use lots of "goop" on the gaskets to make sure they don't leak, but it's very easy to fill in the holes when this is done.