Vintage BMW Motorcycle Owners

I'm in month 3 of my winter frame-up and am making good progress. Frame and other bits in reassembly mode. I now have the engine totally disassembled. The crank felt great, with no discernible end play on the rods with oil in it. I've now cleaned out all the oil and set it up to measure the actual end play, which comes out at about .0005" for one rod and .0009" for the other. Not able to find specs on this, at what point should a rebuild be considered?

If there is any discernible play or “click” when checking then that is the time. I have always sent them out for rebuild since there is no better time than when the crank is out. That being said, I sent my R69 crank out to be rebuilt last year in August to a guy that sends them to “ Vech’s rebuilder”, and I am still waiting for it. He rebuilt a crank for me on another bike that came out beautifully, so I sent this one in, and it’s taking a lot longer. Fortunately I bought a rebuilt complete crank , and that is in the engine now, so I “finished” my rebuild, but will end up with an extra crankshaft which I will use the next time I rebuild it. So… I would send it out, but make sure you get some kind of ETA, or your project will stall. Even better if you can find a crank already rebuilt like I did! If you like peace of mind, I would do it, you’ll only cry once! Change out the rear bearing carrier while you are in there, they always seem “bad” when I have taken engines apart, and for gods sakes, buy NEW slingers, they are cheap. Also check your taper gap!!!! Good luck! Look at the pics, the specs are below

Thanks for the info, Robert. I'll double check the carrier. Do they come sized?

New rear bearing carriers will be tight, requiring more heat than you might think to drop the crank into. Had to heat my R69 case to about 325 to get it to go. That's pretty hot, in case you have any doubt.

Dave

If you order from SALIS, they do offer different sized rear main carriers. Gotta heat the engine in the oven if you want to make it easy on yourself, then hit it with MAP gas as you install it, drops right in!

Just checked with Jan and the rear carriers are on BO. His instructions also recommend reaming the carrier to size after install. Not sure who would have a 71,950 - 71,965 mm reamer. My carrier measures 72,000 as does the removed bearing OD. It and the bearing OD are nice and shiny...not much interference. Lots of co-polishing.

Am looking for other sources for the carrier.

Proper fitment and setup of the crank rear bearing and engine case bushing is crucial.

The Salis BMW Parts rear bushing is a custom made part that Jan markets. The bushing requires the ID to be processed so that it meets the factory interference fit tolerance with the rear main bearing.

The process of reaming the rear bushing seems too tedious, cumbersome and open to causing additional problems (different from just being a slip-fit worn out issue). Reaming a bore that is significantly larger than its length can be quite challenging. Reaming the bushing requires a high end quality mill and the adequate fixturing to secure the engine case.

I process the Salis bushing by honing it to the required interference fit ID spec. I have a system that uses a honing machine, tooling and a fixture such that the required final ID dimension can be held to a tolerance of +/-0.0025mm. The process is relatively quick and gives excellent repeatable results.

I spoke with Jan today, and he has a local machinist with a new milling machine that can hold the tight tolerance of both concentricity and diameter. I may have a friend in my neighborhood that could do this. If he can't no one can.

I have the milling machinery and tooling to do it as Jan processes these bushings to size. His local facility is setup for CNC machining. To each their own, for me, that method is just too cumbersome.

As per your friend....'If he can't no one can.'......That is a slight on all the top notch humble machinists and engineers out there that can do it on a daily basis for fun and/or a living. I have learned from those machinists and engineers that every day is a learning day. A dear friend (happens to be an engineer/machinist), whom is in his late 80's, told me his thoughts on his field, 'Strive to do your best every day and on each project, don't consider yourself the best'. I learn something new and interesting from him every time we converse or meet.

With respect to this part being available from several suppliers, it is fantastic that Jan has his own custom version machined and made available. It is ideal being able to purchase this part and custom fit it to the bearing to meet or exceed factory specs.

DIS295 wrote: ↑

Mon Mar 25, 2024 6:52 pm

I spoke with Jan today, and he has a local machinist with a new milling machine that can hold the tight tolerance of both concentricity and diameter. I may have a friend in my neighborhood that could do this. If he can't no one can.