Forum bmwbike.com

Help! 1965 r50 with Steib S500 chair. Newly rebuilt engine from the crank out. 700 miles since rebuild. Now running with engine vibration at speeds over 45 mph, aluminum sounding rattle. Oil evidenced on rear fender below the plate holder. Do I need rings? Cylinder honing? Overbore? Can I put r60 jugs on instead? Thanks for your help.

You don't give details of the rebuild or the set up for sidecar operation.

For the R50 to pull that sidecar, the bike must have:
1. Rebuilt piston to cylinder clearance of .06 to .07 mm (bored looser than a solo engine).
2. Final drive gearset with 26/6 ratio.
3. A very careful break-in. The manual says don't exceed 12, 22, 34 and 47 mph, and only hold those speeds briefly.

The oil below the license plate must be blowby from the breather tube, though it is odd that you should notice it back there and not all over the bottom of the engine and front of the rear fender.

Pulling that load, perhaps without proper set up and break-in, the engine could have suffered some cylinder seizing, accounting for the noise and blowby. I would not run the engine again until it was taken down for cylinder inspection.

As for putting R60 jugs on an R50, I don't know but it does not look easy. The cylinder heads have same part number and I have heard they are interchangeable. But the R60 pistons are 4mm bigger in diameter, and the con rods have different part numbers with the R60 stroke being 5 mm longer.

The R60 does not supply much more low end pull than an R50. I wolud save your money and apply it to makeing sure that you have the correct clearance and gearing for side car use. Also make sure you are using a quality piston like a "KS" and break in carefully.