I’m redoing cylinders on my R75/6 and noticed I have a little wiggle in one of the wrist pins on a connecting rod. No wiggle movement detected on the opposite side. Also, can slip wrist pins very easily on either connecting rods unlike other google references suggesting these normally must be pressed in slightly with some pressure. Is the lack of force normal for this model bike or indicative of worn wrist pins? Thanks for your reply.
Is the lack of force normal for this model bike or indicative of worn wrist pins? Thanks for your reply.
I have never had to replace the small end bush on BMW connecting rods, but I have done it on other high mileage engines where it is quite common for the brass bush to wear. Not the steel piston pin, only the brass bushing.
The bushing is pressed into place (not beaten or hammered), and then (when finally seated) reamed to the correct internal size. With a BIG bench vise you can get around owning a hydraulic press, but there's no way around the adjustable reamer and a Bushing Driver Set. Heat from a propane torch would also be a welcome addition.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
Thanks for the comment Richard. I think my concern is how much wiggle of the wrist pin inside the bushing is acceptable. Axial movement suggest the brass bushing is worn some. Since I have the beast apart this far, I might as well replace the bushing just to tighten things up. I have started calling around to see what shops might do this. Max BMW will but seems a little pricy. Anyone suggesting a good shop?
I'm with you, that seems loose. I ream the these bushings to barely allow the piston pin to push through using just index finger pressure (at room temp). Drop through (using the weight of the pin) is too loose.
I coat these liberally with multi-grade oil on assembly. Warm the piston with a propane torch to about 150°F, so that the piston pin is able to slide freely, and then assemble. (Don't ever beat the piston pin, you'll only bend the connecting rod.)
► If the connecting rod has to come off the crank AND the engine has over ~100,000 miles, then I suggest the rod be re-assembled with new rod bearing shells. Again, the bearing shells are liberally coated with multi-grade engine oil for assembly.
► Existing rod bolts AND nuts are washed in carb cleaner/ brake cleaner/ thinner and blown dry with compressed air, then assembled with RED LocTite. Marking the 2 parts of the rod before disassembly to ensure the rod and cap go back into place the way they came off is a good idea. Sharpie markers are the most important tool in the tool box.
Hope this helps.
Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.
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