Bore or Hone Advice

[Gibson]

Yes it looks like pitting is from corrosion. Perhaps you could find a good used cylinder, or the big bore kit would be cool...

[tsa]

Yes it looks like pitting is from corrosion.

I would say the same. Piston at BDC, and condensation sitting next to the top ring.

Before deciding what to do, pull the right barrel as well. Even if not smoking as much as the left, there could be similar damage that you ideally would want sorted now you overhaul it. In any case, you'll see if you need to source one vs two R75 barrel(s)/piston(s).

Have you thought of looking for a pair of nicasil R80 barrels/pistons? Many R80 owners have upgraded to R100, so there should be more spare ones around than R75 barrels. They will have to get their cylinder bases machined down from 99 to 97 mm diameter, but that (and a set of new R80 piston rings) will probably be cheaper than a rebore and buying new over-size R75 pistons.

[hudson]

Thanks for all the input guys. Pulled the right side and is in great shape as is - I am am sure honing is all that is necessary - no deep scratches or corrosion (as long as within acceptable bore specs). No smoking and good compression. At his point, I dropped off both cylinders at boxer2valve in Hendersonville, NC. Getting their input. Again, really appreciate the suggestions.

[Roy Gavin]

https://www.ebay.com.au/itm/BMW-R75-5-R ... R-JUG-BARR