I pulled the pistons and connecting rods for inspection. This write-up shows my procedure.
I found a score in one of the rod bearings and I’m going to replace the bearings. The pistons are in good condition, but this bike had the original top end replaced at some point with the later Nikasil cylinders, pistons, rings and gudgeon pin (wrist pin). Unfortunately this reduce the compression from 9.5:1 to about 8.2:1 producing less horsepower and torque. There are European versions of the pistons and rings that provide the original 9.5:1 compression. Hmmm …
Here are a few pictures & a short video or two from the write-up.
Perfect timing Brook. I have the pistons out of my /5 and plan to put them back in over Christmas. I’ve also been debating about pulling the connecting rods to inspect the bearings, and haven’t done it yet. I was waiting until I had time to do more research, which you just accelerated for me. Thanks as always for the detailed write up. You embolden us newbies into thinking we can actually tackle these old bikes!
Well, anytime I can lead folks astray down the “primrose path”, it’s a good day 🙂
All the best on your Christmas project.