I'm rebuilding the engine on my '76 CB750K6 and today began honing the cylinders. Wanted to share what I have so far and ask for advice before going any further.
Overall, the cylinders appear to be in pretty good shape with the exception of #4 which has some corrosion damage, probably from moisture getting in when the bike sat dormant for who knows how many years.
Before starting the process I measured #4 at the top, middle and bottom both 90 deg to the wrist pin and parallel. Overall, the measurements were in the 2.4035 - 2.404 range.
You can see by the first pic that even after honing for 7-8 minutes the corrosion is still visible (and I can feel the surface pitting). Remeasuring the cylinder at this point I am at 2.405 on average.
The factory manual lists 2.406 as the max before having to rebore and I'm thinking that taking it that far with a hone isn't going to clean it up. Your thoughts?
I moved over to #1 which is pretty clean except for some light scuffing 90 deg to the wrist pin. Five minutes of honing cleaned it up fairly well, though you can still see a couple of the scuff marks. See the second pic. A couple more minutes could possibly remove them all together.
Measuring cylinder #1 shows:
90 degrees to wrist pin-
- Top 2.404
- Middle 2.4045
- Bottom 2.404
Parallel to wrist pin -
- Top 2.4035
- Middle 2.4035
- Bottom 2.4025
So, maximum measured out of round is .0015 against the max allowable of .002 and taper is no more than .001.
The piston on this cylinder measures 2.402 at the skirt, 90 deg to the wrist pin, which is in tolerance according to the manual which lists 2.3939 as the minimum.
I'm expecting #2 and #3 to cleanup pretty much like #1.
I'm thinking that even if I can get #1 through #3 cleaned up and stay in tolerance so I can just go back in with new rings, the condition of #4 is going to require a rebore.
I'd appreciate your thoughts and feedback!
