Topic: CB900 con rods with pistons that have low CR in my K6 head.

[PeWe]

Next project: CB900 con rods (more meat than CB750 std)
1,5 mm longer that might work with my old AF pistons that had too low compression with my head with opened chambers 65mm chamber to cyl.   

Old Action fours pistons first that are lower than my new pistons that runs well in my engine. Revving in the garage with door open, no road test yet.

- The AF pistons might need a 1.5mm lift right?
- Or do I need the F2 Head?

[Don R]

Did you clay the pistons before final assembly? They look like my 836, I had a little contact so I shimmed the base gasket.

[PeWe]

Clayed, yes.
I have wished to get wider piston crowns since my head has opened (wider) combustion chambers for 65mm that matched my old RC pistons. I payed extra for that back in the days when the head was ported and RC pistons installed.
When pistons melted I bought action Fours with "normal" crowns with less compression as result.
Compression back with these pistons. I have only revved the engine outside my garage when trying pilot/main jet combinations and ignition.

I have got 67.5mm pistons with K2 cylinder since I wrote this thread. They might need better rods. I have to check if they can be used together without too much extra gasket under the cylinder. The old Action fours 836 with CB900 rods would be fine otherwise, too high crown might need an F2 head if I understand what to do with the oil passages fitting K2 cylinder.

Hmmm... finding new parts for a good price creates new projects for a lot of $$$