compression with plate?

Not open for further replies.
Feb 20, 2008
Just finished the first 200 miles on a fresh rebuild and got a 145 compression on both cylinders. The bike is 750 with a compression plate, I was wondering if that is normal?
I like Debbies advice, if its going well keep riding it. However, being a 750 there had to be a reason for a compression plate being fitted. Check for an ID mark on top of the head, usually above the right exhaust rocker cover.

If its C that means the head is a Combat, the highest compression version of all Commandos. These had a reputation both good and bad. Bad when poorly set up and wrecked crank bearings before Superblend mains came along. Good when set up with correct carbs and ignition they go extermely quick and are durable.

C heads are shaved down to get higher compression and technically speaking the pushrods should have been shortend slightly. Where is the this compression plate fitted - head to barrel or barrel to crankcase?

I second Debby's reply :wink:

Both cylinders are close and 145 psi is quite good (depending on the quality of the gauge and atmospheric pressure).

I wouldn't be concerned about pushrod length even if it is a Combat motor. Most came from the factory with stock length pushrods. The compression plate will help correct the valve geometry.

How does it run? :)
Not open for further replies.