Combustion chamber volume specs needed

I'm trying to get an average spec of the combustion chamber volumes of stock unmilled 750 & 850 heads.

I want it for the most popular heads which had about a .120" step at the squish band.

Measured without the head gasket.

So far I'm getting 48.5cc for the 750

and 50cc for the 850

any confirmation on this?

thanks
Jim

They changed them over the years. 45 for a combat to 50 for an 850 plus or minus a couple ccs. Jim

Plus the volume of the head gasket space...

I want it for the most popular heads which had about a .120" step at the squish band.

Measured without the head gasket.

Plus the volume of the valve cut out, about 4-6 ml each IIRC.

I know this is an old thread, but I thought I would add to it. Today I am building out a 1971 750 and needed to do a compression calculation for my own knowledge.
Bore was 73mm, stroke was 90mm (89mm spec.)
Head was stock with stock valves. Recess lip was .120 " deep from edge of head
Combustion chamber volume was 49 ml to edge of head
Piston protruded 1mm above cylinder, with normal valve cutouts.
A used head gasket was used (combustion ring type about 1mm thick. A grease seal from top of top ring to cylinder height was added.
Assembled head to cylinder and filled chamber to 3rd thread of spark plug hole.
Total combustion chamber now accepts 55ml of fluid (ATF)
My calculation of this combination yields 7.8 : 1 compression ratio..

This was less than I expected but it is what it is and I will go forward with it.

Now to tear it down, add a cam to the mix and check clearances.

Jim, this is a summary of some of the combustion chambers I've measured over the years. Don't know if it will help, but maybe it will be of some use.

Jeff Law’s 750 head converted to 920. Milled and counterbore machined – 44.6 cc.
Steve Shivers’s 750 head converted to 920. Milled and counterbore machined – 45.8 cc.
Head from Marc Field’s Dunstall 810 engine. 850 converted to 750 bolt pattern, milled. – 42.4 cc.
850 head from Jim Schmidt’s race engine. Milled. – 42.4 cc.
Axtell 30 mm port 750 head – 51.0 cc.
Axtell 32 mm port 750 head – 48.8 cc.
Stock Mk3 850 head – 51.6 cc.
Mk3 850 head milled .060” – 43.2 cc.
Stock Mk2 850 head – 51.8 cc.
Short Stroke 750 head – 55.2 cc.
Another Short Stroke 750 head – 52 cc.
Ex-factory Flat Track Short Stroke 750 head as removed from John Hately’s bike – 57.3 cc.
Ex-factory Flat Track Short Stroke 750 head after milling – 50.7 cc.

Nominal factory spec for standard RH4 850 head is 50 cc, and for RH7 short stroke head is 53 cc.

Ken

Ken.. Were those measurements made from the head volume only, or assembled on the cylinder?
thanks.. Bob

Those measurements are the combustion chamber volume in the head. measured with a burette, ATF, and plexiglass cover plate, with stock spark plug installed. No cylinder involved.

Ken