850 Cylinder Head - Pre Skimmed Dimension?

Crockett23

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Jan 3, 2017
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I have an 850 Cylinder Head which has been skimmed, so I would like to know what the step height between the two faces marked in the picture would have been as stock. If anyone can supply this info. I would appreciate it as it should hopefully avoid me screwing around with a dry build to determine the thickness of a base spacer or thicker head gasket, or combination.
850 Head - A.jpg
 
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Crockett23 said:
I have an 850 Cylinder Head which has been skimmed, so I would like to know what the step height between the two faces marked in the picture would have been as stock. If anyone can supply this info. I would appreciate it as it should hopefully avoid me screwing around with a dry build to determine the thickness of a base spacer or thicker head gasket, or combination.
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Crockett,
My RH 10 was shaved in it’s past life. I use a factory base gasket along with a flame ring head gasket.I can’t give you any dimensions you are looking for but after Jim Comstock did the head along with refacing,all is well but you have to go through the process of many re-torque during initial installation.After I did that I have had no problems for over 12,000 miles. I also check the torque at 4,000 miles increments.
Mike
 
IIRC it’s around .110”.

If I’m wrong, hopefully someone will correct me….

But as Ying says, unless it’s had an awful lot removed, you’ll be fine, there’s plenty of scope for increasing the CR a little on 850s without issue.

And I believe that new AN flame ring gaskets are thicker than the old ones, so if you’re using one of them, again you have nothing to worry about.
 
If you really want to know what compression ratio you have, and have a target, or you are concerned something may not have adequate clearance....I recommend....screwing around with a dry build to determine the thickness of a base spacer or thicker head gasket, or combination....

.....and even a bit of plasticine (modelling clay) work, etc. It's all good engine build practice, working on knowledge, not ignorance.

It is what you should do because we don't know what you didn't tell us, i.e. what was fitted previously, your barrel deck height, chosen piston, cam lift, valve size etc.

But, if this is all pretty standard stuff and all you are concerned about really is too much compression for local fuel....I doubt you need to do more than confirm nothing hits....

From the photo we can (just about) see your head hasn't been skimmed 0.040", it's most likely less than 0.020", probably less than 0.010", and was done to return a flat gasket surface, possibly after a blown gasket.

Remember, if it's an 850 it may never have had a base gasket, and it is better not to use one, Threebond 1184 is good. If it had one, or two gaskets and/or a spacer, someone has been here before you!
 
I run a .023" copper head gasket, (half original thickness) no base gasket with an RH10 that's been cut .020".
No clearance problem.
 
I have a stock 750 head sitting around that has not been surfaced and it is .121". Could be a caliper malfunction. And it is not an 850 head.

Side tracking: I was counting on the flame ring being like it was 30 years ago on my current project. The older flame ring gasket compressed down to around .021.

Has anyone pulled a head off that had a newer AN flame ring head gasket under it to see what the compressed measurement of that gasket ends up at?
 
Thanks for all advice and feedback, so based on the .110 dimension provided by two members my heads been skimmed by about .060". I just got a Andover .028" thick compression plate so I think rather than add two of them I will have to do a dry build using one and check for clearance and hope the barrel deck height was not modified as well. Would anyone know what the standard height range should be, mine measures approx. 4.555".
 
Wow that’s a big skim!

You should def do a dry build check. But my guess is your clearances will be fine (assuming stock cam) and you’ll be somewhere around the nine-and-a-bit to one CR.
 
As annoying as it is doing the dry mock up to determine head gasket thickness, it is your best bet. Otherwise, you might end up with a bunch of head gaskets hanging on a nail in your garage wall. Ask me how I know. lol
 
Schwany said:
As annoying as it is doing the dry mock up to determine head gasket thickness, it is your best bet. Otherwise, you might end up with a bunch of head gaskets hanging on a nail in your garage wall. Ask me how I know. lol
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If we lived a bit closer I'd take them off your hands :)
 
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