The Stovebolt Site Forums The Shop Area Engine Shop Milling a 235 head

I want to clean up a rusty 235 head , I would like to know how much can be milled off before valve clearance becomes an issue .

I also need to know what the original thickness was , so I have a datum to work from .

Any links appreciated .

An untouched head will measure 4.000" thick. At the front corner on the manifold side there is a small step...I just checked an 848 casting head and found it to be .090" deep. That step can be seen clearly in this tech tip:


https://www.stovebolt.com/techtips/milledheads.htm


As for facing I would suggest only the minimum required for cleanup rather than inviting other issues.

A trick we used on race engines with radical camshafts was to install a head onto the block without a head gasket, adjust the valves on one cylinder to zero clearance, and turn the crankshaft. If we got no valve/piston contact, the thickness of the head gasket was the safety factor. The same test would apply to a stovebolt engine, and it would be simpler, even. The only valve you need to be concerned with is the intake- - - -there's no way an exhaust valve can get into trouble due to its angle and position in the head.
Jerry

I had a 216 head milled by an old timer 30 years ago. He took just enough off to make it flat. He warned against milling too much off, as even if you don't end up with intake valve contacting the piston, you can still cause poor airflow at the intake valve from lack of quench area from too much milling in that area.
He mentioned that when he was into racing these engines, he would mill them on an angle, taking nearly most of the metal from the exhaust side of the head, resulting in leaving the intake side of the head mostly unmolested. He said that the valve train still worked fine and the difference in the head height could be taken care of since there are enough threads on the rocker arm adjusters to set the valve clearance. I wish I would have asked him what angle he used. I would also like to know what he ended up with in terms of reduced cc's of the combustion chamber and the resulting change in compression.
Hmmm, if I only new a guy who had the machinery, knowledge and the time to experiment with a project like this...
Carl

Thanks guys , I never thought to look in tech tips .. Perfect datum info . I will take the verniers , knock a bit of rust off and see what I am up for .

The angle mill is a triangle. The width is the gasket surface, the height is the maximum mill depth (.100" etc.) minus the minimum mill distance (just enough to make a clean pass, like .002").
This angle also mis-aligns the head bolts, and the piston-to-head & intake-valve-head-to-piston contact surfaces.

Angle milling works- - - -I've won dozens of races with angle-milled heads on small block V8's and the same principle would apply to a stovebolt. It just takes a few active brain cells to make the procedure work right. The nice thing about building "claimer" race engines that way is being able to use heads with casting numbers that dumb tech inspectors will pass without a second glance. "What are ya- - - -stupid or sumpin'? those are low-compression SMOG heads!" He didn't know I was making more compression pressure than illegal-for-class "camel hump" heads- - - -and running the same size valves!
Jerry

Don't do this. This makes me cringe -

The shop where I ran the connecting rod reconditioning department had a BIG belt sander- - - -like 18" wide and 4 feet long, that we used occasionally for cleaning up minor pitting on flathead Ford and MOPAR cylinder heads. For any real milling, we used a Blockmaster mill with a 24" circular cutter head and about 40 carbide bits on it.
Jerry