Inliners International Forums General Discussion MOPAR Flathead 6 valve to head clearence

Hi
I am finalizing my 218 CID '54 Plymouth engine. Cam is reground by Edgy,260° duration, .410" lift.
The cylinder head was cut .060" this time. Of course, its history is unknown.
I put clay on the valve heads, installed the head as a test,and rolled the engine over without a head gasket.
The clay is really thin in some spots; you can see the color of the valves through it, almost nil.
Should I wimp out and use a stock head, or rely on the thickness of a torqued head gasket to provide ample clearence?

Ward

That's entirely up to you as to whether fear is going to get the best of you

Modern hi-po engine recommendations include approximatly 0.050" clearance between the top of the piston and the valve during normal testing and operation, as you described. What is assumed under these circumstances is that valve float will not cause the two to contact if the engine is operated at too high an rpm.

What you need to consider on your flathead is, as you stated, the thickness of the torqued gasket, but also how much you expect the valvetrain to lengthen/expand as the engine comes up to operating temperature. It can be calculated, but I can tell you that it isn't much, probably no more than about 0.001" to 0.002" if even that. And as long as the springs are good quality (preferrably new) and have about 110-120 lbs (or more) seat pressure closed, then a clearance of 0.050" is fine.

Use a micrometer on the clay to find out exactly how thick it is. If you have the old head gasket, you can put it back on and recheck by the same procedure. If you still don't feel comfortable, you can have flat valve reliefs cut into the chamber that smooth out the chamber dome over the valve.

Hope this helps, and give a holler if you have a question.

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David
newbie #4153

Hi
I got my dial calipers from work; they show .461" lift, .442" space in the head above the cylinder deck.
This means I need .019" more space to avoid interference. The new head gasket is .076". So, there will be .057" clearance, minus whatever the gasket compresses. I will go for it.

BUT now another issue: the head gasket, when laid on the head in the only way it lines up, overlaps into the edges of some of the combustion chambers about .040", and leaves the same amount of the head's under surface exposed on the opposite side of thesame combustion chamber. It seems the head's bolt holes are not drilled on center between the cylinders, so the gasket doesn't align on center either. What the Heck?!! The gasket is new, says it fits 218/230 1938-54. Mine is a 54. Date on head is 1-16-53, PN 1405849-8. The engine is a P-24, 218 CID Plymouth.

Ward

Just something to check. If you have the late model head that has the extra water jacket hole on the front of the head, you should use a head gasket that has that feature on it. I ran into that problem when I did a 230.