head clearance

kiwitony

kiwitony

Senior Member
I see many threads on the 50 thou piston to head clearance,is this including head gasket or without gasket?I opologize for my ignorance.Thanks Tony.
 
I'm not the guru here, but it is generally accepted that the clearance is with the gasket and torqued.
 
Correct, and by the way, it's not gospel that it has to be exactly .o5o". Shoot for around 50 at the periphery of the piston. That is usually the tightest point. Now if you have pistons with an abnormally higher dome, it might be tightest at the center. I have run as tight as .025" on a stock rebuild with no problems, but I am not suggesting you run that tight.
 
Re: head clearance (measurement)

I have found that using an aluminum foil ball about the size of a marble works alot better than clay for measuring piston to head clearance. Anyone else try this.
 
Yes the aluminum ball is the most accurate. The purpose for this clearance is to increase turbulence in the chamber for better combustion.
 
I am planing to just put the heads on loose with no gasket and turn it over to see if the heads move. Anybody want to guess if I have a problem waiting? I have a Max1 and Edelbrock heads from Speedway.
 
I am building a block that's been decked a lot, I have copied the curvature of the top of the piston... I machined the same curve onto a used piston, cut out 1/4 off the top to be able to see the curve in the heads, and by using spray graphite and a different block-to stay located- using a bur and porting stuff, doing my own doming job... As I go, I check piston to head interferance with feeler blades between head and block, shooting for .020- to give about .040 clearance with gasket... Karl


Oh yeah, it's lots of fun
 
Karl Wolf said:
I am building a block that's been decked a lot, I have copied the curvature of the top of the piston... I machined the same curve onto a used piston, cut out 1/4 off the top to be able to see the curve in the heads, and by using spray graphite and a different block-to stay located- using a bur and porting stuff, doing my own doming job... As I go, I check piston to head interferance with feeler blades between head and block, shooting for .020- to give about .040 clearance with gasket... Karl
In your case, I'd find it simpler to re-machine the dome on the pistons you are going to use. Most flathead pistons can tolerate some cutting. Unless of course, your going for pop-ups. Need access to a lathe of course.
Click to expand...
Click to expand...
 
Andy said:
I am planing to just put the heads on loose with no gasket and turn it over to see if the heads move. Anybody want to guess if I have a problem waiting? I have a Max1 and Edelbrock heads from Speedway.
Click to expand...
Andy, if you have the new Edelbrock heads that have been CNC machined in the valve pockets I dought that you will have any valve clearance problem with a Max 1 cam. Those pockets are .500 deep. Walt
 
Put a thin film of oil on your head and piston, then mix a small amount of bondo, about the size of a marble. Put the bondo on the piston, bolt down the head and wait about half hour. You will then have a perfect cast of your cylinder head clearence and a more accurate thing to measure. I learned this from an old Bonneville racer, believe me he knows what he is doing.
 
My understanding is instead of a head gasket you use washers of a .050 thickness. The .050 is the thichness of a compressed head gasket. Then use play-doe or aluminum foil ball on top of the pistons and valves. Turn the engine over one complete turn. I have also heard two complete turns. Then unbolt the heads and measure the thickness of the material.
My engine builder says you can run as low as .035 on a flathead. He said even on a small block Chevy turning 7000 rpm will not hit at .035.
They do make thicker flathead ford V8 head gaskets. They cost extra but sometimes they are nessary.
The issue I ran into was I used Ford EAB heads on a Merc. That would be fine but they were rusty like most old heads are. It took .011 to clean them up. That put my piston to head clearance at .035. I haven't fired it up yet but it should be fine. Gene
 
WHOO THERE!!!!!
There is a reason why I picked .050". I know that in the stock car racing engines, the stock rods will stretch at hi rpm. I have a photo of what happens when a piston hits the head at hi-RPM. Some aftermarket pistons are quite heavy and at 5k you might loose some space. The Egge 3 ring piston is quite light and so far non of the engines I;ve built have had any problems. Ross pistons are even lighter and the "H" beam rods won't stretch ay our operating RPM. This is why I put a 4500 RPM limit on my street engines. To rev higher cost more, but doesn't offer any more performance. There has to be a reason for what we do.
 
FWIW I had a problem with Offenhauser heads on an otherwise stock French motor - One or two pistons were just kissing the heads right in the middle. From feeling the dome of the French pistons they appear to have a slightly higher dome in the middle, normal flatty pistons that I have seen seem to have a dome of constant radius.
Mart.
 
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