Piston to head clearance


New Member
Mar 20, 2008
What would be the minimum piston to head clearance on a 1991 5.0?
I have a decked block with a max. .013 out of the hole. Having a small problem finding head gaskets to match World Product Aluminum heads.
World suggests Fel Pro 1011-2 gaskets, but these are only .039 compressed. I don't feel comfortable with only .026 clearance, so I would like to have your opinion. Should I mill the chamber, or take .01 off the piston. Is there a thicker gasket available for the aluminum heads.
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In order to be absolutely certain, I think you should call world's tech line and ask them if they can recommend a thicker gasket. You're right, .026 is too tight, and .039 is where you want to end up. I would not take any material off your pistons, because it will make them weaker. May I ask why the block was decked that much in the first place? Are you using the stock pistons still?
It was decked before I put my hands on it. It was equipped with iron heads, and had the .047 gasket, giving around .034- .035 clearance. There is no evidenve of any problem with that clearance, max rpm was at 6.2K
The absoulute maximum positive deck height is .013, this figure is on the "top" side and when the piston is pushed to the opposite side of the bore (it wiggles in the bore, of course) Measured above the pin, and with piston straight centered, it measures less than .01.
It would be easy to slightly mill the chamber where needed.
That was my primary suggestion, but a machinist said that the rods must be removed. I would prefer not to interfere with the press fit. How much can be removed without weakening the piston top?
Any affects on the quench if oem 5.0 piston top is modified? Will the small amount removed from the piston top upset the engine's balance? Will only cut the piston where head surface is flat, not all around. This makes for a sweep of approx. 25-30% of the piston top surface and .013 deep cut
I would question the two things here;
1. What has the block really been decked too? Too much will throw the rest of your mating clearances off... and that does matter, so you NEED to know how much has been milled off.

2. If the block is good to go, the pistons may be the incorrect compression height. Or it is correct but milling of the pistons is required.

If you have the part numbers to your bottom end... that should give you the dimensions you need to know in order to do this right.

In most cases, milling a piston has no affect on strength when accomplished by a machinist who does this on a regular basis. It should not be dropped off at the nearest machine shop... it will be screwed up once you get it back in your hands.
On average, custom piston machining is done by a very select few performance builders trying to attain the most perfect compression ratio, cylinder psi and custom head designs with radical cam events.
Naah, if you cut off the same amount that piston is above deck, and use a gasket that is .039 compressed, you are all set. if the positive deck is ,013, you cut off .013.
The question is, where should the measurements be taken?