piston to head clearance

[alanwoodieman]

have some used offy heads and would like to check to see if they have been milled before--my question is piston to head clearance, will be using BEST gaskets

[JSeery]

Ol Ron (and others) like around .050, but I have no idea what they would have originally been.

[grumppyoldman]

Get your grand-kids play-do, put it on top of piston, roll the engine over with head on, take it off and there is your clearance. Might check valve's at the same time. Do it without gasket and then add gasket thickness. wont damage anything doing it. Al

[40cpe]

You can just set them on the block without gaskets held on with a couple of bolts just screwed in 2-3 turns. Turn the engine twice and look for head rising off deck. If the pistons/valves hit the heads you can be confident they have been turned. If not, then clay them and add ~.055" for a compressed gasket.

[alanwoodieman]

40cpe-followed your suggestion, but use tin foil balls, head is actually hitting in the middle of the piston with about zero clearance, this contact is about 1" circle, rest of the piston is about .050 or close to it. can I clearance the head in this circle or ???

[40cpe]

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The experts will chime in here. If you put a Best composite gasket on you will have over .100" on the outer edges. Depending on your comfort level you can mill the heads and re-contour the head to match the pistons.

[JSeery]

There have been a couple of resent threads on reshaping cylinder heads to match the piston dome.

[tubman]

Lust curious; does this engine have Egge pistons (if you know)? I have heard that several years ago Egge's pistons had a pronounced "point" that caused this problem. Perhaps clearance the pistons to fit the heads? Maybe someone on here knows more about this than I do.

As to head clearance, I spent about 3 weeks last summer massaging a set of used Edmunds heads to achieve .040" to .050" clearance over the pistons. I'm glad I spent the time. This is the best running flathead I have ever had. Plus, the last time I checked my mpg, it was up from 14 (with the previous stock engine) to 18 with a Mercury running a 2GC. I think getting the heads right may be the most important thing one can do for a mild street flathead.

[alanwoodieman]

not sure they are egge pistons but are three ring type. I also wondered about working on the pistons. took another domed piston and just place it on an original cast iron head and it will not rock around like it does on the aluminum head. since the used head is the culprit I am going to work on it with a contour gauge and massage the head to work and see what happens

[Ol' Ron]

I've been using Egge pistons in all my builds for over 20 years and have never had a problem with them. I use alum balls placed in the center and sides of the piston with alittle grease. I have a .050" shim head gasket, but a used gasket will work fine. I look for .045/.050" clearance over the closes part of the piston. I do this to provode a quench area for better combustion. It works.

[alanwoodieman]

Thank's Ol Ron and all that offered advice, will let you know outcome!

[chap52]

Check past threads about "foiling", [/B][/U]using greased aluminum foil balls instead of play dough. I find that the foil is easier to measure than the floppy dough.

[Floyd]

I do what Ron says.
My opinion.

[alanwoodieman]

checked using a foil balls, used head gasket. near zero over the top of 3 of pistons and 4th had about .020. has any body gained clearance by working on an aluminum head? should have thrown these heads away when I saw them! these heads had been milled is an understatement!!

[hardtimes]

Originally Posted by alanwoodieman

checked using a foil balls, used head gasket. near zero over the top of 3 of pistons and 4th had about .020. has any body gained clearance by working on an aluminum head? should have thrown these heads away when I saw them! these heads had been milled is an understatement!!

Looks like you have pretty well figured out what you want and how to go about getting there.
I wouldn't be concerned about a little piston top mod. I've done this and it has worked for me. Maybe a combo of working a little off of each,i.e.- head/piston, will be your path ? Good luck

[chap52]

You can use a dremel tool or small grinder to grind the combustion chamber area in the heads to attain the needed clearance. Your looking for .040 to .050 clearance. I've done it with cast heads but not sure how much grinding an aluminum head can take.
I believe that Ol' Ron mentioned having used a dremel tool for this purpose in a previous post.
With the poor clearances your reporting I would look for some other heads.

[tubman]

As I stated in an earlier post, I put a lot of of time into a set of used Edmunds heads last summer and I'm glad I did. I think "hardtimes" is right about taking a little off of piston and the head, especially after your remark about the pistons having a high spot in the middle. With everything but the middle 1" at .050, you really don't have a big a job ahead of you as I did (I had to do all eight complete domes on the head).

"CharlieNY" gave me a hint that saved a lot of time. While doing the work, leave the gasket off and put grease on the piston instead of using foil balls. Then remove material where the grease sticks to the head. Since a compressed gasket is about .050 think, once you get no grease transfer you're done.

[alanwoodieman]

well, massaged the aluminum heads to gain the clearance, really did not want to work on the pistons, after all if it did not work I would not have hurt the engine and would have a good pair of wall hangers. so far so good, back together and run till temp came up and then some, will let cool and retorque the heads and go from there. thanks to all who offered suggestions.

[tubman]

Sounds like it worked out, and you have saved a set of heads. Let us know how this all turns out.

[alanwoodieman]

took it out today and ran it. 60/65 mph after warm up, everything seems OK, but I got my fingers crossed. again thanks for the help and fix ideas