Flathead: not enough piston to head clearance: WHAT NOW?

Got the french block with 4" crank, Egge Pistons and new Edelbrock Blockletter heads ready to be zipped up. I clearanced the pistons and valves with clay and used a new dedicated Felpro composite gasket in the process. I only get around .020 to .030 clearance over the pistons, (hard to tell with the clay at that thickness - valves have plenty clearance).

What are my option at this time:
-recrown pistons - Egge confirmed the pistons will take a .030-.040 cut, except at the very perimeter. I have a CNC guy who could do this easily for me. Drawback: dissassemble pistons and rings, etc..
-mill heads: set-up for machining very tedious and much more involved than machining pistons: advantage: lots of meat to safely remove
-mill .040 aluminum shim with same contour as head gasket and mount on aluminum head side. Disadvantage: will this seal?
-Run as is???

I measured several different head gaskets and all seem to be about the same thickness.
What dou you guys recommend in this situation to bring my clearance to the recommended .050 (up to .100")?

Thanks!

 

Run a thicker head gasket?

 

Cut the pistons you need approx .050" clearance. Not much hassle to break down rods and pistons.

TM

 

Which heads did you get .400 or .425" clearance?

 

Do the pistons come above the block surface. The clay maybe giving a false reading at the close clearance. A lot of motors run with a tight quench

 

Have the Edelbrock block letter heads. They only come in one version. I think the .400 or .425 only refers to valve clearance. Piston clearance seems to be identical when I clearance the Edelbrock or the old .400 Offy heads.

If anybody KNOWS that there are thicker gaskets out there let me know. Measured copper, Best Gasket and Felpro and can't see any real difference.

 

Although I dont know of a source off the top of my head. I cant believe that no one makes a thicker gasket especially in copper.

 

Try using solder to check for accuate clearance before cutting the pistons.

 

I used .047 head gaskets from Flathead Jack.

 

If the pistons don't come above the block surface, then you have adequate clearance. .047 is close enough to .050.

 

i just googled "custom made head gaskets" and got lots of links. here's just one: http://www.headgasket.com

 

Great info all! The pistons pop up quite a bit over the deck.
Gotta try the trick with the solder for accurate measurement.
Dragsta- thanks for the link, will give them a call and do some more research.

 

Can you say FLYCUT. That is what i had done to my heads. Older Edelbrock heads. The ole guy charged me 80.00, Trouble is he retaired. He made the tool to cut the heads himself so anybody that rebuilds the flathead and has a up to date machine shop could build a tool pretty easy. He told me he would he would charge 10.00 a hole. It worked for me and that was 6 years ago, and still running strong. 8-BALL

 

I'd love to see a picture of the piston and the pop-up amount - just to see what you're talking about. The EDGE of the piston (next to the bore and deck) should be flush with the deck, or damn close. If the edge of the piston is sticking up beyond the deck, then the piston pin location is wrong - which usually means they are for the wrong stroke crankshaft.

Other things:

1) I've seen some piston manufacturers who used a smaller radius on their domes - which makes the dome stick up more. You might compare the radius/domes on these Egge pistons to stock and see what you see. If the radius is wrong, then you have to consider the following:

a) Using a different piston manufacturer (would be my choice)
b) Modify the piston crowns to the correct radius
c) Modify the heads (which I wouldn't do to brand new Edelbrocks!). I've had older/used heads redomed (folks like H&H can do it), but I've never had to do new heads.
d) Put thicker head gaskets -- which may be the easiest, but not my favorite as you shouldn't have to go this route if everything was designed to work together as it should.

The piston crown should match the heads -- this gives the best (and consistent) quench area and you want about .035 to .040 over the piston with the heads torqued tight. On a race motor we run a bit tighter - like .030 -- as we're not worried about carbon build-up.

2) If the pistons are the wrong stroke, then you can easily have the piston sticking out of the deck by 1/16" or 1/8".

 

I can say FLYCUT and I can also do FLYCUT since I am a machinist ;-)
Cutting a head while retaining the original dome shape is very involved and setting a head up for machining is much more work than redoing the pistons. I only have manual machines available that's why I need to take it to one of my contacts for CNC machining if I went that route.
i have flycut valve pockets, which is no big deal and much less critical than the dome over the pistons.

 

The edge of the piston is still below deck height and the curvature of the piston and head conform nicely with piston having a slightly smaller radius.
I will have to remeasure the exact clearance using the above mentioned solder (or similar harder material). Silly putty does just not measure very accurately. I guess that's why it's called silly...
There is nothing major wrong with the components since I am not that far off the spec. I might very well be at .030, but it's a little too close for comfort.
The french block has never been decked, pistons , rods are correct. Crank has been ground at .030 before I got it so there might be a chance that the crank pins have been ground out of center, but how much could that in all reality be - maybe .010"?

Since this not a high performance build I favor the thicker head gasket / gasket shim
that DRAGSTA mentioned in his post earlier. I found a couple of other companies that can do shim gaskets. 1/32" probably get me in a safe range of .050" -.070.

I understand that after .050 some perfomance loss is expected because of reduced turbulence and such, but since I would not be able to recrown the pistons out to the perimeter that would probably apply in that scenario as well.

I appreciate the advice!

 

Method from an old Flat-Head Race Engine Builder. Mock the engine up with no gaskets. Get the piston to just kiss the cyl head with no gasket !! Install a .047 gasket and it'll scream !!! >>>>.

 

Mike I don't think you ever specified how thick the gaskets you have are. Cometic head gasket are .051 think and come in the standard and big bore option. They can also do custom thickness.

If the head gasket won't get you there I like the "flycut the heads" option.


Link to Cometic: http://www.cometic.com/domesticauto.aspx

 

I just use the modeling clay that kids use -- comes in a '4-pack' with 4 different colors. I put two pencil sized strips of it - left-to-right and top-down. Then once you've slowly turned the engine over, then you can take a razor blade and cut the pieces down the middle to more accurately measure them.

You might want to put a little 'PAM' on the head to keep it from sticking

And as a bonus . . . that one 4-pack will last you YEARS!

My guess is that the Egge pistons have a higher dome than stock -- have heard about that from a few different folks in the last few years.

 

If you have a doubt on the clearance issues. Just leave the gasket out, rotate the engine on the stand so the deck of the block is level, place the head on the block with no gasket, I use a set of turned down studs for guides, now crank the piston to the top and measure how much the head lifts off of the block. You now know exactly how much interference you have >>>>.

 

Henry Floored - good link. I will give them a try for a custom made thickness if that's whats needed. The three different types of gaskets I had measured all about the same, although they are kind of iffy to measure when some are used and some are not.

Engine Pro 5x: Can you tell me your secret to get the piston to kiss the head if nobody's looking? haha.. Either they do or they don't, else you have a forced marriage :-(

Bored&Stroked: I guess I have have to fork out the big bucks for the REAL DEAL. I think the stuff I had was some my wife made out of corn starch and grape juice. At least is provided a pleasant sensory experience!

 

"The edge of the piston is still below deck height and the curvature of the piston and head conform nicely with piston having a slightly smaller radius."
Swissmike, if that's the case, I don't see how you could have a clearance problem by the time you put a gasket on. Beyond that, Bored and Stroked spelled it out nicely. Wayno

 

An even better method for checking clearance is to use balls of aluminum foil. And I also had a problem with Egge pistons hitting the cylinder head. My engine was built originally with Motor City pistons. When I replaced them with Egge pistons, they hit the heads.

 

Yes the .400 or .425 is the maximum recommended cam/valve lift

 

How big is the bore?

 

Ha Ha !! I've already told you too much LOL >>>>.

 

Swiss Mike, I use a Smitty lathe/mill combo and made my own flycutter its easier than doing the pistons made the cutter to match the piston dome and its quick to do..............

 

Wayno- of course you're right. I typed before thinking. I thought of having adequate distance between the top ring and deck height. I think the edge of the piston is very slightly above deck. I didn't pay it extra attention.

Roseville Carl - post a picture of your fly cutter. I am interested to see how you did it.

Flatjack - thanks for the tip!

Wow, learned a lot in the last couple of hours!

 

This is at least the third issue I've heard with Egge pistons...

 

Yep - that is one reason I won't buy or recommend them . . . the other is that everything I tend to build seems to like or need forged slugs

I see no reason why a guy should have to even think about fly cutting the domes on a new set of un-milled heads. Egge has the radius wrong - pure and simple.

I have a big dome fly cutter for this type of work - but it is NOT easy to use! You better have a big-ass mill that is very tight in the ways and you better REALLY mount the head well. It is hard to get them to cut nicely and not chatter unless you are all jigged up and have everything just right (including a sharp cutter).

My recommendation is to not "fix" the domes on your new set of Edelbrock heads, I'd swap pistons or re-crown the pistons before I'd do that. The real problem is the pistons - not the heads. IMHO fix the problem at it's source Okay - time to get the heck off my big ass soap box!