what brand pistons for shave heads

S

swedishsteel

Senior Member
Have an 8ba at the machine shop ready to be bored. Machinist is waiting on me getting pistons. Have 4" merc crank and EAB heads. The heads appear to have been milled quite a bit--no ridge at the thermostat housing. I have read where some have had problems with the dome on Egge pistons not mating well with shaved heads. Does any one have experience with other pistons that may have a more compatible dome? Not hopping it up much--mild cam, 2 stromberg 48's, building a jalopy 36 pickup. Thanks for any input
 
If heads are cut to where pistons hit then standard practice is to re-dome heads. It is very time consuming consuming but can be done be hand if no access to mill or cutter. Ideally you want only .045” clearance piston to head for optimal squish. You will also need to check valve to head clearance. .045” minimum is a good number there.
 
Thanks Kiwi. I did rough measurement above valves with tin foil and have about .125, so I think I will be ok there. The old pistons are long gone, so can't do any measuring until it's bored and have the new pistons. I paid $10 for the heads at a swap meet several years ago, so not out anything if they don't work........but then have to find different ones!!
 
Ideally, the heads should be fitted to the pistons after they are installed. I have done it a couple of times, once on the Merc in my '51, and another time on my 258" "Hot Rod" engine. Use the foil balls to establish where you are; have the heads milled to give you around .050 over the piston head for proper quench, and then clean the head up to a consistent .050 with a die grinder. I think trying to fit the pistons to existing heads is going to be a very tough task. Piston installation should be done first. (Just like you want to have the pistons in hand before you do any work on the cylinders.)

I have built 4 flatheads in my life, and custom fitted the heads on the last two. Maybe it's just luck, but the last two turned out a lot better. I don't worry about the head volume or compression ratio, because when I get the quench right, I end up with 160-165 psi on each cylinder and the engine runs "snappy". There's some grinding involved, so that's why I like aluminum heads. I have several sets of aluminum heads extra (including a nice set of C8BA's) so if you're interested in going that way, get hold of me.
 
Thanks Denny. I will get it bored and assembled and then start on the heads. Speedway has .060 over Egge pistons for $220, so I think that's the route I will go.
 
The most important thing is for the dome profile of the heads to match the dome profile of the pistons. There are two basic dome profiles --> one uses a couple elliptical arcs to build the dome --> which will be a bit "pointy" at the crowns and the other is a consistent radius. Every aftermarket head that I've seen uses a consistent radius type of dome - while many original Ford cast-iron heads used the elliptical style.

The Egge cast pistons that I've seen tend to have the elliptical style, while companies like Ross will have a consistent radius style.

To me, the piston selection must match the head dome shape . . . so start there!

Head Gaskets: Most of the "traditional" head gaskets are about .052 to .056 thick (compressed). I try to tune my quench to match these head gaskets. This way, I can run a variety of head gaskets - depending on my application. (copper, graphtite, mls, etc).

But, there are now options from companies like Cometic that produce different head-gasket thicknesses. These can help tune your squish dimension to get as close to .040 as possible. However, MLS type gaskets require a smooth RA surface finish - so they may or may not seal with original deck surfaces (which tend to be a bit rough, or have some rust pitting). If I'm building an engine to use MLS gaskets, then I have the decks touched up to support the MLS surface specs.

B&S
 
Thanks for the info. We amateurs very much appreciate the knowledge that is shared by you who could build a flathead in your sleep!! If my EAB heads have elliptical domes, hopefully they will match, or nearly so, the Egge pistons I ordered. "Can't learn no younger" as my late Dad would often say.
 
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