Piston/Head Clearance

T

Towd56

Member
I am assembling this engine and as you can see by pictures the pistons extend .050 above the deck. I intend on using a best gasket which I am told compresses to .042? So obviously I need to make a little room. I've searched on this forum and have read about cutting pistons, gasket shims and double gaskets.

I am running a Winfield aluminum head with no cut out in chamber.

I am looking for some real world advice ....... what is the best route?
How much squish do I need?
Can I take that much off the top of pistons?
 

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Towd56 said:
I am assembling this engine and as you can see by pictures the pistons extend .050 above the deck. I intend on using a best gasket which I am told compresses to .042? So obviously I need to make a little room. I've searched on this forum and have read about cutting pistons, gasket shims and double gaskets.

I am running a Winfield aluminum head with no cut out in chamber.

I am looking for some real world advice ....... what is the best route?
How much squish do I need?
Can I take that much off the top of pistons?
Click to expand...

Hey Towd,
Well, that will not work as is !
Looks like you still have engine apart and working it..no ? If apart, that's good , with what you've stated. Because if I were in your predicament , I'd have the pistons cut till flush or maybe a few thou above deck. Gasket will handle a few thou above deck. You should , IMO, try for no less that .040 squish.
Pistons cut even with deck and , as you say, .042 compressed gasket should get you there. You can get even thicker gasket. I consult with 'BEST' gasket rep. I've had their copper type compress to .055.

If you do not like the above , your next best option would , IMO, be to have a 'flycut' machined into your head. That way, you can custom pick out exactly what you want for clearances.

I've used the double gasket method, and I've taken the tops of alum pistons off even with block by hand....very trying/tedious but worked well.

Now third action, and what I'd probably do in your situation. Tod (member here) is making several iron and / or alum flatheads. He can make any flycut depth or no flycut that you request. He now makes an IRON crowfoot Winfield type head. I have one (iron) that had .050 flycut. I removed all of the flycut (8:1CR) and used it on pistons flat with block. Ran great ! Contact Tod and tell him what you want from what he tells you is available.
 
The motor is still apart. I just fitted one cylinder to take some measurements. Based on your response - I'll mill the pistons

Thank you
 
Do this on the piston that protrudes the most.

Rub some motor oil on top of a piston, and in the corresponding combustion chamber of the cylinder head. Put some clay on top of that piston, and install and torque the head. Rotate the crankshaft slowly 360 degrees. Remove the head and measure the thickness of the clay.

My preference is to have 0.06" to 0.09" clearance between the piston and cylinder head.
 
Having had the same problem I took the head to a machine shop and had the area above the piston cut to allow the piston to fit.
 
Try "foiling" to determine the clearances. balls of foil placed on top of piston with grease, install head gasket, then finger tighten head. slowly hand turn engine, remove head and use calipers to measure the foil thickness. Then you can use a dremel grinder to mill the head chambers to size. Just did this on my flathead and it worked out fine, On the V8 your looking for .040 clearances.
 
Snyder and others have a gasket called a "premium gasket" that is .100 thick. I used one to solve a similar problem with a motor that was getting a high compression head and the pistons were too high.
If you try it get the one for a model b motor as it fits the combustion chamber better.
Also you have to torque it several times until it stops compressing or it will blow.
Another place to try is Cometic Gaskets, they'll make you any thickness you want.
We just used them for a flathead V-8 that was decked too much. Just be prepared for the sticker shock.
 
When in a pinch, two copper gaskets with copper coat is a good, cheap alternative.

Since you're mostly apart I'd mill the pistons. About .050" max.
 
I would suggest that you contact the piston manufacturer prior to cutting the pistons and ask how much they recommend as a safe limit.
 
I put the pistons on a little diet. Took .034 off them. I was told by manufacturer that it would not be a problem to take that much off. With the gasket I should have .040 clearance.
 

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Towd56 said:
I put the pistons on a little diet. Took .034 off them. With the gasket I should have .040 clearance.
Click to expand...

Good job ! Ha, you didn't say that you are a machinist ...piece of cake then. Advised not to try it with a harbor freight 'palm sander' :) !

Whose make are the pistons that you show ? Look to be the modern narrow ring type....and , IMO, that's good.
 
No machinist here - just a hack who gets himself in trouble. The pistons Are from Rich at antique engine rebuilding. Small ring and short skirt. They seem like a quality piece. Hastings rings.
 
Towd56 said:
No machinist here - just a hack who gets himself in trouble. The pistons Are from Rich at antique engine rebuilding. Small ring and short skirt. They seem like a quality piece. Hastings rings.
Click to expand...

Thanks and looks like you are on your way to having a fine engine !
I have a set of the modern thin rings in Hastings brand for .125 overbore. Wonder if Rich has pistons including that size ? Did pins come fit to pistons ?

BTW, the engine in my avatar is .125 over and with flat to deck piston tops, with alum super Winfield....no flycut ! Runs strong. I figure 7.5:1
Don't forget to 'clay' your clearance above pistons AND valves to be sure what you want !
 
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hardtimes said:
Thanks and looks like you are on your way to having a fine engine !
I have a set of the modern thin rings in Hastings brand for .125 overbore. Wonder if Rich has pistons including that size ? Did pins come fit to pistons ?

BTW, the engine in my avatar is .125 over and with flat to deck piston tops, with alum super Winfield....no flycut ! Runs strong. I figure 7.5:1
Don't forget to 'clay' your clearance above pistons AND valves to be sure what you want !
Click to expand...

Yes he has those size pistons. In fact, he mentioned having sizes all the way up to .140. Yes the pins came with; they have a tapered center too. Even nicer - he's a sinch to deal with. Very helpful. The engine in your avatar is the same specs as what I am building. Are those heads prone to have valve interference?
 
Check the how high all the pistons are. We had one guy on here break two heads, before he found out that one piston was to high.
 
Towd56 said:
Yes he has those size pistons. In fact, he mentioned having sizes all the way up to .140. Yes the pins came with; they have a tapered center too. Even nicer - he's a sinch to deal with. Very helpful. The engine in your avatar is the same specs as what I am building. Are those heads prone to have valve interference?
Click to expand...

Thanks much for this great info regarding pistons availability :) !

The avatar head has plenty of room for valve heads and I did some relief work , for better flow. Valves are also worked just below head for improved flow. Intakes being 1.750.

I'm not good with cam knowledge, but think that available valve head clearance has to do also with HOW MUCH CAM you are using (i.e.-lift). That's why I said to clay above valves also, particularly if using more radical cam. Cam in this block is a nos original B , that was prepared by Pete (member here) with special Chrysler lifters. Pete match cam grind with lifter faces and it runs/sounds awesome !

Just for reference: Crowfoot IRON picture of TOD Winfield. Alum Winfield. Yours look like alum shown ?

BTW...
Anyone know if Pete is still among us ?
 

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