276 stroker from 35 years of parts

[GB SISSON]

That's kinda scary, Terry. With the extra compression will I need to run premium gass?

[GB SISSON]

Originally Posted by cadillac512

If you have one of those profile checking/transferring tools that is a bunch of hard wires that slide in a flat central sleeve, they are really handy for checking how a piston fits in a cylinder head dome. Rough, but handy reference data. Also, remember that as the heads are milled the dome decreases in diameter and may get close to the pistons around the perimeter depending on how far down the pistons are at TDC.

Terry, The more I learn about the process I am now involved in, the more I understand the principles you put forth here. At the time I couldn't visualize the piston shape as relates to head shape. Now I understand why I need to get a contour gauge as I bring my heads around to conform. You also called it on piston height as I really had to grind to get the outer perimeter into the realm of .040, and still not there yet. Others here as well have offered excellent advice that I didn't quite understand, but should have, as this territory was so new to me. I have always been a 'visual learner', the type that has to take tools in hand and almost ruin something in order to finally get it. This is not to infer that I know jack **** about cylinder heads, but I'm getting a taste for sure. Thanks to all of you.

[cadillac512]

Gary, this is stuff that takes years to learn, and in my case, a lot of good information and research by folks who were nice enough to publish their work so we can benefit from it. It's interesting for sure!
If you have the brand and part number of the pistons you are using I'd be very interested in knowing. The situation you are dealing with,pistons "out of the hole" a bit, is pretty darned rare in the Ford flathead rebuild world unless the pistons are specially made like Bored and Stroked has referenced. It's actually a nice thing to have since you can get the clearance you want all the way to the piston edges. With pistons down in the hole, you are stuck with whatever you have on the outer edges. Can't mill a head to fix that!

I think you'll be delighted with the way this engine will run. Your work quality so far is way above the average home builder's.

[Bored&Stroked]

You'll not have too much compression - just make sure you have enough piston to head clearance (squish).

You want about .040 to .045 with the gasket in place (above the piston). As long as you have that amount (and hopefully not much more), then your engine will run great.

Flatheads like a tight quench/squish area.

[GB SISSON]

I don't have a profile gauge. Does foil or clay work on pistons? And this test is done with a used head gasket and light torque?

[Bored&Stroked]

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Any sort of cheap modeling clay works fine --> just make a couple 1/4" round "snakes" and place two of them on a piston crown (or in the chamber) -- one horizontally and one vertically. Putting a bit of WD40 on the crown and the head helps to make it not stick.

Obviously, you first want to ensure the piston is at TDC.

Use an old head gasket and just cinch the heads down by hand (don't need to torque them down).

Then carefully pull the head and use an XActo knife or razor blade to cut 1/2 of the clay way on each snake. Then, use a mic to measure the thickness. Depending on your brand of piston and head chamber shape, you may find more clearance in the center of the head-chamber than towards the sides.

You need a minimum of .040 over the WHOLE crown of the piston.

On my engines, I make sure I'm at .040 - and if I have to mill the head to get that number, then that is what I'll do. Having a tight quench really helps the performance of any flathead.

Here is an example - Navarro heads and Ross (consistent radius dome) pistons:

2015-07-17 17.59.50 copy.jpg

2015-07-17 18.15.18 copy.jpg

[38 coupe]

I used four balls of tin foil stuck to each piston (center, far left, far right, bottom, didn't worry about the top with the clearance in the factory head) with a dab of grease, bolted the heads down using four head bolts, and spun the crank over a couple times. Pulled the heads and measured the tin foil. The tin foil has a bit of spring, but you can tell well enough what your clearances are. The modeling clay may be a little bit more precise, but I find tin foil easier to grab in short notice.
My friend got a bit enthusiastic on surfacing the heads on this 1950 Mercury engine (.035 clearance) and ended up using a flap disk to carefully add clearance over a couple pistons. This was also not a super precise method, but clearance was verified by a second round of foil balls and dang that engine runs well.

[GB SISSON]

Ok perfect you guys. So, you do one cylinder at a time? I think I'll get that party started in the morning. When my wife gets home from work I'll ask if we have any clay for the grandkids in her toy stash. Thank you to all who have shared your flathead knowledge with me. Like I said before, I feel like I'm getting a college course from the panel of experts. I've got a friend I accuse of wearing a tin foil hat. Wait til I tell him I have tin foil balls.

[38 coupe]

I did one bank (four cylinders) at one time. Had a piece of scratch paper (maybe cardboard?) to make notes on, and measured each ball after spinning the crank a couple times with a dial caliper. The first time I did this I was worried about jamming up a cylinder, but got over it when a friend pointed out I would be the person working the wrench turning the crank.

[51504bat]

Originally Posted by 38 coupe

I did one bank (four cylinders) at one time. Had a piece of scratch paper (maybe cardboard?) to make notes on, and measured each ball after spinning the crank a couple times with a dial caliper. The first time I did this I was worried about jamming up a cylinder, but got over it when a friend pointed out I would be the person working the wrench turning the crank.

Or in GB's case a scrap piece of 1 by?

[tubman]

I seriously doubt that you could hit the head with a piston with anywhere near the force of a power stroke no matter how fast and hard you turned it over.

[GB SISSON]

Well this is not at all what I expected to find. This is with a used head gasket that measures .062 everywhere on it. I took one of the new Best composition headgaskets and it it unused, uncompressed and it also measures .062. I ran the test on #5 and #8 and both had a good portion at .025 squish. I have no interest running on the ragged edge of valve and piston clearance. I got out my other set of EAB heads that were more crusty. I didn't want to set them on my pristine short block so I did some measuring with my dial indicator. These seem to be heavily surfaced too. (Both from the same source and orange paint). When placed upside down, all 4 EAB heads show a space almost 3/8" between a new gasket and the factory milled dome. In other words, 3/8" milled flat 'eyebrow' showing. I then grabbed an 8ba head and flipped it and tried the head gasket. The combustion chamber area lined up perfectly with the domed area in head. No eyebrow.I have a nice looking pair of 8cm heads and various 8ba's as well. I think I saw that the copper clad head gaskets were maybe .070, but when squished we still don't gain enough. Perhaps I have made some newbie error, but those foil balls sure looked flat to me.

[petehoovie]

Originally Posted by GB SISSON

Well this is not at all what I expected to find. This is with a used head gasket that measures .062 everywhere on it. I took one of the new Best composition headgaskets and it it unused, uncompressed and it also measures .062. I ran the test on #5 and #8 and both had a good portion at .025 squish. I have no interest running on the ragged edge of valve and piston clearance. I got out my other set of EAB heads that were more crusty. I didn't want to set them on my pristine short block so I did some measuring with my dial indicator. These seem to be heavily surfaced too. (Both from the same source and orange paint). When placed upside down, all 4 EAB heads show a space almost 3/8" between a new gasket and the factory milled dome. In other words, 3/8" milled flat 'eyebrow' showing. I then grabbed an 8ba head and flipped it and tried the head gasket. The combustion chamber area lined up perfectly with the domed area in head. No eyebrow.I have a nice looking pair of 8cm heads and various 8ba's as well. I think I saw that the copper clad head gaskets were maybe .070, but when squished we still don't gain enough. Perhaps I have made some newbie error, but those foil balls sure looked flat to me.

[Mart]

GB, make sure you check in the middle of the piston dome also. The pistons can sometimes be a little pointy and that can be a problem area.

[GB SISSON]

Originally Posted by Mart

GB, make sure you check in the middle of the piston dome also. The pistons can sometimes be a little pointy and that can be a problem area.

Thanks Mart. I will check the center this morning, but do we not find the entire head to be a problem area so far? If we are looking for .040 we need .015 added. An .070 copper clad gasket would add .008, making the squish at .033, but that is before the gasket is compressed. So how much does a gasket compress and what may be the ramifications of too close? Most engines I take apart have carbon etc build up on the valves and pistons. Do some people here think I am in a good situation with this? I was hoping to be more conservative like .045 if I could choose. Thanks and sorry about all this whining and Pete, you've done it again.

[Ziggster]

I’m going to have to go through this entire thread now, as I’m interested in perhaps doing a 276 stroker if my new block checks out. Lol !

[GB SISSON]

Originally Posted by Ziggster

I’m going to have to go through this entire thread now, as I’m interested in perhaps doing a 276 stroker if my new block checks out. Lol !

It's a roller coaster ride for sure!

[GB SISSON]

Best Gasket website says their big bore copper gasket measures .080 and compressed thickness is .052. Are my concerns valid, or am I just obsessing needlessly? Also when it was suggested that the EAB is a better head than the 8BA or 8CM, is this based on the squish? If so, wouldn't milling 8BA/8CM to 40-50 accomplish the same thing?

[Bored&Stroked]

It "appears" as if the clearance is getting closer toward the crown of the piston . . . so as Mart noted, make sure you measure the clearance on the crown area as well.

This is why I like the modeling clay. When I cut it with an XActo, I can really see the thickness and how consistent (or not) it is. There are two basic styles of piston crowns - one is a consistent radius (like Ross forged pistons), the other is comprised of multiple radius values (like an ellipse) - starting from different origins.

The second type tends to have a more pointy crown - which can be an issue on certain heads. Some head chambers have a consistent radius like Ross' pistons (Edelbrock, Navarro, etc) - while others and some of the stock heads have a chamber with more of an elliptical type of shape (multiple radius values).

Recently I had to have the head chambers reshaped on a CNC machine to use a set of older cast Jahn's 4-ring pistons with new Edelbrock 49-53 heads. I wanted the piston domes to match the heads - such that I could achieve a consistent squish dimension of .040.

This is why it is very important to measure the squish across the whole top of the piston and see how the shapes correlate or not.

If you find you need more clearance, another option is to use a set of Cometic MLS gaskets - they are supplied in thicknesses from about .018 to .080 or so (maybe even thicker). They are expensive - about $280 a set . . . but sometimes yah gotta do what yah gotta do!

One thing to note - the deck/head surface finish needed for MLS gaskets is important - they like smoother surfaces than you can get away with composite gaskets.

Attached are some cross-section views and a couple images I grabbed from my CAD models - you can get a better idea of what I'm talking about - maybe! LOL

Note: I use my 3D models to generate CNC toolpaths to modify chamber shapes.


Egge Cast Piston Shape - Pointy domes
3DSectionView-Ford-Egge-Dome.jpg

Ross Piston Shape - Consistent Radius
3DSectionView-RossEdelbrock-Dome.jpg

Dimensioned View - Elliptical Shape - Egge and Cast Ford
Shows one side dimensioned.
Sketch-Ford-Egge-Dome.jpg

Dimensions View - Ross Style
Shows one side dimensioned
Sketch-RossEdelbrock-Dome.jpg

Note, the "dimensions" are obviously changed/tweaked - based on bore diameter. The above sketches were done for a 3 5/16 bore (exactly what you have!)

Important: Notice the DEPTH difference between the two shapes (center dim). Approximately .265 for the elliptical chamber vs .187 or so for a typical consistent radius chamber. You can use a depth gauge to measure your heads - but the shape does matter!

If you run the Ross style piston on an elliptical style head and achieve enough clearance on the outer edges of the piston, you'll have a BIG gap above the crown - the shapes just don't match up well. If you run the "pointy" style cast pistons on a consistent radius head (like an Edelbrock), the center of the piston crown will hit the head - so you're screwed again. This is why I had to machine the Edelbrock 49-53 heads for a build.

[tubman]

It sounds to me like you need some different heads. I've never had a problem of too little quench. It may be because I've always had access to "virgin" heads. Do you know the history of the heads you are using? It could be they are discards from being resurfaced too many times. It could be a problem in the crank, rod, piston area, but "when you hear hoofbeats, think horses, not zebras".