The Ford Barn

cadillac512 · 10-15-2023, 10:05 AM

I tore down a Merc EAC engine a while back. 4" crank,EAC heads,correct 4 bolt intake,correct accessories...in short looked to be the genuine article. Now, I usually clean up a piston and the surrounding deck and measure piston protrusion or recession as the case may be, but this one was rusty and stuck and I neglected to do so.

The pistons were standard bore size 3.187".

Here's the weird deal: the piston measures 1.475" compression distance (center of pin to top outer piston edge) and yes...I know how to correctly do this. Adding up the numbers (1.475 piston,7.00 rod,2.00 half stroke) it comes out to 10.475" whereas stock block deck height is accepted as 10.445". That means this piston will be .030" above the deck at TDC.

Have any of you engine guys seen this before? It can't be a Ford piston because it's marked EAC and a Ford crank would put it .095" down the hole anyway. So here's a pic for your head-scratching enjoyment.

19Fordy · 10-15-2023, 11:28 AM

Does the top of the piston clear the head when head and head gasket is installed?

cadillac512 · 10-15-2023, 01:08 PM

Yes, it would have since the gasket was approx .055" thick. Bear in mind this was a core I disassembled and am not rebuilding due to the block being cracked so badly as to be rendered worthless. However, .020" piston/head clearance is extremely close and for the factory to assemble it that way seems very strange. The block is now gone so no more measuring to be done on it.

I just wondered if anyone on here had seen this...very odd.

Terry

petehoovie · 10-15-2023, 02:55 PM

Quote:

Originally Posted by 19Fordy

Does the top of the piston clear the head when head and head gasket is installed?

Bored&Stroked · 10-15-2023, 05:38 PM

The compression height should be 1.436" for a 4" stroke piston.

38 coupe · 10-15-2023, 08:45 PM

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I put the piston part number in a Google search and turned up an old Ford Barn post by GOSFAST including a different picture of an EAC standard piston. That picture also states a 1.475" compression height. Not sure what to think about it. Makes me want to measure the compression height on the NOS 8CM pistons I have stashed away. Now where did I leave my dial calipers?
Picture from the other thread here:

cadillac512 · 10-15-2023, 11:09 PM

Thanks for that, 38 coupe! It's an odd one for sure and I don't know what to think of it either.

B&S....Yes, I'm aware of what the height SHOULD be for a 4" stroke and that's what makes this so odd. The fact it's marked EAC means it's a Merc piston and would have had the 4" crank.

Terry

Bored&Stroked · 10-16-2023, 07:30 PM

Kind of strange that we now have 2 different pistons with that compression height. I wonder if Ford made some special pistons for an application we don't know about. The funny thing is that it isn't on a 1/16" boundary over/under 1.436? So why .039"? Maybe some weird cranks?

I've never seen a set of Ford heads that were domed for a "pop-up" piston. I'll have to go measure some older aftermarket 4" forged pistons I have in the shop - just for giggles.

10-15-2023, 11:28 AM	#2
19Fordy Senior Member Join Date: May 2010 Location: Coral Springs FL Posts: 10,950	Re: Odd EAC piston compression height Does the top of the piston clear the head when head and head gasket is installed?

10-15-2023, 01:08 PM	#3
cadillac512 Senior Member Join Date: Apr 2019 Location: Kansas Posts: 922	Re: Odd EAC piston compression height Yes, it would have since the gasket was approx .055" thick. Bear in mind this was a core I disassembled and am not rebuilding due to the block being cracked so badly as to be rendered worthless. However, .020" piston/head clearance is extremely close and for the factory to assemble it that way seems very strange. The block is now gone so no more measuring to be done on it. I just wondered if anyone on here had seen this...very odd. Terry __________________ "It don't take but country smarts to solve the problem" (Smokey Yunick) '41 Merc Town Sedan / 260" 8CM engine '66 Fairlane four door / "warmed up" 302

10-15-2023, 05:38 PM	#5
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,068	Re: Odd EAC piston compression height The compression height should be 1.436" for a 4" stroke piston.

10-15-2023, 08:45 PM	#6
38 coupe Senior Member Join Date: May 2010 Location: South Texas Posts: 1,631	Re: Odd EAC piston compression height Sponsored Links (Register now to hide all advertisements) I put the piston part number in a Google search and turned up an old Ford Barn post by GOSFAST including a different picture of an EAC standard piston. That picture also states a 1.475" compression height. Not sure what to think about it. Makes me want to measure the compression height on the NOS 8CM pistons I have stashed away. Now where did I leave my dial calipers? Picture from the other thread here:

10-15-2023, 11:09 PM	#7
cadillac512 Senior Member Join Date: Apr 2019 Location: Kansas Posts: 922	Re: Odd EAC piston compression height Thanks for that, 38 coupe! It's an odd one for sure and I don't know what to think of it either. B&S....Yes, I'm aware of what the height SHOULD be for a 4" stroke and that's what makes this so odd. The fact it's marked EAC means it's a Merc piston and would have had the 4" crank. Terry __________________ "It don't take but country smarts to solve the problem" (Smokey Yunick) '41 Merc Town Sedan / 260" 8CM engine '66 Fairlane four door / "warmed up" 302

10-16-2023, 07:30 PM	#8
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,068	Re: Odd EAC piston compression height Kind of strange that we now have 2 different pistons with that compression height. I wonder if Ford made some special pistons for an application we don't know about. The funny thing is that it isn't on a 1/16" boundary over/under 1.436? So why .039"? Maybe some weird cranks? I've never seen a set of Ford heads that were domed for a "pop-up" piston. I'll have to go measure some older aftermarket 4" forged pistons I have in the shop - just for giggles.