Odd EAC piston compression height

cadillac512

cadillac512

Well-known member
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.
 

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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
 
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:
198425
 
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. :confused:


Terry
 
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.
 
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