If you're messing with flatheads, the number on the head is only academic for the most part. We still need to do the physical work our grandfather's did to put one of these together.
As best I remember from the old guys, you must maintain .050" clearance between the head and top of the piston. You determine that by "claying" the heads. Make small ***** of clay or tinfoil and lay on top of your piston at top dead center. Install the head with a gasket on the engine and torque it down. Then remove the head and measure with a micrometer the thickness of the clay pellet. It must be at least 50 thousands of an inch to maintain adequate clearance.

I put a set of unmarked heads on my merc flathead that had 71 cc's of volume as best I could measure it. This should be the same as EAB heads which bumped up the compression over EAC heads. Installed with a standard gasket. I didn't bother to clay the setup. 10 years and 80,000 miles later I had too much blow-by so I recently tore it down and discovered all 8 pistons destroyed and all compression rings broken. I screwed up somewhere by taking a shortcut.

Just trying to save you guys a future problem. I no longer care what the cast number or letters say. This is especially important if you have your machinist start shaving/milling material off your stock heads.
Your mileage may vary....

 

Yes, any of these generation heads will fit the block and can make for a running engine. This discussion stems from what was on our trucks initially from the factory, and some choose to retain/obtain that factory correctness today. It is pretty much basic knowledge that compression can be affected by the any machining, and any machinist involved in a rebuild will take into account gasket height and the necessary piston clearances and so on. As for the Mercury 255, it wasn't just the heads, but the increased piston stroke of 4" as well.

 

Exactly, I'm glad you know. Unfortunately too many shop operators these days don't have a practical knowledge of the unique characteristics of the flathead. We have to know when we take equipment in to them exactly what we need them to do. Scarcity of parts requires this additional education so I posted for the guys who have never seen this stuff before.

I tend to trust the parts books, so I'm in the camp that says 8RT heads belong on '52 trucks but not earlier for 100 point concours restoration. Enjoy your trucks gentlemen and ladies - do it your way!
Tim

 

Feel the same. Parts book indicates 8RT heads so feel like those are correct. That said, milled 8BA heads, a 4” stroke, and a merc cam sure does run and sound nice. I am still smiling from my Sunday drive!

JB

 

thanks for linking that article. I didn’t know it meant engine knock!

so would you think Ford changed to the 8RT heads in trucks to eliminate or reduce engine knock? Because truck engines specifically and presumably under a good load would be more susceptible to engine knock?

 

I wouldn't say it was primarily to reduce engine knock.
I'm not sure Ford understood everything they were dealing with - they made running line changes trying to solve problems as they showed up.
If you look at the water passages in flathead heads from 32-53 you will observe a variety of shapes, numbers and locations of coolant holes. From what I've read and observed, by '52 8RT/EAB/EAC heads, they were still trying to get the hot coolant from the back of the engine into the heads where it could flow to the radiator faster.

 

I’m looking for a pair of 8RT heads if anyone has any good ones for sale let me know -Scott are you still out there?

 

Yep, I still have the 8RT heads. I had them bolted to my block when I pressure checked it and no leaks. However, they do need to be surfaced. I got my truck from the daughter of the original owner and this engine has not been rebuilt, but I don't know for sure if the heads have ever been surfaced. All threaded holes are good.

I don't know what they are worth or what they would cost to ship.

 

terrific! I emailed you if you can find that let’s talk about shipping etc. PM me if you can’t find your email Scott!

~John