How To I.D. a Merc Flathead

RalphG

RalphG

Well-known member
I know a guy claims to have a Mercury flathead engine for parts and I am wondering just what to look for to tell if it is really an 8BA Mercury engine or just a Ford. Its many miles away and likely to cost more than the engine is worth to ship it here. And while I'm at it, where do I look on my own 255 in this 53 to see if the engine number matches the one on the firewall plate?
 

Attachments

  • IMG_0312[1].jpg
    IMG_0312[1].jpg
    63.5 KB · Views: 54
  • IMG_0313[1].jpg
    IMG_0313[1].jpg
    59.2 KB · Views: 50
The main thing that makes it a Mercury engine is the crankshaft stroke
( 4 inches )
This would have to be measured.
Most likely had no engine numbers as the US did not have any.
Don't waste time looking for one.
 
Only sure way is to pull a head and measure the stroke. I once bought an engine advertised as a Merc. It had Merc heads, Merc water pumps, and a stamped steel Merc 1/2 bell but not a teapot carb. Pulled it apart and it had a 3 3/4 inch crank. Lesson learned.
 
If you can get the pan off, the counter weight width and the size of the oil plug thingy are also tell tale signs of a Merc crank.
 
Ralph, you already showed a pic of the engine with the heads off. If one of the pistons is at the top, or near, measure how far down the one is that is lowest in the bore. If one is at the top, hopefully the lowest one will be at 4" down the bore. If one is 1/8" down the bore, and the deepest one is 3-7/8 down, add them together and it makes 4". You can only do this near TDC/BDC, it does not work elsewhere.

As long as you get a dimension over 3-3/4 you have a Merc engine, or at least a Merc crank. The crank is the only real big difference between the Merc and the Ford.

Mart.

Edit: Here's the pic. How far down is the edge of that rearmost piston from the block face?

342628
 
Last edited:
Crankshaft Identification​
The intent of this article is to enable you to identify the crankshaft you are looking at as either a Mercury 4" stroke or a Ford 3-3/4" stroke. The description will enable you to make a somewhat positive identification and the pictures can be used to clear up what is foggy. Click here for the complete paper in PDF format. By Bill Boomer (4tford) from fordbarn discussion Forum
 

Attachments

Already checked mine for numbers and it is just the C1-8BA which likely does not mean much.I like the suggestion of measuring the stroke on mine with the heads off but I was more inquiring about how a guy with one to sell, that is not disassembled, might tell if it was a Merc or Ford engine. I'm assuming the one in my 53 is the original Merc engine.
 
There really isn't such a thing as a 49-53 Merc Block that I know of - just a regular 8BA block with a Mercury Crankshaft and other parts. I've seen every combination known to man - so the key thing is if you're looking for a Merc 4" crank - then measure/verify that . . . tells you nothing about the rest of the engine (as being special to a Merc). You never really know what car the engine came out of - so you have to check the individual parts to validate that they are what you're looking for.

PS: The only flatheads that I know were specific to Mercs (and some other wartime engines, etc) - were the 39-42 Merc 99A type of engines. The Ford cars usually came with 221 cubic inch engines (81A) - while the Mercs came with the first generation of the 239 cubic inch engines (the 99A). This was only true these three years. After the war, the blocks were all the same (between Ford and Merc) -- though in 49-53 they came out with the 255 cubic inch Merc variant . . . which was basically an 8BA block with a 4" stroke crankshaft and the associated pistons. Now - with that said, there were other differences in the parts that bolted up to the block --> oil pans, heads, intakes/carbs, etc . . . but the basic block was all the same.
 
And don't think the guys rebuilding those engines in large factory-authorized shops weren't putting in ford cranks and slipping the mercs out the door during a smoke break.

Lonnie
 
Doh! Sorry Ralph, I didn't reply straight away and forgot you were asking about a prospective purchase.

Mart.
 
One thing we have to remember is: All the ford blocks are the same, yes there are some differences like valve seats and maybe a few other things. But they're interchangeable with the Ford and Mercury as well as the 8rt engines are concerned. The difference comes with the parts added to the block. BTW that Merc crank wil fir all the blocks from 39 up. But that's another story.
 
Measured the distance from piston top up to the top of the block and its 4 inch so I know what I've got. This other one I've been inquiring about, now it sounds like the owner is not even sure its a flathead as he referred to Mercury "valve covers".
 
He might mean “Mercury “on the heads.

I’ve had younger folks look at my flatheads and wonder why a six cylinder has eight spark plugs. :)
 
You must log in or register to reply here.
Back
Top