I have 2/239,s, one is a '51 Mercury and the other came out of a Ford Truck presumably around 1950. Both need rebuild and my question is which one to rebuild if indeed they are rebuildable. I have been told that the Mercury motor would have more power but that is not a major concern. I just want to get the thing running. Also would it be possible to take parts out of one to make the other motor viable?

 

A lot of parts can be swapped between a lot of the flathead Ford V8s. Before planning to rebuild one specific engine I would pull heads, intake, and oil pans, and post pictures so we can identify what you have. Over the decades lots of engines have been swapped and lots of parts have been swapped on those engines. The odds that you have two completely stock V8s isn't zero, but isn't 100% either. If the Mercury engine is originally from a Mercury it will be the larger displacement 255 cubic inch engine which is nice to have.

Assuming you do have a genuine F series ford truck engine, and a genuine 1951 Mercury engine, and assuming you are building an engine for a Ford truck since you are on this forum, I would rebuild an engine using the following parts:
- A crack free block, if either one is crack free. Carefully inspect. If both are magically crack free, whichever one already has hardened seats in the exhaust in good condition (over the years 49-53 Ford eliminated first the intake seats, then the exhaust seats). Also be wary of a block that already has been bored over +0.125 or larger.
- Stock truck intake, heads, oil pan, carburetor, distributor, etc. Make the exterior look like a stock truck motor.
- Mill the heads to get 0.050 distance between the pistons and the heads.
- Use the 4" stroke Mercury crank, if you actually have one. Measure the stroke of both motors after pulling heads to check before final disassembly.
- The Mercury 1CM or 8CM cam, if it is good condition. Otherwise any good condition 49-53 stock cam.
- New water pumps

 

Fred, you mentioned using the Ford heads with the Mercury crank. Do you know what the compression bump would be with that combination over using the Mercury heads, all else being equal? How much increase would you see with the milling you suggested?

 

Long answer to a short question - the combustion chambers of Flathead Fords are frequently out of specification due to casting variations. Typically the chambers are a bit bigger, not smaller, than stated in the various Ford literature. Also, the piston dome shape varies a bit between original and the various manufacturers today so stating a compression ratio without actually measuring is pretending accuracy you don't have. That said, someone went through a lot of effort to try to be as accurate as reasonably possible and compiled a huge list of flathead compression ratios using all the combinations of bore size, stroke length, and head types that can be put together. The table can be found here (I saved a copy on my computer a while back for reference). According to that chart a 0.030 overbore (assumed since that is typical first rebuild size) with a 4" crank (260 cubes) and stock 8BA / 8RT heads results in 7.25 to 1 compression ratio, up from 6.76 with a stock bore 239 cube 8BA / 8RT motor, and up from 6.67 to one for a stock bore 255 cube 8CM motor. Milling the head for piston clearance doesn't raise the compression much, but does improve the mixture turbulence and combustion event.

 

I couldn't get the link to load, I suspect it is for this table?

 

It is the expanded version of that table, findable from HAMB and Ford Barn threads, one here, hopefully with a working link to the attachment here.

 

 

That doesn't look promising...

 

Hard pass... it would take a lot of work and $$ just to find out if it is cracked or not. I'd guess every one of the valve guides is stuck hard, likely have to cut the valves to get them out. If you just want a runner, there have to be better choices out there.

 

Why, it ran very well for about 2 weeks and then quit. What problems do you see.

 

There is a lot of rust in the bores, valves, and ports. The color of the sludge in the crankcase looks like water and oil mix. Thick baked on looking sludge in the valley. There is what looks like old gasket on the oil pan rail, if it isn't gasket then the block is cracked a the bolt hole.

 

What ^^^ he said. Did you change the oil before you ran it? if so then all that water got in there during the 2 week run, almost certainly means the block is cracked.

 

Looks like it ran for 2 weeks and then set for 20 years in less than ideal conditions.
Lots of good advice above.
Why not just take both engines to your reputable flathead rebuilder and let them guide you through the process?

 

Will **** can that engine and save what parts I can. Will put the ford truck engine on the stand and send pics of it. Thanks for the input.

 

If it still rotates, measure the stroke to see if it is really a Merc motor. If it is, and the crank isn't rusty, it could be worth $300+.