8CM to 8BA

[Solo_909]

Hey fellas,

So the 51 merc 8CM is shot and needs to be rebuilt good news is I have a 8BA rebuilt motor in the garage and was thinking about just swapping parts and running it Instead. ( yes I know I should rebuild the 8CM, but I don’t want to spend the money ) with that said I remember reading that the 8CM and the 8BA are the same blocks so everything such as the intake, heads, water pumps, oil pan, bell housing, and crank pulley all from the 8CM fit the 8BA?

Any wisdom would be greatly appreciated.

Thanks!

[GB SISSON]

If you could use the crank, it makes a huge difference in torque(hill climbing and pulling power). Just my .02

[quickchange34]

Water Pumps are different on the 8CM.

[Solo_909]

Will they fit on the 8BA?

[51 MERC-CT]

If you have a completely assembled, rebuilt 8BA , to me the only thing most necessary to swap would be the water pumps that fit the 8BA and if you find it really necessary the intake to run the original carb.
To swap the heads would be a waste of time and if you don't like looking at the 8BA on the heads just grind them off.

[40 Deluxe]

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Simple answer; Yes, 8CM and 8BA blocks are identical. Swap pumps, intakes, pans, exhaust to your heart's content! Just don't put 8CM heads on an 8BA block! Compression will be way down.

[Solo_909]

Thanks guys! Anyone else with any incite?

[Flathead]

If you are putting it in a 51 Merc you can swap parts as needed but you will probably miss that extra stroke crank in the 8CM.

[Mike51Merc]

The blocks are identical, so everything that bolts on can be swapped over.

I'd put the Merc crankshaft and connecting rods in, together with a new set of pistons and rings, and have a nice 255 again.

[19Fordy]

I think you will need to install the Merc rear sump oil pan in order to clear merc steering linkage.

[rotorwrench]

If your not going to use the longer stroke crank then you may want to look for some EAB heads from 52/53 Ford to increase the performance a bit. Mercs are heavier than shoe boxes so any extra power is nice. A 239 will get better performance with those heads.

After you run it a while, you will likely want to rebuild the 255 and put it back in there. A Merc just ain't quite a Merc without the 255 crank & pistons but it's your car man.

[scicala]

I have heard before on this forum that putting 8CM heads on an 8BA motor will lower the compression ratio. So seems like keeping the 8BA heads on your rebuilt 8BA would make sense.


Sal

[Mike51Merc]

Originally Posted by scicala

I have heard before on this forum that putting 8CM heads on an 8BA motor will lower the compression ratio. So seems like keeping the 8BA heads on your rebuilt 8BA would make sense.


Sal

That's true. I even considered putting a set of 8BA heads on my 8CM, but then I'd lose my 8CM markings that I'm so proud of.....

[tubman]

I went the other way and put a '51 Mercury engine in my '51 Ford. I used the Ford bellhousing, flywheel, clutch, water pumps, and oil pan on the Merc engine. I don't remember changing the oil pump pickup, but it should be obvious with both engines open. There were no problems at all; everything bolted together as it should. Going the other way should be just as simple, but probably not as satisfying.

I would have used the 8BA heads except that I already had a carefully prepared set of Edmunds finned aluminum units.

[Solo_909]

Originally Posted by tubman

I went the other way and put a '51 Mercury engine in my '51 Ford. I used the Ford bellhousing, flywheel, clutch, water pumps, and oil pan on the Merc engine. I don't remember changing the oil pump pickup, but it should be obvious with both engines open. There were no problems at all; everything bolted together as it should. Going the other way should be just as simple, but probably not as satisfying.

I would have used the 8BA heads except that I already had a carefully prepared set of Edmunds finned aluminum units.

Yeah seems pretty straight forward now that I have everything apart. I did have to change the oil pick up though.

The only thing I’m still wonder is if the crank pulley will fit. They are two different size belts so it does need to change.

[tubman]

You should have no problem with the crank pulleys as the crankshafts snouts are all the same. One piece of advice I can offer is to be careful removing cast crankshaft pulleys as they are kind of fragile and can be easily broken during removal. Ask me how I know.

[FortyNiner]

On this same topic, are the fuel pumps different between the Merc and Ford versions?

[51 MERC-CT]

Originally Posted by FortyNiner

On this same topic, are the fuel pumps different between the Merc and Ford versions?

Both the Ford and Mercury can use the same type 'Double pumper' and 'Single pumper' fuel pumps, just a matter of preference.

[Ol' Ron]

The only difference between these two engines is internal.

[Red98]

Originally Posted by tubman

I went the other way and put a '51 Mercury engine in my '51 Ford. I used the Ford bellhousing, flywheel, clutch, water pumps, and oil pan on the Merc engine. ...

Originally Posted by Ol'Ron;

The only difference between these two engines is internal.

Does this mean the bellhousing, flywheel, clutch, and oil pan are different between 49-50 Merc CM engine and the '51 CM requiring changing those parts between a '51 CM engine but not a 49-50 CM engine to fit the Ford?

[Ol' Ron]

the answer is quite simple. just change the parts that need to be changed. Not sure the flywheel has to be changed, but if it does just change it. I'd keep the 8BA carb and dist tho.

[rotorwrench]

The Mercury cars of the mid century era did use a different clutch than the Ford cars. They wanted one that was a bit heavier duty than the 9.5-inch Long type so they used the Borg & Beck 10-inch. It has an evenly spaced bolt pattern like the later diaphragm type clutches. The 49 & 50 were the same with the 1 3/8-inch 10-spline type input and sometime in early 1951 around February or so, they changed to a different transmission & bell housing set up. The later 1951 transmission is more like the earlier Ford types with the narrow 4-bolt pattern, diamond cut gears, and a 1-inch 10-spline input pinion. The clutch was still Borg & Beck but was changed for the smaller spline & new style throw out bearing.

Early 1951 Mercs were same as 49 & 50 but the later 51 Mercs were different. The bell housing is a larger cast iron unit but still had the rotating fork equalizer set up for the clutch. In 1952, the Mercs used the same transmission & bell housing as the 52 Ford cars since both made further update changes for commonality.

The Mercury 885 Holley carb would be out of place in a Ford car application but it is a decent carb for a Mercury application. It has a bit larger CFM rating than the Ford 8BA type. The 8BA type is easier to work on and the carb kits are less problem to get a good one. If a person changes away from an OEM Holley type then the ignition has to be changed as well since they are matched as the Holley Load-O-Matic system. Use either the 8BA with all its components or use the 885 but don't try to mix & match. There are slight differences that might cause problems.

[Solo_909]

Okay for future reference here’s a list of everything that needed to be swapped over. Fairly simple stuff. Thanks fo all the help guys.

Heads, Intake, carb, Oil pan, oil pickup, oil filter, crank pulley, crank extender, water pumps, flywheel, clutch, and bell housing.

[tubman]

That list may be OK if you want to make your 8BA LOOK like an 8CM, but again, using the 8CM heads will cut compression from an already low 6.8:1, and combined with the larger (and rarer and harder to work on Merc carb), may cause performance problems. Since the Merc is a larger and heavier car, it will probably be a slug. It'll get you around town OK, but that's about it.

[lonewolf]

If the Merc is an automatic the crank is machined to work with the air cooled converter. It has kind of a pilot about the size of quarter machined into the end that the converter goes into .If the 8ba was a manual transmission the crank may have to be machined to work with the automatic converter. If the Merc was a manual transmission you will be good

[Solo_909]

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Originally Posted by lonewolf

If the Merc is an automatic the crank is machined to work with the air cooled converter. It has kind of a pilot about the size of quarter machined into the end that the converter goes into .If the 8ba was a manual transmission the crank may have to be machined to work with the automatic converter. If the Merc was a manual transmission you will be good

Good to know, they both are manual so I guess I’m good.

[Solo_909]

Originally Posted by tubman

That list may be OK if you want to make your 8BA LOOK like an 8CM, but again, using the 8CM heads will cut compression from an already low 6.8:1, and combined with the larger (and rarer and harder to work on Merc carb), may cause performance problems. Since the Merc is a larger and heavier car, it will probably be a slug. It'll get you around town OK, but that's about it.

Hmmm, I’ll be able to tell that much just from swapping the heads? I could use the 8BA head. They just need to be painted. I just wanted things to appear stock.

[tubman]

Originally Posted by Solo_909

Hmmm, I’ll be able to tell that much just from swapping the heads? I could use the 8BA head. They just need to be painted. I just wanted things to appear stock.

Or, you could have the 8CM heads milled enough to get you to a .050 "squish" over the piston . You would probably have to do some grinding to bring the head to a uniform combustion chamber. Then you would have the best of both worlds. I believe it is common knowledge that increasing compression is the easiest way to pick up power in an otherwise stock flathead. You might as well take advantage of today's better fuels.