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Old 01-01-2019, 09:29 PM   #1
Solo_909
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Default 8CM to 8BA

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 donít 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!
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Old 01-01-2019, 10:06 PM   #2
GB SISSON
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Default Re: 8CM to 8BA

If you could use the crank, it makes a huge difference in torque(hill climbing and pulling power). Just my .02
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Old 01-01-2019, 10:24 PM   #3
quickchange34
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Default Re: 8CM to 8BA

Water Pumps are different on the 8CM.
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Old 01-01-2019, 10:43 PM   #4
Solo_909
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Default Re: 8CM to 8BA

Will they fit on the 8BA?
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Old 01-01-2019, 10:44 PM   #5
51 MERC-CT
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Default Re: 8CM to 8BA

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.
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Old 01-02-2019, 02:29 AM   #6
40 Deluxe
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Default Re: 8CM to 8BA

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.
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Old 01-02-2019, 12:16 PM   #7
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Default Re: 8CM to 8BA

Thanks guys! Anyone else with any incite?
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Old 01-02-2019, 01:39 PM   #8
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Default Re: 8CM to 8BA

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.
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Old 01-02-2019, 02:39 PM   #9
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Default Re: 8CM to 8BA

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.
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Old 01-02-2019, 03:04 PM   #10
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Default Re: 8CM to 8BA

I think you will need to install the Merc rear sump oil pan in order to clear merc steering linkage.
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Old 01-02-2019, 03:39 PM   #11
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Default Re: 8CM to 8BA

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.
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Old 01-03-2019, 07:05 PM   #12
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Default Re: 8CM to 8BA

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
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Old 01-04-2019, 08:27 AM   #13
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Default Re: 8CM to 8BA

Quote:
Originally Posted by scicala View Post
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.....
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Old 01-04-2019, 09:59 AM   #14
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Default Re: 8CM to 8BA

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.
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Old 01-05-2019, 10:57 PM   #15
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Default Re: 8CM to 8BA

Quote:
Originally Posted by tubman View Post
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 Iím still wonder is if the crank pulley will fit. They are two different size belts so it does need to change.
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Old 01-06-2019, 01:25 AM   #16
tubman
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Default Re: 8CM to 8BA

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.
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Old 01-06-2019, 07:50 AM   #17
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Default Re: 8CM to 8BA

On this same topic, are the fuel pumps different between the Merc and Ford versions?
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Old 01-06-2019, 08:22 AM   #18
51 MERC-CT
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Default Re: 8CM to 8BA

Quote:
Originally Posted by FortyNiner View Post
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.
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Old 01-06-2019, 08:35 AM   #19
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Default Re: 8CM to 8BA

The only difference between these two engines is internal.
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Old 01-06-2019, 08:02 PM   #20
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Default Re: 8CM to 8BA

Quote:
Originally Posted by tubman View Post
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. ...
Quote:
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?
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