Flathead V8 question...

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Dec 3, 2018 | 12:30 PM

JPMallory

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Laughing Gas

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From: Behind the wheel, IN

Flathead V8 question...

I'm looking at rebuilding my flathead. If I were to swap the crank out with a Merc crank, what else would I need to change? Pistons? Rods?

Dec 3, 2018 | 01:12 PM

ALBUQ F-1

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From: NM

Pistons are the only difference with a Merc crank. The Merc will boost your compression, cubic inches, and low end torque. Breathing is still the limiting factor.

Dec 3, 2018 | 01:12 PM

BlueOvalRage

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From: Oxford, Indiana

Ford and Merc rods were the same length. The pistons have to match the stroke, though.

(Ross beat me to the punch by mere seconds!)

Dec 3, 2018 | 01:21 PM

JPMallory

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Laughing Gas

Joined: Feb 2014

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From: Behind the wheel, IN

Awesome. Thanks for the help. I've got a lead on what sounds like a good Merc crank. I just wanted to be sure I know what I'm getting into.

Dec 3, 2018 | 01:26 PM

RattyFord

Senior User

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From: Northern Colorado

You'd probably be putting in new pistons anyhow, so it sounds like a win for you!

Dec 4, 2018 | 02:07 AM

fish pond

Tuned

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From: Pinckney Mi.

hi folks, whats the difference between a merc. and a ford flathead/
I have a 51 M3.
Thanks
Greg

Dec 4, 2018 | 07:17 AM

EffieTrucker

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From: Kentucky

Quote:

Originally Posted by fish pond

hi folks, whats the difference between a merc. and a ford flathead/
I have a 51 M3.
Thanks
Greg

In a nutshell, the Merc flathead V8 has a longer stroke (4" vs Fords 3.75") giving it more cubic inches (255CID vs Fords 239CID). To compensate for the longer stroke, the wrist pin is higher in the pistons to keep them from hitting the head. To compensate for the larger volume of the cylinder, they have a slightly larger combustion chamber.

Merc crank and pistons with Ford heads give more cubic inches and more compression. Merc heads with a Ford crank and pistons give less compression.

Merc heads, crank, and pistons give you more cubic inches and the normal compression. Basically, it becomes a Merc engine.

Here is a great source for Flathead history, specifications, and identification: http://www.vanpeltsales.com/FH_web/f...ifications.htm

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Dec 4, 2018 | 10:01 AM

EffieTrucker

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From: Kentucky

Quote:

Originally Posted by 52 Merc

So the "Merc" Mercury 4" stroke engine only came in the cars?

Dec 4, 2018 | 10:26 AM

#10

52 Merc

Hotshot

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From: Burbank, WA

Quote:

Originally Posted by EffieTrucker

So the "Merc" Mercury 4" stroke engine only came in the cars?

That is correct.

Dec 4, 2018 | 10:47 AM

#11

EffieTrucker

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From: Kentucky

Quote:

Originally Posted by EffieTrucker

So the "Merc" Mercury 4" stroke engine only came in the cars?

Quote:

Originally Posted by 52 Merc

That is correct.

I didn't know that. A new fact for the day.

Thanks!

Dec 4, 2018 | 12:52 PM

#12

ALBUQ F-1

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From: NM

There is one exception to that, for '52 Canadian Merc M-5 and M-6 trucks.

Dec 5, 2018 | 11:59 AM

#13

52 Merc

Hotshot

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From: Burbank, WA

You got me on that one, Ross. And I should have known better since I was the one that posted that chart. I must be starting to catch up to the age of our trucks...

Dec 5, 2018 | 12:48 PM

#14

ALBUQ F-1

Fleet Owner

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From: NM

I thought that's where I got it!

Dec 5, 2018 | 01:19 PM

#15

jmadsen

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From: Utah

I was out in Northern Arizona a couple years ago picking up a truck and parts and notice a flathead crankshaft laying on the rear blade behind an 8N Tractor as a counter weight and i thought , nah. Just a rusty old ford crank but i had to look and lo and behold it was a merc crank. I was buying more parts and pieces from the pile in the shed and had him throw it in on the package deal thinking its probably no good anyway, turned too many times. Bent or ??? From bouncing around on the blade.
But nope it was cleaned, checked and turned from standard with rust and now back in a running vehicle. I still laugh about it everytime i think about it.