m head swap

lee. s · Feb 13, 2010

i have a 1940 m with kero.head and ive got a 400 head manifold and carb and was thinking of putting them on the m. anyone know what kind of power gain this would be

lee. s · Feb 13, 2010

and yes it has original size piston/sleeves

james rumph · Feb 14, 2010

It all depends on the combustion chamber size of the given head. I don't think you will see any real gains with a stock 400 gas head.

When you go up to the 450 gas and LP you see the big gains based on their smaller chambers.

Now if you have the 400 head cut then you will pick up some power.

I have had and seen "M" based heads cut .125 and in my opnion this is to much. All sorts of other problems come with this.

Do a nice .060 cut and be safe. With the .125 your putting spacers under the rocker pedstals to get the correct adjustment back in the rockers.

I had a 8060 that "was" cut .125 and it developed cracks in the corners of the combustion chambers that were not their before.

Get a fresh cut and a good valve job and it will run great.

Just my thoughts and advice .

D Slater · Feb 14, 2010

Can't say exactly what power you would get. Should be a little more than you would get from putting a M type gasoline head on the tractor. Thats if you have a 400 head casting # 362174 or 362433 or even more power over the previous 2 if you are lucky enough to have a # 364586.

pete 23 · Feb 14, 2010

A 400 gasoline head will give you a considerably higher compression ratio than you have with a kerosene head. Should gain a few ponies. I think I would try both carburetors to see which one gives you the best performance. As the 400 used a 25 degree spark advance at full throttle, you may need to adjust your M ignition. Most M's used 40 degree with battery ign and 35 with magneto. Bore size will also affect comp ratio.
I would only resurface head if it is needed for flat true surface

Pat-CT · Feb 14, 2010

Im not sure if an M has the same type of head as an h But i know that an H has a smaller combustion chamber in the head than a SH head. I think an M head would be ideal with some steped head pistons

CJ_1080 · Feb 14, 2010

It depends, but it should give you some. If you shave it .125 it would be better. You may have to shim up rocker arm pedistals. You DO NOT WANT a 40 degree distributor in it if the compression is going up a bunch. What are you doing pulling or just looking for power? Email me if you need some pointers?

m head swap

lee. s

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lee. s

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james rumph

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D Slater

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pete 23

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Pat-CT

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