Farmall m heads

I got a question for you all, I'm rebuilding one of my m's and am going to take the head over to a friend of mine that has a machine shop to go over the head, I want him to shave it some as I'm going to pull the tractor at antique pulls and I use it for work, Its a gas head, with standard bore high step pistons in it, how far can I safely shave the head with still running pump gas and not having any problems??

My opinion is that your decision must not depend on us, but on actual "measured" compression. A slow turning (even if it is cranking 2300) engine requires spark
advance evaluation and spark knock assessment to get it dialed so it is at the edge of knock under full load. People have taken off .100" and made it work.
Core shift and production variability could hit water jacket at that cut on some heads. Has it been trued before? how does one accurately determine the depth it
has been cut to date. CCing the chambers is a start, then looking at piston clearance to the Chamber edge. Some grinding is probable. Valve to piston
clearance is to be considered, especially if modified rocker ratios are used, or a custom cam. Pump gas includes 93 R+M ethanol premium. Good luck. Remember
it has 3 main bearings. Jim

(quoted from post at 07:44:55 01/09/19) My opinion is that your decision must not depend on us, but on actual "measured" compression. A slow turning (even if it is cranking 2300) engine requires spark
advance evaluation and spark knock assessment to get it dialed so it is at the edge of knock under full load. People have taken off .100" and made it work.
Core shift and production variability could hit water jacket at that cut on some heads. Has it been trued before? how does one accurately determine the depth it
has been cut to date. CCing the chambers is a start, then looking at piston clearance to the Chamber edge. Some grinding is probable. Valve to piston
clearance is to be considered, especially if modified rocker ratios are used, or a custom cam. Pump gas includes 93 R+M ethanol premium. Good luck. Remember
it has 3 main bearings. Jim

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Let me clarify a little bit, I don't want to go anything major I still want a dependable tractor, but I want to add a little horsepower I was just wondering what a lot of people shave off on the heads and still have piston to valve clearance and dependability, thanks for your help

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My opinion, take it for what it is worth, but my opinion is that you should never remove any more material than necessary to clean it up and provide a nice, flat surface.

Same formula for cylinder displacement only calculate the amount shaved as cylinder length. Get Auto Math Handbook for more info.

Ok so you want to mill the head , What happens when you do this is that the VEE shaped water passages start to get wider and then they get to wide for them to seal against the head gasket . And you now have a great boat anchor . Ya want to gain more pony power ya need CUBIC INCHES and higher compression . So ok you install the over bore kits that are out there along with a gas head off a say a 450 then ya have the cam done ya do some carb work , you do some valve work on the 450 head and some flow bench work then ya have everything balanced do some dist work , Now keep in mind here we are making a PULLING engine NOT a Drag race engine and tricking out a dist is NOT the same as both ( took me several years to figure that out ) . And one more thing here never believe what you read in some of the adds on how is pedalling the best pulling parts . On a basic M that has had some of this work done you will end up with someplace around 60-65 Hp at around 10% above stock RPM . The best one that have put together and is still used on the farm as awork tractor is my buddy's S/MTA and it will out do a 706 and it will run the feed grinder almost as well as the 806 . That one is sporting 4 and a 1/8th high alt. pistons a 450 gas head (not LP) a reground and blue printed 450 cam a 450 intake a recurved Dist. some mild head work with a larger intake valve a balance job and a little carb work and every thing was hand fitted , The down side is that when working she get thirsty and ya can get about four hours to a tank when ya put the 4x16'sbehind it at 8 to 10 inches deep in third . Mine will not do it . Next to think about is the fact that someone out there will always have more and willing to spend more or cheat more for the bragging rights . and to win that trophy . Keep in mind here i don't care what you try to do with a M there will be that guy that comes in with a YELLOW hunk of iron that will knock your socks into the creek and will have far less in his . Yep already did that and built and engine usen all JUNK parts except rings bearing and gskt and went dumpster diving for the pieces and parts and put together a monster motor .

Guy I worked for a couple summers when I was in college had a son who farmed across the creek from the
farm my Folks owned. That Son had his M rebuilt, sent the head to a machine shop for truing up flat and
the paperwork got messed up, they cut .125 inches off, 1/8th inch! They went ahead and used it. Boss
told me he was down just across the creek bridge waiting for his son to come up to the road plowing with
IH 3-14's, running a couple passes away from the creek. And when he was about half way to the road just
like you pulled the plug out of the wall on a tv or radio, it got real quiet. Tractor ended up going to
town to IH dealer. I saw the crankshaft, and the mechanic that built the engine told Dad and I the
crankshaft broke right next to the center main bearing. In the 55 years since then I have never seen
another H or M crankshaft broken, I have heard of one other M breaking a crankshaft.

(quoted from post at 13:42:53 01/09/19) Guy I worked for a couple summers when I was in college had a son who farmed across the creek from the
farm my Folks owned. That Son had his M rebuilt, sent the head to a machine shop for truing up flat and
the paperwork got messed up, they cut .125 inches off, 1/8th inch! They went ahead and used it. Boss
told me he was down just across the creek bridge waiting for his son to come up to the road plowing with
IH 3-14's, running a couple passes away from the creek. And when he was about half way to the road just
like you pulled the plug out of the wall on a tv or radio, it got real quiet. Tractor ended up going to
town to IH dealer. I saw the crankshaft, and the mechanic that built the engine told Dad and I the
crankshaft broke right next to the center main bearing. In the 55 years since then I have never seen
another H or M crankshaft broken, I have heard of one other M breaking a crankshaft.

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I know of 2 other Ms that broke the crankshaft. In the same place. Not common, but apparently it does happen. These tractors were not pulling tractors. Just good ol' Ms that were still working for a living.

When I bought my Super M it ran but pretty wheezy, had oil pressure but real noisy rocker arms. Found the center cam bearing spun and the center block webbing busted and shifted. Never expected that, asked an old machine shop guy and he said he never heard of it before. The crank shaft was good though.