Farmall M with 400 head

I have the M farmall tractor that my grandfather used to farm with. The motor stuck from lack of use in 90. Did a short block overhaul. Orginal head was cracked. The shade tree mechanic doing the work for me put a 400 head on it. The engine has the high domed fire creater pistons in it. I am not sure of the bore size. The tractor runs o.k., but I am not sure if it is timed right. It has the original mag on it and I would like to keep it this way. Would anyone have an idea where it should be timed?

(quoted from post at 21:53:58 02/14/10) I have the M farmall tractor that my grandfather used to farm with. The motor stuck from lack of use in 90. Did a short block overhaul. Orginal head was cracked. The shade tree mechanic doing the work for me put a 400 head on it. The engine has the high domed fire creater pistons in it. I am not sure of the bore size. The tractor runs o.k., but I am not sure if it is timed right. It has the original mag on it and I would like to keep it this way. Would anyone have an idea where it should be timed?

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The magneto must be timed so that the impulse trips when a piston is at top dead center on a compression stroke. Here is how to get it timed correctly. First, loosen the two mag mounting bolts and then rotate the mag all the way toward the engine, then slowly turn the engine over half a turn until the pin in the end of the crankshaft is exactly horizontal, finally slowly rotate the mag away from the engine until you hear the impulse click, tighten the mag mounting bolts and you are good to go.

The thing is that all the fire crater pistons were supposed to be timed to 22 degrees btdc but the magneto has a set 35 degree advance ( spark lag). There was a special impulse coupler made for magnetos when used with fire crater pistons on the M. If you are satisfied with the way it runs ok, but if you intend to pull it heavy I am sure you will have detonation with a std magneto. Not good. I am sure you would have a smoother better running M with a 22 degree, properly tuned, battery ignition distributor on it.

If it has a mag and it starts and runs it is timed rite. Quit worrying

May not matter if its not used for heavy work. But as Pete said IH recommended a 17 degree impulse coupling rotating unit complete be installed in the magneto for FC pistons in a M.
On a 400 and 450 IH recomended only using fire crater with a distributor. Also not to have total timing over 25 degrees at the crankshaft. They had a template in some sets to mark the crankshaft pulley if it didn't have the mark.
Not sure if IH recommendations can be compared with now. But in the sixties when a lot of fire crater kits were being put in I think the gas octane was as good as todays. At least what Dad used on the farm, we used it in 10.5 to 1 compression engines with no problem.

Nope the gas of today is not as good as back in the sixty's . TRW had a write up in the high performance cat. about what pistons could be run on what gas in what engines . And on todays gas the max comp ration on the 93 is 9.5 to 1 and only with limited timing . And justy like the 706-865 gassers if your going to use them as a work tractor ya got to run the 93 as that is the lowest octane ya can go . Back in the sixty's the reg. gas was 95 octane the only thing lower was Gulf Tane and it was 90or 91 and you could get a old Cheve 6 cylinder to rattle on that stuff and diesel at shut down . Back then there were Premium fuel engines and reg fuel engines . and 10.5 to 1 was common and some of the higher end engines were sporting 11 to one . I tryed to run a 11 to one engine in my one pick up on the hightest not good . ended up changing pistons and heads to get it down to something that would run what you could buy at the pump. The first big truck that i started driving was a B60 Mack with a huge 6 cylinder gasser and it ran on High Test as all the gas powered semi's did back then. Oh for the old days as i would buy my gas where we got gas for the semi's on the company account for 17.9 a gallon and it did well in my 56 ford rag top with the 292 with dual quads 312 blower head and a isky fullrace cam with a mallory dual point dist. and headman headers . I could run the gas at Gas Town the truck stop or i could run Sunoco 240 and i could run Ashland hightest the rest would ping . also back then the pistons were FORGED and today they are Cast. and a cast piston will not carry the heat away as fast as a forged one will. I did a lot of playing around with lets go fast engines in my younger days and i made my fair share of shell we say SPARE parts..I had a saying back then that WHEN THEY GO THEY GO , But WHEN THEY GLOW THEY BLOW .when that one 706 gasser seized up because of pistons getting so hot that they seezed in the bore when i saw where they seized i knew that they got super hot to swell over .025. as they miced out at between .0195 to .020 smaller above the top ring then the skirt and i had built .004 skirt to wall into the engine miced each piston and miced each hole and fitted each to the hole . Ran that engine in at the shop for about 7 hours on the dyno varing load and speeds . The farmer never worked it hard all winter just feeding and hauling manure . When it was time to take it to the field to plow he got gas at a local station and went to plowing sometime that day he had fuel brought to the arm and put in his tank . The first day the tractor never missed a beat . The next day he filled from his tank and never made it to the far end of the field when it seized . when i opened up the engine and saw what had happened i knew what went on and that is when we sought out a lab to test the gas and the lab repor confermed what i though had happened . The fuel suppier brought out 87 octane and the gas that he got from the station was 93 and according to the fuel requirements of a 706 the lowest is 93. And this was taken from a 706 owner manual. But back to like Pete said timing on that set uppp makes a lot of dofference and myself i would make a paper weight out of the mag and set up a dist that would maxiumiz the components that are in that engine .