allis model b max rpm

I have a 39-40 i think model b in the process of rebuilding it and wanted to tweak some little things on it and wanted to know what the max rpm one could turn one of these old tractors before they blow. and what weak points they have on them. i cant find any info. on these anywheres.

 We have installed the d15 series two gov spring on them and not blown them . youre valve springs and points should keep you from blowing it . points usually bounce and cause a miss the weak valve springs usually let the valves float keeping the rpms down.

To get the maxim RPM.s, in my opinion and experience,  you would need to go to a pressurized oil system to the rods thru the mains. You would need to have the engine balanced by an engine shop that has the proper equipment. Line boring the mains and reconditioning the rods would be more than necessary. You would have to put a larger venturi as well as a larger main jet.

On a well balanced engine with changes above you could get 4000 RPM's and above.

Doing so will loose lugging power. Also doing so would most likely cause the governor to fly apart in prolonged high RPM's which would mean that the governor should be removed.
You would then have a racing engine not a tractor engine. You would not have a pulling engine that would have a lot of extra horse power. You could pull a light load like a bat but when the load started to increase like on a transfer sled the RPM's would drop quickly and with the larger venturi you would fall flat fast and the little B that was at factory RPM's would clean your clock.

     

hp are torque values on a dyno are the same at 5250 rpm.  To get to that rpm takes balancing everything as Dick mentioned and alot stiffer than factory valve springs  a cam shaft with more than factory lift .   A d15 series 2 gov spirng works well . Governor springs do more than just set high idle they also try to maintan  a  full load rpm.  In the d15 case that is higher than the b full load rpms. Same thing with the 175 spring vs the d17 and combine spring they all control at the same high idle give or take a few rpms but one seperates itself  from the other two at full load rpms. ps if at cranking speed the carb. will suck the palm of youre hand up to it and youre engine dont lug its something besides the carb for its none to big to recieve adequate signal from the engine .

Edited by mlpankey - 30 Jan 2010 at 1:56pm

if it dont make a horsepower more if the rpms allow you to drop a gear to maintain the speed rule youre mechanical advantage is better. another words say you can run 3 mile an hour at 2200 rpms in first and youre competitor runs 3 mile an hour in second at 1500 rpms and both engines make the same ponies same gearing .my money would be on the first gear tractor.

Just buy the 3 7/16 standard over bore kit.

2200 rpm in first gear will blow the horn with the B at 3 mph with 11-2 24's
You can run the 2200 with the C at 3 mph almost.

You just have to hold tight until you have tire slippage before you open it up.
I always on all my tractors started pulling at a bout 1/2 throttle and opened it up a little at a time as the weight box came up and would be wide open just before the tractor was at full load. Then it would lug, start to die down or start to spin.

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