Farmall H motor rebuild

1945FarmallH · Jan 6, 2015

I just rebuilt the motor on my 1945 H. Did rings and bearings and had the head redone. before the rebuild i always had a strait pipe exhaust on it..i was told that after having the head redone that i should run a muffler on it to ensure back pressure. is this true or am i safe running it strait piped on the new head? any info would be great help...thanks in advance!!

J.Wondergem · Jan 6, 2015

Are you working it hard, or just putting? I think the trouble comes in when the valves are red hot, and you shut it off, let the cold air in on them.

Janicholson · Jan 6, 2015

Though controversial, there is no real way that the issue is real. Radically higher powered airplanes have had stub exhaust pipes 4 or 6 inches long and do not warp valves, or need back pressure. It is just nonsense. A open valve could have somewhat cooler air blow into it. It will however cool rather evenly as a result. Back pressure can only help an engine if the pressure pulses are timed through real research/dyno testing to hold in intake charge that would be exiting the port from supercharging or radical cam timing. Usually the header systems are designed to be a partial vacuum at the port to assist in scavenging all exhaust out. I recommend a muffler however. Because an H with a straight pipe has given me tinnitus in both ears (it is very not good) Jim

1945FarmallH · Jan 6, 2015

Thanks guys! It's not gonna be worked real hard. Pulling two bottom plow every now and then and raking hay. She sounds so good Strait piped I didn't wanna loose the nice sound haha!!

Steve@Advance · Jan 6, 2015

I wouldn't see it as an issue. Since the main jet is adjustable, simple enough to adjust it accordingly.

The problem occurs on engines with fixed jets. Relieving back pressure tends to lean the mixture. Rejetting a carb is a tedious procedure, most people don't bother or even realize there is a problem until it's too late.

used red MN · Jan 6, 2015

Let the naysayers come, I agree with Jim. Let's say Mr. 45 Farmall was just pulling the eye teeth out of his H for 3 hour straight. What magic force field is protecting the hot exhaust valve from the cool intake mixture of vaporized gas and air each time the intake valve opens? Have you ever heard of exhaust/ intake valve overlap? Not real important in a tractor engine, but in a cammed up race engine quite the opposite. Bring on your straight pipe, even though I would prefer the muffled note.

gene bender · Jan 6, 2015

Most of the new mufflers dont have a baffle anymore so how could there be bc pressure. If you add an extension on the new mufflers it does quiet them down a bit more but if you like the noise fine. Just dont annoy fellow drivers on a ride.

Allan in NE · Jan 7, 2015

Bull feathers. :>)

Allan

Eric in IL · Jan 7, 2015

Ever attend a tractor pull ?

Did it feature a modified class ?

Any of the "tractors" have six V-8 engines ?

See any mufflers ?

I think your H will be fine whatever you decide.

Mike M · Jan 7, 2015

Yep that's when it happens. But mostly if you have really short pipes and no manifolds.
That's why the BIG BOYS put caps on or plugs into their pipes when they shut them off.

showcrop · Jan 7, 2015

Denny's Carb shop has a special pipe for Farmalls. When you put one on you will be able to out pull a Ford N :wink:

Christopher Mikesell · Jan 7, 2015

It is a real issue, just not with most older tractors. It has to do with heat transfer rates caused by the speed of the exhaust gasses. In high performance motorcycles, it doesn't take long to warp valves if you go to a straight pipe. This is not speculation talking, it is experience.

kevinj54 · Jan 7, 2015

(quoted from post at 09:17:11 01/07/15) Bull feathers. :&gt

Allan

I would agree since mufflers were an option back then.....

sotxbill · Jan 7, 2015

airplanes run a constant speed, unlike automobiles..

TomH in PA · Jan 7, 2015

Guys with open pipes love the sound of their own motors. But unless you're way out in the country you're going to annoy everyone around. They probably won't say anything, but eventually they'll decide that neighborliness goes both ways.

GVSII · Jan 7, 2015

The idea that all engines , your H included,need back pressure or need a muffler or pipe to save your exhaust valves ranks right up there with the idea that an engine without a thermostat will always run too hot and hotter than the same engine with a t'stat.Just not true.I don't recommend running without a manifold.The manifold and a short pipe is all thats really needed.

buickanddeere · Jan 7, 2015

"needing back pressure" is a steaming heap of bull dung. A high quality muffler is required so the operator goes deaf slower. A straight pipe is just irritating noise, it isn't cool.
Pulling the sleeves and running over size high compression pistons on the block along with a re-ground cam makes those H's into a powerful machine.

Ellis Kinney · Jan 7, 2015

Building a motor without sleeves ruins the block
for a re build. I bought a Farmall M in 1973 that
was set up that way and when I went to rebuild the
motor the block was a boat anchor. It was much
cheaper to buy a used block, than try to re
machine the block I had. Ellis

Rollie NE PA · Jan 7, 2015

Without some back pressure the exhaust will scavenge the combustion chamber of fuel. If you can't keep all the fuel in the combustion chamber, you can't burn it.

The formula for MEAN FLOW VELOCITY is (average piston speed / 60) x (bore [squared] / exhaust pipe inside diameter [squared])=FPS
Now to find AVERAGE PISTON SPEED to plug into the formula AVP is (stroke x rpm) / 6= average piston speed

buickanddeere · Jan 7, 2015

Just bore it another 20-30 thou larger.

Farmall H motor rebuild

New User

Well-known Member

Well-known Member

New User

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Member

Well-known Member

Well-known Member

Well-known Member

Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Similar threads