Farmall H Piston-Sleeve clearance

JohnG(TX)

Member
Does anyone have a good spec for the clearance for used pistons/sleeves? What would be considered too much? What is it for new pistons and sleeves?
 
(quoted from post at 08:47:32 09/16/14) Does anyone have a good spec for the clearance for used pistons/sleeves? What would be considered too much? What is it for new pistons and sleeves?

Go to Goggle-Everything you need is there.
 
The question cannot be answered. The difference between cast and forged pistons, expansion control inserts, type of cooling (including oil jets on pistons from under them) size of bore, and many other details make the answer or formula impossible.
Set it to factory, or piston maker's clearance for the application. Jim
 
I have a set of used step head pistons and the block I believe they came from. I am wondering if they are worn beyond use, or if I can make a go with them. I can measure the pistons and their corresponding cylinders, but I won't know if the clearances are excessive.

I have Googled piston clearances, and for street vehicles it looks to be around 1- 3 thousands, while marine and air-cooled applications are larger. Agricultural applications may be closer to marine, if not larger.

My question is what would be considered excessive based on the intended use of the tractor, which would be for fun, not heavy ag use.
 
First check your cylinder bore for out of round readings. If the cylinder is good, then insert the piston with rings and check the ring to wall gap. That should give you an idea anyway. I guess you could tolerate more than .01, but that would be a trial and error thing.
 
If the sleeves are worn .010 or more they should be replaced. Check the top grooves in the pistons. They may need to be squared up & a spacer installed.
 
I have a sinking suspicion that the sleeves have been either bored or honed. There is no ring groove and the insides look fresh. They 'might' be new sleeves, but I am not banking on it. I'll measure them and see what is up. These are nominally 3 3/8" pistons, not the newer overbores.
 
If you can live with some oil consumption you can get by with more clearance. As the pistons and sleeves wear the worn piston skirts will allow the pistons to rock slightly in the sleeve. When this happens the rings will not be held squarely in the sleeve and oil consumption will be greater as a result. If the clearance is too great the skirts will break off and oil consumption will increase greatly.

I have overhauled many H and M tractors that had skirts broken off the pistons and the engines still ran fairly well. The worst one was an H that has six of the eight skirts broken off.
 
According to I&T, Super H (aluminum pistons) calls for 2.1 to 2.9.

Mentions "other series H-4" (which I'm going to assume is for iron pistons) at 3 to 4.

Personally I think I would stop if they were beyond 7. With fresh rings it would probably run at 10 with amazing blow-by.

The greater the clearance the greater the chance of skirt breakage so you'll have to make the call on balancing cost effectiveness, even for light duty. Mr. Aaland is right on in that the ring just can not get stabilized.

If there are machine shops in your area, you might be able to get the pistons knurled. You could then file fit each piston to its bore. It's not top tier but will work for light duty. This could be the way to go if the sleeves measure out ok.
 
.002" to .004 will work. If the sleeves have little ring wear at the top,(where the top rings stop) of one thousandths or so, and the ridge is reamed out, it will be fine. Jim
 
I measured the pistons, and they pretty much measure 3.370. The sleeves are a different matter. I do think they have been bored out. There is a ridge at the bottom where the boring bar did not make it to the bottom and there is no ring ridge. The top of the cylinders are very uniform without any evidence of a ridge reamer. I took a few measurements and they came out to be 3.38+, So they are at least 10 thousands out.

Can cast iron pistons be knurled? How much will it add to the diameter? Any idea on cost? I foresee a whole piston/sleeve kit in the future (distant at this point).
 
The standard bore would measure 3.375. I don't know for sure how much clearance they gave the cast iron pistons. I guess I installed one set back in 1958, rest were always aluminum. Don't have specs right handy. I like to fit the aluminum with right at .0035 clearance if possible. Had scoring when less than that on an H. I never heard of someone boring a cyl and using same pistons but you never know. I would measure below that bottom most ridge in cyl to get the original bore size. Normally any ridge in bottom indicates ring wear caused from lower end poor oiling or just plain wore out from long hours. As far as knurling cast iron, I don't think anyone will do it due to cracking the pistons during process. At .010 clearance all up and down the cyl you can not expect real good results. If it was just the top inch or two you would get by fairly well.
 
Cast iron pistons will not knurl, the material is not malleable, and spalls off or cracks the piston. A ridge at the bottom is dooms day for sure, it will wreck the piston, new or old.
.010 clearance is also deadly. it would rattle and slap so bad it would remind you of tin can with 8 steel balls in it being shaken by a deranged ape.
Haveing sleeves, the existing sleeves (or what remains of them) should be removed, and a new sleeve and piston kit installed (bigger bore more compression, and long life) The cost is probably 800$ including fluids. This site sells good parts for competitive prices. Much less than doing it twice. Jim
 
When I felt the step in the lower part of the sleeves, I knew they were toast.

Are 3.375" sleeves available new? Just the sleeves without pistons?
 
You will likely find that by the time you buy new sleeves and a ring set you will be very near the price of a sleeve and piston kit.
 
Sounds to me like someone was boring the thick wall sleeves for the use of 3-7/16 pistons used with thin wall sleeves and didn't finish the bore big or deep enough.
 

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