Engine rebuild?

Tore into an engine on a farmall H cause it had a good amount of blow-by. It really was a lot better off than I thought it would be. Small ridge in the cylinders and the rings look ok so now I am wondering what I can get away with.

What are some tolerances where you normally rebuild? Cylinder to wall tolerances and how do you really determine if your rings are bad? Where else could all this blow by be coming from?

Tractor will see little use so looking for a good compromise between a good engine and price.

get a ridge reamer to cut the ridge off the top of the bore, then "hone it and ring it". With only light use it will last many years.

If the oil pressure was good put new rod bearings in it too.You gotta drop the pan and push out the pistons and rods anywho.If pressure was low roll some new main bearings into it. Hoss

Measure the pistons and the sleeves. For something that would not get much hard use, a set of rings will go a long way toward sealing it up and stopping oil smoke. A new set of sleeves and pistons should be very reasonable though. The H is a very popular tractor.

if you can catch the ridge with a finger nail,theres more wear than you would think.also taper on the cylinder walls ,more wear at the bottom of the cylinder verses the top.also for each .oo1 of wear the ring gap opens up .003.the rebore sets are cheap ( oops inexpensive )

Ring gap is very important. This would be to much gap.





Ring gap spec. for an H .010. Piston clearance between the bore and piston is .003 - .004

Not removing the ridge at the top of the cylinder before removing the piston can break a ring and sometimes damage the piston.

What kind of tests did you do before your tear-down? Compression? What was the compression for each cylinder with and without a little oil added? How many hours of operating did it take to use one quart of oil? What weight oil were you using? Tom

If you pull a hair out of your head and measure it with a micrometer its around 7 thousandths.If your cylinder has enough ring groove that it will catch your fingernail,its probably more than 10 thousandths.10 thousandths is as much as you can go if you want the rings to last a long time.Over that and every time they go up and down it is like twisting a piece of wire and after a while they will break.Harder rings break quicker.Now I have put new rings in a worn out motor and it quit smoking and ran a lot better.The main thing is deep scratches in the liner straight up the side that wont come out when you hone it,will let oil past the rings bad.If you just used it for light work and not a whole lot it would work for a while.I think I remember them saying about 10000 miles on a motor in a car before the rings give up on egg shaped cylinders.Say it went 20000 miles,and old motors would run 100000 miles new,so you could expect about a fifth of the life or less.Depending on what rings cost compared to the whole thing would be how I would decide.If you can get rings for 50 dollars and not use the tractor much and lightly then,it could last years.If you put it all in it would probably put out more power than it did new and last a long time,plus you should have the valves ground probably too since the head is off.A head can cause one to smoke especially if the seals are gone off of the valve guides.
All motors have blow by.Some seem bad but run a long time like that.Watch a tractor pull some time and you might see one shooting a lot of blow by but pull out the gate.If its burning oil and doesnt have compression and lots of blow by is a sign its worn out.Also Im no engineer,but I think if it ever got real hot it might not be worn out,but the heat might make the rings loose some tension and cause blow by.
Also when I took the rings out of my H and compared them with the new ones,the old ones were about half the size of the new ones.Mine was blowing oil out of the exhaust pipe and had non foulers on the plugs to stay running,and smoked bad all the time it ran especially when you first started it.The head was worn out and 4 of the valves all of the guides,rod bearings,sleeves,and it still ran alright,but about half the power it should have.Running it would get oil all over you in just a little while.

Some good info below but perhaps something here might help.

If no internal micrometer, check ring gap in the worn part of bore and at the bottom in the unworn part. The ring gap difference can be worked back to bore wear.

If the cylinders are oval, new rings will struggle to seat.

Side clearance of rings, particularly in the top groove is important. Rings may well 'oil pump' if sloppy. Pistons can be reconditioned for this fault but probably the cost and other wear factors would make it uneconomical.

Look at the bore with a light from the other end. You will see if the reflection is distorted (oval bores).

Some top rings can be obtained (or perhaps not, these days) with a step to avoid the ridge problem.

The workshop manual or a generic manual will give the serviceable limits for the engine.

You said 'Where else could all this blow by be coming from?'

Well, was the timing too far advanced? Has the head been shaved previously (raised compression ratio), Higher compression pistons fitted? Rings sticking in piston grooves?

Actually sounds like it is worn to some extent, probably oval. For you to check out. For you to decide how far to go. My view is - if you can get the parts, do the job properly, unless just a parade tractor.

Fixing the blow-by may well mean sorting the crank, as extra load imposed by a strong engine may well find any weakness in the lubrication system and bottom end bearings, if worked hard.

As is often said 'do it properly;only do it once'.

Regards, RAB