1938 Farmall F-20 Engine

Hello, I am restoring a Farmall F-20. I just recently removed the pistons. I've been searching, trying to find the o-rings, but with no luck. If someone could describe to me where the o-rings are in a very precise manner, I would greatly appreciate it. Also, do you guys think I need to do anything else to the engine? Any help you could give me would be greatly appreciated. Thanks in advance.

ok, the O rings are at the bottom of the sleeves, between the sleeves and the block. The only way to see them is to remove the sleeves. The are in the very bottom of the sleeve opening, inset into the block.

once the sleeves are out, mic them to make sure they are not worn out or egg shape. If they are good, cut the ridge and hone them. New rings. New O rings. You will basically have a new tractor. Oh, also, make sure you do a valve job on it with new guides ( unless the guides aren't too worn).

Thanks Tom. As you can probably tell, I'm not very mechanically
savvy. I am wondering how you remove the cylinders, and what
does it mean to "cut the ridge and hone them." Thanks much.

Dylan, you have two real options here-

Number one, read everything and anything you can find on engine rebuilding, especially regarding to the older tractor engines. Pay special attention to what is said about machine work, tolerances, how an engine wears as it is run(thus requiring rebuilding)etc....Educate yourself in that manner, and then what was posted above will seem simple.

Option number two, find a local machine shop you can trust and let them rebuild your motor. Make sure they are familiar with older tractor type engines...not all are these days.

In addition to what Ron said, here is the skinny on what a ridge is. As the piston travels up and down the cylinder bore, it starts to wear and the bore starts to wear. A properly fitted piston and rings will allow the piston itself to actually "float", and the only metal -to-metal contact is the rings with the bore. You may have heard the term "piston slap", that is where there is too much clearance between the bore and the rings (or also a worn wrist pin).

There is an areas of the bore (sleeve) that the rings do not rub against, because it is at the top of the bore beyond where the rings travel. After hours of running, a small "step" or ridge will form because the area the rings travel in has worn down a bit. There are specific tolerances for how much wear is acceptable (which is why they make + .002 rings). There is a ridge reamer tool that will cut the ridge out. This is important because not only do rings wear around the circumference, they also were on the sides (top and bottom). When you install new rings, if you haven't removed the ridge, you run a big risk of breaking the rings when you first run the engine after rebuild. This is because a new ring is full-width, and at the top of the stroke will hit the ridge, thus breaking the ring.

Honing a cylinder is nothing more that smoothing it up, and also making small "scratches" in the cylinder walls. Properly done, this is known as cross-hatching. Cross hatching is VERY important to allow the new rings to wear in and "seat".

Feel free to keep asking questions, that is how you learn. That is also what this board is here for. For people who "know" to share that with people who "don't".

here is a pic looking up from the bottom of the block. The o ring is in the groove cut in the block

Thanks so much Tom, you're really helping me understand this.
I have just two more questions for you. How do you hone the
cylinders, and how do you remove the cylinders. Thanks so
much.

Removing the sleeves will likely be difficult. I have removed a lot of them using a 20 ton hydraulic press and several have taken almost the full 20 ton to get them to pop loose. You may want to consider testing to see if the block will hold water and if you don't see any water leaking past the O-ring and out the bottom of the sleeve, then you would not HAVE to remove the sleeves and replace the O-rings.

Here is a picture showing the device I made to hold F20 engine blocks upside down in my press without removing the head studs for the purpose of pressing out the sleeves.


To hone the cylinders you need what is known as a cylinder hone. It has 3 spring loaded arms with a fine grit stone attached to the end of each. You put it in a drill and run it at a slow speed while also moving the drill up and down to put in the "cross hatch" pattern.


http://www.ebay.com/itm/GearWrench-...76&pt=Motors_Automotive_Tools&vxp=mtr

Thanks for the advice everyone. If I do decide to put a little
water in the block to test the o-rings, then how would I get the
water out? Thanks so much.

On the left side of the engine there is a hole with a cast iron elbow that bolts to the side of the block, a rubber hose goes from the elbow to the bottom of the radiator. If the radiator is still mounted and connected to the engine, just fill it with water until there is a few inches in the engine, check for leaks and then just remove the drain plug from the bottom of the radiator and the water will drain out. If you have already removed the radiator, then plug the hole on the left side by bolting a piece of flat steel over the hole with a gasket. Then fill with water and check for leaks. Remove the steel plate and the water will drain out.

Here is a pretty good video on honing to get you started:

https://www.youtube.com/watch?v=AYC2vre2P38

Here is one for cutting the ridge:

https://www.youtube.com/watch?v=79i-_-u3HzA


Now, both videos are "modern" engines, so yours is a bit different, however, the concepts are exactly the same.