172 Gas 4 cyl - general advice and cylinder bore specs?

1963 4140 heavy duty industrial serial number 19120


I recently removed the engine to fix a rear main seal leak. The seal was done by someone dropping the oil pan. It wasn't offset at all and one side seal pin was not all the way in and bent 3/8" over. I found a bad rear main bearing and #4 rod bearing. After polishing, new main bearings, I used plastigage and got 0.002-.0.003" on the crankshaft main journals. Still waiting for rod bearings. I measured the roundness of the rear crankshaft journal and it was less than 0.001" with the fowler magnetic stand and displacement gauge.

I removed the cylinders to inspect them. It looks like they need replacement but please inspect the images and advise.

The cylinders are 0.040" over bore EAF6108J. I can't tell if there are sleeves or not. The block is C0NN6015J. I have read that these later model engines were sleeveless. Can anyone confirm this?

I know the cylinder bore is 3.901" + 0.040 = 3.941". Is there a +/- tolerance?
I have received a fowler bore hole gauge today but still waiting for the 3-4" fowler outside micrometer which I will get on Thursday.

Is there a tolerance on the cylinder diameter? I have measured them at the top with a range of 3.908-3.911" with a caliper. I know I need more measurements... I have a 3-4" micrometer coming. Where to measure them?

I'm hoping that I can either reuse the existing cylinders/new rings and deglaze bore with the flex-hone, or new cylinders/new rings and deglaze bore.

I did get a complete gasket/seal kit for the engine.

This is my first time diving into an engine so all advice will be greatly appreciated. Please keep in mind that I don't have the money to get any machine shop work done. This tractor had an oil pressure of 45-50 psi. It didn't smoke at all.

The bottom of the head and top of block were all black with carbon. The exhaust manifold was cracked between between 1-2 and 3-4 cylinders.

I also got a new clutch plate... the old one didn't look very good.







It looks like you are calling your pistons cylinders. You want to compare your bore diameters top to bottom to see what the wear is. Sorry I don't have specs. Those side seals with the pins are hateful. They will be obsolete soon. The trend is to filling the space with silicone. Victor Reinz has it. I got a Micky D's milkshake straw to get the silicone to the bottom.
(quoted from post at 20:22:37 04/24/23)
It looks like you are calling your pistons cylinders. You want to compare your bore diameters top to bottom to see what the wear is. Sorry I don't have specs. Those side seals with the pins are hateful. They will be obsolete soon. The trend is to filling the space with silicone. Victor Reinz has it. I got a Micky D's milkshake straw to get the silicone to the bottom.

Lol... your right, I did mean to say piston everywhere I said cylinder. Can you comment on the condition of the pistons I posted?

I did get the permetex the right stuff sealant aerosol can with the nozzle to get it pushed/squeezed into the side seal holes.

I'm working outside, unfortunately I don't have a garage yet. It's raining today and tomorrow and everything is well covered up.

I did get a set of telescoping bore gauges and measured cylinder 4 bore at center depth and got 3.940" transfered to the caliper which is right on spec. I'll measure 2 sides top, center, and bottom of the pistons and post a result.

Thank you for your reply
The amount scoring or scratching on the piston skirts
particularly of number one piston would be concerning
to me. If the cylinders walls looked that scratched up I
am surprised the engine did not use quite a bit of oil.
Looking at the manufacturers online parts diagrams
your engine in what I see as original equipment has
sleeves. See number 31 in the linked diagram.
However, it is very unusual for a sleeved engine to
have 0.040 inch oversized pistons. Should be able to
take some mediums grit emery cloth to the head
gasket deck at the top edge of the cylinder bore. You
should be able to see the line of the sleeve by doing
this. I would also think you could tell by looking at the
bottom of the cylinders as well. If it does have sleeves
replacing the sleeves and pistons would probably be a
good idea. If the finances are not there for it I would
question if it would have a good chance of burning oil.
Not much of a Ford guy so my info may also be way
CNHI Ford 4140 online parts catalog

Thank you. I use the same one but always looked at the interior engine diagram being where all that is. I never saw the sleeve in the diagram before. So, that's a good thing. I'll use emery cloth as you suggested to find the liner seam.

The engine doesn't smoke and exhaust appears clean. I've never noticed any thing when using the tractor... all seems normal. It was leaking oil. I got it last June.

The pistons are stamped 0.040 on top. I don't want to go down the financial rabbit hole on this. Removing and installing liners sounds a bit more complicated. If the bores measure okay, I'm hoping I can hone the bores a little to clean them out and get some cross hatching and get new pistons/rings.

That amount of skirt skuffing looks excessive to me. Normally skuffing is prevented by the crankcase oil coating on the cylinder wall, and as the piston descends the oil ring clears this coating off. Since it is running well I think that the skuffing could have been caused by a temporary condition, such as overuse of ether to start, or oil diluted by gasoline, or failure to start with a lot of use of the choke so that unburned gas was washing the cylinder walls. I think that it is a good possibility that you could just smooth them up and get 2,000 more trouble free hours out of her.
Thank you again...

In January this year I did go through a period where it wasn't starting, hard starting, starting and running rough and dying, carb was overflowing gas out of air horn during all of this. It was a new carb. I took it apart and the bowl float was not connected to the assembly, it was sitting stuck up at an angle. It was not connected with the pin through it. The needle wasn't engaged. However, even after I fixed the carb, it still wouldn't start. I was chasing my tail and changing parts out. You name it, I replaced it. The distributor was in really bad shape so I bought a new one. I timed it with the wad pop method and finally it would start as soon as I turned the key after pulling out the choke. I ran it for awhile making sure it was finally fixed and drove it down the road and began using the backhoe. The oil gauge was broken. I checked the oil and it was very low. I looked underneath and saw oil leaking from the rear main seal and trans cotter pin. I did an oil change with new filter and started using it sparingly. I installed a new oil gauge getting 45-50 psi. It was running great but leaking too much oil for me to ignore so I decided to pull the engine and get to the bottom of it.

It's not raining today so I'm going to measure the cylinder bores with the fowler bore gauge and post the results. I'll look into smoothing up the cylinders.

Thank you Sir, your help is greatly appreciated!
(quoted from post at 11:36:21 04/25/23) Here are the bore measurements. I think they look good...

<img src=https://www.yesterdaystractors.com/cvphotos/cvphoto153161.png>

Number one is at the general service limit for an engine that is intended to be working daily at what it was originally built for. You would expect more taper with the amount of skuffing that it has. For the intended use of the tractor though it is certainly acceptable.

I found the correct cylinder bore specifications.

The FO20 paragraph 103 gives:

172 Gas standard cylinder size is 3.8998 - 3.9018".
Adding piston size 0.040" gives a range of 3.9398 - 3.9418".
Center spec 3.9408"

Cylinder 1 Average = 3.9407" Range: 3.9404 - 3.9409"
Cylinder 2 Average = 3.9407" Range: 3.9407 - 3.9409"
Cylinder 3 Average = 3.9407" Range: 3.9405 - 3.9409"
Cylinder 4 Average = 3.9403" Range: 3.9402 - 3.9404"

This looks good to me with the correct specifications from the book. I'll remeasure the bores again tomorrow and see if I can get cylinder pictures. I received the 4" flex-hone today.

Assuming these measurements hold up, would it be best to get new pistons? I can buy those. I have a ring set coming. I am cleaning up the pistons and they're looking much better. I found defects on the skirt bottom edges. I chamfered the sharp edges.

Thank you.

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