Need help identifying correct piston rings

[t17wilson]

Posting the question here instead of the Farmall section since the pistons may cross over or someone may have an idea.

I'm working on a 1951 Farmall M whose engine was stuck. The 248cc engine has 4" aluminum pistons. According to the IH parts book the rings should be 3 3/32" rings and a 1/4" oil ring. This piston, which may have been replaced, has a 7/64" top ring, 2 3/32" rings and a 1/4" oil ring.

The bore is 4”. I’ve measured and remeasured to make sure that’s right. I’m using a set of new digital calipers and I’m pretty confident in them. The piston measures 3 63/64” and the bore is 4”. The part I’m not confident about is where these pistons came from. I have a feeling the engine has been overhauled but the only markings I can find on the pistons is the IH logo on the outside just below the wrist pin and the number “838” in the inside just above the bottom lip.

I've been unable to find a set of rings that I think will work. Any ideas? Thanks.

 

[showcrop]

I just go to the local automotive machine shop. They are equipped to enter the data and the rings pop out of the top of the 'puter.

 

[Steve@Advance]

Like showcrop said, get a machine shop involved.

It is impossible to measure cylinder bore with calipers. You need a dial bore gauge, or telescope gauges
and a micrometer to get down in the cylinder. The measurement is then compared to the piston skirt to get
the clearance.

Without proper equipment and the engine specs, there will be a lot of guess work, which will add up to so
many ways something can go wrong, something bad is bound to happen!

Sounds like the pistons have been changed. Could be later model factory pistons, could be aftermarket.
Possibility they are oversize, in which case oversize rings will need to be ordered. A good shop can sort
it out for you.

A shop manual will be a very valuable investment!

 

[teddy52food]

If the top ring groove is worn, have a machine shop put in spacers & use the 3/32 rings.

 

[t17wilson]

Was looking around some more this morning and found a number up inside the piston. There is a "D" inside a diamond and then a box with either X3 D7, or X3 07 inside. I haven't been able to find anything yet with google searches. Anyone have any ideas?

Yes, I already believe the pistons have been replaced and no, the top ring is not worn. It is consistently the same size on each of the pistons. And I have a repair and parts manual but that doesn't tell me what pistons someone may have used!

 

[Den N Ms]

Wilson,You might give these folks a call.
Otto Gas Engine Works

 

[pete 23]

Like others have said, you need to use a inside micrometer or bore gauge to check cylinder for wear. Top ring groove you have only .006 clearance maximum with a new ring before ring will start to flutter and break and also not seal on the worn ridge in the ring groove. Ring has to seal in the piston as well as on the face to the cylinder bore. All IH Farmall M tractors came with cast iron 3 7/8th pistons. Any aluminum piston, even 3 7/8th would have been a replacement. Most ring suppliers can come up with a combination of the sizes you have listed.