B20 - D950 parts diagram shows two different pistons?

[Mark15]

I am working through the rebuild of an old B20 with a 3 cylinder D950. I have ordered a "Kumar Bros USA" rebuild kit for this engine with 3 new STD size pistons, as the originals were very deteriorated / pitted on top.

I noticed the Kubota parts diagram shows two different pistons (actually 4 if count the 0.5 over bored ones).

Part number: 15532-21110 "PISTON" specifies 2 needed
Part number: 15531-21123 "PISTON 2" specifies 1 needed

My Kumar Bros kit came with 3 pistons, all with the same part number. They appear to be a perfect match with the old ones other than the branding stamp on the top surface.

Additionally, the Kubota WSM only lists dimensions and tolerance specs for one STD piston size.

Anybody have any idea what the difference is with the two different pistons in the parts diagram?

 

[Mark15]

I called the Parts Hotline for Messicks, where I ordered some of my other parts from, to see if they had any idea what the difference was. They were not sure either, and are going to try to check into it.

Just hoping my aftermarket pistons will work out okay! Hate to put all all this back together and re-assemble the tractor without understanding what the actual difference is between the two different pistons the Kubota parts diagram calls for.

 

[North Idaho Wolfman]

Look at the skirt of the piston, I think the rear piston will have a slightly shorter skirt.
Your new pistons will probably all be the same short skirt length.

 

[Mark15]

Look at the skirt of the piston, I think the rear piston will have a slightly shorter skirt.
Your new pistons will probably all be the same short skirt length.

Ah that might be it! I checked the diameter of each one pretty closely and they all seemed to identical, but I hadn't thought to pay attention to skirt height. I will check the old ones and see if that is it.

Thanks!

 

[100 td]

Following - I would have thought if any piston was different it would be number 2 due to increased heat, I'm interested in the outcome from a general knowledge perspective!

 

[Mark15]

Well, the skirt height on all three of the old pistons look the same. I suppose it's possible this engine has been rebuilt before though. I don't know the full history and its an old machine.

I am also consistently measuring the cylinder bores to be about 3 thousands UNDER the min factory spec. I knew the previous owner, who it ran great for many years though until it developed an issue due to overheating. He bought it used as well. I am not sure if its possible it was bored smaller than spec from the factory, if it was re-sleeved / bored once before, or if I have too many thumbs to work my dial calipers!

So I guess whatever the difference is, be it skirt height, or heat tolerance, it must be pretty small / inconsequential.

The plan is to put it back together with the three new identical pistons from the rebuild kit and then try to forget there originally was a difference, so I won't lose any sleep over it!

 

[North Idaho Wolfman]

The plan is to put it back together with the three new identical pistons from the rebuild kit and then try to forget there originally was a difference, so I won't lose any sleep over it!

Good plan!