We trying  to restore  a Cat fifteen. Problem is that pistons have worn grooves , so the top pistonrings are too loose.
Some top rings are broken. What to do.
Does anyone know someone who can deliver  new pistons or pistonrings for a bore 3 3/4 inch.
Also a headgasket we need.

ACMOC Chapter 19 here in Australia should have new copper head gaskets for that tractor, another option for rings is get oversize piston rings made and machine the piston's, that's easy to do, there are several piston ring makers in the USA, I've used Otto's with good results

We Will try to get oversized rings and hopefully the pistons can be machines.
Tanks for advise Mike and Niel
 

You can also use thin ring spacers to fill the gap in your piston ring lands, they are cheap and usually available off the shelf.

Contact www.ringspacers.com that is the website of Otto Gas Engine Works in America, I bought new oversize piston rings from them 2 years ago for a Caterpillar 30 and the cost was around $US230, they can make rings in any size, another company in the USA is Niagara Piston Ring Works, they also make piston rings
Good luck
Mike

That Otto Gas Engine shop once made me some 1-1/16 inch rings for some old model airplane engines. They are pretty amazing at what they do.