[dundee222]

Muriatic acid will dissolve the welded on aluminum on the crank throw. Just soak it for a bit, in a well ventilated area. You need the crank out to do this and you will need it out to measure the bearings properly anyways. I did a kohler a couple of years ago. Took about half an hour. Another tip, When you mike the bores, be sure to measure at the top AND bottom of the cylinders in both directions. Onan cylinders often wear even more egg shaped at the BOTTOM of the bore due to rod angularity mid stroke.

 

[dundee222]

If the bore is egg shaped/out if round new rings will leak/and take forever to seat and it will burn oil and loose some compression. If you download the engine manual here, all the specs and tolerances for the cylinder and bearings are in it. To measure, while a dial bore gauge is sweet, with a little practice, telescoping bore gauges work nice too. You also will need to borrow a micrometer for the crank journals and another for the cylinder. Once you get your measurements, then you can plan your path forward.

 

[dundee222]

Since the rod "grenaded" in there I'll bet there is shrapnel all through the engine. I'm sorry but a full disassemble/cleaning is in order if you don't want to throw good money after bad. The oil screen only filters out the big chunks. It is not hard, actually a learning experience but you will need a cam gear puller. Not hard to make if you have the tools.