XR400R XR350 Top rebuild questions

[Ramanonos]

I have a nice 1985 XR350 (single carb), that I’m doing a rebuild on. Last night I took off all the essentials jugs, etc. I left the piston on the dowel. Going to order rings on ebay. Do I need to take piston off to do the rings? The cylinder is 83.9mm within spec. The piston jug is 84.0mm with spec. 

 

[dieseleveryday]

The only thing I would worry about is piston fatigue on something this old pulling the piston to look at the rod is probably not a bad idea just for verification of condition

[creeky]

I would replace the piston, the ring grooves and pin are probably worn and, as said, metal fatigue has probably set in. Measure the bore according to the manual, it is probably out of spec by now and will require boring to the next size.

[Ramanonos]

I may just order a new wiseco piston ring kit. But my cylinder is right in spec at 83.9 mm and nice a smooth.

The only piston option online is 84+0.5”... https://www.ebay.com/itm/391900678678So should I take it to machine shop to bore out, and at what size should I tell them to bore—84.5mm? I don’t want to make a mess.

Maybe just reuse piston with fresh rings, and hone? What would you do?

[dieseleveryday]

Have you checked that measurement throughout the bore with a dial bore gauge?