I have a project basket case 75 RD350 I've been working on for a little bit. I recently pulled the top end apart and noticed a little bit of rust in the right-hand cylinder. There appears to be a little bit of pitting (highlighted in red).
I was able to measure the bore, and it came back at 63.98mm. I measured a few different places within the bore (both vertically and front to back/side to side) and it was all in spec.
After cleaning the cylinders, pistons and unsticking the rings, I did a compression test and got 95psi in both cylinders. I know that's still pretty low, but for an engine that hasn't run since 1998, I figured it wasn't too bad. Both the clean cylinder and the cylinder with the spot of rust tested the same.
I'm trying to figure out if I need to bore the cylinder out one, or if I can just hone the cylinder and replace the piston/rings. I would rather not spend a few hundred dollars to bore out the cylinders if I don't need to.
I'm wondering if anyone could offer some insight or advice on to bore or hone the cylinders.
depending how you are measuring.. eh. age has zero to do with it, rings sound toast. easy way to remedy is hone and rering or find a set of std pistons with rings, the yambits tkrj (?) ones are good and dirt cheap. anything in the 90s is ring or bore time. 0.02
https://yambits.co.uk/rd400c-piston-kit-std-p-7986.html
I agree with Mark.
If there are no score marks and the bore measure out good stock size a light hone and new stock rings should fix the low compression and run just fine.
Thank you both.
The engine is currently torn apart so when I put it back together I'll get some cheap rings to put in it and see how it does.
After I know what I'm doing with the cylinder I'd like to throw some new pistons in it. Possibly pro x, but we will see.