Two summers ago I completely rebuilt the motor for my CT1. EnduroNut did the first over bore work and DEET rebuilt oil pump. Well apparently I did not tighten things well enough on the oil pump drive gear and at some point the gear fell off so the oil pump stopped working. I could hear the motor squealing badly on a ride and shut it down. I figured out the problem, put two stroke oil in the fuel tank to pre mix to get home, and the bike seemed to run fine.
For over a year it has run fine, but now it’s having issues idling and running at WOT. Plugs keep oil fouling. It could be a number of things but I pulled the cylinder anyway as I never really assessed what damage it took when it over heated. From the photos you can see the effects on the piston and cylinder. The cylinder walls are still smooth except for a small section up top that have a very slight ridge.
My question is should this be bored to a second over or can the cylinder walls be honed slightly and I can stay with the same piston and rings?
Bike seems to have great compression and starts second kick every time. Any thoughts?

Tight correct tolerances - improper lubrication.

FIAT: Fix it again Tony..

Next time -- run premix -- 32/1 in addition to the oil pump.. one main jet size larger ...
Capt. Approved..

If it was having trouble idling & also wide open throttle then i was thinking lack of compression, but you say it has good compression!!. Check the crank seal incase the wayward oil pump plastic gear damaged the crank seal flooding the motor with trans oil--& would also run terrible. Whatever the cause it'd be a good lan to fit a new piston & rings & get the cylinder deglazed & start again. Leave it on premix if in doubt about the pump drive.
If you go that far you may as well check that the seal behind the mag is still in the case.

Thanks RT325. I am considering replacing the wet side crank seal as I am figuring that as a source for the oil getting on the plug. I wanted to keep my original post short and I'm basically going to go over everything including timing, points, etc. I measured new transmission oil last week and put in exactly 750ccs. I only rode it 10 miles and it fouled the fresh plug badly. I drained the oil and was about 5ccs short of 750. Of course, I have considered the fact that 5ccs could still be in there but didn't drain, but more than likely some tranny oil is getting into the crank.

I sent an e mail to Bill Bune with the photos. I am hoping they have a second over piston and ring set in the event it needs to be bored. It's unfortunate if it has to be bored again, but it's a learning lesson and nothing I can do about it. I still have three other bikes to ride!!

Anybody else want to weigh in on the photos/solutions?

I ended up splitting the cases and resealing with Honda bond #4, (Yamabond not available) in order to fix my tranny oil issue leaking into the crank. Of course this required another set of crank seals just to be sure.

I’ve been corrected several times by my machine shop guy when thinking my cylinder looked fine. It’s all about clearances and tolerances not what it looks like with the naked eye. Also been surprised by thinking just next over size needed when it actually took two. Just my experience. BTW my machine shop has done numerous motors for me for all kinds of vehicles and I trust him!