Piston question with a long preamble

[DaveJ]

I bought my '06 EC300 brand new and have ridden and raced it for 3 and a half years now. In my last race, I dropped the bike on the right side and when I picked it up and kicked it over, it was locked up. I thought I had siezed it.
Long story short, the inner water pump shaft bearing had slid down when I dropped the bike and when I picked it up and tried to kick it over, the flywheel jammed it into the plastic gear. It looks like the bike came from the factory missing a 'C' clip to hold the bearing in place as there is a groove cut in the shaft for one. But looking at the parts diagram, this is not the case, it only shows one 'C' clip and it is holding the plastic drive gear up to the shoulder on the shaft.
Anyhow, since I have the engine half apart already, I decided that I might as well throw a new piston and rings in it. I'm sure the piston is starting to become fatigued and even though it still looks brand new, it's probably best to do it before it fails.

This leads me to the question about pistons. The rear of my jug is stamped with an 'A' and the on the top of the piston, there is an engraved 'B'. Is this normal? And does it matter what piston I put in if I'm not replating?

I also noticed one of the PV bearings had damaged dust covers on both sides. Not too impressed that the bike would come from the factory like that. It made the bearing have a sticky spot. AND, the PV actuator bracket stud (the little one that's welded in that the linkage attaches too) was sheared off. No wonder I fell over, I had no power to keep me upright.

[jostby]

Originally Posted by DaveJ

This leads me to the question about pistons. The rear of my jug is stamped with an 'A' and the on the top of the piston, there is an engraved 'B'. Is this normal? And does it matter what piston I put in if I'm not replating?

My '00 is stamped "A" on the cylinder, the original piston was marked 66.33mm which is the "A" size piston. My kids bike was a "B" but I don't remember what was marked on the piston. If you do a search on here this subject has been covered pretty extensively, along with the A, B, and C piston sizes. I haven't yet seen a piston engraved with A, B, or C but others may have. When I replacede my "A" piston I installed a "B". Pretty common practice. Find out what size your piston is and give GoFasters a call for piston advice.

I'm no help to you for your other questions though I know the PV stud has always been an issue.

[jostby]

oops, sorry. I didn't notice you had a 300. Info was for my 250's.

[stay_upright]

Originally Posted by jostby

My '00 is stamped "A" on the cylinder, the original piston was marked 66.33mm which is the "A" size piston. My kids bike was a "B" but I don't remember what was marked on the piston. If you do a search on here this subject has been covered pretty extensively, along with the A, B, and C piston sizes. I haven't yet seen a piston engraved with A, B, or C but others may have. When I replacede my "A" piston I installed a "B". Pretty common practice. Find out what size your piston is and give GoFasters a call for piston advice.

I'm no help to you for your other questions though I know the PV stud has always been an issue.

Where is it stamped and which way up?

[jostby]

I'm working away from home so I'm guessing here.. I think the cyclinder was stamped at the rear at the bottom, somewhere around where the read block attaches under the carb? I will correct Monday or Tuesday after I am able to verify. Both Mine are visible if there isn't any dirt/mud/grime on the cylinder.

"which way up?", I don't understand?

[DaveJ]

Anyways, I got the bike all back together. I had a local machine shop re-weld my PV bracket and I cleaned up the PV assembly. I've never cleaned the assembly since I got the bike and will now do it at least once a year because holy crap the bike is like brand new.
I ended up using a Wiseco forged piston. The instructions in the box said to set the ring gap at 0.004" per inch of bore. Since the 300 is just under 3" I figured about 0.012" would be right then gave it a bit more just incase. I think I ended up at 0.015". Today I read in the GG manual, it says the end gap should be 0.5mm which I believe is around 0.019". Do you think my rings will be too tight?
I've already raced it and everything seems great.

[widebear]

Fifteen thou is plenty.