This isn't just an easy question to answer first off I had my '06 YZ 125 modded by eric gorr to 144 with the high compression head mod's mid/top porting. The bike runs great but I want to know why every time I pull the top end the lower half the piston skirt always has rub marks on it.
I'm running them at max 40 hrs on the top end mostly moto ridding I'm not a huge over rev'ver.
my current settings on the jetting when I read the plug actually tell me i'm alittle rich cause it's a gray color not white gray. gone richer on the jetting two up on pilot and 4 up on the main needle stock in the 3rd clip.
Other then the first time I got it back and siezed it within 40 mins dude to some bad jetting advice (some of us know who they are) cause he had an '05 YZ 144. Other then that I have not siezed it once since then and it's ran great.
Every time I pull the top end there appears to still be plenty of lubrication even mixed at 40:1 with 927 I could probably go 50:1 no problem.
This will be my 4th top end now and ever time right over the cooling holes there are rub mark obviously from the exhaust bridge on the piston you can see n feel by hand.
This last time there was alittle bit left on the cylinder wall lower portion right on the upstroke. I was able to clean it up with scotch brite pad and I can still see there is good cross hatching left on the rub spots so thats usually good sign the plating is intact. There is no real rub marks on the upper half of the piston and no damnage is done on the ring. It's just the lower portion of the piston BTW I run eric's 144 piston on the bike.
Other then this it's been great and I clean the power valve every time no parts are never re used when I rebuild the top end piston/ring wrist pin etc.
I'm kinda at a loss on this it almost seems like a siezure issue I'm think it could be lack of lubrication but like I said when I pull it apart there still appears to be plenty on the cylinder walls and i'm using Trick 114 leaded race gas and it's not i'm using old gas either.
Any suggestions? I don't think that going back to 32:1 will make any difference cause I ran that on the first top end and it too still had some marks left on it in the same way.
btw: I forgot to mention the crank is still within spec but just in case I got a hot rods as a back up.
I'm running them at max 40 hrs on the top end mostly moto ridding I'm not a huge over rev'ver.
my current settings on the jetting when I read the plug actually tell me i'm alittle rich cause it's a gray color not white gray. gone richer on the jetting two up on pilot and 4 up on the main needle stock in the 3rd clip.
Other then the first time I got it back and siezed it within 40 mins dude to some bad jetting advice (some of us know who they are) cause he had an '05 YZ 144. Other then that I have not siezed it once since then and it's ran great.
Every time I pull the top end there appears to still be plenty of lubrication even mixed at 40:1 with 927 I could probably go 50:1 no problem.
This will be my 4th top end now and ever time right over the cooling holes there are rub mark obviously from the exhaust bridge on the piston you can see n feel by hand.
This last time there was alittle bit left on the cylinder wall lower portion right on the upstroke. I was able to clean it up with scotch brite pad and I can still see there is good cross hatching left on the rub spots so thats usually good sign the plating is intact. There is no real rub marks on the upper half of the piston and no damnage is done on the ring. It's just the lower portion of the piston BTW I run eric's 144 piston on the bike.
Other then this it's been great and I clean the power valve every time no parts are never re used when I rebuild the top end piston/ring wrist pin etc.
I'm kinda at a loss on this it almost seems like a siezure issue I'm think it could be lack of lubrication but like I said when I pull it apart there still appears to be plenty on the cylinder walls and i'm using Trick 114 leaded race gas and it's not i'm using old gas either.
Any suggestions? I don't think that going back to 32:1 will make any difference cause I ran that on the first top end and it too still had some marks left on it in the same way.
btw: I forgot to mention the crank is still within spec but just in case I got a hot rods as a back up.
