The compression was 215 psi cold( done to Duncan's compression check tip). Wasn't able to start the bike and warm it up. The neighbors would have really been pissed off. I will start it to tomorrow when I get home from work and check it again warm. Either way I guess racing fuel it is. I figure if anything the compression should go up when the engine is warm due to the thermal growth of the metal and everything sealing better when warm. At least that's how it works on Gas Turbines.
Let you all know what happens tomorrow.

 

Well today I did the warmed up engine compression check. It was 205psi[img]i/expressions/face-icon-small-confused.gif[/img] I didn't expect that I thought for sure it would go up not down when warm. So much for theoretically. Well after that I decide to do some more investigating on this engine. I could not find a part # on the Pro Design Cool Head, but it definately has a copper head gasket. After reading on Plant Sand some stuff about needing a spacer for reed valves that might extend to far into oversized cylinders causing the piston to catch the reeds and trashing them. I thought about the old reeds I took out that were trashed and the fact I don't know how much this cylinder has been bored. I decided to check the new ones since I've started the bike up and warmed it up a couple of times since installing them. To see if this might have been the problem. Nope that wasn't it, but I did take a better look into the cylinder head through the intake and saw some MAJOR SCORING!!! OUCH!!! The piston is all scratched up. I'm guessing the fact the the old reed petal tips broke off they had to go somewhere and probably caused alot of the damage. The intake port wasn't dirty as if sand went through there so I'm going to blame the old reeds. I guess I'll try to finish this season( 2 more trips if I'm lucky) then tear it down over the summer and see exactly what I have.

 

well the only thing I can say is, if the piston is scored like you say, your done!!!! I would stop where you are at and get it punched and a new piston kit (in my opinion). I would get it fixed while you can go a possible 1 size overbore rathen than 2 or 3 . I had to punch mine 1mm (40 over from stock)!!!!!! because the last guy that owened it was a idiot! You will only be down for about a week; out $130 (what it cost me) and you are up and running for the entire summer. PLUS while your in there you can messure the bore and stroke and find out what your engine is !!!!!!!! (lol) [img]i/expressions/face-icon-small-happy.gif[/img][img]i/expressions/face-icon-small-happy.gif[/img][img]i/expressions/face-icon-small-happy.gif[/img]

 

I found a engraving on the side of the cylinder head that said sleeved 7/96, but not a size. Idiot!!! Not that it is the same by now anyway. With the compressin being still good, don't you think it will be ok for a trip or 2? Summer riding??? This is Cali we don't ride in the summer here. Way to hot in the desert then. Summer is for fixxing bikes around here.

 

That is the part I don't understand; You have 200+ psi, but you cylinder is scored..........Do you just have a few scratches .......a "true score" is where some of the metal of the piston has melted and smeared along the cylinder wall (best I can describe it). If you think the piston is scored and you want to ride it a bit more, maybe bump your mix up a touch, and stay off the MAX RPM stuff!, [img]i/expressions/face-icon-small-happy.gif[/img][img]i/expressions/face-icon-small-happy.gif[/img][img]i/expressions/face-icon-small-happy.gif[/img]

 

From the small part I could see it was more than a few scratches(8-12) but that maybe the only damaged area possibly from the reeds that broke who knows when. They easily catch your finger nail if you rub across them.

 

That is the exact reason why I am noteing everything I do to my bike. Bought a new book for the YZ and in the "note" section (back of the book ) I wrote the date / size / and part # of the piston I used! I'm getting old and someday I may need to remember what I did to the bike!, lol [img]i/expressions/face-icon-small-happy.gif[/img]

 

Remember, I just got this thing a few months ago. I have definately been writing down what I have done to it, including oil changes. I just had it in a note book. But the note section of my 250R shop book would be a better place to keep them.