any how please give me all your opinions on this.engine in question 2002 cr250(sorry its not a 500 but it is relevant to its prob area)
so we pulled the engine apart and it had the tiniest crack and pealing on the ehaust bridge,nickasil had started to peel at this point but the rest of the cylinder was fine,engine was running satisfactorly...so we order a new mitaka piston kit and send the cylinder and piston away to nz cylinders for a replate with a formal request for extra releif on the bridge,they call me a say they will have to weld the cracked bridge prior to replating which would be certain practice,so we receive the piston and cylinder back,job looks good nicely finished,checked piston clearance and ring gap,all fine,asseble engine,new gaskets etc,start the engine running 32:1 let it gradually warm up,do all checks all is fine run for approx 3 5 mins and turn off and let cool,drain carb and leave engine,come back the next day and turn fuel on and start and run engine to operating temp,put in to gear and drive engine through gears up and down nicely for approx 5 mins,turn engine off let cool and recheck all ancilaries,all is fine,start engine again,sounding crisp,run engine increasing rpm range and speed,going to 2 thirds throttle for a couple of runs..then it rains so we stop the bike and return to the workshop.now my friend texts me you should come and have a look at this piston it doesnt look to good! now i though he wa having me on so i rushed round there,looked up the port,n thought wtf! ther was slight seizing inthe xhaust bridge area,so i pulled the head off and couldnt beleive it was running so mint the nickasil had completly gone and the crack that was welded up was right back ther in the xact same spot???????????? hmmmm i pulled the barrel off and inspected the piston it was scuffed up and groved/fuked in that area a coresponding exhaust bridge groove and seizure on the piston and a vertical crack on the skirt in the same locality...so what would you think????i am a motorcycle mechanic of 17yrs,service manager at the local kawaski dealer ship honda for 10 years bla bla bla,,any how i have used mitaka pistons and have found them to be reputable so far, i have assebled 100s of two strokes and specialise in 500s,i am very aware of the nature of the bridge etc..so apply very stringent critisium to this area when building my engines....my opinion is this quite evidently the xhaust bridge has not been repaired properly,the crack has still been evident beneath the replate and this has quite clearly pronouced itself against the piston causing heat, damage and eventually hairline fracturing in the skirt
the rest of the cylinder and piston is fine..so am not happy as the run in procedure even though not complete was textbook to this point,i call nz cylinders and explain the situ,i send the components back for inspection and wait for there response,this is what i got"we have looked at the piston and cylinder and also called wayne "wobbly" wright(x gp mechanic, and the piston has caused the damage,mitaka dont make there pistons correctly and this has cracked in the skirt and caused the exhaust bridge to crack!!!!!!!!!in turn fukin the cylinder!!!" i couldnt beleive my fukin ears..... whats youir take on that,,all opinions more that welcome on this one
