mew905
New Member
Took my bike out a couple days ago to run an errand, after all the porting I did and cutting the piston, When I went to go throw a stock piston (from a GT5, mine's a GT5-a) in my motor I found a peculiar set of markings about 3mm down from the top edge of the cylinder starting right above the exhaust port and running half way to the transfer port, and a second marking, narrow, a few mm between the first marking and the transfer port, starting about 5mm and running almost the entire length down the cylinder. I thought maybe this was from me cutting the piston... but these were on the exhaust side. Also some notable features include the piston having burns all over the exhaust side, only at the top of the piston where the exhaust port is, and intake port area is completely clean. Burn markings reach almost all the way to the intake (evenly) between the piston rings, and there are two burns on the exhaust side almost reaching the bottom of the skirt, separated only by the approximate width of the exhaust port. My exhaust port was expanded to 25mm wide, and a 1/4" higher near-square at the largest points, tapered to the normal exhaust diameter within 1/2" exiting the cylinder (the rounded-edge square tool in MS Paint could make the shape of my exhaust port). Well, on my fateful ride on Thursday night, the motor gave up.
Well, I'm not entirely sure what the cause was. Could have been too little oil (at the time it was around 20:1 dino), could have simply been all the cold starts (its hard for me to judge when the motors warm and ready), or it could have simply been running the motor too hard after modifying the piston/cylinder (maybe I have to break it in again each time I modify the cylinder?), or maybe a chance the denser, colder air now that winter's coming, could have leaned out the mix (Even though I'm pretty sure it four-strokes at some point in the power band). All I know is the gouges were from the piston rings because of the position of the markings, however I'll be taking the motor off this morning to diagnose. the piston retainer clip was bent when I re-inserted it but I didnt thing that'd be much of an issue. Noone says anywhere (that I've seen) that after removing the cylinder you need another break-in period either, so I'm not sure if maybe thats what did it. Either way, I know for sure because of the sound its making that not only am I going to have to replace the cylinder and probably the piston, but also replace that pesky small bevel wheel (remember I was asking how to remove a stripped one haha), cuz I'm going to have to crack open the crank case and remove metal shavings. I dont mind doing the work, I just wish I had a second motor to run while I was working on this one (I may have, if we hadn't harvested so many parts off my roommates motor)
Help diagnosing so this doesn't happen in the future would be greatly appreciated. i had time to engage the clutch so no loss of control or dangerous maneuvers were experienced, simply started screeching, stopped running, and bike slowed down about the same rate as a badly adjusted brake (not skidding, just... from 30mph it would come to a dead stop within 25-30 feet). If I ride and let the clutch go, it'll keep screeching, but wont fire.
Well, I'm not entirely sure what the cause was. Could have been too little oil (at the time it was around 20:1 dino), could have simply been all the cold starts (its hard for me to judge when the motors warm and ready), or it could have simply been running the motor too hard after modifying the piston/cylinder (maybe I have to break it in again each time I modify the cylinder?), or maybe a chance the denser, colder air now that winter's coming, could have leaned out the mix (Even though I'm pretty sure it four-strokes at some point in the power band). All I know is the gouges were from the piston rings because of the position of the markings, however I'll be taking the motor off this morning to diagnose. the piston retainer clip was bent when I re-inserted it but I didnt thing that'd be much of an issue. Noone says anywhere (that I've seen) that after removing the cylinder you need another break-in period either, so I'm not sure if maybe thats what did it. Either way, I know for sure because of the sound its making that not only am I going to have to replace the cylinder and probably the piston, but also replace that pesky small bevel wheel (remember I was asking how to remove a stripped one haha), cuz I'm going to have to crack open the crank case and remove metal shavings. I dont mind doing the work, I just wish I had a second motor to run while I was working on this one (I may have, if we hadn't harvested so many parts off my roommates motor)
Help diagnosing so this doesn't happen in the future would be greatly appreciated. i had time to engage the clutch so no loss of control or dangerous maneuvers were experienced, simply started screeching, stopped running, and bike slowed down about the same rate as a badly adjusted brake (not skidding, just... from 30mph it would come to a dead stop within 25-30 feet). If I ride and let the clutch go, it'll keep screeching, but wont fire.
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