wacko2000 Posted February 20, 2009 Report Share Posted February 20, 2009 Okay, i just got back from glamis, I was having some problems when i got there, Me and the boys where hearing a air noise coming from the bike, sometimes the left cylinder didnt wanna turn over. when it was idling the left silencer wasnt hitting as hard as the right. I did a compression test twice and everything was good. I took the carbs off 10times and made sure they where clean, and sync Tues me and nycmarine Andy and a few people where ripping back to camp and shee blew up on me, didnt fuck with it until wed morning bc i was in such a good mood from the riding we where doing. Pulled the head off and i have a hole in the left piston the size off a quarter. what would cause this? Crank seal? Me and Andy (hollisatp) pulled off the flywheel and when we kicked it over slowly we notice the crank was goin up and down as it spun. Some guys there said that was from a bad crank seal. Any help would be appreciated.. Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted February 20, 2009 Report Share Posted February 20, 2009 if you have wobble on the crank itself, then you have a bad crank bearing, the bad bearing lets the crank wabble, therefore it lets the seal leak air, . i would say this is what caused your lean condition and melted your piston... so it sounds like you will be splitting the cases,. let me know if u want to have them powdercoated while ya got it apart.. hope this helps man Quote Link to comment Share on other sites More sharing options...
wacko2000 Posted February 20, 2009 Author Report Share Posted February 20, 2009 Okay that might have been what I was told, But what causes a crank bearing to go bad? I have never split the cases before, but this time around I will be doing it myselve, sine I have another bike to ride and im in no rush. So what causes a crank bearing to fail? Quote Link to comment Share on other sites More sharing options...
sheerider1026 Posted February 20, 2009 Report Share Posted February 20, 2009 its really hard to say. wear mostly . maybe a defective bearing, some bad metal in the bearing?? who knows, just fix the dam thing joey!!!! lol Quote Link to comment Share on other sites More sharing options...
wacko2000 Posted February 20, 2009 Author Report Share Posted February 20, 2009 its really hard to say. wear mostly . maybe a defective bearing, some bad metal in the bearing?? who knows, just fix the dam thing joey!!!! lol O0o0 no doubt Im def going to fix it. I just wanted to hear what usually causes this to fail. There has to be something. 0 and its a 4mil long rod crank, forgot to mention that. Quote Link to comment Share on other sites More sharing options...
sleeper06 Posted February 21, 2009 Report Share Posted February 21, 2009 Was there a pressure test done on your motor after the crank was put in. Did your builder use new seals????? Quote Link to comment Share on other sites More sharing options...
swrbansheeboy Posted February 21, 2009 Report Share Posted February 21, 2009 its kind of hard to figure out what caused a bearing to let loose after the fact... it could have been that the seal went bad and caused the piston to detonate and once it melted down it shoved all that aluminum through the bearing causing it to fail. it could have been a lean condition on the left carb that caused the bearing to heat up and fail so it took out the seal once it went. it could have just been a beat bearing that finaly went and took the seal with it causing an air leak that leaned it out and melted the piston. theres many different scenarios for what caused it but any way you slice it your stuck fixing it now, just pay attention when your in there replacing everything to make sure you dont miss anything that could cause it to happen again. Quote Link to comment Share on other sites More sharing options...
hollisatp Posted February 21, 2009 Report Share Posted February 21, 2009 its kind of hard to figure out what caused a bearing to let loose after the fact... it could have been that the seal went bad and caused the piston to detonate and once it melted down it shoved all that aluminum through the bearing causing it to fail. it could have been a lean condition on the left carb that caused the bearing to heat up and fail so it took out the seal once it went. it could have just been a beat bearing that finaly went and took the seal with it causing an air leak that leaned it out and melted the piston. theres many different scenarios for what caused it but any way you slice it your stuck fixing it now, just pay attention when your in there replacing everything to make sure you dont miss anything that could cause it to happen again. well like joe said... we checked the carbs and if there was an air leak we would have heard it from that area.. where he heard it was from the left side of the engine, (correct me if I am wrong joe) Would have to say that it was a defective berring that heated up and caused the seal to deform. jaming on it the way we were that day, would have definately heated it up.. honestly..... I wonder if the guy that rebuilt your engine used new seals and berrings Quote Link to comment Share on other sites More sharing options...
toolman Posted February 21, 2009 Report Share Posted February 21, 2009 It could be many things.Crank out of spec, just plain bearing failure, fly wheel problem, lack of lubrication , jetting?????? Bottom line check everything when rebuilding and do not cut corners to save money it will only cost more to do it again. Quote Link to comment Share on other sites More sharing options...
wacko2000 Posted February 21, 2009 Author Report Share Posted February 21, 2009 Was there a pressure test done on your motor after the crank was put in. Did your builder use new seals????? Honestly im not sure if he did a pressure test. The new motor had about 5-7 rides on it before the trip to glamis. All new bearings and seals where used. its kind of hard to figure out what caused a bearing to let loose after the fact... it could have been that the seal went bad and caused the piston to detonate and once it melted down it shoved all that aluminum through the bearing causing it to fail. it could have been a lean condition on the left carb that caused the bearing to heat up and fail so it took out the seal once it went. it could have just been a beat bearing that finaly went and took the seal with it causing an air leak that leaned it out and melted the piston. theres many different scenarios for what caused it but any way you slice it your stuck fixing it now, just pay attention when your in there replacing everything to make sure you dont miss anything that could cause it to happen again. Okay, thanks for all the info. I will be fixing it myselve, Im kinda excited bc it will be my first time splitting the cases. well like joe said... we checked the carbs and if there was an air leak we would have heard it from that area.. where he heard it was from the left side of the engine, (correct me if I am wrong joe) Would have to say that it was a defective berring that heated up and caused the seal to deform. jaming on it the way we were that day, would have definately heated it up.. honestly..... I wonder if the guy that rebuilt your engine used new seals and berrings Yea Andy the noise was coming from the left side. Ill guess we'll see what happened when I open this bitch up. All new bearings and seals where used. o0o0o and the YFZ is a fun little bike. That bitch is getting all long travel suspension though and a bunch of other goodies. It could be many things.Crank out of spec, just plain bearing failure, fly wheel problem, lack of lubrication , jetting?????? Bottom line check everything when rebuilding and do not cut corners to save money it will only cost more to do it again. I was messing with the jetting the whole time i was there trying to get it perfect. I will be rebuilding it soon, and I never cut corners, only costs ya more money in the long run. thaanks Joseph Quote Link to comment Share on other sites More sharing options...
hollisatp Posted February 22, 2009 Report Share Posted February 22, 2009 did you get your crank welded and trued? Quote Link to comment Share on other sites More sharing options...
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