too_fazt Posted July 31, 2007 Report Posted July 31, 2007 alright i have a low 90s banshee, and in the span of the year i have had it i have blown the left side three times. the bottom part of the piston is what goes everytime while the top looks perfect. my question is, what could be causing this. poor porting? bent rod? thats all the guesses i have so far any more infor would be great thanks Quote
J-Madd Posted July 31, 2007 Report Posted July 31, 2007 alright i have a low 90s banshee, and in the span of the year i have had it i have blown the left side three times. the bottom part of the piston is what goes everytime while the top looks perfect. my question is, what could be causing this. poor porting? bent rod? thats all the guesses i have so far any more infor would be great thanks Do you mean the skirt breaks off of the piston? Sounds like excessive ring clearance. If the ring is still ok, check the ring gap to see if it is in spec. Quote
blowit Posted July 31, 2007 Report Posted July 31, 2007 alright i have a low 90s banshee, and in the span of the year i have had it i have blown the left side three times. the bottom part of the piston is what goes everytime while the top looks perfect. my question is, what could be causing this. poor porting? bent rod? thats all the guesses i have so far any more infor would be great thanks Sounds like a porting or port chamfer problem. Brandon Quote
too_fazt Posted July 31, 2007 Author Report Posted July 31, 2007 (edited) Do you mean the skirt breaks off of the piston? Sounds like excessive ring clearance. If the ring is still ok, check the ring gap to see if it is in spec. yea the skirt breaks. how go u check the ring clearance. i took the motor apart it looks the same way it has the otehr two times. how could i fix this. i could get pictures of everything if it could help narrow it down. id hate to put money into things that arent the problem Edited July 31, 2007 by too_fazt Quote
blowit Posted July 31, 2007 Report Posted July 31, 2007 yea the skirt breaks. how go u check the ring clearance. i took the motor apart it looks the same way it has the otehr two times. how could i fix this. i could get pictures of everything if it could help narrow it down. id hate to put money into things that arent the problem Post pics of the ports close up. That will be a god start. Brandon Quote
als660r Posted July 31, 2007 Report Posted July 31, 2007 use your other piston and check the skirt clearance maybe break becauce of piston slap. Someone may have honed the cylinder to big. Quote
J-Madd Posted July 31, 2007 Report Posted July 31, 2007 yea the skirt breaks. how go u check the ring clearance. i took the motor apart it looks the same way it has the otehr two times. how could i fix this. i could get pictures of everything if it could help narrow it down. id hate to put money into things that arent the problem Take the ring off of the piston and place it in the cylinder. Then push the ring into the cylinder with the top of the piston a little ways to straighten the ring up (make it perpendicular with the cylinder wall), then check the distance between the ends of the ring with a feeler gauge. I don't remember what the gap should be, but someone else will, I'm sure. If its too big, that may be your problem...leading to piston slap. Quote
sheefreak Posted July 31, 2007 Report Posted July 31, 2007 I would also immediately think piston slap. If you have a good machinest in town, tear down the top end and have him check piston to cylinder clearance. You can check ring end gap and it can give you an indication of the cylinder being to large, but it may also just tell you the rings are worn. It is possible your crank has issues as well(out of true, rod bearing worn, etc.) but easiest place to start is w/the top end. Also have someone look to make sure your ports are chamfered correctly. Non or poorly chamfered ports will usually snag a ring before a piston skirt though. Quote
too_fazt Posted July 31, 2007 Author Report Posted July 31, 2007 alright i got the pictures of the pistons.....the two on the right have been ones blown on the left side....the piston on the left is from the right side.....ill try and get pictures of the jugs sometime today, but it might take me a day since i keep my bike at a shop. if it is piston slap, would a good bore and new set of pistons clear it up. im also in need of a crank def., the last blow sent shards into the crank wedging itself in and locking it up and bending it for good Quote
XxMeltIcexX Posted July 31, 2007 Report Posted July 31, 2007 Check clearance with a feeler gauge at bottom of the sleeve the exhaust and top, they should be all within spec(between piston/ring and cylinder wall), lmao im having a brain fart also so i dont remember the clearance either, im going to start keeping my clymer up on my desk. What was your compression, that should have told you if theres some problems with clearances. The front/back of the sleeve will probably show more wear than the right/left will, nature of the beast (if its got some hours on it). And yes if it its bored correct and you have a good set of pistons that fits the bore within spec it should clear things, after the first time i would have found out why it happend, not the third time! Get the crank checked out if things are in spec... Goodluck Eric Quote
blowit Posted August 1, 2007 Report Posted August 1, 2007 alright i got the pictures of the pistons.....the two on the right have been ones blown on the left side....the piston on the left is from the right side.....ill try and get pictures of the jugs sometime today, but it might take me a day since i keep my bike at a shop. if it is piston slap, would a good bore and new set of pistons clear it up. im also in need of a crank def., the last blow sent shards into the crank wedging itself in and locking it up and bending it for good Listen, the correct and only way to check your bore is with at least a dial bore gauge and set of mics. Since you will likely not own these, it is best to allow a pro to check the bore dims. Feelers and "checking slop" simply are not good enough. I would bet the bore is worn out and you may have installed new pistons in a worn hole when they broke. I would say, with most certainty, that a fresh bore and set of pistons will fix your problem. The rings are no indication of piston wear whatsoever and if you intake ports are not chamfered, it can cause skirt damage but will rarely break the piston. This looks like a classic case of "worn out bore". Brandon Quote
too_fazt Posted August 1, 2007 Author Report Posted August 1, 2007 Listen, the correct and only way to check your bore is with at least a dial bore gauge and set of mics. Since you will likely not own these, it is best to allow a pro to check the bore dims. Feelers and "checking slop" simply are not good enough. I would bet the bore is worn out and you may have installed new pistons in a worn hole when they broke. I would say, with most certainty, that a fresh bore and set of pistons will fix your problem. The rings are no indication of piston wear whatsoever and if you intake ports are not chamfered, it can cause skirt damage but will rarely break the piston. This looks like a classic case of "worn out bore". Brandon thanks for all the info guys, im taking them in to get bored and shave the head while im at it. time for an overhaul Quote
_Hex* Posted August 1, 2007 Report Posted August 1, 2007 i think depending on bore size stock should b .010-.011 something like that if i remember correctly Quote
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