August 3, 201412 yr A mates just text ma asking how much play there should be on the piston on his '09 EVO 250? Think he's got the barrel off so what slack should there be between the piston and bore, and also should there be any movement on either end of the con rod?
August 4, 201412 yr Answers: A bit! No! and: Same as what they came off! These questions require precision measurements. What was the problem?
August 4, 201412 yr Author Answers: A bit! No! and: Same as what they came off! These questions require precision measurements. What was the problem? A bit (im an engineer so don't understand that, I need measurements) No (none at all in any direction? ) Same as what they came off (I don't think he checked before undoing them so need values)
August 4, 201412 yr Unless the bike was ridden every day a piston is unlikely to need replacement from wear. Watercooled electrofusion lined cylinders don't wear pistons like the old steel sleeves unless a lot of dirt gets in. Having said that I realize it doesn't answer the question but newbies to trials bikes from other disciplines where pistons are changed like socks often make the mistake of thinking the need a new one. have him check his rings first. If the cylinder is clean and shows no wear and the piston is undamaged it's probably fine. The will be a bit of play in any bearing that operates hot when examined cold. Have him examine it for flat spots or damage to the rollers and cage or scratches in the top of the connecting rod. If it looks good it probably is.I think I torque head bolts to 15.5 N/m but to be sure search this forum for "torque" and you should find a thread from a few years ago with a bunch of torque specs which I don't think have changed for many years. Found it searching for "torque settings". http://www.trialscentral.com/forums/topic/28936-torque-settings/ Edited August 4, 201412 yr by dan williams
August 4, 201412 yr In most cases rod and wrist pin bearings are either good or very bad, when they go south it happens Very quickly in human time and usually shows overheated (coking) on the rod Very unlikely and usually the engine stops running or has a horrible rattle And you will feel some side to side play as the lower bearing is quite narrow
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