March 3, 201115 yr hi i have a swm 240 and have no idea how long the current piston has been fitted. what lifespan would you expect to get from a piston before changing it or the rings? also could i tell the condition of a piston with a cylinder compression guage and what would be a good pressure? thanks for any help matt
March 3, 201115 yr Somewhere between 5 minutes and 30 years depending on how well the bike is maintained, how it is ridden and how frequently it is ridden No a pressure test will not tell you if the piston is worn and neither will it indicate the ring condition unless they are so worn it will barely run. Piston, ring and cylinder wear can be physically measured with the top end apart. Someone with mechanical aptitude and experience with your model of bike will probably be able to judge how worn the rings are when kicking it over and riding it. Similar with the level of noise generated by the piston when hot and cold.
March 3, 201115 yr As per above post there is no accurate time period for how long a piston will last. Back in 2000, I bought a new Yamaha YZ426 for enduros. The manufacturer's recommendation was to replace the piston every 3 races (motocross) The bike was used regularly for over 3 years in many many enduro and H&H events, ridden hard, regular oil changes but never abused. Also used it on the road with supermoto wheels and did the Weston beach race on it. The bike was still on its original piston and rings when I sold it and would still wheely off the throttle in 5th. You don't say why you're concerned about the piston. If it's because of performance and you're not sure how it should run, as mentioned above get someone else to try it who has experience of them if possible. It could appear to lack power depending how it is tuned, The rotax engine can be fitted with a flywheel weight - easily checkable by removing the ignition cover as it is held onto the flywheel by 3 bolts. If one is fitted it will slow throttle response. Also, the disc timing can affect power delivery I believe so something else to look at, also ignition timing, points gap and state of the carb. If you're just wondering as a matter of course how often it should be changed, there is no specific answer. Just change it when it rattles so much that you can't put up with it any more...
March 3, 201115 yr As above, Rotax motors tend to be a bit noisy anyway. Had the same piston in for 20+ years (2stroke at 32:1) was still running fine until it was stolen from my trailer. (got it back and running fine having been seized by the thieving w*nkers)
March 3, 201115 yr Author the reason i asked is because i have had the bike about 8 years, it sounds fine and runs well. i have recently decoked and repacked the exhaust, the carb clutch gearbox and ignition are also good. i dont know if its down on power as i have nothing to compare it to but dont want the piston to fail and cause other damage.
March 3, 201115 yr Hi The only way to check the piston is to remove it & check it, measure & inspect it with a magnified glass. For sizes etc, speak to Peter Knight on 01761 414106, doubt anybody knows more about Rotax's in this country than he does.
March 3, 201115 yr As above, Rotax motors tend to be a bit noisy anyway. Had the same piston in for 20+ years (2stroke at 32:1) was still running fine until it was stolen from my trailer. (got it back and running fine having been seized by the thieving w*nkers) I'm curious why my comment got a negative (reputation) My observations were based on my personal experience, and as such accurate. There again if it was Justin getting his own back
March 3, 201115 yr anyone reading this post ever had a piston or rings fail on a modern bike? Yes, but only as it was raced with no oil! (my dad failed to mix the fuel), it seized and locked up the rear 3 times, the third was fatal. The piston (and the ring, melted into the piston), is now an ornament on my desk...
March 3, 201115 yr anyone reading this post ever had a piston or rings fail on a modern bike? About 2 years ago my son was videoing a 3 month old Gas Gas which had lost grip in a section.The rider nailed it and was struggling to keep it moving forwards.After about 5 seconds it stopped absolutely dead - seized solid. Was the second time it had seized..... Edited March 3, 201115 yr by jon v8
March 3, 201115 yr About 2 years ago my son was videoing a 3 month old Gas Gas which had lost grip in a section.The rider nailed it and was struggling to keep it moving forwards.After about 5 seconds it stopped absolutely dead - seized solid. Was the second time it had seized..... Would be interesting to know if it was down to too little oil in the mix as people seem to want to run leaner and leaner oil mix. Dont quite get the obsession with it. Then again i only run classics on 50:1 and the clearences on a Villiers when just built are probably worse than a Gas Gas thats worn out so less chance of a seizure. Did think they were a thing of the past on trials bikes with the superior oils we have nowadays but obviously wrong again
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