beewee Posted October 31, 2010 Share Posted October 31, 2010 I have a 4 month old yw 100cc 2 stroke BeeWee scooter. At 1500 km it fried the piston. The damage was down the side of the piston over the rings where the exhaust port lines up. A new piston was fitted by the dealer (who is great) and off I go again. Another 1500-1600 km and Im riding along yesterday at only about 75kmh and the engine just died as though I turned off the key. Its done it again. The dealer was baffled by what caused the first melt down. After fitting the second piston (bore not damaged) he slightly opened up the auto oiler to improve lube to system. This scooter is 4 months old and has fried 2 pistons within 3400km, has anyone encountered a similar problem with these engines? As it was a new bike I have riden as per instructions for run in period (with both pistons)and this situation is now a nasty mystery. What the hell is going on with this engine? ps. I have only run Yamalube oil in the oil tank, and 91 octane gas in gas tank. Link to comment Share on other sites More sharing options...
2 Wheels Posted October 31, 2010 Share Posted October 31, 2010 Wrong plug heat range,,,,,,too hot,,,,,,,causing piston to swell with the extra heat,,,,,then the rings catch the exhaust port,,,,,,,then it dies Champer the exhaust port in any case just to eliminate Just a guess. Have ya a pic of the damage on the old piston. Link to comment Share on other sites More sharing options...
jebb Posted October 31, 2010 Share Posted October 31, 2010 Wrong plug heat range,,,,,,too hot,,,,,,,causing piston to swell with the extra heat,,,,,then the rings catch the exhaust port,,,,,,,then it dies Champer the exhaust port in any case just to eliminate Just a guess. Have ya a pic of the damage on the old piston. Take it back to the yam dealers. It obviously is'nt right Link to comment Share on other sites More sharing options...
Moderator Airhead Posted October 31, 2010 Moderator Share Posted October 31, 2010 Ignition timing out? too much advance can cause problems. Ask them to check it. Link to comment Share on other sites More sharing options...
beewee Posted October 31, 2010 Author Share Posted October 31, 2010 Take it back to the yam dealers. It obviously is'nt right This is a brand new scooter (4 months use)If the exhaust port needs chamfering to prevent ring bind I am amazed. 2 stroke engines have been around for over 100 years, and if yamaha havn't figured out the bugs they should not be selling them. The spark plug was fitted by dealer at first service and is therefore correct. I will not modify any part of this engine or move away from factory fitted parts. My suspicion is with the oiler system perhaps being faulty. I am a car mechanic so understand the basics of the two stroke principal. I do not have a picture of the first piston damage, but did see it. The damage extended from the top ring down past the bottom ring, and was approx half an inch across and lined up with the exhaust port. I will bet bucks that the replacment piston shows the same damage when it is removed. I have riden this scooter from new as per instructions in hand book, and love the scooter. Its just the engine that is now the letdown. Link to comment Share on other sites More sharing options...
2 Wheels Posted October 31, 2010 Share Posted October 31, 2010 Hit the left side of the crank with a BIG heavy hammer, then wait till the bike falls over on its right side,,Then you can really go to town on it,, then you can easy :lol: New bike brought from deeler----------demand another one The one you have could have a problem from the word go,,,,,ya know,,,,from the factory Link to comment Share on other sites More sharing options...
beewee Posted October 31, 2010 Author Share Posted October 31, 2010 Ignition timing out? too much advance can cause problems. Ask them to check it. This is a brand new machine, if the timing is out I need a HONDA Link to comment Share on other sites More sharing options...
Moderator Airhead Posted October 31, 2010 Moderator Share Posted October 31, 2010 This is a brand new machine, if the timing is out I need a HONDA New or not I would ask for it to be checked, who's to say it was assembled correctly? I'm just pointing out that this can cause major overheating problems. Link to comment Share on other sites More sharing options...
beewee Posted October 31, 2010 Author Share Posted October 31, 2010 Hit the left side of the crank with a BIG heavy hammer, then wait till the bike falls over on its right side,,Then you can really go to town on it,, then you can easy :lol: New bike brought from deeler----------demand another one The one you have could have a problem from the word go,,,,,ya know,,,,from the factory Thank you for the great suggestion, I am VERY tempted. This is sooooo disapointing. Link to comment Share on other sites More sharing options...
blackhat250 Posted October 31, 2010 Share Posted October 31, 2010 This is a brand new machine, Sounds like to much Air, jetting , air leak , Is it being run flat out when the seizure occurs ? even running out of fuel will lean-out engine:unsure: Link to comment Share on other sites More sharing options...
beewee Posted October 31, 2010 Author Share Posted October 31, 2010 New or not I would ask for it to be checked, who's to say it was assembled correctly? I'm just pointing out that this can cause major overheating problems. Thank you, yes I do understand what you are saying BUT because this is now a double meltdown I am going to leave it to the dealer who has said he will contact Yamaha New Zealand for any options. I am now so nervous about this bike I cannot trust it as it is. Link to comment Share on other sites More sharing options...
beewee Posted October 31, 2010 Author Share Posted October 31, 2010 Sounds like to much Air, jetting , air leak , Is it being run flat out when the seizure occurs ? even running out of fuel will lean-out engine:unsure: My understanding is that leanout causes most damage to piston top rather than the side of piston. Jetting is factory so surely it has been tested as appropriate. Link to comment Share on other sites More sharing options...
beewee Posted October 31, 2010 Author Share Posted October 31, 2010 Sounds like to much Air, jetting , air leak , Is it being run flat out when the seizure occurs ? even running out of fuel will lean-out engine:unsure: Never run out of fuel, and both meltdowns happened at part throttle. I have been sooooo careful about fuel and oil levels, I would not try to kill a new machine, I depend on this bike too much. Link to comment Share on other sites More sharing options...
blackhat250 Posted October 31, 2010 Share Posted October 31, 2010 Yip factory set , air leak some where i think,,, oil setting on pump, i doubt this unless its a failure,[ then instant seizure] Coz with fully sinthetics nowadays , can be 70/1 with no problems Iv seen a barrel off a scooter with 15,000 mls on it , with no wear at all , amazing stuff modern oils , my moneys on air leak. As for piston damage wen lean-out , I seized my DT400, [ Jetting] when flat out, and both sides [ inlet/ exhaust] of piston had score markes , where it welded itsell to the bore, Top of piston would only be damaged from heat,[ combustion] with wrong Sparkplug. [ or detonation] no lubrication required here. , leaning will damage sides of piston, Link to comment Share on other sites More sharing options...
beewee Posted October 31, 2010 Author Share Posted October 31, 2010 Yip factory set , air leak some where i think,,, oil setting on pump, i doubt this unless its a failure,[ then instant seizure] Coz with fully sinthetics nowadays , can be 70/1 with no problems Iv seen a barrel off a scooter with 15,000 mls on it , with no wear at all , amazing stuff modern oils , my moneys on air leak. As for piston damage wen lean-out , I seized my DT400, [ Jetting] when flat out, and both sides [ inlet/ exhaust] of piston had score markes , where it welded itsell to the bore, Top of piston would only be damaged from heat,[ combustion] with wrong Sparkplug. [ or detonation] no lubrication required here. , leaning will damage sides of piston, Thank you, does seem strange to have an air leak in system on new bike. It ran sooo sweet and gave no indication of air fuel imbalance. I accept what you say about leanout, and really im just as stumped as the dealer was when this first happened. Link to comment Share on other sites More sharing options...
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