Help with trouble shooting a failure
- Thread starter griffbones
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griffbones
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- Sep 12, 2006
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- #28
Why did the original run almost 8 hours before failure? It was fresh premix at 40:1 so how did the lubrication go away? The bike had stock jetting so it should not have been lean, and previous to the first failure it was running a nice tan plug.
I did check the ring gap and it was well with in Wiseco's specs of .012 - .020, I think the specs are? I don't remeber the exact range and my instruction sheet from Wiseco is at home on the work bench.
What ever caused the first failure I believe caused the second failure, so what I need to find out is what changed and why so quickly? Or was my son really running it too hard on a long straight away? After words it started right up and ran fine just sounded noisey. So maybe the exstinsive dammage was because we continued to run it after the failure. Maybe the second went becuase the cylinder was in worse shape than I thought, or maybe my sanding of the scratches with 440 grit paper and WD40 was the wrong thing to do???
I did check the ring gap and it was well with in Wiseco's specs of .012 - .020, I think the specs are? I don't remeber the exact range and my instruction sheet from Wiseco is at home on the work bench.
What ever caused the first failure I believe caused the second failure, so what I need to find out is what changed and why so quickly? Or was my son really running it too hard on a long straight away? After words it started right up and ran fine just sounded noisey. So maybe the exstinsive dammage was because we continued to run it after the failure. Maybe the second went becuase the cylinder was in worse shape than I thought, or maybe my sanding of the scratches with 440 grit paper and WD40 was the wrong thing to do???
griffbones
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- Sep 12, 2006
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- #31
Yeah, the water circulates as I watched it after redoing the top end. I always bleed the system and then start the bike up the first time with the cap off to let any remaining air escape, and I could see it circulating. The carb seems to be spotless, I had kind of wondered the same thing.
Boy I sure appreciate the input that all of you guy's are giving me, Thanks!
I'm beginning to wonder if I will ever know for sure what caused this, that is with out having another disaster happening.
Boy I sure appreciate the input that all of you guy's are giving me, Thanks!
I'm beginning to wonder if I will ever know for sure what caused this, that is with out having another disaster happening.
When the bridge seized all bets are off,from mild to catastrophic failure,it started at the exhaust bridge and the excess heat will damage a piston a lot worse than the first pic!It can seize and put the rod through the piston,been there,done that! You need a few to 4 thousandths clearance from bore to piston skirt,AND A FEW MORE THOUSANDTHS CLEARANCE FOR THE BRIDGE THAT EXPANDS A LOT FASTER,flashing build up is bad and on the bridge compounds the trouble.All the frigging oil in the middle east will not help a bore out of spec.They even drill holes for insurance!
griffbones
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- Sep 12, 2006
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- #34
Does the exhaust bridge expand more due to it being such a narrow strip of metal (for lack of a better term)? Would this clearence have been off from the factory? Why did it run for a few hours before blowing up? I know this sounds like a lot of stupid questions, but I am really trying to figure out for sure what happend.
Yes,its size is why it is got to be checked.2000 rm 250 has 2 intake bridges almost the entire length of the cylinder,what a nightmare.And yes chamfering the ports is crucial also.To tight means to much heat and bye bye aluminum piston!The tolerances are not exact and all engines vary.Manuals usually cover these areas to some degree or another.I quit screwing around a long time ago,I send it to the professional,Eric Gorr@forwardmotion.com,done deal and you would not believe what he can do to motors!
High Lord Gomer
Poked with Sticks
- Sep 26, 1999
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It may not have been enough to cause it, but running hard and then coasting is bad for 2 strokes. You get the engine up to a significant RPM then shut off the fuel (and oil!) while the engine is still spinning fast. It's actually better to leave it pinned than to coast in gear. If you're really worried about him running it too hard for long periods of time, have him intermittently press the kill switch while still leaving the throttle open. That way you still get oil into the turning engine and the gas helps cool it, too.
griffbones
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- Sep 12, 2006
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- #39
Ding Ding Ding I think we have a winner!High Lord Gomer said:
There were no normal signs of overheating, no signs of detonation, the engine had about 8hrs on it before the failure so I doubt that the exhaust bridge clearence was off by that much from the factory. BUT my son was doing exactly this and it would have shut off the fuel/oil mixture to the engine at high rpm's. The piston really looked like a big lack of lubricant. I had just mixed up fresh fuel and I know how much oil was in it, I am very thorough. I really think this is just what caused the failure, so it looks like I need to teach my son a little different method for those situations, as this is really MY fault not his!
Thank you so much for everyone's input, I learned several things from this thread and I really apreciate everyone giving it their time and attention.
griffbones
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- Sep 12, 2006
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- #41
No, I wasn't but I really think the cylinder was too far gone to try and re-use it with out first having it repaired. I got in a hurry to get the bike going and shouldn't have even stuck a piston back in it. I did clean it up and it looked pretty good, but I now think not good enough. Also I did not remove the engine and check to see if I could flush any debris out of the crankshaft cavity, I thought it looked pretty clean, but maybe I just sand blasted the new piston with crap from the first episode? I have been riding and working on these bikes for a long time and I really should have known better, I guess I broke some of my own rules and paid the price, but never again!kx125412 said:
What about rule #1?Anytime you fear debris has entered your cases,split them,you can not safely clean anything between the seal and crank bearing.This could have been a seized top end and roached another piston cause flashing from the last meltdown got another one!
I would also double check compatability of the engine to the bike eg radiator capacity, I know you said the exhaust was changed with the engine but was the silencer also (wrong silencer wrong back presure would not let burnt gases escape quick enough). If i was you I would maybe go to a library and a read the differences of specs.
Good luck from Oz
Good luck from Oz
griffbones
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- Sep 12, 2006
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- #45
Everything on the two bikes ae 100% identicle except for the expansion chamber, cdi, cylinder, head & piston. I have thoroughly checked this out.DaveKLX said:
And Fox, that is exactly what I am saying, I should have never broke my own rule of putting one of these things back together without first splitting the cases. I know you can't tell by my pulling this stupid stunt, but I am really a very picky and detail oriented person. Most people that know me probably think that I am way too anal about my machines. I really do want everything done right, I just broke one of my own rules for probably the first time in 20 some years and I paid the price. Nobody can kick me in the a$$ any harder than what I am doing to myself right now! BUT, It WIll Never Happen Again.
The short cuts are like a drug eating at your common sense!Yes,been there,done that and a few more!Good Luck
