blow center cylinder!! WHY?

joehunt

joehunt

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Canada BC
hi

I just bought my sled last Satarday, I made it about 12miles and had a catastrophic center cylinder failure, I phoned the guy up that I bought it from and he wanted to have a look. So he pulled it apart today and the piston skirt broke off and end up out the bottom of the crank case. So he said that the piston had detonation marks on it and this could be the cause of the failure. I'm new to yamaha triples, but I had a 01 Zr 800 and and my wife has an 03 rmk 600 and we have alway just run reg. fuel with no problems so the yamaha had a half a tank of fuel when I got it and I topped it up with reg. Could 12miles of 50/50 mix couse this? I just want to make sure it does not happen again.

Thank for your help
 
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need more info show pics of piston need to see what youre workin with could of been anythign did the skirt break off did the piston look like it overheated
 
I will try and get some pic for tomorrow. By the sounds of it the piston had detonaion marks on the top and both skirts broke off and pushed through the bottom if the case.
 
My question is how built is this sled, stock? How many miles are on it? If you bought it and topped it off with fuel and went for a ride and this is just an average sled it should have not blown up... Were the carbs cleaned? Sometimes "stuff" happens. If it has detonation marks on the piston thatmeans it shows sign of a lean fuel mixture.
 
That 12 miles on yamaha was better than 1000 on a cat though right? Trust me I feel your pain! last sled I bought was a 2000 sxr 700. It made it 3.2 miles YES 3.2 MILES from time of purchase to center cylinder meltdown! Guy I bought sled from had just cleaned carbs, sat there and idled like a champ. Bought sled hauled it home and girlfreind made 10 or so laps around the property b4 problems. Tore into carbs my self and the little rubber tip of the float needle had broken off and lodge in seat SEVEARLY restricting flow of much needed fuel/oil.
 
Devilin AblueDress! said:
That 12 miles on yamaha was better than 1000 on a cat though right? Trust me I feel your pain! last sled I bought was a 2000 sxr 700. It made it 3.2 miles YES 3.2 MILES from time of purchase to center cylinder meltdown! Guy I bought sled from had just cleaned carbs, sat there and idled like a champ. Bought sled hauled it home and girlfreind made 10 or so laps around the property b4 problems. Tore into carbs my self and the little rubber tip of the float needle had broken off and lodge in seat SEVEARLY restricting flow of much needed fuel/oil.
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yikes!! i never heard of that happening.
 
depending on how old the fuel in the tank was. Old fuel is terrible for motors, especially 2 strokes that rely on the fuel for lube & cooling. Old fuel is very "dry" & detonates very easily. When I get a new machine of any kind, sled, bike, chainsaw, whatever, I ALWAYS dump the fuel & start fresh. Then, when you have a problem like yours, you can rule out the fuel being the cause.
 
Buying any 2-stroke is a huge crap shoot at the best of times.There are some things that you just can't check when you go to look at it and it seems these days you can't take anyones word for anything.Don't believe anything you hear and only half of what you see.For me it's just one more reason to go 4-stroke.Not saying you can't get stiffed on a 4-stroke,but I think I could tell more about the condition of the motor than I could a 2-stroke.At least you could go for a ride with dirty carbs for a couple of miles without squeaking the motor.JMHO.
 
Sorry no pics yet, but I will tell you a little about the motor it's not stock, slp pipes, porting, reeds and reed spacers. I have to say it is a lot better then riding a cat. This really sucks for me becuase I sold my running Zr, bought a RMK 800 that need some work but ran excellent for cheap, did some of the work, took it out to try it and blow the pto rod bearing in 10mins, decided that it was not worth putting a motor in and doing the rest of the work it needed. So this time I did my reseach and heard that the yamaha redhead is one of the most reliable 2 strokes out there, so that was what I was wanted to buy. I found this one. You guys will have to look in the sled garage at it, its got 3200kms on it. And I'm out a bunch of money and still don't have a running sled. I guess on the bright side at least I have a nice yamaha to fix now.
 
it sounds like the motor has thing's done i would think that you need to run 91 octane gas i have the same mod's and i would never run any thing but 91 because ethanol is in everything below in octane so i would say that what cause your problem.
 
well here they are
 

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you can see that it went lean and i bet it also took out the center rod bearing on the crank i still stand on that you should of been running 91 you been bit by the corn gas bug
 
Ya we have a crack and cases ordered, I know that the gas contributed but if it was just the gas that did it would there not be signs on all of the pistons. So Darv your saying that I need to look for a fueling problem with the center cylinder?
 
i would not look towards detonation to be your failure. any marks in the head on that middle cylinder? looks like chunks broke out of the piston, possibly from the skirt coming back up from the bottom end? i think it may have started lower.... look at how blue the crank got on the pto cylinder....
 
from what i can see of the mag piston crown in the pic, looks like its lean. i don't see piston wash. i would check them carbs for crap, and post up the current jetting.
 
I have talked to 10 or so off my sleedin buddys and they have never heard of it either, Wish I could still say the same! My meltdown wasnt nearly as bad as his. Tore down split cases cleaned and reassembled with used jug/piston and back at it! Down for a couple days, $350-400 in parts. Being as Purchase price was $1500 for sled with 4000 miles still not in too bad of shape with sled.

:letitsnow :letitsnow :letitsnow :letitsnow :letitsnow :letitsnow
 
I bought a parts motor at the begginning of the year and it looks EXACTLY like your motor down to the crank being discoloured. I was told that the motor was run to hot for to long on a warm day. Piston tops look the same on the other 2 cyl as well no wash just baked on oil. Probably nice sized black marks on the bottoms of your pistons as well from being hot.

Not saying that is the reason your motor went but I would see if your wristpins are all messed up, the ones on this motor are grooved from high heat/no oil and the piston wasnt able to rock back and forth and I think thats why the piston broke so high on the skirt in the engine that I have. They were almost impossible to remove and the one on the piston that went was the worst.
 
Hard to tell from the pics, but I also suspect bottom end issues as well as lean condition (dirty carbs?). I wonder if it was run without oil at some point.
 
Well thanks for all of the replies. I don't know what jets were in it but I think that they were spot on looking at the other cylinder. If it was a lean problem it was just in the center cylinder and it could not have been leaned right out becuase the thing did not miss a beat until it blew, didn't show me any sing of overheating I also put some oil in the gas to make sure the oiler was working and the oil tank was down 2 or 3 inches when it blow, could it maybe be that the skirt was just ready to let go?
I've heard that the redheads are known to do that.
 
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joehunt said:
Well thanks for all of the replies. I don't know what jets were in it but I think that they were spot on looking at the other cylinder. If it was a lean problem it was just in the center cylinder and it could not have been leaned right out becuase the thing did not miss a beat until it blew, didn't show me any sing of overheating I also put some oil in the gas to make sure the oiler was working and the oil tank was down 2 or 3 inches when it blow, could it maybe be that the skirt was just ready to let go?
I've heard that the redheads are known to do that.
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don't get so quick to think that there is nothing wrong w/the jetting. i'm not saying that the jetting was the cause, but i can still see that there is not enough wash to feel safe in my book. also, just because it didn't miss a beat, doesn't mean all is well. now many sledders out there will tell ya that there sled ran fast as hell, right before it blew??? i bet 90% of the riders out there will tell ya that.
 
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