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Discussion Starter · #1 ·
HERES WHAT WE DID; REBUILT ENTIRE MOTOR, NEW CRANK, ALL BEARINGS, NEW CYLINDER, NEW HEAD PORTED W/ +1 TI VALVES, CP PISTON 13:1 STOCK BORE

-IT RAN PERFECT FOR OVER 1 HOUR. I RODE IT UP AND DOWN THE STREET A COUPLE TIMES. RAN IT ON THE
DYNO FOR AT LEAST 45 MINUTES JETTING IT, ALL WAS OK. THEN THE LAST RUN ON THE DYNO(OBVIOUSLY) IT BLEW UP, CYLINDER BROKE IN PIECES. DISASSEMBLED, FOUND CRANKCASE HAD PLENTY OF OIL IN IT, THE BOTTOM OF THE PISTON AT THE WRIST PIN, THE PISTON BROKE IN PIECES. THE ROD BROKE AWAY FROM THE
PISTON COMPETELY W/ WRIST PIN IN ROD STILL, WHICH IS WHAT BROKE THE CYLINDER AND THE CASES. LOOKING AT THE BOTTOM OF THE PISTON AND THE ROD, IT WAS BONE DRY! NO OIL TO THE TOUCH. OBVIOUSLY IT WAS GETTING OIL BEFORE HAND OTHERWISE IT WOULD OF BLOWN UP RIGHT AWAY. ANYONE EXPERIENCE THIS, WE CANT THINK OF WHY IT WOULD LOSE PSI ALL OF A SUDDEN, ANY ADVISE WOULD BE APPRECIATED. THANKS, DAN
 

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Discussion Starter · #3 ·
NO I DIDNT. BUT ID THINK IF IT WAS A PROBLEM IT WOULD OF HAPPENED SOONER WHILE RIDING IT AND ON THE EARLY RUNS ON THE DYNO. BUT I KNOW I WILL BE BUYING 07 CASES AND OIL PUMP THAT HAVE IT DONE!
 

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well now you know why...... p.s. you can do the oil mod in the 04-05 cases,
 

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you will also need the 06+ oilpump and also the oil squirter
 

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Ok guys. His bike did not blow up because he didn't do the oil mod. I never done the oil mod on any of my three YFZ's and they all ran well over 300hrs. I'm not sure what the problem could be.. but it almost sounds like you got a faulty part.
 

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QUOTE (KB Motorsports @ Feb 26 2009, 11:40 AM) index.php?act=findpost&pid=751270
Ok guys. His bike did not blow up because he didn't do the oil mod. I never done the oil mod on any of my three YFZ's and they all ran well over 300hrs. I'm not sure what the problem could be.. but it almost sounds like you got a faulty part.[/b]
We know that. But not having it sure didn't help.
 

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why did you do the rebuild in the first place? did you have a cylinderworks cylinder that cracked? I had the same thing happen to me but the rod broke because i had got a bunch of water in the cylinder after the cylinder cracked and as soon as i put it back together and had about an hour on it the rod broke destroying everything. the reason the rod broke is because of all the water in the cylinder, you can compress water, so the compression jumps way up and causes small breaks in the rod that you cant see unless you magnaflux the rod. it sucks to have to rebuild it 2 times. got any pics of the rod so i can see if it looked like the one i broke
 

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QUOTE (KB Motorsports @ Feb 26 2009, 11:40 AM) index.php?act=findpost&pid=751270
Ok guys. His bike did not blow up because he didn't do the oil mod. I never done the oil mod on any of my three YFZ's and they all ran well over 300hrs. I'm not sure what the problem could be.. but it almost sounds like you got a faulty part.[/b]

how do you know it wasnt from not doing the oil mod? i ran my no oil mod for a long time no problem....... iv also reuilt 2 or 3 yfz's that had low low hours on them because of wrist pin failures.....

The 05-06 yfz's used the "splash idea" to lube the wrist pin..... when you ride the quad the oil would "splash" up on to the wrist pin.... I dont know wbout you but i doubt there was a whole lot of splashing going on if it was strapped to a dyno!
 

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Discussion Starter · #14 ·
QUOTE (climb-101 @ Feb 26 2009, 12:47 PM) index.php?act=findpost&pid=751298
why did you do the rebuild in the first place? did you have a cylinderworks cylinder that cracked? I had the same thing happen to me but the rod broke because i had got a bunch of water in the cylinder after the cylinder cracked and as soon as i put it back together and had about an hour on it the rod broke destroying everything. the reason the rod broke is because of all the water in the cylinder, you can compress water, so the compression jumps way up and causes small breaks in the rod that you cant see unless you magnaflux the rod. it sucks to have to rebuild it 2 times. got any pics of the rod so i can see if it looked like the one i broke[/b]

I REBUILT IT DUE TO THE FACT IT WAS STOCK WITH W/ RACING AND DUNE RIDING FOR 3 YEARS AND NEVER OPENING THE MOTOR. IT FINALLY LOST POWER AND THE LOWER ROD BEARING WENT PRESIDENTS DAY WEEKEND AT THE DUNES.
 

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I am no engine builder, but here are a couple things I think to look at.

I would not for a minute think that not having the oil mod done would cause this problem with hardly any time on it. Yamaha built the motor, and I'm sure it was all done correctly that is why it ran as long as it did. Not saying whoever built it, did it wrong, just a observation.
There are many more factors that could have caused this to happen.
For some reason oil was not pumping through the motor. Could have been an o-ring missing, failed oil pump, blockage of an oil line, along with other possibilities I'm sure. Just a few that came to mind.

Who rebuilt the motor?? Was it done by a service shop, engine builder, or someone else?
What components were used, crank, piston, cyl., main bearings. etc...??
Did you put in a new oil pump?
 

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did who ever built the motor use appropriate lube during assembly? the wrist pin should get oil, even strapped to a dyno, the crank will sling it up there. just not near as much as with the squirter spraying it under the piston...

was there oil in the cases? i dont see how the pin was dry if there was oil in the cases, unless right before it blew, it heated up enough to basically cook the oil off of it.
 

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Did you make sure the wrist pin wasnt tight? What did you gap the rings at? What was the piston to cylinder wall clearance?
 

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Discussion Starter · #18 ·
YES WE USED PLENTY OF ASSEMBLY LUBE. I WAS THERE WHEN THE GUY PUT IT TOGETHER AND EVERYTHING GOT LUBED WHILE PUTTING IT TOGETHER. THERE IS OIL IN THE CRANKCASE AND THE CRANK IS IN IT. WERE STUMPED AS WHY ITS
DRY. I DONT REMEMBER WHAT WE GAPPED THE RINGS AT BUT THEY WERE GAPPED. NOT SURE OF THE CLEARANCE BETWEEN THE PISTON AND CYLINDER. IM LOOKING AT THE CYLINDER NOW AND BESIDES BEING BROKEN THE CYLINDER WALLS LOOK EXCELLENT, THE PISTON DIDNT SEIZE AT ALL. THE CYLINDER WAS NEW ALSO. AND THE WRIST PIN FELT GOOD. IT SPUN FREELY AND WASNT LOOSE OR REAL TIGHT IT MOVED SMOOTHLY.
 

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Did you check the screen going into the oil pan? It could have been stopped up and kept oil from going to the top.
 

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QUOTE (CMAT @ Feb 26 2009, 08:16 PM) index.php?act=findpost&pid=751515
Did you check the screen going into the oil pan? It could have been stopped up and kept oil from going to the top.[/b]

My thoughts exactly, maybe a bad or weak oil pump, restricted oil line...was there oil in the stator side side of the engine, and did you bleed the metal oil line before starting?
 
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