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MotoSarge

2012 YZ450F blown motor?!?

20 posts in this topic

So.. I was going through my Yamaha book and fixing up my bike. I came across IDLE SPEED.. hmm. I always went by ear and never had a problem. I installed a tach meter and I have been idleing at 800 or 1000 RPM. Now the book says to idle the bike at 1900-2000 r/min. Thats nuts! I thought so too! So I tried my best.. the bike was nearly maxed out on the idle speed controlicon1.png and the throttle free play was maxed. The bike is a 2012 YZ450F by the way.. brand new.. maybe 50 hours... never ever had a problem. So I checked my valves and I cleaned up my air filter all nice.. Got it back running, but could not reach 1900. Im still boggled, thats waaaay to high. But whatever.. I got it up to idle at 1400. And it just didnt feel right to me, but I rode it and man she ripped. For about 10 mins... then I heard a loud ass noise, as if like the header exhaust pipeicon1.png came loose or something.. you know what loud gwaaaa sound, aswell as this knock sound. Sounds like its comming front the cylinder head. I shut it off.. looked at the case and I didnt see any cracks or oil leaks.. but now she will not start.. and the kickstart is not smooth.. it has a jagged like feel.. but there is still compression. Any ideas??? Im so pissed... I cant believe this crap.

UPDATE--- I got the cams off... and she wont even crank now.. its seized right up. She had to have gotten too hot and seized. I'm gonna take the head off and see if the piston will move.

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It sounds to begin with as if you had your tach set up wrong. The YZ450 fires the spark plug every revolution, not every other, and when you were showing 900 on the tach, it was probably already at 1800 RPM.

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Grayracer.. I did not know that. So when I was at 1400 on the tach I was really at 2800.. LOL. holy shit.. I knew it was WAY too high. I always use to go by ear and the tach said 800. I should of went with my gut instinct and not technology.... So in this case.. now that I have my cylinder head off and the piston wont move... its all seized up. Am I looking at doing a top and bottom rebuild?

Edited by MotoSarge

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Really sorry to hear about the locked up motor, that never fun. But if you've got the head off, you should be able to pull the jug off the piston. You'll be able to tell at that point if its the lower end of the motor, or the piston seized in the bore. If its seized in the bore there's a good chance you'll have to fix the jug one way or another.

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Yeah So i got the jug off too, now its just the floating, but she wont move at all. The whole crank is seized up

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So it was a HARDLINE tach/ hour meter. The directions did not say anything about the spark firing every rpm or every other, and there is no way to adjust this meter. This is the one that wraps around the plug wire and then comes up into the meter. You guys thing I have a chance filing a claim with the company to fix my bike?

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You guys (think) I have a chance filing a claim with the company to fix my bike?

None at all.

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So it was a HARDLINE tach/ hour meter. The directions did not say anything about the spark firing every rpm or every other, and there is no way to adjust this meter. This is the one that wraps around the plug wire and then comes up into the meter. You guys thing I have a chance filing a claim with the company to fix my bike?

None at all.

Well, you can file as many claims as you want to... but I think you've got a 0% chance of having someone else pay for the repairs your engine needs.

Chalk this one up as a tough learning experience, a really tough learning experience. BTW, having your bike idle at 2800 rpm won't cause it to blow up **. I wouldn't suggest having it set that high, you were right when you had it set "by ear". I understand you recently had re-shimmed to get okay lash to a near perfect setting. My money would be on something that was done improperly during that process.

** so long as the bike is moving and getting enough air through the cooling system. Think about it this way, you could be in 2nd, 3rd, 4th, 5th gear at 3000 rpm (or above) all day long and you wouldn't have a problem. The issue isn't the bike running at that rpm, these things are incredibly durable. But, if you take them apart then reassemble and something isn't right... Well, the consequences of that aren't usually favorable.

Edited by crf450319

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I never took anything apart. The only thing I had done was measure the clearences, and there were all in spec except for one which was off just a very small amount and I did not touch it. The only thing that came off was the valve cover

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Well, of course in that case you can rule out a reassembly mistake on your part. Have you split the cases ? I'd be interested to hear what you find in the bottom end.

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Not yet. I am going to buy a flywheel removal tool and look at the cam chain, I did notice after the incident happend, that the timing was off, so when I was trying to re time it.. the cam chain was really tight and I could not get it on both cams. I think the cam chain may have came off the crank down in the bottom end and or jammed the motor from spinning. Because at first the engine would turn but would not start. It kinda sputted and popped. So the timing could have just skipped a beat and then the cam chain cam off towards the bottom end jamming it up completely so that now the kick start wont go down at all

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Ok well here is the latest. I took the top end apart again, and this time I got to the flyheel and stator. The cam chain was kinked down in the bottom end on the crank. So I got it back on track, and the piston moves freely. So I think all that happend was the high rpms may have or I may have done something to throw the timing off. So I'm going to order some new gaskets and see how she does

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If your timing was off then there is a chance you may have hit a valve into the piston, you will need to check for this. You also need to find out what caused the timing to jump. Running 2000 rpm will not cause the bike to jump timing or blow up, these engines are designed to run over 11,000 rpm without problem.

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If your timing was off then there is a chance you may have hit a valve into the piston, you will need to check for this. You also need to find out what caused the timing to jump. Running 2000 rpm will not cause the bike to jump timing or blow up, these engines are designed to run over 11,000 rpm without problem.

Well before all this happend I checked my clearences and everything was fine. I dont see any marks on the head or the top of the piston. I'll be sure to check clearences very carefully before I tighten everything up and run it again

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Be sure to get a new timing chain also. Cheap insurance.

My buddy said the same thing. The chain looked fine and I was going to re-use it, but after 2 people telling me to replace.. I bought a new chain today.

Edited by MotoSarge
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My buddy said the same thing. The chain looked fine and I was going to re-use it, but after 2 people telling me to replace.. I bought a new chain today.

For the effort involved, and the cost ($20) I replace mine every 50 hours of MX use. Like others have said, it's cheap insurance.

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