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phatte95

Yamaha yz426f knocking very loud

16 posts in this topic

My yz426f 01 is knockging very loud when i have it on idle but whent im driving its knocking even more from the front of the cylinder.. so i wounder if someone had the same problem or if someone knows what it is? Very greatfull for answers!

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My yz426f 01 is knockging very loud when i have it on idle but whent im driving its knocking even more from the front of the cylinder.. so i wounder if someone had the same problem or if someone knows what it is? Very greatfull for answers!

Is this a new to you bike?  Is this a noise that it just started doing that it did not do before?  There is some normal mechanical noise in these engines.  If it is something that just started, I would take it apart and figure it out before it takes itself apart.  Possibilities off the top of my head are worn or damaged crankshaft bearings, broken piston skirt, maybe a loose timing chain.  Check for loose or leaking exhaust also.  Without hearing it, it would be impossible to try and figure out.  Might try posting a video.

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I bought it for about 3 weeks ago. It was knosking when i bought it but not this much.. something is wrong cause the only thing i hear when im driving is the nock. I'll post a video when im driving and in idle!

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here u have a video on how it sounds

 

It sounds to me like lower rod bearing is bad.  Unfortunately, it will most likely need a new crank and bearings.  Only a tear down will tell you for sure.  You will have to split the cases to do this.  Start tearing it down and keep an eye on anything that could be causing it as you disassemble it.  If you do not feel comfortable with this, find someone who is.  Where are you from?  Maybe someone local from here could help you.

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Yea have been thinking of that to.. i will think a little on that to see if i give it to someone who knows what hes doing or do ig myself! I am from sweden so don't think we have the same locals:p thank you for the awesome answers!

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Sounds like a rod to me too. You can check the rod bearing for play without splitting the cases,,just like you're doing a top end check to see if there is any up and down or lateral play. You don't want to run it with a bad rod or even more expensive things will happen.

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There will typically be some lateral play in the rod.  Check the manual for the spec on this.  There should be 0 up and down play in the rod bearing.

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Ye i will manage to take of the cylinder head by myself and check if the rod have some play! If i have ro splitt the cases i will let someone else do it.. i tear it down some day now so i will return with some answers !

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There actually HAS TO BE vertical play in the rod, or it would seize.  The problem is that the actual play will be something on the order of 0.02mm or less (.002"), and because of the way it's situated, it's nearly impossible to measure it accurately in any direct way.  So, the spec is given for how much the rod should rock from one side to the other (without sliding back and forth from left to right on the crank pin).  Since the only reason it can rock at all is the clearance between the rod, bearing, and crank, and the looser it gets, the more it will rock, this provides a simple way of evaluating the condition of it. 

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When I said 0 vertical play, I should have said you should not feel any vertical play when checking by hand.  A knock that loud will have an obvious amount of excessive play.

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Okey thanks for applying that ! Ye the knocking gets louder when the motor gets warm (15 mins of riding) so it would be easy to spot. Could it not be the main bearings also if its not the rod?

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It could be a lot of things, staring with a loose nut on the crank gear.  The 2000 models, and the YZ400F, used a square key to locate the balancer shaft gear on the crank.  They were somewhat notorious for loosing that nut and having the balancer gear rattle around until it beat up the key itself and often the crank in the bargain.  In '01, the cranks and balancer gears went to splines, and that mostly cured the problem, but not 100%.  Still see one get loose after a while. 

 

Main bearings generally make a heavier sounding noise.  Too much piston clearance could also be the culprit.  Tear it down and check everything as you go. 

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I have checkt evrything on the clutch side evrything was fine, the nut to the balancer was good so it have to be somthing in the cylinder. Greatfull for all the answers anyway ! :)

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