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yz426 Piston Slap? *With Video*

2 posts in this topic

hey guys names jordan, im out of ec wisconsin. i traded one of my sport bikes for a 2000 yz426 motard. saturday i got it, she was mechanically sound. no problems, no ticking, no bogging. nothing. so on saturday i brought it home i rode it for about 6.5 hours and just beat the snot out of it. wheelies, endos, dirt trails, killing the streets, you name it i did it.

at the end of the ride i noticed that the bike was getting noisy, very noisy. i only ride kawi zx6r's (636) and they have a notorious kawi tick so im used to loud engines but this was bad.

i brought it straight home and decided to go through it the next morning.

so on sunday i did NOT start it and i just tore the head off to check the valves. brought it to TDC and the valves were within spec. cool right.


it didnt start.

checked compression, good

checked spark, good

checked gas, good

long story short ended up being a foul plug.

took her out for a ride after that and she was riding like shit, bogging down and everytime i cranked on the throttle it seemed like it wanted to die. so i brought it back home.

local moto mechanic took a look at it, hes a yami nut huger and has been servicing them for 30+ years. very reputable guy. he says its piston slap but before i drop $300 on a legit kit i wanna make this is it.

so here is where i am at now.

valves: within spec

cam tensioner: good

cam chain seems a bit tight but its in good shape

new plug

i do have hot cams with auto decomp and theyre in time (starts on first kick every time)

oil is good, drained alittle bit of it, no metal shavings and still has some golden color in it so i didnt change it

so i really dont know where to go from here. my supercross buddy who knows just about everything on this bike is out of town till sunday and i just want to ride. i dont know what to look for if i pull off the entire top end so ill wait for my buddy or input here. is it carbs? (it runs worse and worse with each ride) is it piston slap? is it a bad cam chain? would the notorious cb key affect performance?

so recap:


perfect valves

fouled plug

more ticking

cam tensioner good

new spark plug good

riding gets worse and worse with each ride


click here to see video


Edited by elitemoto

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Hi There

Only just joined forum, This sounds to me like cam chain, i wonder if the tensioner & guides are any good, other than that mechanical noise such as bottom end, maybe piston slap, noise travel's top end can often be bottom end, check the cam chain setup, then if no joy it needs to be stripped and inspected,

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