i know this isa blaster site ..BUT i got a 400 ex question

[smallz33]

my buddy said he has a knocking sound in the top end and lost allot of power.. and it might be burning oil? any ideas ofwaht this could be ? please help lol I need someone to go ride with so if i can find out whats wrong with his quad I can help hm fix it before he blows it...

 

[brandoz28]

sounds like its probably time for a top end rebuild

 

[motoman9911]

Could be a valve. Maybe it has came loose or something. Take the topend apart though.

 

[smallz33]

thats what i thought too.. Just needed some ideas of what was wrong before we go tearing it apart

 

[smallz33]

how much does a bore usually cost? and you think he could just hone it and put stock piston back in? a new one of course not same one..

 

[revin-it02]

how does he ride? is he always on the throttle? he could of bent a valve, causing it to not fully seat and hit the top of the piston at TDC

sounds to me like a perfect time for a 440 kit

 

[smallz33]

would bent / bad valve cause it to burn oil?

 

[Brute71]

worn out rings would more than likely be the cause of burning oil, but a bent valve is a good possibility for the knocking sound and power loss since it could be hitting the top of the piston and would cause a serious compression loss.

 

[DirtDiggler]

its probably a combination of several things . 1 worn rings and or leaking valve guide seals , a simple leak down test will tell you if there is a problem with the intake or exhaust valves . The knocking sound could be low compression due to the blow-by if the piston was hitting a valve like that , it wouldnt last more than a few minutes before catastrophic engine failure .

 

[ron89]

i think all 400ex has a little knock or a little noisy valve train. mine had a little noise but the valves were in spec and the top end was fresh. i would check the valves make sure there in spec. if he is burning oil, does it do it on hard acceleration or all the time?. cause i think if it does it on hard acceleration then its the valve guides if it does it all the time then its the rings?.

 

[smallz33]

not sure when it does .. He said it just started knocking and lost mas power

 

[mr_3_0_5]

trade it for a blaster.. lol

j/k.. i agree with everyone else.