400EX Engine experts, Help needed??

[blacknblue#2]

Ok i got a 400EX in my garage that belongs to a friend of mine. He talked to me last night about adjusting the valves and he got ahold of me again later last night and told me it was too late. Well He said he was going down the road and it just lost power and died. Now i have it half way tore apart and i find that the tensioner is junk. So im thinkin maybe he just skipped time??? but my question is, Is the tensioner a common problem on these engines and do you think it for sure bent some valves when it jumped time. I havent work on one of these engines since 03 so any help would be greatly appreciated. Thanks guys

[REPOMAN]

if you got to the cam chain tensioner then surely you have the head off already. just look at the valves and see if they are bent. if they are bent valves arent expensive.

[blacknblue#2]

Ok heres a little update.....i got the head off. The valves look to be seated good and i turn the head over, poured gas in the combustion chamber and it aint leaking down through the ports so the valves must be good. The timing chain and tensioner are both junk on this thing. The chain is kinking something aweful (sign of real bad stretching from my experience?) and the tensioner has no spring pressure. But before i pulled the head off everything was in time. So could the stretched chain and bad tensioner be the reason this thing lost power and died?? Last time i junked a chain on my 450 it still ran it just didnt sound like i would wanna stand within 15 feet of it haha?? ANd also if this is my problem what is this i hear of doing the CRF cam chain mod????

[Honda#4]

The 02 CRF 450 cam chain is the HD chain you use in the 400 to replace the stock one thats the "cam chain mod " you hear of. As for the motor replace the tenioner and cam chain and turn it over by hand to see if it still makes noises, make sure to look at the sprokets to see if any of the tteth are broke and misssing.

[skatrdude20]

When you say that the tensioner has no spring tension, is this just when you push on it with your fingers, because if so, it will not have any. It is an automatic retracting tensioner and as your chain loosens, the tensioner feeds more of the tension, but just by pushing on it, you wont feel anything, Take a screw driver and compress the tensioner, and then let it spring out, you may only need the chain. Iv seen two stock chains stretch fairly easily.