It just died, but I found the problem, (I think)

[eprovenzano]

My son was on the 400, 5th gear tapped when it just died... A little history, Its a 99 400ex, engine was stock (was still on original piston), I rebuilt it over the past winter, new valve seals, bored 2 over, new piston, rings, and valve seals . The quad ran well, in fact we just finished a long ride 3 days prior to it dying.

I took the plastic off, set the timing at top dead center and checked the valves. 3 were way off, and one was too tight. Something's not right, so I pulled the valve cover and behold I see the problem (I think). On the cam gear side, the barrel had come out of its slot, allowing the bearing to slip off the cam. The timing did not change, its dead on. But with the bearing off the end of the cam, the valves would not open properly so of course it died... The bearing are showing a little wear, so I'm going to replace them, and the barrels that keep the cam in place.

I don't believe the valves were damaged, they should be fine. Is there anything else I should look into before I put it back together?

Thanks

[eprovenzano]

I was looking at the bearing on the end of the cam shaft. Yes they are original, and I'm sure they have some wear, but I think I'm going to put it back together without replacing any parts. I planned on replacing the timing chain this winter, and I'll revisit the cam bearing at that time. My son is in college, so riding time will be slim. If mother nature cooperates and we are able to go for a ride, we can go. I'll dig into her deeper this winter when I replace the timing chain.

[trailrider894]

Originally posted by eprovenzano
I was looking at the bearing on the end of the cam shaft. Yes they are original, and I'm sure they have some wear, but I think I'm going to put it back together without replacing any parts. I planned on replacing the timing chain this winter, and I'll revisit the cam bearing at that time. My son is in college, so riding time will be slim. If mother nature cooperates and we are able to go for a ride, we can go. I'll dig into her deeper this winter when I replace the timing chain.

if you replace the cam chain use the CRF450 cam chain, and get a new cam chain tensioner for the 400ex.