bad top end noise, loss of power

[underpowered]

so i went to clay city this weekend, had a blast. was riding around the MX track, was on the face of them step up and all the sudden i lost power and a bad noise started coming from the top end. sounds like a valve horribly out of adjsutment. the bike will not idle, but starts easily.

trying for a quick fix, i tore it down partially. valves are within adjustment range, cam chain is still tight, bearings still on cam (once had a problem with a dowel pin coming out and bearing slid off cam) nothing i can see from teh top end. head gasket is still good, no oil leaking around it and motor seems to have good compression still when cranking. does not have much power, and makes a very loud clanking noise when running. any ideas? broken piece of piston, cracked cylinder? trying to get an idea before i tear it down later this week.

[AutoRoc]

I had the cam splines strip INSIDE the timing gear before. It made for no valve action... Do a visual and see if maybe it is moving or is out of sync.. goodluck! I think I hurt mine BAD riding last week too...:(

[dariusld]

I had my cam bolts back out, that made a funny noise, they were rubbing on the head. It still ran fine though, just the noise.

[underpowered]

cam gear bolts still tight. and i doubt it is the splines, only third ride on this cam after i junked my stage 2. plus it starts way to easy to be out of time or anything. it still runs and starts with only a few cranks, but has no power. no smoke i could see really, it has me stumped till i pull it apart

the valve cover is off, but don't have time to tear it the rest of the way down right now.

[GOTFEAR]

time to replace the cam chain

[underpowered]

Originally posted by GOTFEAR
time to replace the cam chain

nope, chain is still tight as can be, just replaced end of last season with a CRF chain. The Entire Valve train has been checked and is all good, so it has to be deeper in the motor.

[okieRrider]

Hello, Just curious if you ever found out what the problem was here? Mine did this same thing yesterday, but without the bad top end noise. Was out riding with my son and was going along great and then just all of a sudden was like I was taking off in 3rd gear, but I was in first gear. It starts easy and runs good but no power at all. I haven't tore into it yet. Any advice would be appreciated.

[underpowered]

well i tore it down on friday. found out it was a bad cam chain. not stretched, but it was stiff. i could barely flex the chain with my fingers. my guess is it stiffened up and made it jump a tooth somehow. causing the loss of power, and the noise i guess was the chain, and also my intake valves were very lightly tapping the piston, just enough to make a small clean spot in the valve relief.

[okieRrider]

hmmm ok thanks i'll check it out

[JOEX]

Originally posted by underpowered
well i tore it down on friday. found out it was a bad cam chain. not stretched, but it was stiff. i could barely flex the chain with my fingers. my guess is it stiffened up and made it jump a tooth somehow. causing the loss of power, and the noise i guess was the chain, and also my intake valves were very lightly tapping the piston, just enough to make a small clean spot in the valve relief.
What cam chain were you using?

[underpowered]

have a CRF chain in it now, only a little over a year old with maybe 30 hours on it total. no idea why it got stiff.

[okieRrider]

Fixed mine today. Seems that the screws that attach the throttle arm to the top of the slide had come completely out. Weird, put some lock tight on the screws and put her back together. An easy fix and she runs just as good as it did before that happened....Chris

[underpowered]

Originally posted by okieRrider
Fixed mine today. Seems that the screws that attach the throttle arm to the top of the slide had come completely out. Weird, put some lock tight on the screws and put her back together. An easy fix and she runs just as good as it did before that happened....Chris

common problem actually, happened to my buddy twice lol

[400exwheelieboy]

i hate to be the bear of bad news buddy but it sounds to me like u need a crank... or new crank bearings... mine just blew the crank about a week ago and has the same symptoms as yours.. so i bought a brand new motor instead of having to deal with the old one.

[underpowered]

nope, crank checked out fine. no play at all in the rod bearing or crank bearings. and it was a top end noise, not a lower end noise.

but it would not be bad news if the crank was bad. just would mean it is stroker time:devil:

but no stroker just yet. got all my parts so it should be going back together this week sometime.