my 406 just went Clank..

[maxamillion]

my 2002 406ex has about 7-8 hours on it, still on break in oil, has ran great since I rebuilt it. It has a JE 406 10.6:1 piston with flexsteel gaskets, new valve seals,head was cleaned up, stock cam and cam chain, stock rod.

I just went ridn in my yard, it started fine, ran good for the first 5 minutes. Then i went over a small natural jump, blipped the throttle in 3rd or 4th gear, and my motor made a nasty clank noise and shut off. It wont start, I turn it over and it doesnt seem like there is much compression. When I hit the starter it just goes clank clank clank. I think i dropped a valve. Do u guys have any suggestions before I go tear into it?.....Again.

thanks, max

[rooster300ex]

I bet your gonna have to tear into it.

[h400exrydr]

mine did that too a while back, wat happend to mine was the spring in the cam chain tensioner broke and the cam chain slipped and it jumped time and then valve hit the piston, if u do tear into it chek ur tensioner and make sure the spring isnt broke, i think it is kinda stupid to have a lil $50 part break and then cost u like 200.

[maxamillion]

http://www.imagestation.com/picture/sraid198/p29ecc81616761e82b9e9150f3ca0cbe1/f0f316e7.jpg

turns out my cam chain snapped right in half! luckily it snapped towards the bottom end so it did not fall deeper into the motor. when i opened up the head the chain was still resting on the cam sprocket! looks like its time for me to upgrade to the crf450 cam chain. I should have done that the first time around.

[JOEX]

You may want to check for piston and valve contact:ermm:

[h400exrydr]

and make sure the valves have no gaps between the valve and the head.

[maxamillion]

is there any way to check for piston and valve contact without taking the head off? that way i dont have to buy a new head gasket. I was thinking put the new cam chain in there, align everything, then rotate the motor by spinning the flywheel a few times...if everything turns smoothly it should be fine right? Would i be able to tell if a valve was bent by doing this? By the way, there were no metal shavings in the oil when i drained it.

[h400exrydr]

well im sure u wouldnt b happy to get it all back together and then it wont start because of some bent valves, then you would have to take it all back apart, if it were me i would jus take it off and make sure that the valves are still good, that is jus me

[2muchquad]

[QUOTE]dont have to buy a new head gasket. QUOTE]

you should be able to reuse that headgasket,just take your time

[maxamillion]

i will go ahead and take the head off. ur rite, i wouldnt be happy to get it all back together and it not start. ill ask c&d if its alrite to reuse the head gasket. thanks for the help guys.

[maxamillion]

http://www.imagestation.com/picture/sraid198/pb5162a9415c1b002cd051f9e1d762078/f0f0d53f.jpg

http://www.imagestation.com/picture/sraid198/pd06bbff29b31dce542ec8a928ff62488/f0f0d520.jpg

http://www.imagestation.com/picture/sraid198/p789b03324c1ca60d458139185e276f71/f0f0d4fd.jpg

http://www.imagestation.com/picture/sraid198/p435b530a4f131e9ac7920ecc95403ad9/f0f0d4e8.jpg

http://www.imagestation.com/picture/sraid198/p10cfb4bc256cdc63ea2f865d0411a563/f0f0d4c8.jpg

well i got the head off. it appears that the piston barely tapped both the exhaust valves. it just looks like little scuff marks. is that anything to worry about? there were no metal shavings. thanks, Max

[dork]

you could've done a leakdown test (if you have the tools), that would tell if the valves are leaking with out pulling the head. for now, pour some kerosene or solvent in the ports and check for leakage around the valves.

[ak_stick]

As long as you take your time and dont rip it, you can re-use just about any gasket or O-ring. While its nice to use new hardware, there comes a time when your replacing good stuff. if it does not have any rips or pinches, put it back on and call it a day.

[Barney]

Look at the very outside edge of the valve pocket on the piston is were it will hit on the exhaust side first. It does't look like it did
but look at it close.

[h400exrydr]

you could also take a bright light and shine it on the top of the head and see if there is ne light comin thru where the valves are.that is how i found mine were bent. i didnt even realize it b4 i looked

[XCRACER26]

Put the head valve side up and fill the dome with water and wait 15 MIn to see if any water has leaked out of the intake and exst. that will tell you if you have a leak.