Snapped Intake Cam and Timing Chain!

[Daryll]

So to keep this short, i fired up my bike and let it run for a little bit, drove off. 1st gear to 2nd no problem, 2nd to 3rd, no problem, 3rd to 4th, no problem but i wasn't keeping track of what gear i was in so i just pulled up on the shifter to feel if i was in top gear or not...not a second later...motor lets go, didn't take more than a split second for the motor to die, didn't lock up the rear wheel, just made some ugly sounds as it rolled to a stop in gear...my first thought is maybe i blew 4th gear...didn't find out what happened until i pushed it home and pulled the motor apart. Disconnected the battery, pulled the wiring, pulled off the valve cover and what do you know...intake Cam snapped, and so did the chain. i can put the 2 pieces of the cam back together and see a perfect fit so i know there isn't any chunks down in the bottom end...the chain goes back together quite well just 2 little pieces to flush out from the chain snapping obviously. Should also note that the intake valves are stuck open. Where does this leave me? Is the motor worth it to fix? Did it really get stuck in between gears? did the chain just let go? did the Cam let go? Let me know what you guys think!


1982 Yamaha XS400J Maxim

 

[arfstrom]

On my SOHC, the cam chain tensioner/guides where shot? what is your looking like. (mind you I know nothing of the DOHC)

 

[Daryll]

ignore all the debris...i was cleaning gasket surfaces with a razor blade

 

[Daryll]

 

[Stpierre]

If one of the valves is staying open I would say it's bent. Change out the valves that are bad and reassemble.

 

[Daryll]

both intake valves are open as shown in photos posted earlier on this thread

 

[Daryll]

Also, how should I go about removing them?

 

[Stpierre]

Also, how should I go about removing them?

You should have a garage do it for you. If you must try then do lots of reading. Take out the old valve, put in the new valve, lap the new valve, adjust the new valve.
http://www.xs400.com/search/674836/?q=Valve+removal&o=relevance

 

[Stpierre]

http://www.xs400.com/threads/yamaha-xs400-manuals.4503/

 

[Jeff0133]

Takes some force to snap a cam like that...bent valves jammed and the rotational force snapped the cam and chain when the lobe hit those...is my guess....if you can't source the stuff locally I have a maxim motor in pieces.
PM me and i'll be happy to help

 

[drewpy]

i think the cam chain jumped the sprocket, sending the cam timing out. Piston meets intake valve and bends valve and breaks cam at the same time. Poor chain has nowhere to go too.

check tensioner