timing chain jumped off

[400man]

I was riding my 400 the other day on my trails and it started ticking alot louder than normal, ticked for about 5 or 10 seconds and then the bike just shut off. I was riding down a steep hill climb in 2nd gear with the clutch out, using the engine as a brake when it started ticking and shut off. at the bottom of the hill I tried to start it and the starter would spin but it wouldnt turn the motor off and it would roll easy in gear.

so I get it back to the house and pull the clutch cover and see that the timing chain had jumped off the crank shaft. pulled the top valve cover and seen that its still on the cam and everything looked normal. so next I pull the cam chain tensioner and it looks like its shot. doesnt seem to hold any pressure. I guess I got lucky that it didnt tear up anything. and since im into the topend Im replacing the tensioner and timing chain as well as putting in some new rings and hone job and valve seals and cleaning the carbon off in the head. the bike is a 2000 model and it looks like the motor has never been touched inside, all original. I measured the piston and bore and its all within spec and the piston still looks good.

[F-16Guy]

Put it back together with an OEM XR400R gasket set and throw a stage 1 HotCams Cam in it, or find a used XR400R cam on eBay. Since it's apart, you might as well add a few HP!

[400man]

well I already bought a moose complete gasket and seal kit today. the head gasket is the paper material one and not the 3 layered metal one like the stock one that came off it. im planning on buying a crf450 timing chain for it while im waiting on parts. im not gonna worry about a cam right now, just freshening the motor up and get it back together and ride it.

but I got a question about the oem xr400 head gasket, is it different from the stock 400ex head gasket? cause if its alot better than the moose head gasket then im gonna order one along with my crf450 timing chain. i'd kinda like to keep the motor close to stock for reliability reasons, about the only thing I might try first will be the +6 advance timing flywheel key. ive read alot about it on here and it should be a nice bang for the buck for a stock motor.

[BlasterEaten250]

The xr 400 gasket raises the compression a little bit.

[TRXRacer1]

XR400 gasket is a multi layered steel gasket but is supposed to be a hair thinner. Couldn't tell you by how much though. I'd be willing to be it's practically unnoticeable.

[F-16Guy]

The muli-layered steel gasket is better than the fiber one. I would buy OEM or a Cometic MLS set. The Cometic set is as good or better than OEM and is complete with head, base, and timing chain tensioner gaskets, as well as o-rings for the valve adjustment covers. If I remember correctly, the EX gasket is 0.040" compressed and the XR is 0.025" compressed. With a mild cam and the XR gaskets, you'd see a nice little gain. If you just do the gaskets, you probably wouldn't notice much, but it would run a little stronger. I just looked on eBay and saw a Stage 1 HotCams cam for about $135 shipped.