Motor Problems. Rebuild Questions

[yamablaster24]

Alright i got this POS 99 motor all stock out of a quad that was returned after being stolen. When being turned over it KNOCKs like hell. Its really really loud. It started once then after that it sat for 2 weeks and now it wont start again. Im thinkin the timing chain slipped and messed up timing. ( it keeps back firing ) So im thinkin pull it all down, bore it .80 over to 416, put in High Comp JE or Wiseco Piston to run on 110, Clutch kit, Hot cam, and CRF timing chain. Sound good?

[mikeboone]

Originally posted by yamablaster24
Alright i got this POS 99 motor all stock out of a quad that was returned after being stolen. When being turned over it KNOCKs like hell. Its really really loud. It started once then after that it sat for 2 weeks and now it wont start again. Im thinkin the timing chain slipped and messed up timing. ( it keeps back firing ) So im thinkin pull it all down, bore it .80 over to 416, put in High Comp JE or Wiseco Piston to run on 110, Clutch kit, Hot cam, and CRF timing chain. Sound good?

It may not be timing; could be crank bearings gone. Pull the cylinder and you can tell by lifting/pushing down on the rod. There should be nearly no movement either way though will be some side to side.

These bearings are on bottom of rod where the crank halves are pressed together and are available aftermarket.

[yamablaster24]

I pulled rocker cover off ( the one you sold me mike) and the cam chain has a lot of play and i took it off the cam by mere ly pushing it a little to one side. The cam can move up about 3/8-1/2" up and down. Is there supposed to be this much play in cam chain?how do i tighten it? Re-time it?

[yamablaster24]

Well i need a new cam chain. It has way too much play. how do i go about replacing this?

[mikeboone]

If it was assembled last 'in time' it will still be provided the chain is on the same teeth on primary drive gear and cam gear.

The cam tensioner is adjustable. You may find you dont need a new chain; just an adjustment. When I break down 400ex motors I back both the 8mm bolts off tensioner and assembly comes out. If doing motor work you can remove the center screw. You will notice another screw inside that you can increase/decrease tension on the cam guides. This action simply pushes the plunger in further or retracts it.

You CAN run it in too far. The best way is to have the motor running and use a long screwdriver to 'set' the tension. If it's too tight you will hear high pitch squeal.

After all that; I would replace the chain with a new HD or stocker if it's been in since 99. Just giving some info on adjusting your new one.

May as well check valve lash since you have the gas tank and such off.

[mad440]

i just rebuilt my 400ex motor and im pretty sure the cam chain tensioner is self adjusting there should be a spring that keeps tension on it at all times. so if the cam chain has that much play in it its time to replace it or the tensioner is messed up. as far as the knocking nosie if its that messed up i would just do a rebuild with all the components u talked about and make sure everything is tight in there again. but i would def fix the cam chain thing first u might get lucky and that could be the prob