TRF Forums

hi wondered if anyone can help, my wr 400 has developed a rattle in the engine when under load ie accelerating in too high gear. It seams to be getting worse, am i right in thinking it is the cam chain being loose, stretched or the tensioner worn out. if this is right while the top is off is there anything else i should get replaced or checked.
Thanks in advance for any help Dave

Are you sure its the engine?

How many hours on the piston?
How long since the valve clearances were checked?
Has it got all fresh fuel in? (could it be 'pinking'?)


My crf450x is reknowned for making clanking noises but its normally the chain 'slapping' the swinging arm .

If it is just the cam chain tensioner it can be changed from 'outside' without doing any engine dismantling, if however it's the cam-chain that has stretched beyond adjustment then you have no option but to replace the cam-chain (IIRC it can be done without disturbing the head anyway)

My only experience is with a 250F (son's MX race bike) and we changed the camshaft for a 'later' year cam with the automatic-decompressor which made it a lot easier to start, i don't know if the 400 is similar or not though

Good luck with finding out the problem but be aware that if the cam chain is 'slack' and it jumps a tooth or two it can cause major damage
ian

As usual i thought the worst and didnt check the obvious the chain sliders on the swing arm and rear guide where worn through and the chain slapping on the swing arm
thanks for the help