[Spooling]

Hey guys;

I recently picked up a 2008 400ex which appears to be in good condition.

This past week however when trying to start and run it in cold weather. (-5c) Once we got it started when it was idling low as we're trying to get it warmed up. The engine would make an intermittent knock/clank sound. The sound goes away at normal idle speed or if the motor is warmed up. The quad seems to run well otherwise.

Any ideas what this may be or what I should check?

Thanks

 

[SlammedRanger]

Timing chain tensioner morr than likely. Or it could be the auto decompression mechanism on the cam. I wouldnt worry to much until it does it when warmed up. My .02

Welcome to the forums!

 

[Spooling]

Thanks for the super fast response! Thanks for the welcome!

Yeah, it only does it at sub regular idle rpm's, but it a nasty sounding knock. Is the timing tensioner something which is fairly straightforward to check?

 

[SlammedRanger]

Yeah in most cases the tensioner itself isnt what fails. Its just what causes the noise. The actual problem is a stretched timing chain. Which this engine is very very well known for doing. A crf450 timing chain is a direct drop in and is thicker and stronger. I have installed many of them to solve the tensioner knock or timing chain slap noise.

 

[Spooling]

Great, thanks again.

I'll keep an eye on it, but it seems like something I'll be planning on checking/replacing. I presume if you're replacing the chain you'd do the tensioner, maybe guides at the same time?

I've watched some videos and looked at the service manual. Doesn't seem too too crazy of a job. I was planning on checking the valve clearance in the spring, but this is quite a bit bigger job.

 

[SlammedRanger]

I always inspect the guudes for any abnormal wear. Usually they are just fine. And tensioner actually isnt bad its just at the end of its adjustment since the chain is so stretched. When you replace with a chain of the right length the tensioner is back in its adjustment range and your good to go. Alot of people run the manual tensioners but i havent had a stock one fail me yet and im far from easy on my engine. Still running stock one to my knowledge. And your welcome! Always glad to help!

 

[Spooling]

I'm going to order the CRF450 chain so I have it. I presume the chain for is the same for all the CRF450 models?

Is there anything to watch out for when changing the chain? From what I can tell, I have to pull off the valve cover then dig into the side of the motor a bit to get the chain out.

 

[SlammedRanger]

Mine is an 06 crf450 chain. I think the way newer ones. Like 12 plus are different? Not 100% sure though. Nothing to really look for. Very straight forward.

 

[Spooling]

OK, thanks, good to know!

 

[SlammedRanger]

No problem. Glad to help!

 

[Spooling]

So I've ordered and am waiting for the arrival of the chain. I was now wondering if I should have ordered any gaskets or anything else which may need to be replaced?

 

[SlammedRanger]

Clutch side cover gasket will be necessary and a new valve cover gasket aswell. Aside from that everything else should be fine. The tensioner gasket should be able to be re-used.

 

[Spooling]

Great, thanks!

 

[Spooling]

I finally got back up north and took a video of the issue.

 

[Spooling]

Hey SlammedRanger & Everyone;

I haven't gotten around to doing any work on this atv yet but I have the parts on hand. (new chain and gaskets, didn't grab a new tensioner or chain guides ).

I was thinking of doing the work this weekend, but wanted to be somewhat sure it looks like the bike is experience chain slap, and not something else like an issue with the decompression pin. Otherwise I may just do a valve clearance adjustment.

Any input would be appreciated.

 

[Spooling]

Well I ended up just adjusting the valves for now to see how it goes. I'll leave the chain replacement for when the weather is warmer. (above 0C)

This is the first time digging into this bike, getting the plastics, off etc., so it was a good experience.