Puzzling engine noise

I've got a street-legal 2000 WR400 w/o any major modifications that has developed a strange rattling noise in the engine when gassed in low-ish rpms. The sound could be described as the sound of two light metal parts vibrating against each other very rapidly.

The noise disappears if I rev the engine a bit more (change gears) or if I let go of the gas. I have tightened every bolt I might suspect of causing this, but I'm beginning to suspect it's from the engine... Could it perhaps be the cam chain tensioner that needs a look? Anything else that can cause this?

The bike has been run nearly 10 000 km, mostly on roads and some gravel pits/forest trails.


I had the same identicle noise. I thought it might be the water pump...Come to find out it was a dry set of front wheel bearings. The noise was traveling up the forks and sounded like it was coming from the front of the engine. You might want to check that, only takes 5 minutes and might save some aggrevation.

Bonzai.... :)

This may be a long shot but have you checked your chain tension? WRs need to have the chain tension set correctly or you will hear a rattle at acceleration! This baffled me for a full 60 mi woods ride!

Just a thought...Good luck!

When's the last time you had the valves adjusted? Does your bike start harder now than when the noise was non-existant? My 98 made a "clicking" sound when I applied the throttle, I had the valves adjusted (which is normal) and it fixed the problem. Dry wheel bearings? Yep, that also happend to me when I busted a fork seal and the fluid ran down the fork tube and conviently washed all of the grease out of my front wheel, that just made a horrible "squeel" until I was able to service the bearings..

Just my thoughts.....

Thank you all for your replies!

I'll be sure to take a good look at the drive balancer gear key -- sounds nasty.

I'm not too sure about the sound being related to valve clearances (I checked them recently) or wheel bearings, but I'll have a second look anyway.

Thanks again!


balancer drive key is not too bad..

about two hours for me.

That doesn't sound too bad (although I suspect you're a faster mechanic than me). Do I need to order anything in addition to the drive key in question? Perhaps a new cover gasket and lock washer to be on the safe side. Anything else worth replacing while I'm there?

Living in Norway, some parts can take quite a while before they arrive. I'd better get everything right the first time...

If your gbalancer drive gear isn,t cracked

all you will need is the key.

its just a little square piece of metal

you can have it built at any machine shop cheap & fast

they are exactly in inches

.196 square by

.388 long

I used keystock

these are nice and snug

I took mine apart twice and still used the same gasket

here are the yamaha part numbers.

balencer drive gear part# 5BE-11536-00-00

Straight key part# 90282-05034-00

the gear was about $50.00

the key was about $1.20

both items were on backorder in the U.S.

so I had to make my own key

and waited three weeks for the gear

good luck


I also used my old lockwashers

its not the right way to do it but was cheaper and I did not notice any reason while there to replace them

if you are going to buy them there is one on the clutch basket and the drive balencer gear you will have to remove

Sounds to me like it may be a bad rod bearing. My WR400 had this happen. Remove the flywheel cover (you can lay the bike on its side so it won't loose oil). Grab the flywheel with your hand and rotate it back and forth slightly. If you have a bad rod bearing you will feel a little slop and hear the noise. Don't just use a socket on the flywheel nut, as you won't get a good enough feel that way, take the cover right off!

[This message has been edited by Tony Miller (edited 08-01-2001).]

I can almost guarantee it to be the drive chain. Don't be alarmed, and DONT TIGHTEN THE DRIVE CHAIN TOO TIGHT !


Tony Montana

01 WR426

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