Chain-like rattle, left side of cylinder

Hi all! About 50 hours on my 426 and after about 10 laps in the mud this weekend I began hearing a chain slapping noise from down below under hard acceleration and hard decelleration. Though it was maybe a rock wedged between the chain & guard/case, cleaned all the mud out & same sound. Left the ride (bumming too - 1st time on Broome/Tioga!) cleaned the bike up real good, started again - can hear a little slap in the engine at idle. Took cam chain tensioner off & it's working fine. Put back on & still noise. Noise seems to be coming from the cylinder area right infront of the front sproket.

Before I tear into the poor old thing, has anybody heard of cam chain problems, or what this sound may be? It really sounds like a worn, loose drive chain - but within the engine.

I appreciate any help, and am finding this board/page is making my day!

Boz, 2000 YZ426, AMA #733256, Dist 3#805

And... if you ever get your bike up central NY area, stop by "Bozadilla" for a ride!

I haven’t heard of any cam chain problems. If your tensioner is working I would suspect something else is making the noise. It seems to me that if the cam chain was loose enough to make that kind of noise you would be made aware of the problem via another noise or poorly running bike.

These bikes are noisy to begin with so you may not have any problems.

If I were you I would yank the head cover and right side cover (water pump, kick start, brake lever needs to come off) and check:

Valve clearance (something you should check every now and then anyway)

This will also give you a better opportunity to check the cam chain, cams, gears etc.

Right side:

Clutch, check clearance with case. Some 426 clutches contact case (with rivets that hold damper plate and gear onto basket) around head bolt boss, some also hit oil pump drive gear.

Counterbalancer drive gear. Sometimes this gear eats the straight key that holds it in place. Check for play.

Water pump. Pump is driven by counterbalancer shaft. Inspect shaft and bearing for wear, galling on shaft surface sometimes extends to area contacting bearing, not sure if this is noisy but I guess it could be.

The only potential for noise from the left side, other than cam chain etc., would be a bad bearing or worn/bent shifting fork that is allowing gear dogs to rub when in neutral. Let’s hope that isn’t what your problem is…

Good luck, hope this helps!

Thanks Hick!

Am definately going to pull the side covers & valve cover off & poke & prod before diggin deeper. Great suggestions - printed it off & will attack the 426 w/ list in hand.

JBOZ: While you have the valve cover off, you try could this to see if you can trick the engine into making that mysterious noise. Remove the round plug that exposes the crankshaft nut and slip on a socket with a breaker bar. While jerking that breaker bar back and forth, check out the cam chain for slack and listen for other noises. You might want to shine a flashlight down into the cam chain cavity while yanking back and forth on the breaker bar. This way, you can verify that the cam chain adjuster is keeping proper tension on the chain. Also make sure the upper cam chain guide is in place. That cam chain resembles an industrial conveyor belt chain and looks like it will outlast everything else in the engine. I'm very curious as to what is causing this unusual noise. Everytime I walk by my 426, I look at it and wonder if some strange catstrophic part failure is gonna jump up and bite me! So far, I haven't had a single mechanical problem...knock on wood.

[This message has been edited by Boit (edited 10-23-2000).]

Thanks Boit!

I will definately give the cam chain a good going over & post what I find.

I knew it was too good to be true... Was enjoying it too much, figured heck! it's a new bike. Didn't even want to think about tearing into a 4-stroker. :rollin

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