2000 YZ426F engine noise

[criggs]

Hey guys, need a bit of help with one of my big bikes.

Just recently started restoring my dad's old 426 that has been sitting around collecting dust. It had been started maybe 2-3 times since he passed away in 2009, and not once since 2012. About a month ago I re-built the carb, gave it a tune-up, and got her running like brand new again, and actually got to take it out on a day trip and have some fun with it. It ran perfectly with no problems whatsoever. About a week later I started it up at home and noticed that the engine seemed kinda loud, but wasn't really sure and didn't think much of it. Started it up again a few weeks after that to get ready for another day trip, and could REALLY notice the noise now. At this point it's almost louder than the exhaust. The engine has had 1-1.5 hours of run time since I got it back up and going, and in that time it's gone from normal to this crazy loud knocking noise.

There is a known problem with the right side crank primary drive gear coming loose due to a worn key, but I've already pulled the side cover off and found no noticeable play on the crank/primary drive gear and nut. At this point I'm stumped, as I am not experienced with noise diagnosis on these machines, and would really appreciate any input you guys have to offer.

Before I tore the covers off I ran the bike and listened to it with an automotive stethoscope, and the noise seemed to be coming from the low end, most noticeable near the clutch cover, water pump cover, and front most area of stator cover (near the balance shaft). Temperature made no change, it was noticeable immediately when started cold, and sounded exactly the same when fully warmed up. It can be heard at idle, is consistent with RPM, and can even be heard while RPM comes down after snapping the throttle.

Here is a quick video of it running, let me know what you guys think.

Unfortunately I trusted my GF to get the loudest area on video and she didn't, but what you hear in the video is the noise I'm describing. Thanks again, guys. Any help is much appreciated.

 

[low_rb]

Sounds like you need to get the ol wallet out and rebuild.

HVe you checket the cam chain tensioner? Ive seen some pretty noisy bikes because the chain was slapping arond doing its own thing.

 

[my67xr]

I think it could be something like a worn timing chain too, does it seem to have a touch more low down power ?
If so when the timing chain stretch's it will slightly advance the ignition timing giving you a bit more power when taking off and accelerating from lower rev's
You could check the tension on it by removing the tank and then the rocker cover

If it seem's loose then the chain could be stretched, also check the chain guide's for any wear

Here is a good timing chain (note no sagging between the gear's)

This one is stretched

There are a few manual timing chain tensioner's available for them too
CNC Blue Billet Manual CAM Chain Tensioner FOR Yamaha YZ WR 250 400 426 450 98 | eBay

Timing CAM Chain Tensioner Manual Adjuster 2000 2002 Yamaha YZ426F WR426 YZ WR | eBay

Check everything out if you can, even thing's like the flywheel nut, and keyway if you have the flywheel remover tool.

If the noise was in the top end then i'd be suggesting you check the valve/rocker clearance's and reshim them to spec's
Worth checking while you have the rocker cover off, do you have a manual ?

If you need any part's look at boats.net, they stock a heap of part's and have decent price's too
Ebay and some motorcycle dealer's clearing their new old stock have some bargain's from time to time too
Search the part number's of the stuff you need from the dealer, then copy and paste them into a search on google, might some a few $$

 

[criggs]

Thanks for the reply, guys. I did check some stuff out, and ended up finding metal shavings in the oil filter reservoir. My best guess, based on the sound and location of it, that the crank bearing was finally starting to go. As I don't have the money to rebuild that kind of bike, and I am currently saving for a 250 two-stroke, I decided it was best to sell the 426 to someone who wanted to spend the time and money on her. It was very sad to see her go, lost my appetite for a week, but I feel that it was the best decision all things considered.