Need help for 2001 WR 426 engine noise

I have a 2001 WR 426 that is YZ timed and that the rings were just replaced about five hours of ride time ago. The bike has been sitting for a few months but I've started it up every week or so to keep it in shape. Because I'm in high altitude in Peru, (9000 feet) I had some problems with plug fouling. I changed to a 38 pilot and it seemed to fix the problem, however a few times the bike has intermittently lost compression and then gained it back. I checked the decompression cable and actuating lever on the cylinder and it seems like everything is working fine. However now there is a clunking sound that eminates from the right side of the engine after the kickstarter has gone through it's stroke. It's almost like the crank is reversing it's direction......probably couldn't do that though! Definitely sounds like something is much more loose than normal. I checked the valve lash and it seemed good, however would the lash be different if the bike is now YZ timed? Could anyone describe what the symptoms are for a crank failure.:thumbsup:

The lash for WR and YZ timing is the same. Crank failure is usually a catastrophic event (like a hole in the case or no piston stroke). Could be a main bearing starting to fail.

When you set the lash check and make sure you don't have a valve that is sticking. That might explain the loss of compression. It could also be a loose timing chain so make sure that the cam chain adjuster is working properly.

Good luck!

When I stripped the engine apart on my YZ426 the crankshaft nut was loose. It's on the right side that it holds the clutch drive and water pump gears. Only a suggestion.

If the crank was reversing , then the kickstarter would try to push your leg back up when you stopped kicking downwards.

Thanks so much for the help! Anyone else out there have some ideas before I tear it apart?

Check the crank nut for sure. Over the past three years I've had 3 Yamaha 426's come into my shop with loose crank nuts.:thumbsup:

Yup, loose crank nut caused me to replace the crank on my 426

Part of your loss of compression could be due to the fact that you are "starting the bike every week to keep it in shape". Unless you are fully warming the engine up to operating temps , you may be creating condensation in the engine , especially at your altitude. I suggest for all WR owners to set the engine at TDC with the kickstarter, by hand, when leaving the bike sitting even over night. Get in the habit of doing this and the valves are all in the closed position. If there is any condensation in the engine it can cause the valves that are open during engine off periods, to stick and cause compression loss. This can also be accomplished with the newer auto decomp engines , it's just a bit harder to feel the stop point. The cluncking may be that crank nut that has been mentioned. WR Dave.

While you're checking the crank nut, check the nut on the counter balancer too. I've seen a couple of those come loose as well.:thumbsup:

Thanks guys for the advice. I'll be checking it out this week and reporting on what I find.

I suggest for all WR owners to set the engine at TDC with the kickstarter, by hand, when leaving the bike sitting even over night. Get in the habit of doing this and the valves are all in the closed position. If there is any condensation in the engine it can cause the valves that are open during engine off periods, to stick and cause compression loss. WR Dave.

This was a big problem for me, but the condensation would freeze on the valve stems, holding them open. I think that the engine will generally stop at TDC if you shut down from idle with the killswitch. Every now and then I'd kill the engine in gear and let the clutch out before it had stopped spinning, and that's when I'd lose compression.

I also lost compression once in a while as I was riding, and it seemed that flooding fuel was washing down the cylinder walls. The engine had a lot of miles on it so ring to cylinder seal probably wasn't great to start with. Since you have new rings, they may not be completely seated yet, same problem but caused by too new instead of too old. I popped out my spark plug and dripped a bit of oil in the hole and the compression came back instantly and the engine restarted, so I knew those times it wasn't the valves.

As for your other problem, does the engine sound change if you pull the clutch in and release it (sitting still, in neutral) ? One thing to look for on the right side is broken clutch basket finger or broken fiber clutch plates. Since you have an 01 you probably have a lot of miles on the engine. If you haven't replaced the clutch basket, it's very possible that the fingers are notched.

This happened to me and caused me to start breaking fiber plates. The first time my engine started rattling I noticed the sound changed with clutch pull. I opened it up and found shattered fiber plates. I replaced them and they broke a few days later. I noticed that the basket fingers were getting notched, and thought the tabs on the plates may have been getting hung up in the notches, causing them to break.

baskets.jpg

I filed the notches smooth and a few days later my basket grenaded. Now I run a Hinson basket and have no problems. You can pop off the clutch cover easily to see if the ends of the fingers are all there. To check for broken plates, you have to remove the clutch pack. My plates broke into large pieces and all stayed in the clutch pack. Looking at the pack you'd think nothing was wrong. I opened it up and the plates fell out in pieces.

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