Random engine lock-up, now running fine again?

I had just started riding home from my friends place the other night and I just turned down a hill when my 'motarded :ride: 02 WR426 died. I thought this isn't unusual as my bike doesn't like running when it's cold, so just pulled in the clutch, put it in 3rd or 4th gear and let the clutch out. It fired once then the back wheel locked up. I tried again but the engine didn't even turn over. I coasted to the side of the road and tried kicking it but the kickstarter wouldn't move .

At this point I was getting rather nervous :eek: and thought I'd dropped a valve or something. I tried kicking it again and this time it moved, but had no compression, another common occurrence with this bike when it's cold and I've pumped to much fuel into the cylinder. Gave it a good kick, compression returned, next kick it was running normally and I road home no problem.

It has been running fine since with no abnormal noises or the like but I'm just curious as to what you guys think might have happened. My bike does had an auto-decomp cam, although it was in it when I got it so I don't know if it's a WR or YZ one. Could it have been just compression lock or something simple like that? I remember being unnecessarily freaked out the first time it lost compression, only to find it was just another quirk with these bikes.

Thanks for any input :thumbsup:.

Sounds like a conrod bearing locking up on the crank. Saw the same thing on a WR400 2 months ago

Sounds like a conrod bearing locking up on the crank.

Is there any definitive way to test this short of exploratory surgery? I use my bike every day as my only source of transport so I don't want to go tearing into it without good cause. I have taken it for several more rides since it happened and all seams normal. Anyone else got any ideas?



Maybe a tooth or two or something else come off in the gearbox.

My WR450F engine sometimes locks like this.

This is called "to hydrolic" a very dense mixture of gas and air is trapped in the cylinder in the compression stroke.

With motors that have 12,5 : 1 compression ratio, this can happen. Specially when you stall the motor trying to gas it in low RPM´s with a obstacle in front of you.

Put a constant pressure, with your foot, on the kickstart lever and hold, and the motor slowly turns and releases this pressure and is up for a regular kickstart.

Just changed the oil, cleaned oil and air filter and checked the valve clearances. There was only a small amount of metal in the oil filter (a failing big end tends to leave a lot of metal in the filter) and all the clearances where in spec :thumbsup:.

It must have just been hydraulic lock as described above, thanks for you guys input.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now