help with 02 426, low compression and no start.

those pics are from my wr426f. they look a little off in the pic but when i wiggled the rotor a little one way they looked lined up about right to me. the bike ran well as well. i pulled the cam caps and took the nut off the flywheel but im waiting on my puller to come to get off the flywheel. when i time the bike to the yz timing will the exhaust cams marks no loger line up with the head? on this site it says there should be 12pins for the yz timming and 13 for wr timing like mine had above.

http://www.thumperfaq.com/yz_timing.htm

The site you just linked to is for a YZ250F, not a YZ426.

http://motoman393.thumpertalk.com/tech/yztime.html

DO NOT attempt this with an engine using auto decompression.

at the top of motoman site that you linked it says the mod Works on 98'-02' WR250F/400/426 models. i think the site i linked for the wr250 mods is pretty much the same thing. from the pics i should have 12 pins inbetween the marks when im done. another question sorry to hijack this thread kind of but to get the nut off the flywheel i put the bike in gear and was able to just twist it off cause the motor wouldent turn over. im thinking the cam chain might have jamed on the crank gear and i hope its not damaged. i had the chain tensioned by zip tie. is this normal????

Edited by bakeyz426f
at the top of motoman site that you linked it says the mod Works on 98'-02' WR250F/400/426 models. i think the site i linked for the wr250 mods is pretty much the same thing. from the pics i should have 12 pins inbetween the marks when im done.
The problem with the ThumperFAQ site is this:

The process is the same, but the pin count info at the ThumperFAQ site can be misleading to a YZ4** owner because the normal pin count on a YZ250F with stock cams AND on a WR250F with stock cams is 12, not 13.

Thus, the Motoman page is better because it makes no specific reference to that one way or other. It says simply to start with both cams timed correctly as built, then moving the cam in a WR one tooth clockwise to retard it and arrive at YZ timing.

i see what you mean. it does make it a little confusing to the yz4..f owners

Greyracer,

So to clarify: a stock WR426 has 14 pins, a YZ426 has 13?

So when the I/E marks are "correct", it is YZ timed and a WR has the exhaust cam rotated 1 tooth counterclockwise?

One more thing: does the "WR cam" have the "I/E" marks in a different spot from a "YZ cam"?

Sorry for so many questions, I just like to understand things from every angle.

So to clarify: a stock WR426 has 14 pins, a YZ426 has 13?

It shouldn't, no. In stock form, with stock parts, they should both have 13 pins between cams. Once again, for the upteenth time overall, counting pins is NOT how cams are timed.

So when the I/E marks are "correct", it is YZ timed and a WR has the exhaust cam rotated 1 tooth counterclockwise?
Not when both engines have stock cams, no. The I and E marks line up correctly in both cases.

One more thing: does the "WR cam" have the "I/E" marks in a different spot from a "YZ cam"?

Absolutely. The sprockets are the same part in both engines, and in '02 and earlier engines, they are the same on both cams. The exhaust camshaft is also the same between the two models year to year at least up to the '06 models. The only difference in a WR cam and the YZ cam is that it is pressed into the sprocket in a different position.

Thanks Grey. :smirk: This is great info.

Hey guys, was trying to start my bike again lastnight before i took it apart.

I was kicking it through how it shows to do on the video and nothing, i try with choke, without choke, with hot start, some more without anything still nothing. I kick'd it through kinda slowly once trying to find tdc and while doing so it shot a good 5 inch flame out the pipe.. To me, it sounds like timing..? But yet everything is lining up..

Any advice?

bump, pleaasse help guys!!!

double bump

thanks for the bump!!

Sounds like you could have a exhaust valve hanging open just a touch,causing it to be an awsome flame thrower.

Before you rip the head off I would check a few things.

Double check your valve clearance,try to stay on the upper half of the spec range.

And if you can find a leakdown tester to use on it, that will give you some idea of if things are sealing up inside the combustion chamber.

This is what i thought also, valve clearance is good tho. dedomp lever isnt touching lifter at all unless i use it. I dont have the right size fitting for my testers to fit the spark plug hole. Thanks for the reply

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