wr426f help?????????

90 replies to this topic
  • matt4x4

Posted December 21, 2009 - 05:22 AM


Weird - the center bearing surface on the cap looks the worst...would not have suspected that - would have thought the furthest right would be the worst.
Almost makes me thing at some point prior to this adventure - the center 2 bolts on that cap were overtorqued....
I agree - work with what you got, if the head does go - there's usually plenty on ebay to be had for a decent price - just gotta be real sure you're getting a good one. For the 30 bucks it costs - buy another timing chain, who knows what kind of weird stresses acted on the old one during this!

Make a list - check it twice - not because it's Christmas but because - if you work off a list of steps that you have to perform and inspect and check off - you tend to make less mistakes.

  • bakeyz426f

Posted December 23, 2009 - 03:47 PM


put it back together and it turns over and tries to start but i didnt get get it to fire after kicking it for a while i quit trying.a couple times when i kicked it it got stuck before it went all the way down like before. but if i did the procedure right and didnt decompress it too much before i kick it it kicks all the way through. should i take the valve cover off to see if everthing is still in the right spot still? could be old gas or spark plug mabye. mabye the cams are damaged and off a few degrees idk. any ideas

  • jbrooks26

Posted December 23, 2009 - 04:30 PM


First I would ask what the temperature is. If it is below 50, it could be that the oil is heavy enough that you can't kick it through fast enough to get it fired up. If you are certain that everything was timed properly to begin with, I would try to bump start it or park it inside a heated area for several hours and try again.

  • bakeyz426f

Posted December 23, 2009 - 08:10 PM


about 30 degrees farenheight/ yamalube 10w 40

  • matt4x4

Posted December 24, 2009 - 04:17 AM


well, I've NEVER had an issue with my bike getting "stuck".

Stuck tends to be an indication your bottom end bearings might be on tehir way out, however, in your case, I think you may need to check some other things.
I would say because of the strange situation that occurred, it may well be that your cam gear spun and you are now connecting with a valve.

First, press your decompression lever, put a ratchet on your crank and see if you can turn your motor over forwards, if it moves smoothly - good, if it doesn't move, see if you can free it up by moving it backwards, if it frees up, try moving it forwards again beyond the point where it was stuck, if it moves beyond, it may well be bearings since those would be inconsistent in where/how they jam, however, piston/valve jamming will occur in the same spot.

Next, I would remove the cam cover, and have a look to see what is what when it's turning over - where are the cam lobes pointing at TDC, where are the cam lobes pointing when getting stuck, also - before you disassemble everything again, look up some pics of cams and cam gears for the bike (there are plenty on this forum) that show you the approximate location of timing marks vs cam lobes.

Also - if you do take the cams off again, it might be beneficial to see if all your valves are moving smoothly and freely - place a socket slightly smaller than the bucket onto it with extension and ratchet attached, cup the ratchet and push down and release slowly - you should be able to get a good feeling of how each valve is moving and be able to see if it is moving through it's full stroke.

  • jbrooks26

Posted December 24, 2009 - 02:22 PM


30 degrees is pretty cold for a any oil, and it may keep you from being able to kick it all the way through. I had a different interpretation of "stuck" than Matt did, but if what he describes is what you are feeling, then he has it pretty much licked. All good information. One other question to throw into the mix, do you have the stock cam installed or is it an Auto-Decomp cam? If it is the AD cam, then there is a 3rd possibility. I have seen, and others have experienced this as well, the decompression pin can become lodged and not retract properly causing a "stuck" feeling when kicking through. The way to clear this when it happens is to place the bike in gear, any gear, and rock it backward to allow the pin to free itself. Hope this helps, let us know what you find.


  • bakeyz426f

Posted December 24, 2009 - 10:10 PM


it only gets stuck if i do the starting procedure off a little. if i push down the kick start lever too far with the the decompression lever in then let it rachet up and kick it it gets stuck before it kicks all the way through. when it got stuck once i pushed down on the kick strater with a good amount of force and it went down all the way. it didnt make any wierd noise when it freed up either, it felt like it just found compression or something at that spot and when i pushed down hard it freed up. when i do the proceduure perfect and only push the kick starter 1-2 iches down with the decompression lever and then rachet all the way back up it kicks through normal. with the decompression lever held down the kick start lever always goes all the way to the foot peg. today i tried to start it again and failed. it seems like it has no spark almost. illl kick it all the way through perfectly and everthing sounds normal when im kicking it but it doesnt fire up or backfire. i have stock cams and i think the problem is some where in the head of the engine not the bottom end bearings. the two most likely things to me are bad cams or spark plug. Merry Christmas! thanks for the help guys

  • jbrooks26

Posted December 25, 2009 - 08:39 PM


I don't believe that you have bad cams. The timing could have jumped a tooth or something strange like that. Or you could have mixed up the valve shims when you had the head apart. Did you ever remove the valve buckets? Check the timing, and the valve clearance closely. If all of this is good, make sure that the lobes are facing the proper directions at TDC, timing could look spot on and still be 180 degrees out. If all of that checks out, warm the bike up by heating the garage, or moving it inside. I have struggled with the temperature on mine too many times, and if it is below 40 degrees, it gets much harder to start because you just can't generate enough speed on your kick to fire it off. Hope this helps.


  • bakeyz426f

Posted December 31, 2009 - 12:50 PM


well im still stumped. i took the valve cover off and checked the timing and it seems to be right to me. here are some pics.

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  • bakeyz426f

Posted December 31, 2009 - 03:20 PM


should i be feeling compression at tdc? when i turn the crank counter clockwise with a wrench to the tdc mark it has compression and resistance in this spot. when i turn the the motor over and go to the tdc mark every other turn or something the cams dont line up but if you turn it over one more time it lines up as shown in the pics. is this normal? the cam sprokets and lobes move together so they appear to be alright.

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  • jbrooks26

Posted December 31, 2009 - 07:36 PM


I don't see the pictures, however, no you should not feel compression at TDC, it should come just before TDC as the mixture is compressed. Do you fee the same thing with the Decomp Lever pulled it?

Also, your cam lobes should be opposing each other, if they are facing the same direction, then one of your cams is 180 degrees out of time. This will cause all of the valves to open at the same time. Your cams will only line up every 2 revolutions, or 4 strokes. Hope this helps.


  • bakeyz426f

Posted December 31, 2009 - 08:54 PM


the pics are on page three. went out and checked the cams again and turned the engine over a few times. the bike has compression and resistance when it lines up like the pics in page three. after it gets past the compression the next revolution has little compression/ resistance when you turn it over and line it up on the tdc mark, the cams are basically upside down at the tdc mark on this revoulution. should i be lining up the cams on this revolution with the least compression?? mabye i have the cams lined up on the mark but not on the tdc revoulution. sorry if im not making sense, im new to working on bikes but im trying to learn.

  • jbrooks26

Posted January 01, 2010 - 06:50 AM


OK, I got the pictures to load, and everythign looks pretty good there. I can't really tell if your flywheel is lined up properly or not, it should have the "I" lined up with the two notches in the opening. This I is part of the word "HI". If I remember correctly there is another mark that could be confused as the I. The next thing you need to do is verify that you are at TDC when this "I" is lined up with the notches. This is easily done by removing the spark plug and dropping a straw or anything you have down the plug hole that is long enough to stick out above the engine when you reach Bottom Dead Center. Rotate the motor until the piston is at its highest point, doesn't matter if you are on the compression stroke or not. If everything lines up properly, then your timing is correct and you can stop messing with it and move on.

I'll try to explain the process of the 4 stroke motor for you. There are "4 Strokes", 1 for intake, one for compression, one for power (Ignition) and then one for Exhaust. The cams configure which is intake and which is exhaust by opening the valves at the proper timing intervals. The piston will rise to TDC twice in each cycle, and the spark plug will fire on both the Compression and the Exhaust strokes when the pistion reaches TDC.

I hope this helps, if you have any questions let me have it. Thanks,


  • jbrooks26

Posted January 01, 2010 - 06:59 AM


OK, I was trying to remember what this website was called. There is a wealth of informatino on this site for the older YZ-WR. All of the informaiton for the 250 applies to the 426 as well. Hope this helps.



  • bakeyz426f

Posted January 01, 2010 - 09:29 AM


yeah ive been to that site before when i changed the timing to yz timing it is very helpful but i guess thats when i didnt torque down the cam cap bolts properly. starting to think its not the cams too unless im not at tdc. the mark im lined up on in the pics is the I mark that came right after the H mark so thats right. is it possible im still not at tdc while on this mark though? i was going to turn the engine over one revoulution and line up the cams on the I again.

  • jbrooks26

Posted January 01, 2010 - 09:43 AM


Yes, it is possible that you are not at TDC with the mark lined up. However this is not a problem with the position of the cams. It would be a sheared woodruf key on the crank shaft that holds the flywheel in place. I would not mess with the cams any more until you verify that you are in fact at TDC by placing a straw through the spark plug hole as described in my previous post.

  • Birdy426

Posted January 01, 2010 - 11:21 AM


Everything does look pretty good in the pics. Early on in the posts, Bakey, you said something about pouring oil down the spark plug hole to "keep the cams oiled up". My guess is that's your problem. Your plug is probably oil fouled. Try pulling the plug, leaving the plug out, and kicking the engine over about a million times to try to pump the oil out of the cylinder. Then, put in a fresh plug and see what happens...

Also, while you have the tank off to change the plug, do a quick visual to be sure you haven't accidentally disconnected any electrical conections.

  • jbrooks26

Posted January 01, 2010 - 12:01 PM


That is a good piont, I had forgotten about him putting oil in the cylinder. If the plug is oily when you remove it, you could add about 1 tablespoon or an ounce or two of carb cleaner into the plug hole to help cut the residual oil and let it burn easier. It won't take any real time to verify the TDC while you are at it. Thanks Birdie.


  • bakeyz426f

Posted January 01, 2010 - 02:00 PM


im not sure i have the right socket for the spark plug. do you have to buy one made for the bike or will a certain size deep well socket work. also it could be the wooddruf key i guess because i was down in that area when i replaced the timing chain. i over tighted the bolts on the rotor puller and ended up having to get a new rotor. i have also added a keyed ignition to the bike but never had a problem with once it was hooked up. i could try cutting the wires to it. would oil in the cylinder explain my kick starter to get stuck on some of my kicks? im not sure a fouled plug is my problem though cause i had the bike running after the oil was pored down there, but it might of fould up after i didnt ride for a few weeks and then couldnt get it to start, but thats when i discovered the exhaust cam wasnt torqued down.

  • byggd

Posted January 01, 2010 - 02:26 PM


im not sure i have the right socket for the spark plug. do you have to buy one made for the bike or will a certain size deep well socket work.

A 5/8 spark plug socket with a universal attached to a 6" extension will do the trick.


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