Starting after rebuilt/mods after my last thread/post...I got a decomp cam for this 01 WR426. I am very excited and my friends that ride these are jealous :D But not when they find out about this one: I can't get the thing to run now.

I put the cam in and put it all back together.

First a little history: This bike was a victim of a valve break. The head replaced and all Kibblewhite black diamond SS stuff put in...I replaced the cylinder, and new piston kit, and all that crap. I put it all back together closely following the service manual. I had 2 hotcam's in it, pulled the exhaust one out to put the decomp hotcam in. Put it all back together again....

So, I kick the bike over after pulling the choke out, and in about 4 kicks..the bike fires right up :naughty: It ran for about 30 sec or so, and just quits! I kick and kick, and it just doesn't fire at all.

Where do I start? I carefully followed the instructions for the cam/timing, and it seemed to run really good while it was running. The kick over is smooth, and doesn't seem to have any binding or anything. There is a clattering when trying to roll start it but can't tell if it is abnormal or just valve train noise.

Plz help!! :naughty: Thx

irok was the day of attempting to get this thing running. Well...the bad news is: All the the intake valves are bent and stuck open. My guess is the clankin noise I was hearing was the piston smackin up against them.

The exhaust valves are fine.

I guess my next question is: What could have cause this? was the day of attempting to get this thing running. Well...the bad news is: All the the intake valves are bent and stuck open. My guess is the clankin noise I was hearing was the piston smackin up against them.

The exhaust valves are fine.

I guess my next question is: What could have cause this?

If you're certain that you followed the instructions for the cam timing, and the bike ran fine for 30 sec's or so, then the timing chain might have skipped a few teeth on the gears? You did re-set the chain tensioner, didn't you?

Check the static timing now, and see if it's moved from where you set it.....

I checked several times, as I was suspect to the same thing myself. the cams were lined up precisely as I put them, even to the crank. I followed the directions to the letter in the actual Yamaha service manual. I also did the little "wind up" procedure for installing the tensioner every time. The tensioner seems to work good, tightens the chain right up when put in place, and everytime I took it apart the chain was very firm in place.

When it quit, there was a slight "clank" sound. it was running really good until that time. It idled smooth, and was quick to blips in the throttle, and no decernable valvetrain rattle. The motor came to a sudden stop...with the slight clank. for a while it would clank like so, I check the timing several times with no issues. Then it started like a binding every other kick. After taking it apart I found all the intake valves were stuck open about 1/4 in.

At this point the bike is apart down to the piston. I am not sure if the head is any good, I know the valves are screwed.

So...I am still at a loss...I am sure I am just missing something.


I just put new rings and re-installed the head after adjusting the valves...

I'm at the point of re-installing the cam-chain in place.

I'm following the service manual.

Your post scares me to death :D:naughty::naughty:

Hmm... So other than the intake cam, EVERYTHING above the case is new? Valves, piston, head, cylinder, etc...?

Did you check the piston-to-valve clearance with clay and manually turning the engine over, then pulling the head prior to starting it?

Did you use new springs? Are the springs rated for the lift/duration of the cams?

Are you positive the valve keepers were seated?

Sorry to hear it... that's a major bummer. I know that feeling well... your head gets all warm as you realize that something is going to cost a lot of money.

"Did you check the piston-to-valve clearance with clay and manually turning the engine over, then pulling the head prior to starting it?"

I understand we can put some clay (special kind of clay I assume) on the top of the piston, install the head, cams, cam chain... make a few revs manually, then unmount everything to see how deep the valves prints are in the clay? Is this what you mean?


It's generally not needed if you are simply replacing stock parts, but any time you are replacing the piston, especially with aftermarket, or have had any machine work done on the head or cylinder (or replaced with new), it is mandatory. Same for going to a new cam that runs higher lift or significantly altered timing than stock.

Wow! This is nice information. I had never heard about that... thank you.

When you do that, I assume you need to torque the head to specs. Do you sacrifice a brand new head gasket ( the one between the cylinder and the head) or can you re-use it after you checked the piston-to-valve clearance? In other words: when the check is done and you put the engine together definitevely, do you use the same gasket?

I'm asking that because I torqued my bike's engine head to spec and I need to pull it back to check something (timing chain guide is not properly installed on the exhaust side). I'd like to know if I can use the same gasket when I install the head back to its place.

Thanks again for the information.

Irok, this sounds a bit similiar to a problem I'm having. I bored my 400 to 430 and installed Hotcams intake and exhaust. Are your cam sprockets slotted, mine were and I assume yours are too. Hotcams says the cams are shipped with the sprockets set to original Yamaha specs so they should just pop in. When I installed mine I couldn't get the marks on the sprockets to line up exactly with the caps no matter what I did, and the cam chain was brand-fire new. The stock cams would line up properly. I picked the alignment that looked the best, checked the valve to piston clearance, and everything appeared to be fine. I did have a valve that was borderline on the tight side of clearance specs, but shims are a couple of weeks away for me and I was cracking to get riding so I went for a spin.

The bike ran great for a couple of hours but started to lose power on a long stretch when I opened it up in top gear. I coasted to a stop and kicked the engine and had zero compression. I kicked again and it brought up solid. I figured I had bent a valve. I rolled the bike backwards in gear and kicked slowly again. It turned over and then brought up solid again, definitely felt like the piston was kissing a valve. I was far from town so I sat for a while and tried winding it backwards and kicking over. Gradually it would turn over without binding and the compression came back and I got it running and it worked fine and I rode for the rest of the day with no problem.

I originally thought it was tight valves, expanded more when the bike got hot and the valves wouldn't close. Funny thing was once I got it running it had no power and was backfiring for 5 to 10 minutes and then smoothed out and was back to normal once it was warmed up. This isn't how the bike behaves during a normal cold start.

My shims arrived and I set the valves to spec.

I was out yesterday and lost all compression again. I sat for 1/2 hour and compression gradually came back and started and I rode for another 4 hours with no trouble.

Both times I lost compression seemed to be when the engine was under steady strain for a while. The first was flat out on the stretch, yesterday was a long hillclimb in 3rd gear wide open. This has me puzzled. I'm thinking that maybe a valve is sticking in it's guide. If the hotcams are opening the valves more than the stockers, the varnish deposits on the valve stem would now be getting pushed into the guides and may stick. I didn't take my head apart so I thought that may be it, but if you've got new valves they shouldn't stick, so there goes that theory.

We may have 2 different problems, but they seem similiar to me, except I stopped the engine before a valve bent. My next step is to get a degree wheel and dial indicator and check to see if the slotted sprockets are set properly. I don't understand why the problem is intermittent for me and why the bike will run fine for hours after the compression comes back.

Let me know if you find the cause.

If I may, just a little hook off the current subject. Can sticking valves be the reason why I often can't find TDC when I try to start the bike for the first time on one of these cold winter days?

Now, back to Irok's issue. :naughty:

Math, when you say you can't find TDC do you mean that you're a bit down on compression sometimes when the bike is cold? I found that if I left my bike outside overnight, once in a while I would have very little compression. It was condensation forming and then freezing on open valves, not allowing them to seat properly. I've heard of guys down south with the same low compression after sitting for a while but it was rust forming on the stem and holding the valve open. My problem is easy to fix, I just heat up the head and the ice melts. Now I set my bike to TDC when I park it and don't have the problem anymore.

What I mean is that while I do the routine, I come to set the bike at what I would say is TDC (feeling from my right leg) but then I realize I can push the kickstarter down without effort... like I can pass TDC without the manual decomp. Usually, my entire weight would not be enough to push the kicker down...but sometimes this thing happens when it's cool outside (-5 to -10 celcius (20 far. deg.))

So mostly what you are saying is that you let the bike sit with all valves closed (seated) so nothing gets in between the valve and its seat while resting. Is this correct?

Sorry to make you repeat :naughty: but you know that we, people from Quebec, don't speak English as a first language and I just wish to make sure I got you right... :naughty:

but sometimes this thing happens when it's cool outside (-5 to -10 celcius (20 far. deg.))

So mostly what you are saying is that you let the bike sit with all valves closed (seated) so nothing gets in between the valve and its seat while resting. Is this correct?

Correct Math, when you shut the engine down, condensation can form on the open valves as the engine cools and then the -10 can turn the condensation to ice. It may form between the valve and seat, or may be on the stem. The valve springs are not strong enough to overcome the ice. When you try to start the next morning the valves won't close completely so you have less compression, as you are experiencing. If ice forms when the valve is closed, the camshaft can open the valve since it is a much stronger force than the spring. If you set to TDC at night you shouldn't have a problem. When it's warmer the condensation probably drips off or evaporates.

Sorry to scare you Math...just take it from someone very frustrated and sad that I can't ride this thing (I have had it for mos and have never got to ride it). Everything I have learned about this bike...timing is very specific and needs to be done exact and properly. I am seriously considering having the local Yamaha dealership AT LEAST checking the timing once I have the bike back together before I run it, although I should be able to do it..the procedure is pretty clear and straight forward. I really don't like other people working on my stuff...but it is better than going through this sh*t again. That is if I choose the rebuilt path again.

Headsup: Yes...actually everything above the case was new.

Wisco piston/ring set, new cylinder, new factory Yamaha head, all brand new kibblewhite stainless steel valves/black diamond valvetrain, brand new Hotcam intake and a brand new Hotcam decomp exhaust cam, new timing chain, new exhaust gaskets, top end gaskets, blah blah...all new stuff.

The head/valvetrain was put together professionally, as I don't have the tools or knowhow to do valves. after getting the head, I followed to a tee all the instructions in the service manual.

As mentioned before, I am not sure about the valve train/seats etc, so I am not a real help there identifing any issues there.

yes this really sux. I have wanted a dirt bike for years, and this opportunity worked with the money and time I had to get it... I was so stoked to ride this like you said major bummer.

Frostbite: Wow..that is a wierd problem. I am not sure if my original starting issue was totally bent valves at that time or not..but sounded similar to yours before things got really bad.

Mabye you have a warped head? Have you checked the oil for coolant/vice versa? Have you check the torque on your head bolts? Have you checked your spark plug?

One thing I have found as I research these bikes as they are pretty sensitve to jetting. you may have a problem with richness. Another guy that has one says that when they get rich in the cylinder, it takes a while before they will start back up, and would also explain why you get crappy response out of it after these conditions. So it may not be a compression problem but maybe a bad mixture in the cylinder...which kinda makes more sense if you are WFO or in it pretty heavily when you have the problem. I have seen similar "loading up" problems esp in high gears on the highway with carbed sportbikes.

If you can replicate the problem you may be able to get a compression tester and check the compression while you are having the issue...this will eliminate the variable of compression/show it really is a compression problem. My guess is the paths for solving fuel/air mixture or compression problems are two totally seperate troubleshooting methods. what do I do? what are the chances of my head still being good? Should I just be able to replace the valves...maybe the seats, and be good for round 2? how could I go about seeing what my options are?

thanks for all your posts...this is a very trying time lol

Irok, mine is definitely a compression issue. Both times I could spin the engine easily with my hand on the kickstart, like the sparkplug was out. When the compression comes back I can't kick it over without setting the decomp lever.

You do have me thinking now though. Since there's not a lot of hours on the rebuilt engine, the rings may not be fully seated. I'm wondering if it's possible to run rich enough to wash the oil off the cylinder walls causing the compression loss. I did notice there seemed to be a lot of blow by from my crankcase vent tube when I stopped. The snow packed around the skidplate was black. I removed the snow and when I got it running again it ran for hours without the black blow by.

It may be flooding due to ice in my carb vent tubes, which seems more likely to wash down the walls than running rich.

Hey irok, I'm VERY sorry to hear your experience. I don't have any tips aside from taking it back to the person who assembled the valve train for you. Maybe they can shed some light on how to move forward. I'm waiting for my head/cylinder to come back from Forward Motion. KPMI valve train and Wiseco piston. You've done a very good job at scaring the crap out of me! I hate other people working on my stuff too but you've got me thinking...

Anyway, I know you want to ride the thing but you might as well take the time to get things checked out before reassembling it. GOOD LUCK and keep us posted if you don't mind.

Take care.

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