Need help with cam positioning

26 replies to this topic
  • upthemaiden

Posted July 30, 2011 - 10:17 PM


I've been fighting with my bike for a couple days now and I think I'm ready to give in and ask for some help. My bike is a 2001 yz426. I just got it a week and a half ago, it was running well, and then all of a sudden stopped running so well. I've gone over a number of things on it... cleaned carb, new spark plug, changed the oil(&coolant). Eventually I remembered the day it started acting weird I had also messed with the timing belt tensioner. Long story short I think I tried to start the bike with the tensioner too loose and the timing chain slipped a tooth on one of the cams. So tonight I pulled it all apart and took a look and I could see that the timing marks definitely weren't lined up. From the left side of the bike, looking at the timing belt, I had to rotate the intake cam counter clockwise. From what I could see in my manual at TDC the "E" should be on the left side of both, and the marks on the outer edges of the cams should line up with the top of the engine. I actually had to move it 2 positions to get them to line up. Thought I had it for sure this time. Buttoned it all back up, pushed it outside, and still no luck. Before it would eventually start, and just not run well. Now it doesn't even want to let me through the whole kickstart stroke. I made sure to spin the engine slow a number of times first to make sure the valves were clearing the piston, and even if I pull in the decomp lever it'll let me spin the kickstart nice and easy, but when I get it in position and try to kick it'll go about 90 degrees and just stop like it built up a ton of compression.

Any ideas?? I'm wondering if I should've only moved it one position instead of two, if that has anything to do with it. One thing I did notice that caught my attention was that when the marks on the gears were lined up, the lobes weren't pointing completely away from each other. The intake lobe was slightly angled up. I wouldn't have thought much about it, but I swear I saw a picture somewhere of the two of them pointing directly away from each other. Only problem is if they're pointed way, the dots on the gears won't be completely lined up. Well I guess the marks could still line up, they'd just do it lower. The only thing making this more complicated is that my bike has the Baja designs stator on it, so I have no way to pull off the side cover and just rotate the engine with a socket and use the mark to know when it's at TDC. I was just slowly rotating it by hand with the kickstarter and a straight piece of rubber in the spark plug hole to tell when the piston was at it's highest. I know that's not ideal, but I'm not sure what other way I'd be able to tell.

So to cut the down to a simple question, should the cam lobes be pointing exactly away from each other when the piston is at TDC or are they slightly offset from each other??

  • grayracer513

Posted July 31, 2011 - 06:59 AM


The lobe position should look about like this:

Posted Image

Regarding compression, I don't know how long you've had this bike, but in good health, a 426 is almost completely impossible to kick through a complete compression stroke. The correct starting technique calls for bringing the crank up against compression, then pulling the compression release and moving the kick starter down about one more inch. That moves the crank about 20-30 degrees farther up the bore, but still before TDC, from which point you will have less compression to overcome, but still enough to start the engine.



  • upthemaiden

Posted July 31, 2011 - 12:31 PM


Thanks! It looks like my intake cam is still 1 tooth off. Gonna go try to adjust it right now.

As far as the compression goes. I know it won't let me through a full kick if I don't use the decompression lever, but in this case I've been doing what he says in the video, and the lever will still only go about 90 degrees and them stops. I'll see how it does when I readjust everything. Thanks again!

  • dgcars

Posted July 31, 2011 - 01:02 PM


Hey Gray.....nice fence.

  • grayracer513

Posted July 31, 2011 - 01:28 PM


Hey Gray.....nice fence.

Not mine, not my bike. :smirk:

  • dgcars

Posted July 31, 2011 - 01:31 PM


Not mine, not my bike. :p

Yeah...Thought it looked too clean :smirk:

  • upthemaiden

Posted July 31, 2011 - 03:21 PM


Will you two focus?!

just kidding :p

So I pulled it back apart, and looked at it, and it looks like I actually had it set right. This how it was when I was having the problems listed above...

Posted Image

Posted Image

That little yellow thing sticking out of the piston hole is what I've been using to tell when it's at TDC. Not exactly scientific, but it's the best I can do with that baja designs cover on. It looks about right though, correct?

Just to be sure I moved it one tooth to see how it looked, and I think it definitely looked better the way I had it. This is how it was after I just moved it.

Posted Image

Posted Image

From what I gather, those marks on the camshaft should be exactly at the level of the edge of the motor, although everything I said just said to line it up with the motor so I didn't know if they meant right on the edge, or just line the dots up so they run parallel. Either way, I buttoned it back up to see if it felt any different and it didn't. Exact same problem. I push the kickstarter down slowly until the compression stops it, let it back up and move it a little bit with the decomp lever, back to the top, and try to kick it. It goes about 90 degrees then just stops as if the motor built up a bunch of compression that I can't get past. I know it's gonna build some compression again, but back when the bike was running right it would let me kick it down to the foot peg no problem. The bike didn't even sound like it was trying to start either.

I can still pull in the decomp lever and spin the motor freely so I don't think there's any issues with the valves hitting the piston or any of that, it's only when the motor has compression. I think my next step is to pull off the baja stator, reinstall the original engine case so I can be 100% sure that the motor is at TDC, and make sure everything is lined up from there. If I did have everything right I'll have to pull apart the top end just to see if I notice anything else going on. I thought for sure I had it last night when I realized the timing was off.

What am I missing?? :smirk:

  • grayracer513

Posted July 31, 2011 - 07:42 PM


In your first picture, the intake looks good, but the exhaust is one tooth retarded (needs to rotate forward/counterclockwise 1 tooth. In the 426 and the 450 engines, both the marks need to be aligned as you mentioned, but also, there should be 13 pins of the chain between the two marks at 12:00 on the sprockets. The exhaust cam is out of position.

Also, you need to remember that the front and top runs of chain are drawn tight in operation, and the slack is on the back side. To simulate this more closely, always rotate the engine backward about 15 degrees, rotate bot cams back against the chain, then turn the engine forward just to TDC. Then check the marks.

  • upthemaiden

Posted July 31, 2011 - 08:43 PM


Thanks! That 13 pin rule will help out a lot in the future. Can't believe I've been toying with the intake cam this whole time when it was the exhaust cam that was out of place. I knew my symptoms sounded more like an exhaust cam issue because of the compression, but I swore it was the intake that looked like it was out of place. I got stressed and had to give up for tonight, but I'm gonna go back at it as soon as I get home from work tomorrow.

  • upthemaiden

Posted August 01, 2011 - 02:32 PM


No such luck, still having the same issue. I'm gonna pull off the baja stator and put the original parts back in so I can just line it up and be 100% sure the engine is at top dead center and just line up the cams accordingly. I think I've got the motivation for one last shot and then I'm just gonna start tearing the whole top end apart. I feel like it has to be the exhaust cam though.

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  • upthemaiden

Posted August 01, 2011 - 04:57 PM


Alright, last time posting pictures, I swear. I pulled off the aftermarket stator and put on the old engine cover to make sure the piston was at exactly TDC. First, my bike doesn't look like it does in the service manual. Instead of a big "l" the same size as the hole, my bike just has some smaller marks right on the edge that looks like "H l", I assume I should just be lining that l up with the mark in the cover?

After I do that it looks like the intake cam is spot on, you can see the mark right at the corner of the engine:

Posted Image

The exhaust now looks like it's slightly under the top of the engine. How exact are these dots supposed to line up with the frame? it almost looks like it should be one tooth higher, but then I'd only have 12 pins between the marks, instead of 13.

Posted Image

I don't really think there's much more adjusting I can do. The timing has got to be right with what you've said. I guess I'll start pulling the top end apart. Can you think of anything in specific I should be looking for once I start to get it apart? Anything that misaligned would to a motor. I know the biggest concern would be if the piston hit a valve, so I'll check that out, but I don't remember there being any kind of issues like that.

  • dgcars

Posted August 02, 2011 - 12:18 AM


Well...If you set TDC on the 'I' just past the 'H', you should have been at TDC. As far as the cam timing goes, the inlet is spot on, but the exhaust does look like it is one tooth out. I guess there could be 2 reasons for this;

1. The cam chain is stretched
2. There has been a top end partial seizure and the gear has slipped on the cam.

If you are satisfied that the motor is healthy on the electrical side, it should run with either this or your earlier timing set-up.

On reading your initial post, specifically where you had 'messed' with the chain tensioner, after which the bike had stopped may have other issues now. I am not sure whether or not there would have been any piston/valve contact when the inlet was 2 teeth out....maybe Gray could enlighten you on that score.

  • grayracer513

Posted August 02, 2011 - 08:19 AM


Well...If you set TDC on the 'I' just past the 'H', you should have been at TDC. As far as the cam timing goes, the inlet is spot on, but the exhaust does look like it is one tooth out. I guess there could be 2 reasons for this;

1. The cam chain is stretched
2. There has been a top end partial seizure and the gear has slipped on the cam.

If you look at the exhaust, and imagine the mark being one tooth higher than it is, that would make it farther from right, not closer.

The chain could be worn, which would make it difficult to put the cam into an ideal position regardless which way you go with it, but a cam seizure has no effect on the position of the timing marks. That doesn't appear to be involved here in any case.

  • dgcars

Posted August 02, 2011 - 08:40 AM


If you look at the exhaust, and imagine the mark being one tooth higher than it is, that would make it farther from right, not closer.

The chain could be worn, which would make it difficult to put the cam into an ideal position regardless which way you go with it, but a cam seizure has no effect on the position of the timing marks. That doesn't appear to be involved here in any case.

I'm with you on that...Then the only feasible explanation for cam to be in that position, with the chain under tension, is a stretched chain. It does seem to be a long way out for it to be attributed solely to that. (???)

It should still have run though, all else being as it should. (???)

  • upthemaiden

Posted August 03, 2011 - 04:13 AM


The part that baffles me the most is the sudden change. I agree the cam chain might be stretched, but that doesn't explain why the bike ran perfectly fine a week ago, then went to running, but just poorly, and now the kickstarter won't even go through a whole stroke.

I guess first I should ask, since this is my first bike with a kickstart... When I start the bike, should the kickstarter go all the way down until it hits the stop on the footpeg, or should it stop itself before it hits the peg? When I got the bike, and when it was running well, if I kicked it well it would go down until it hit the peg.

Of anything that could be wrong with the bike, I need to figure out what it is that changed just in the past week. The timing chain stretching would be a long term issue and I must've screwed something up short term to be having issues I didn't have a week and a half ago. I wish I would've paid more attention to my previous adjustments so I could reset the cams exactly as they were to see if it would at least start and run poorly like it was when it was there just to give me an idea if it's something to do with how I adjusted the cams, and some kind of compression issue, or if it's worked it's way down to the bottom end of the engine somehow.

One other random thing to confuse me more. I hooked up the compression tester on Monday night, and when I started kicking it it would do the same 90 degree rotation it was, but after a few kicks it started going all the way down to the footpeg again. I thought I had won, buttoned the bike back up, tried kicking it again, and back to nothing again. Maybe it worked because I could only get the compression gauge screwed in hand tight and it was letting air pass through the threads and compression wasn't as high as with the plug in it? I was just checking to get an idea though, I know you're supposed to hold the throttle open when you check compression, but I've never had a bike with an accelerator pump, and I didn't want to squirt a bunch of gas in the cylinder. Is it ok if I'm kicking it over because it'll just blow the gas out of the exhaust, or do I just need to completely remove the carb to test the compression?

  • dgcars

Posted August 03, 2011 - 08:14 AM


Are you sure your problem is not electrical. If not, how have you confirmed this? Pull the spark plug and see if the motor will kick thru' its stroke.
Back to cam timing....the bike, if all else is as it should be, will start.
Without appearing the pessimist....after you were messing with the cam chain tensioner...did the bike run. Was it after this it wouldn't kick thru' its stroke.
There is too much going on here.....rewind.

  • upthemaiden

Posted August 03, 2011 - 09:23 AM


I have no way to confirm it's not electrical, but with my limited knowledge in electrical, I can't picture any reason that any kind of electrical problem would interfere with the kickstarters ability to go a full rotation.

The 2 things left that I can think of is that for some reason there's too much compression keeping it from going through a full stroke, or there's something machanical inside the engine not letting the gears spin. I can spin the kickstart all day long if I pull in the kickstart lever though, which makes me feel like it's not an internal gear/transmission thing. It gives me the same result as if I would just try to kick over the motor without using the decompression lever how you're supposed to. If you just hop on the bike and try to kick the lever it'll go so far and just stop because you don't have enough momentum to get past the compression. In this situation though I push it until it stops, pull in the lever, push it the extra 2 inches, let it back up, same as I did before, but now when I kick it it stops. There's no metal noise and thud like you'd get if gears are locking up, it just feels like it but compression again.

As far as the rewind...

1) After I initially toyed with the timing belt tensioner, the bike was hesitant to start, but it still did. It would kick through a whole stroke, it just wouldn't fire up right. Despite being hard to start it would run. Idle wasn't as smooth/strong as it was and the bike felt like it was missing about 5-10hp, but it still ran.
2) Eventually I swapped the spark plug and cleaned the jets, it seemed to start easier, 1st or 2nd kick, but it still ran kinda weak.
3)It wasn't until I started trying to adjust the timing that it stopped starting all together. As far as removing the spark plug, it'll spin perfectly normal when I pull the plug out, and the same if I pull in the decomp lever, it's only a problem when it has compression.

  • dgcars

Posted August 03, 2011 - 11:18 AM


As far as my asking about the problem being electrical....I was relating this to the non-starting issue, not the motors inability to be kicked thru' its stroke.
Determine if you have a strong spark.....put a good plug into the cap, ground it against the cylinder and turn the engine over.
For the motor to run, you need a source of ignition (spark), fuel and air.
So....start at the beginning

  • banda

Posted August 03, 2011 - 11:20 AM


Maybe I'm misunderstanding something - But on a 2001 YZ426 with a stock exhaust cam, you _shouldn't_ be able to kick it all the way through the compression stroke without using the compression release. You'd have to have a monster leg to do that. I am suspicious of an unmodified 426 that allows yo to kick all the way through.

  • dgcars

Posted August 03, 2011 - 11:28 AM


That was pretty much explained to the OP in post 2 by Gray.

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