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Discussion Starter · #1 ·
I'm looking to gather some information regarding a timing problem that I've been chasing for the last 6 months on my z400 which is otherwise a great quad.


To make this short and quick, this atv will jump time after about 3 or 4 hours of hard riding. Both the intake and exhaust side seem to be out every time. I bring it into the garage, set the timing, everything is fine for another 3 or 4 hours and the same thing happens again.


Into a little more detail::


I bought the quad non running. Put a new DID timing chain in along with new rings, adjusted valves, timed it and everything was fine for about 4 hours. This happened only once before I bought a Namura big bore kit, fresh intake valves, and a manual timing chain adjuster. All of that was installed and valves adjusted. Same result after about 3 or 4 hours of riding. This time I inspected all bolt torques, checked the flywheel key, valves were within spec, set the timing and called it good. Same result. Runs fine for about 3 hours and then begins to run worse an worse until it will not start (by this time I am able to get it back home as soon as I notice it start to act up)


With all of that being said, when it does jump time it is always about 2 teeth off. The exhaust and intake cams are both off, not just one which would point to the flywheel key being broken (in my opinion). I have checked it and it is installed correctly and not broken. Another point to note is it does not appear to jump all at once. When riding it I can notice a loss of power, it then starts to run lean (at least what I think is lean). After this it will only start and run without sputtering with the choke on, and then it will finally die and not start at all. Bring it home, adjust the timing and it will fire right up.


I am following the service manual procedure for setting timing, adjusting valve specs, etc... As far as the manual Cam Chain Tensioner that is being adjusted per the instructions that came with it. About 1/4 turn after all chain noise is gone.


I welcome all suggestions and information that may be useful.
 

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There's one you don't see every day.
With it happening using both the stocker and manual tensioner, I'd have to look at a worn chain guide, the gear on the crank jumping teeth, or cam gears spun on the cams.
 

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Discussion Starter · #3 ·
I guess I should have mentioned that I replaced the exhaust cam due to an accidental drop onto the concrete floor. This did not help anything. Still had the same result, out of time after 3 hours. I would assume the cams are okay due to this.


Also, I did a pretty thorough inspection of the lower timing gear, chain guides, and the key that sits on the crank under the gear. Everything looks good.


Maybe one of the guides is slightly bent? There does not appear to be any amount of serious wear.


What would cause the lower gear to jump teeth? It does not look to be worn and the nut is torqued to spec.


Also, I have not checked anything under the stator cover. Could the stator bolt or woodruff key have anything to do with this problem? I wouldn't thin so...
 

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I set my manual tensioner with the valve cover off, so I can check the chain up top with the guide off between the cam caps. Maybe you are setting it too loose without knowing it?

I also had the lower bolt shear off for the rear cam chain guide once. I got real lucky and didn't trash anything else, but the timing did jump on me when it happened.
 

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Discussion Starter · #5 ·
Ill have to tear the clutch cover and take another look. As far as setting the tensioner I usually do it with the valve cover off. I think 1/4 inch of play is what the box for the cam chain adjuster says. I may have it a little bit tighter than that but not too much. I would say the chain tension is comparable to the chain t
ension on my 12 and 02 yzfs.
 

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Now that I read this again, are you setting the timing so it is correct AFTER the tensioner is adjusted? Putting everything in place with the chain loose, closing up the valve cover, and then installing the tensioner would describe your symptom.
To explain it another way,
1) Pull the slack out of the chain at the front of the motor.
2) set exhaust cam where it should be.
3) pull rearward on chain and set intake cam
4) install tensioner and ensure nothing has moved, including timing T on crank.

Or maybe the metal guide that goes between the cams is missing/bent?

Just wanted to be sure you aren't doing a step wrong and causing it.
 

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Discussion Starter · #7 ·
Correct. I am setting everything with tension on the chain. What I have done once or twice is after everything has been tightened is to start the motor and back the tension off until I hear the chain barely start to slap and then tighten a quarter turn like the instructions for the manual cct say. This made no difference the two times that I have tried doing this.

Another thing to note is my timing arrows on the cam gears do not perfectly line up with the top of the head. They are pretty close but always off just a little. I can get them to line up perfectly with the t centered in the timing window but not with the line next to the t. It seems like when it pops out of time the t is always lined up in the window, not the line. With the timing in this state it will start and run but only with the choke on. Also compression is down to about 50 psi. Readjust by one tooth to center the line but not have the arrows perfectly level and it starts and runs fine with compression up over 100.
 

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You should set the cam chain with tension via the manual specs of play. no need to mess with it after that. You should have no way of a cam chain jumping teeth if your doing this correctly.
Are you sure your setting your cams up correctly in the first place? And if a cam jumps teeth your gonna have a bad day really fast.

You also want the line next to the t to be in the middle of the window.

Also did you try replacing the chain instead of messing with a chain that has jumped teeth a bunch?
 
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Discussion Starter · #9 ·
I replaced the cam chain when I first got this quad. I would say probably about 12 or 15 hours ago. I can not seem to get the arrows on the sprocket to line up perfectly with the cylinder cover mounting surface when the t line is centered in the inspection hole. Ive tried several times. Someone mentioned spun camshaft sprockets. How exactly would this happen?
 

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Usually from piston-to-valve contact at some point.
 

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Discussion Starter · #11 ·
Okay that makes sense. At some point in its life there looks to have been a problem. When i bought it there was evidence of piston to valve contact (ding in the piston top and 2 New exhaust valves) the piston, timing chain, and exhaust camshaft have all been replaced since then. I replaced the cam with a used stock cam my buddy had sitting around so who knows the history of it. Could this have affected the intake cam as well? Maybe this is my next step...
 

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Seems unlikely that both have spun, but possible, I guess.
 

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open your valve cover, set your timing and chain tension correctly then turn the crank several time. Look if it jump teeth or if you have a problem with a bad ''crank to cams ratio''(«---probably not that one but it's a possibility) or what ever you will find!!

Be sure nothing can affect the ''free rotation'' of the engine like a worn chain guide that block the chain, worn cam bearings, sticking valves...
 

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Following this thread, I want to see the outcome. I say bad chain, cams not sitting correctly, or guides on backwards :wink2:
 

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Discussion Starter · #15 ·
Okay so ive got an update. I tore into the motor on this thing once again. The cams spin freely, no wear on the cam caps, everything seems to fit and spin nicely. Valves depress and return when pushed down. I replaced my good exhaust cam with another that I have here and have the same result. Can not get the timing marks to line up. I tore the clutch cover off to inspect the guides again to make sure I didn't overlook anything. Everything is in place. Lower gear isn't worn or missing any teeth and the key is intact.

I wanna say the chain is not stretched because it was just replaced about 10 hours ago and only takes about 1/4 of the adjustment on my manual cam chain adjuster. What about the guides. Could I possibly have bent one out of shape? Thats my best guess.
 

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Did you verify the DID chain was the one for your bike, maybe count links recheck part #? I don't know sounds like possibility wrong chain?
 

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Maybe it's the flywheel. If you'r key is sheared or something that would be throing off TDC. Might be totally wrong but my limited skills in mechanics are no secret..
 

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Maybe it's the flywheel. If you'r key is sheared or something that would be throing off TDC. Might be totally wrong but my limited skills in mechanics are no secret..
No way if the keyway sheared it wouldn't run right. Happened to me.:grin2: On startup the flywheel wouldn't spin to send the electric to the spark plug.
 

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Discussion Starter · #19 ·
Okay guys I tore the clutch cover off to take another look at the lower gear and I think I found the problem. It looks like the key that sits inside the lower timing gear may be the issue. I noticed either end has about 1mm worn off about half way through on the edge. Also the slot for the key to fit on in the gear is about 45 degrees off from the keyway on the crank. It looks like I didn't have the key all the way in causing the lower gear to spin. Can someone confirm that the key needs to hold the lower timing gear as well as the gear that slides over top? Also how would i go about getting the lower gear back to where it needs to go? I would just tap it with a screwdriver and a hammer but maybe theres a better way. Ill get some photos if I can.
 
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