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FLFX4

08 yz 450 timing...

55 posts in this topic

For some reason the timing on my cams is off. I just replaced everything on my top end, piston, rings, valves, cylinder head...you get the picture. The bike now has about 3 hours since the rebuild incluiding an hour and a half hare scrambles. The bike was running a little sluggish today then refused to start. I pulled the cam cover off and the lobes on the cams did not line up when the piston was at top dead center, which ment the dimples weren't where they are supposed to line up on the head. What would be causing this? I could really use some insight on how to fix this issue. I'm almost completely over 4 strokes!!! HELP!!! thanks!:thumbsup:

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Did you replace the timing chain when you rebuilt it? These cam chains stretch fairly quick. Replace it if you didn't already. Also, use the punch marks on the cams to check timing not by eyeballing the lobes.

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I replaced everything, aligned everything per the manual and after popping the cap off the punch marks weren't at all close to where they should be when the piston is at TDC...I'm at a loss...thanks for the reply

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Check that your camchain tensioner is working properly. Then you need to pull the cams, flywheel, etc. and re-time so that you're timing is correct. Your risking alot of damage running it with improper timing.

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It was working properly when I put it back together. I will double check it again though. Any idea what is causing the timing to slip? Possibly something in the bottom end since the top end is completely fresh?

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Well the only thing i can think of is that the tensioner isn't workining properly or it was installed improperly. If the motor was run with a severely worn out timing chain then possibly the gear on the crank could be worn out or the camshaft gears could be worn out too. But i think that would be highly unlikely on an 08.

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I guess you can say this bike is kind of a rescue. The guy I bought it from is a great rider but not so much of a great mechanic. I did replace the intake cam with one from hot cams and the exhaust cam looked to be in good shape. The timing chain was stretched out but not too bad. They cylinder head was cracked in several places on the inside which caused a serious oil burnage. After replacing all the innards and outers it ran great until today. I'm going to check out the gear on the crank because it did seem to have less compression today. Thank you so much for your help! Its truly appreciated!

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Ok well the cam chain tensioner seems to be ok, but I'm going to replace it just to be safe. Once I got the tensioner off, the cam chain didn't gain any slack and was VERY tight. Is this just because its new? Also, I was about to break the flywheel nut loose to correct the timing marks on the cams when I realized there is about a 1/4" of play which seems to be causing the chain to be uneven on the cams...is the play normal and if not could that be causing my timing issues?

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Start over:

  • The chain is tight with the tensioner off
  • There is a quarter inch of play

How do I make these two dots connect?

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I can grab the flywheel and move it back and forth about a quarter of an inch left to right which makes the cam chain fit correctly on one cam and then off on the other. As far as the cam chain goes, there is almost no slack at all with the tensioner off...does that make more sense? I apologize, I'm not the best at explaining myself.

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I can grab the flywheel and move it back and forth about a quarter of an inch left to right which makes the cam chain fit correctly on one cam and then off on the other.

Is that with the tensioner off?

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Whenever you set the cam timing on any engine that uses a tensioner, you have to allow for the slack present in the chain when no tensioner is installed. To check the timing correctly with the tensioner out, you have to be sure that the front side downward run of chain is drawn snug and slack free between the crank and exhaust cam, and the top run of chain is drawn tight between the two cams, so that all of the slack is on the back side.

I normally suggest that that you turn the crank backward (clockwise) from TDC about 10 degrees, then turn both cams back a little until the front and top chain runs are tight, then turn the crank forward back to TDC again to check the timing marks. This simulates reasonably well the condition the cams will be in when they are running.

You may have positioned the cams when the slack was on the wrong side of one cam or other and had them out of time to begin with.

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I set the cams per the manual lining the dots up on the indicated area but must've not made up for the slack in the cam chain. But being that there is not much slack in the cam chain, do i need to remove it in order to set the dots to their correct position?

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The only way I know of to reposition one of the cams is to unbolt the cam cap and lift it out of place. If they had asked me to, I would have done it differently.

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I'm over cams and valves! Once this thing is fixed its back to a two smoke! Thank you for all your help, its truly appreciated! This is the first time I've ever had to work on a four stroke, I've been fortunate in the past to only use a bike for a season and then sell it while it was still fresh..this has been a truly wallet opening and humbling experience! ha!

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I set the cams per the manual lining the dots up on the indicated area but must've not made up for the slack in the cam chain. But being that there is not much slack in the cam chain, do i need to remove it in order to set the dots to their correct position?

When I redid mine there was enough (barely enough) slack to turn the cam's (I'm running a full hot cam setup), one tooth at a time with out removing the chain you have to pull all the slack up to the cam's and then hold the chain up and carefully turn (by hand) the cam. go one tooth then position the slack on the back side of the motor (where the tensioner is then check your dots keep doing this until the timing it on spot then put the tensioner in (after you have ran it through the manuals checks to see if it is good, my manual gave a procedure) and turn the engine over by hand and a full rotation each way. Then go back to TDC and check your timing if the dots are still lined up you should be ready to roost if they aren't adjust again and then check again.

FYI if you have a small enough screw driver you can turn the tensioner all the way out and lock it there so you don't have to remove the housing every-time.

If you do this several time's and you are still having problems check to make sure that your seating the chain onto the gears on the crank properly. if somehow you get the chain on top of the gears when you time it when you go to turn the engine over it will slip down on the gear and the tensioner will take out the slack and the timing will be off.

The top end isn't that complicated don't get frustrated just take your time and follow the manual's instructions to a tee (I think that mine mentioned taking the slack from on front of the engine) You can't go wrong if you follow the manual's timing procedure.

Good luck and don't feel bad for asking questions gray will send you a bill later :thumbsup: I'm sure that my bill is pilling up!!

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Hopefully the bill won't be too big! I'm going to try that strategy before I take the cams off completely, it should be manageable. I figured out the tensioner real trick really quick, but I took it off anyways. I'm pretty busy between school and work this week, but I'll post an update as soon as I find a few minutes to work on it. My next race is May 15th so hopefully I can have it done before then!

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... turn the engine over by hand and a full rotation each way.
I want to make the point here that you should NEVER turn the engine over withe the tensioner backed off or removed. The chain WILL skip time unless you are very lucky.

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I agree with both greyracer and sledtrash, take your time, ensure that the timing chain is correctly mounted over the cranksprocket. Another method - when your ready to check everything, ensure the motor is on TDC, slide a plastic (or similar) rod into the tensioner hole - taking up the tension. This will allow you to see if everything is lining up without fiddling with the tensioner. Also check that the chain guides have not come out of there locaters.

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