03' yz450 timing....no crankcase cover

Just want to say how awesome I think this forum is.  I just joined up, but have lurked for a while since picking up a 03' yz450f.  Looking for a little advise, hopefully someone can chime in.


I just picked this bike up, and have honestly, very little info on its history.  I'm pretty sure however that the cam chain is in need of replacing.  It seems to be quite noisy when running, but I have very little to compare the noise level to.  I have several issues with that though.  


1. I come from sportbikes, just getting back into dirt after years away, and every sportbike I've torn down in the past, the cam chains are pretty much taught, there is no slack to speak of with a proper tensioner in place, and tolerances are usually pretty tight.  I'm assuming this is correct for this machine as well? 


2. I bought this bike as a SM with a baja designs kit, also all the dirt goodies.  My main problem with the kit so far is that the left crankcase cover is replaced with the baja designs stator and cover and does not allow for you to use the crankcase window to line up the timing marks per the service manual.  I have put the bike to what I believe is TDC via a rod in the plug vacancy, and the cams seem to be in correct time, but I'm not sure that this is sufficient to measure TDC.....I really wish I had the crank/flywheel marks available. Opinions?


3.With what I believe to be TDC, there is quite a bit of play in the cam chain between the cams.  I can easily grab it and move it up and down for a full range of about 1/8" to 1/4".  I believe this to be out of spec, but could not find a source that gives any hard number for measurement. 


4. I also have been unable to find a proper way to test the tensioner.  At this point, I'm assuming replacing the chain is a cheap and realistic thing to do, and then the tensioner if there still seems to be slack post new chain installation. 


If anyone has any advise, or could give me a little confidence that I'm at least on the right track here, it'd be greatly appreciated. I just don't want to go around replacing parts just because. 





There should be no play in the cam chain you can pull the bolt from the back of the tensioner and with a small screwdriver increase the tension on the chain. If the slack won't adjust it is worn out, the Yamaha tensioner is pretty good and if there is play just plan to replace the chain. As for TDC just use a thin probe of some sort in the spark plug hole and find TDC that way and check the marks.

There is no 180 out situation

There is a torsion spring located inside the tensioner. If you pull the bolt out of the rear center of it then like previously mentioned put a small flat screwdriver in it you should be able to turn it clockwise (I think that's right) and feel the spring wind up. If you turn the screwdriver loose it should freely unwind and automatically take up the tension in the chain - it's not a manual setup. If it's sticky or the spring is broken you'll need a new one. The chain should be fairly snug - similar to the sportbikes you're familar with. Definately replace the chain as they're cheap. I'm betting if you pull the outer cover off of the stator side you'll have timing marks to use. I'm not sure but that's my guess. As for the noise, it should be pretty quiet in the top end but they do make sort of a grumbling sound in the bottom ends. Not really loud, but not dead quiet either. Clay

Thanks for the quick replies. I'll be getting that cam chain on order.  Hopefully all will be well after that.


 I dont' think I'll be running it again until then....


Will post results. Thanks again.

The cam chain tensioner will not remove the slack shown from the chain.  It's not supposed to.  The engine pulls the front vertical run of chain tight up to the exhaust cam, and that then pulls out the slack on top between the cams.  At that point, all the slack is on the back run, and the tensioner removes it then.


Find TDC by probing for the piston through the spark plug hole, then back the engine up 5 or 10 degrees.  Roll the cams back to remove the slack on the front and top runs and then roll the engine back to TDC slowly to check the cam alignment.  Then set the tensioner, roll the engine through twice to the compression stroke and recheck the timing.


The only way of testing the tensioner is to be sure that it will advance freely when the plunger is released, and that it cannot be pushed back in from any point in its travel without turning the drive screw.


Yes, this is almost exactly what I did. I set the motor to tdc, reset the tensioner, and all slack seemed to be taken up. The chain was tight. I thought all was well after that. I did not however roll back the 5 to 10 degrees. However, after running the motor for 5 minutes after doing this, I pulled everything back off and checked the chain again only to find that it is loose again between the cams when at tdc, it has tension in other spots other than tdc.

So my assumption is that because the tension was taken up by the tensioner, I believe it is functional.

Because the chain lost tension after running the bike, it seems it would need replacing. I have new chain on order.

Is my thought process correct here?

Thanks to everyone for taking the time to respond.

I would be suspicious of your cam chain.  Any sign of stiff, binding links?  If so, discard and replace it.

I haven't taken a really close look at the chain itself. I would think it would be easiest to see kinks once it's off no?

Of course. And it's not such a big job to get the chain off, either. 


The reason stiffs chains have to be avoided is that the chain tensioner is not intended to put any real tension on the chain.  It just takes up any real slack that it sees on the back side run.  The tension is all produced just by the operating load the chain is placed under, and the tensioner keeps it from getting any looser than that when the load drops off.


Now, if the chain starts getting stiff, it will tend to stay kinked as it rolls off the crank sprocket, and the tensioner doesn't have the strength to push those kinks out. As the chain wears, the kinks get bigger, holding the tensioner plunger back progressively farther than it should be.  Then one day something happens to suddenly reverse the drive load on the cam chain.  Maybe it kicks back when starting, or bounces off compression, or whatever else, but when the engine is turned backward, the drive load is shifted to all of that built-up kinkiness in the chain on the tensioner side, and when all the kinks are yanked out straight, there is suddenly a big wad of slack on the forward side, and the exhaust cam slips as soon as the lobes hit the buckets.

Thanks for the explanation. It's always easier to understand the systems once explained and few people are willing to take the time out to do so. I'll be pulling the chain off, hopefully next week when the new one comes in. My hopes are that it's all kinked up, and my problem is explained.


Ok, I have an update, and unfortunately, not good, but I'm hoping everything isn't too far gone.


I received the new cam chain today.....took forever to get from ProCaliber...never ordered from there, but be aware that if you do, expect a long (10-14 buisness days) for standard shipping. Parts are cheap though.


The old chain came off quite easily, and compared to the new, definitely had some stretch to it, but nothing that I would consider extreme.  I did not see any kinks.


However, this is what I found when I pulled the intake cam, see pics...


Now, this bike was bought used in full SM trim.  The owner (in Missouri) bought it from his brother who lives in Colorado, I'm in Missouri, and knew very little (or at least acted) about the bike itself.  The carb was all gummed up as it had set for about a year.  After cleaning the carb out I had the bike running in the neighborhood, and it pulled hard, but I did not get a chance to do any hard runs or prolonged runs. But to me it ran strong.  It was when I pulled the valve cover to inspect the valves that I noticed the slack in the chain and decided to replace it as I did not know the maintenance history on the bike.


 All valves were within spec with the exception of the 3rd intake which is where the damage is on the cam, it measured 0.18.  My service manual says 0.15 is the upper limit.  I'm thinking this damage is most likely from a previous incident, and not related to the current valve clearances. 


I'm wondering if it would be possible to clean this cam up, or if I should just source another cam, or not worry about it at all and see how it goes? I'm not sure how long I plan to keep this bike.  I bought it because I thought I got a good deal, and it came with a ton of extra stuff, including all the dirt parts, which is really what I was looking for when I bought it...a dual sport bike.  I now realize that there are many other options that would better suit the style of riding I'm hoping to do.


Thanks again for all the help.






Oh boy, that looks like a hot mess man. Must've been oil starved. If it was mine if keep going and take the head off and have a look at the cylinder. You are gonna need a new cam of say, but I doubt any cam is gonna live long with those journals in that condition.

Oh boy, that looks like a hot mess man. Must've been oil starved. If it was mine if keep going and take the head off and have a look at the cylinder. You are gonna need a new cam of say, but I doubt any cam is gonna live long with those journals in that condition.


Yeah, I know it doesnt look too good. Not sure I quite follow your post though.  I'm trying to figure out if trying to clean it up at all will help or not.  I'm afraid it may be too far gone and that by removing material, the tolerances will be far too off and may cause even more damage.  I'm assuming the best bet would be to find a good retainer and cam and possibly try to clean up the surface of journal in the head.  This is all just kind of disappointing as like I said before, the bike ran great.

I doubt that there's any repairing that cam it's too damaged. I'd be more worried about the gouges in the journals in the head. I'm not too sure those can be fixed without throwing off the clearances. Maybe somebody else will chime in with some advice.

The head is repairable.  Send it to EDCo in California.  Probably around $300.  The cam is complete junk. 

Thanks for the help guys, not sure what I'm going to do with it at this point. No fun.

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