Issues with yz426 cam timing w/AD cam

Hey guys, I posted another topic about my bike having issues starting, anyways it has lead me to taking off the valve cover and checking valve clearances and timing chain...


I've got my piston at TDC on the compression stroke (both cam lobes are facing away from each other and I've got a punch in the cylinder which when I rotate the engine confirms the piston is at TDC) and the two notches on the timing hole are perfectly aligned with the "I" on the rotor.


So i measured my valve clearances and all three of my intake valves have between .16-.17mm gap and my two exhaust valves have between .26-.27mm gap.


The manual calls for .10-.15mm gap for the intake and .20-.25mm gap for exhaust. This would indicate that my valves are loose than. Ok so I will order some shims.


Then I get to looking at how my cams marks are aligned with the cyclinder head surface and they are off. My bike has the auto decompression cam and I believe that changes how the exhaust cam marks line up from the stock exhaust cam right? My question is: do my cams look like they are lined up properly? my Intake cam marks should at least line up with the cylinder head cover when the timing hole marks are aligned with the "I" on the rotor right? because mine doesn't.


Hopefully these pictures help with what I'm trying to describe.



photo 1.JPG

photo 2.JPG

photo 3.JPG

photo 4.JPG

photo 5.JPG

Let's start by clarifying which exhaust cam you have.  Was it a cam originally made for a YZ450, or a cam made by an aftermarket company specifically for a YZ426?

Edit: it appears to be an oem yz450 cam

Edited by fdme

I does look that way.  And because of that, the timing looks correct, except for the fact that the chain appears to be stretched.  That's why the intake isn't lining up better.  If you imagine what it would look like if the mark was moved one tooth either way, it would be farther off than it is, so it is actually set where it belongs, but the chain running from the front of the crank up to the intake cam is too long to bring the timing mark as far forward as it should be.  Replace it.


As to the exhaust cam, being made for a 450, which has different head geometry, the timing marks on the cam can't be used in the conventional way.  This cam has top be timed relative to a properly timed intake cam.  The intake is correctly timed, and then the exhaust cam is set so that there are 14 pins between the two 12:00 o'clock timing marks, just as you have it now.  That is only true if it's a 450 cam.  Cams built for the 426 with AD will have correct for the 426 marks on them, and be timed in the normal manner.

Thank you so much, that explains it very clearly now. Time to order a timing chain and the valve shims. I'm hoping that since my chain is stretched and threw my timing off a bit, that was causing the hard starting condition.


One last question: Will I be able to get a accurate valve clearance reading with the stretched timing chain on there now? I'm thinking maybe it would be best to get the new chain on and get it all timed right and back together, then do a valve lashing, take measurements and adjust shims accodingly?


As it is now I suppose I could move my intake cam so that it is matched up to the cylinder head and record those measurements... but then my exhaust cam would be advanced ever so slightly because of the stretched chain right?

Timing has no effect on clearance between the cam and lifters at all.

Out of curiosity, wouldn't the valve clearance become less and less (tighter) over time? Because mine are actually so loose they are actually out of spec if my feeler gauge(s) are to be believed.

What would cause them to be so loose?

Edited by fdme

Normally, they do get looser, however, certain out of the ordinary conditions can cause the opposite effect.  Breakage or mushrooming at the top of the valve stem, wear in the cam bores, valves bent, or excess carbon on the stem can cause looser readings.  Then, too, so can being put together wrong by the last guy to adjust them.

Then, too, so can being put together wrong by the last guy to adjust them.

This sentence has haunted me throughout owning this bike :)

Although it has still been incredibly reliable, pretty much all the problems it has had were caused by the PO's.

Alright so I've got my valvetrain issues sorted out now... 1/8" of carbon on all the intake valves and probably 1/16" on the head and pistonI am on to the next thing...


Apparently my clutch is not a 2000 yz426 clutch, I ordered a replacement for the years 2000-01 but the kits plates where slightly larger diameter than would fit into my existing basket. Does this mean I have an earlier model wr or yz clutch in there now like a 400 clutch instead of a 426? was the 400 clutch basket a slightly smaller diameter I guess is what I am asking before I waste time ordering more parts that dont fit.


The nightmares of owning a bike piece milled together by the previous owner.

Yes, the 400 clutch is smaller.  The gearbox is also lighter. 

Thank you, that answers my question... I'm curious so the 400 clutch bolts up to the 426 with no issues?? My title says the bike is a 426 but I guess the engine or its various pieces could have been swapped for a 400 at some point.

ImageUploadedByThumper Talk1411878343.980566.jpg

Is it possible to identify whether I have a 426 or 400 by these markings on the head? I've read several conflicting things from various websites what the markings mean... Part numbers I'm finding for the head for any year seem to always go 5B11... Mine is close but is 5B10? I'm trying to determine if I have a 426 or not and what piston rings I need to order.


EDIT: just looked at the head and it's says 399 cc cubed, I guess that solves it right? A 400?

Also my case stamp starts with a H309E which from what I can gather is the wr400 case

Edited by fdme

"5BE" is generally associated with things first issued or created for the 400. The 399cc casting on the cylinder is absolutely a 400 part.

Alright so I finally got around to getting this thing back together and the engine seems to run well so far...

Only my problem now is my clutch... heres the story: Before I rebuilt the top end, the clutch was dragging/sticking pretty bad (this was the oem stock clutch). So I pulled it apart and inspected everything, all the fibers on the stack still look healthy compared to the pictures I've seen? Nothing looks excessively worn and there isn't any real knotching on the basket, you can see marks where the stack was but if you feel, you can hardly discern a difference.

I figured I would try to replace it with a cheap clutch pack to see if that would fix my problem and if it didn't I wouldn't be out too much money and I could continue troubleshooting. (I would've just replaced with OEM right there if the plates or assembly looked like it was actually worn.) But since I had doubts that this was actually the problem I went ahead and ordered a Tusk stack. So I received the tusk stack and promptly dipped all the plates individually in oil and rubbed it around on them until they each seemed saturated. (I'm thinking maybe I should have let them soak?) I installed them the same way my OEM stack was installed (with the slightly thinner plate on the most inside of the basket.

I checked the pushrod and it seemed ok and like I wasn't missing any pieces of the assembly according to the parts diagram.

I did notice however that you could pull on the basket and you could pull it away from the engine maybe a few millimeters and also push it back the same amount, I wonder if this play is a bad sign??? I torqued the spring bolts to spec (I installed the tusk clutch springs which feel like the same stiffness as oem). I pulled the clutch lever before I put the cover on and I notice that the stack doesnt really move that much even when the clutch lever is all the way in and I even set the cable excessively tight to see if it would make a difference, not really.

So I return the cable to proper settings and put the cover back on, I start the bike and let it warm up at idle for a few minutes. I hop on and shift to first whilst having the clutch pulled and and bam I peel out of my garage and down the driveway I go. Basiclaly I shifted into first as if I didn't have the clutch pulled at all. I tried driving it around and reving it with the clutch in but it wouldn't ever let go like the plates are stuck together. Also the clutch pull feels really weird, I don't remember what exaclty it felt like before since its been so long but there is literally no feel at all to it like I am pulling in the brakes on a bicycle or something. It feels especially weird when comparing it to the feel of my wifes quad and my friends bike which both also have cable clutches.

Any suggestions on what I should do next? Is it possible that the plates could be THAT stuck to each other? Could laying it on its right side for a while help anything?

EDIT: I have since laid the bike on its clutch side to let the plates soak for about an hour, drove it, still did the same thing.

After that I swapped back in my old clutch, still does the same thing. I also compared the height of the stacks, they are almost exactly the same, you cant discern a difference with the eye, only with calipers.

I feel like maybe I am somehow assembling it wrong?? Just to make sure, the ONE plate that is slightly smaller than the others goes into the basket FIRST right? Well shit, the parts diagram actually shows the smaller single plate on the outside, shit, guess I got the stack in backwards.

I might sleep on it and see if I can think of anything if flipping the stack doesnt work.

EDIT 2: well my dumb ass put the stack in backwards >.> <.<

So yeah now it works!

Edited by fdme

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