Tapping sound after valve adjustment/cam swap. Damage from turning engine backwards ?

I have a 2012 WR450F.  I'm posting here because its the same basic engine as the pre 2010 YZ450Fs and I'm betting YZ guys adjust their valves more often than YZ guys.


I have about 70 hours on my bike.  It wasn't starting really well like it used to, so I pulled the valve cover and checked the clearances.   All the valves were uniformly tight.  By tight I mean they were right at the lower end of clearance range.  Exhausts were no go on 9 thou, tight on 8 thou, spec is 8 to 12 iirc, etc.


So I pulled the cams, pulled the valve buckets, noted the shim sizes, got new shims, replaced the buckets in the original positions, etc.  Lubed everything as I went.   I installed 08 YZ cams (or so the seller told me) when I put it back together.  Double checked the clearances, etc.  Used a proper torque wrench, etc.  Double checked the timing, etc.  The whole job went well.


It started on the second kick.  I accidentally left the exhaust plug in the muffler, so it quit after a few seconds.  However, when it was running it made a strong tapping sound like when you hold the kick starter down on a running engine, only much louder.


I pulled off the valve cover and double checked the timing.  It looks perfect.   I rechecked all the valve clearances.  They look good too.   I turned the engine over 2 turns and watched everything.   The timing chain looks perfect and its tight.


The only thing I noticed is that the engine seems to bind when the intake cam pushes the intake valve buckets to their fullest depth.


I did an Internet search and found this post:



Unfortunately, it has a bit of an ambiguous ending.   Apparently the OP bent or broke something in the valve train because he turned the engine backwards while working on it ? 


I may have turned my engine backwards a bit, maybe 10 or 20 degrees while finding the timing mark on the flywheel after it slipped a bit when I was installing the cams.  I never felt any binding when I did and it never turned hard.  The timing chain was never tight on either side.


Any ideas on what is wrong (if anything) with my engine ?

Edited by MidlifeCrisisGuy

The OP in that post must have been referring to this diagram for his bike.

cam drive system.jpg


The cam chain is #4.   His part #9 must be one of the guides, # 11 or 12 in this diagram ?


All this stuff is outboard of the main cases.  It sits behind the flywheel.  Why would they have to do an engine tear down except if it was for debris ????


Time to pull the side cover and check what is going on behind my flywheel ?



Turning the engine backward 20 deg at TDCF to find the timing mark isn't going to hurt anything.  If you are 100% certain the timing is correct, lash is within spec, and you feel no interference when turning the engine over by hand, my guess would be normal increased valvetrain noise from more aggressive ramp rates, lift, and so on.


Piston-valve interference would be happening near the beginning of the lift and not near peak lift if the timing is correct.  The binding you are feeling is likely just the force required to compress the valve springs and you should feel the engine spin away as the valve springs put their energy back into the timing chain on the other side of peak lift.


Other than triple checking everything all the way down to the seating of the shims, I would suggest reinstalling the WR cam to see if the problem persists.

Thank you for your reply, mbirt.


I played around with it some more.  I'm pretty certain that there is mechanical binding as the intake valve reaches maximum lift, just before the nose of the cam. 


From the shop manual for a 2009 YZ450F, I calculated the lift on the new cam to be 8.75mm.  The lift on the stock cam in this engine is 7.7mm.   Is there a chance that the bucket travel isn't sufficient or that the valve springs are binding ?


I agree on putting the stock intake cam back in.   Should I put in the stock exhaust as well ?  It would be better to just do the intake so that it isolates the problem to just it.  Any issue running a stock WR intake cam with an 08 YZ exhaust cam ?


I'll post a picture of the timing shortly.

Edited by MidlifeCrisisGuy

Can the timing chain and/or chain guides be replaced without pulling the cylinder ?    Can they be replaced without splitting the cases ?   Not saying its going to come to that or its the problem, just curious.



Here is the valve timing with the flywheel in the middle of the H pattern.




I had to take the picture at this angle otherwise the engine mount bracket on the frame obscures the intake cam timing mark.


Assuming you guys think I have it timed correctly, I have following possible causes.


1) Something with the timing chain guides has gone awry.


2) Piston/valve interference issue.


3) Cam bucket travel issue.


4) Intake valve spring issue.


5) ???


#1 requires pulling the flywheel.


#2,3 and 4 require pulling the intake cam.


Being that I feel binding in the engine motion, I'm leaning towards 2, 3 or 4.


What say thee ?


mbirt: have you ever put an 08 YZ intake cam into a *stock* 2012+ WR450F engine ?

Edited by MidlifeCrisisGuy



I pulled the YZ intake cam out and put it back in for laughs.  I'm not sure if its my imagination but I think I can still feel some binding when the intake valve reaches full lift.


I put in the WR intake cam and the engine seems to be freer.  As a matter of fact, it wants to turn backwards on its own accord in parts of the cycle.  It was not doing that with the YZ cam.  I double checked the cam journal ODs between the cams and they are close and within spec.


FWIW, I had my valve clearances mixed up last night when I measured them.  Exhaust clearances are 8 to 10 thou, intake 4 to 6 thou.   Right now my exhaust clearances are spot on and the intake clearance is just a bit loose.  7 thou is pretty tight but it will go, 8 thou won't go.  6 drags when it goes, its not super easy.


FWIW, most of the dealers in my area wanted me to buy a shim kit with a hundred or so shims for a ridiculous price.  ONE dealer would sell me individual shims from their kit.  However, when I got there I found out that when they adjust the valves on an engine, they throw the used shims back into the shim kit, thus they never run out.  It didn't stop them from charging me full price on the shims they sold me.  I mic'd the shims I bought and a few were just a we bit skinny.  I think this is why my intake valve clearances are just a wee bit loose.


The other thing to note is that the camshaft base circles can possibly differ between these tow sets of cams.


Dimension B on the WR intake cam is 22.550 to 22.56 0mm.

Dimension B on the YZ intake cam is 22.450 to 22.5500 mm.


Ditto for the exhaust cams.    This could have thrown the valve clearances off a bit, but I quickly checked them last night and they were reasonable and shouldn't have been causing the noise I heard when I started it.


I'm going to put the rest of the engine back together and start it.


Moderator: please move this to the WR section as the engine is a WR and I've tortured the YZ community enough.

Edited by MidlifeCrisisGuy

I believe the TDC mark on the flywheel is a single line, not the H. It should be to the right of the H. Make sure the flywheel is aligned with that single line when checking cam timing. The H is there for ignition timing, not cam timing.

I believe the TDC mark on the flywheel is a single line, not the H. It should be to the right of the H. Make sure the flywheel is aligned with that single line when checking cam timing. The H is there for ignition timing, not cam timing.

You are right.  However the difference is about 1 degree on my WR.  I like being in the center of the H, just for security purposes, its easier to see, not that there is really any problem seeing the single mark.

It purrs like an (angry) kitten with the stock intake cam and the 08 YZ exhaust cam.


It started on the 2nd kick, gotta love EFI.   No tapping or abnormal noises at all.  Its idling too fast.  I haven't ridden it yet.


I shut it off and restarted it about 5x.  It restarted on the first kick every time.  


It seems to kick easier with the (non eStart friendly) YZ exhaust cam.  It seems to rev freer too.


I have 2 thoughts about this experience.


1) I don't know if the binding at full intake lift with the YZ cam is real or my imagination.  Given how much freer the engine spun by hand, I'd say it has to be real.  Plus I was able to feel the binding and then look at the cams and every time I found the intake cam in the same position.   So its a repeatable feeling if nothing else.  


And it feels like something more than the nose of the cam coming up on the bucket.  It has a definite stop/binding feeling to it.  When I first put it together and felt it, I didn't look at the cams and just chalked it up to the decompressor working on the exhaust valve.   Its a subtle binding feeling, not a crunch or anything, but its there.


I'm afraid to put the 08 YZ intake cam back in and try running it, for fear of damaging something.  


2) The ONLY thing I could think of valve train drive related that I might have done wrong is that maybe I should have wound the spring in on the valve tensioner again, ie it was over tensioning the chain guide ?  Is that possible ?   Could that have caused the tapping noise ?  FWIW, I poked at the intake chain guide when I removed the valve tensioner both times and it moved freely.


mbirt (or anyone else who has one of these engines apart): I'd love to know the piston to valve clearance on a 2012+ WR450F engine with an 08 YZ intake cam if you ever get the chance to measure it.


I'd love to hear from anyone else who puts an 08 YZ intake cam into a 2012+ WR450F.


I hope this helps someone.

Edited by MidlifeCrisisGuy

You just heard the engine noise more since you had the exhaust plug in. I'm not sure why someone else didn't mention this. This is really a big to do over nothing. It is fine. I hope you get some better help next time on here.

You just heard the engine noise more since you had the exhaust plug in. I'm not sure why someone else didn't mention this. This is really a big to do over nothing. It is fine. I hope you get some better help next time on here.


I doubt it.  I left the exhaust plug in the first time I started it this season and I didn't catch on until I started it 3x and thoroughly flooded it.  It didn't make that noise or anything close to what I heard.


I'm just happy it quit immediately and I didn't run it for a few minutes, wrecking something in the process.


It would only take a minute to replug the exhaust and repeat the experiment...

Edited by MidlifeCrisisGuy

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