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, September 01, 2014 - 12:06 PM.