the evil rotors 31A-11 and 31A-10

After finally getting replacement valve shims for my Maxim X (20 free form my local Dealer). I decided it was time to set the cam timing and recheck my clearances. The first thing I noticed was that I was missing the little index to line up the "T". No big deal I have a spare parts bike, so I removed it and installed...

No problem getting the cams in place with the dots pointing up and gears in place cam tensioner installed. Slowly I rotated the motor and then all of a sudden things came to a full stop. I reversed the motor lined up the "T" and tried again. Slower than before I rotated the motor counter clockwise again and it came to stop. Knowing something was wrong I removed the cams and shims thinking I might have installed a larger shim or one was not seated properly. Everything checked out fine no mistakes that I could see. I reassembled everything timed the cams and installed the cam tensioner. Slowly I rotated the motor and again it stopped in the same spot.

I've done this procedure on many cars and bikes even the mighty V-max with 2 cam chains and 4 cams never a problem.

So once again off come the cams this time I decided to put a small straw in each plug hole and rotated the motor. I noticed that when the "T" was lined up #4 cylinder was on a compression stroke and with the cams in place the intake cam for that cylinder was opening the valves causing the piston to touch the valves. Valves kissing pistons is never a good thing.

I observed the rotor position on that motor and went to my parts bike to compare.... would you look at that!!!! I have 2 identical motors with different rotors. I removed #4 plug an my parts bike inserted a straw and rotated the motor to line up the "T" and #4 piston was at top dead center. The way it should be.

I haven't swapped rotors yet, that will happen tomorrow.

I've attached pics of the 2 different rotors for your enjoyment and to compare.

As you can see the index for the "T" is slotted and can be adjusted. Anyone know how to set it in the proper position?

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Read this thread, it may help.

http://www.xjbikes.com/forums/threads/maxim-x-shim-check.68116/#post-468291

 

thanks Rooster53

mystery solved.
The motor I'm working on is a 86 750 and my spare one is a 85 750. leave it to Yamaha to mess with our heads.

Toolman