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Rotor markings not lining up with TDC [SOLVED]

JBerd

New Member
Joined
Mar 3, 2023
Total Posts
5
Total likes
0
Location
Boulder, CO USA
The problem is that when I put the left piston at top dead center (TDC), the LT mark on the rotor is about 9° past the index mark on the stator. I can see the piston rise and fall easily with a flashlight (plug out), so I'm confident I'm at TDC. The bike (1974 CB360K) is pretty stock with about 8,000 miles on it. It rode mediocre before discovering this. Any ideas what could be causing this. Clearly this can't be good. Thanks.
 
Put a straw in the plug hole so it's resting on the piston. Rotate the engine at @TDC forward and backward to see where TDC begins and ends on the rotor, mark those and split them for true TDC.
There is always the possibility that the woodruff key, crankshaft groove or rotor groove is worn causing the problem.
 
With the age of these bikes and all the potential hands that have been laid on them, it's possible some things may not be original. I wonder if the alternator stator or rotor is not original causing the timing mark difference (the indicating pointer on the stator or a different rotor from another twin that is similar nut not correct). Pictures might help in this situation, though pictures typically help in most situations.

The other possibility I can think of right off the top of my head is not as pretty. There have been cases of a 180° crankshaft slipping out of phase slightly causing the pistons to no longer be exactly 180° apart, but that's a lot less common.
 
Thanks. I've done the pencil/straw technique and it's the same TDC as visual. I checked the new rotor and new stator and they are at the same degrees as the ones they replaced. The rotor key and groove were good. I'm thinking it is something with the pistons and crankshaft. Nine degrees is pretty far off. I was hoping it was something simple but I don't think so.

I've scheduled a top end rebuild with a Denver mechanic (A.K. Cycles) in April. Time to pop the hood and see what's going on inside.
 
I would scribe a new line on the rotor, to match actual tdc, then check the other cylinder to see if the mark is off the same amount.
 
If that woodruff key slot in the crank was that far off from the factory that would explain the "mediocre" running. It could perk things right up with the timing set, using some corrected marks. I wonder how many other 360s are out there, using cranks from that batch.
 
My bad. I took the rotor bolt off and looked down the rotor key groove and the key looked off. Turns out I did not "tap" the rotor in far enough to really seat the key. After tapping in the rotor all the way, the TDC lines up with the LT mark and the stator index. Thanks for all your advice. I should have checked this out first thing but was incorrectly "sure" the rotor was in all the way. Glad it wasn't something more serious. Now I can move forward with timing, etc.
 
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