Ignition Timing

[Guzziando]

Hi, yes it does have the woodruf key, but there was some play. I am however now completely confused (easily done!). When I took the cam belt off, the camshaft sprocket mark was pointing at the TDC mark (top of the case). Both valves were closed. They are now both open, and to get to a position where both valves are fully closed, the cam has rotated through 180 degrees? No idea how this could have happened. The sprocket on the cam is keyed on (I am assuming so)

Any ideas?

[MickeyMoto]

At tdc on the compression stroke on the front cylinder the dot on the camshaft wheel is 180 degrees from the tdc mark on the crankcase. At this point the dot on the crankshaft sprocket should align with the dot on the crankcase.

Well, that was how mine was when I changed the belt two weeks ago

One thing to look at is when the cambelt is removed the camshaft will turn as cylinder 2 is somewhere in its cycle and a valve will be open to some degree and the spring tension will unwind pushing the cam around. I always check the crank mark and set the cam dot 180 degrees from the tdc marker before fitting the belt and then checking it with the belt partially on.

[Guzziando]

I have now removed the nut holding on the camshaft. The woodruff key appears to be there, so I will reassemble it. The sprocket is tight on the shaft, and if it is keyed in place, I am happy that it is not moving, and is in the right place, as there is only one slot.

PXL_20250822_145350276 (1).jpg (498.94 KiB) Viewed 28 times

[MickeyMoto]

If this is in response to my above post, then the slot is irrelevant. The dot on the camshaft pulley needs to be at the bottom (180 degrees from the notch on the crankcase where the ignition timing is set) when the crank is at tdc on the compression stroke of No. 1 cylinder i.e. the Woodruff key on the crankshaft for the rotor is pointing to the dot on the crankcase. I can see the dot on the camshaft, which appears to be about 30 degrees out) and the dot on the crankcase but not the position of the Woodruff key on the crankshaft.

I have no photos to explain, but my bike has just done 136 miles with the pulleys as above.

[Guzziando]

Thanks, yes, I will set it at that. It was just about self reassurance that everything is OK. I now need to set up the valve timing, using the the correct slot in the sprocket to ensure that it is within 3 degrees tolerance.

[norbert]

Normaly you should take off/cut the belt when the 1st cilinder is on the "overlaping(?)" tdc, not at compression tdc. At that moment there are all 4 valves under presión and the cam will not move, taking off the belt.

Normaly the overlapping tdc is when the dot on the upper sprocket is at 12 h at "modern" motors. With the older motors the dot should aline with the crankcase mark at 9 h.

It´s easy to see when you take of the rocker covers. You will see that at compresion tdc 1 on the flywheel there is clerance on both valves on the front cilinder (this is the tdc you need to adjust the pickup/ignicion). There is no dot seen on the upper cam belt sprocket (because the spot is hidden behind the flywheel)Turning the crank 360° the tdc 1 mark again is at 12 h (or 9h) but now you can see the dot on the sprocket at his refernce mark and there ist no clearance at any valve, not on 1st and not on 2nd cilinder. That´s the overlapping tdc!

[MickeyMoto]

There you go, from an expert. Looks like I have been doing it all wrong!

Anyway, good luck.

Ps can't find the embarrassed emoji.

[norbert]

Cannot believe it Mike!

I allways put it spot on overlapping tdc and cut off the belt without any danger to loose the timing. Then put the new belt on as far as I can and then turn the crank. Pressing lightly on the belt it enters itselve after a few turns to his place.