Problems timing my CB77

GregMcN · Post by **GregMcN** » Sun Aug 06, 2017 3:13 pm

Hi

Tried to time my CB77 but if I set up the RH cylinder the points gap to time the LH was out of spec. My thinking was that maybe the valve timing was out so I took off the head cover to check it was not off a tooth on the cam sprocket ..... but I can not see the punch mark mentioned in the manual or the line on the head to align it with. The only marks are what looks like on O or a zero and a D on the sprocket. You may be able to see on the picture.

So question is how do I check the valve timing?
Thanks Greg

cknight · Post by **cknight** » Sun Aug 06, 2017 3:38 pm

Assuming that the "T" on the rotor is lined up with the pointer (right piston at TDC), the flat surface on the cam sprocket hub (adjacent to the stamped "O"), should be parallel to the cylinder head top surface. Yours would then appear to be retarded a tooth. Regards, Chase

GregMcN · Post by **GregMcN** » Sun Aug 06, 2017 4:05 pm

Thanks Chase,

So if I understand correctly you are saying that no punch mark and line required, the sprocket carrier flat just needs to be parallel.
I can not remember if I was on the T mark when I took the photo but will check tomorrow.

Hoosier Tom · Post by **Hoosier Tom** » Sun Aug 06, 2017 8:15 pm

GregMcN wrote:Thanks Chase,

So if I understand correctly you are saying that no punch mark and line required

No, you are not understanding. The 0 (zero) is the punch mark or indexing mark on the cam sprocket. There are 2 flat spots on the cam sprocket, 180 degrees from each other. Align the flat plane of the cam sprocket that has the punch mark with the flat plane of the top of the head (gasket surface) while the right piston is at TDC with the "T" on the rotor aligning with the pointer and the slash or hash mark on the points cam pointing up at 12 o'clock relative to the aforementioned plane.

HT

G-Man · Post by **G-Man** » Mon Aug 07, 2017 2:24 am

The sprocket has been welded up at some time owing to the rivets becoming slack. This may also indicate that the advancer mechanism is not in the best of shape.

The marks are clearly visible in your picture.

G

GregMcN · Post by **GregMcN** » Mon Aug 07, 2017 4:16 pm

I did wonder about the welding G-Man. You suggest the advance mech may not be in great shape - anything that can be done about it?
Are there electronic ignition options? Is the advance replaced or still mechanical?
Greg

GregMcN · Post by **GregMcN** » Tue Aug 08, 2017 3:27 pm

When I checked the flat on the cam sprocket did not seem to be exactly parallel but was definitely better than if I had moved the chain a tooth, so I have tried timing again to make sure I had not messed up but I still can not get it spot on without having one set of points out of spec, not massively so (about 0.45mm) but still can not see why unless the points cam is worn?
In practice will a larger points gap matter?
Greg