E: Engine Large Timing Gear Factory Markings

[tom wilson]

Hi again I have a Comet it is fitted with a steel large timing gear without any timing marks. I would like to re-instate the factory marks on it. Can anyone point me in the direction of a large photo or drawing of the gear clearly showing the mars and teeth so I can copy them onto my gear? Or maybe someone could email me a large photo of an original gear showing the marks and gear.
Yes I know I can set my own marks and my cams etc may have slipped or been altered, having the original marks on the gear would be a good start point for me. many thanks in advance..

 

[vibrac]

I am in no doubt that this post will be followed by all the converted who simply time up their machines with the equal open at 4deg BTDC method I must admit I stopped looking at timing marks a decade ago,

 

[ClassicBiker]

Tom,
You'll find a drawing of what you are after on Page 111 of Paul Richardson's book. But be advised the book isn't quite correct. The discrepancy is explained in the link.

https://www.vincentownersclub.co.uk/resources/comet-valve-timing.1684/

Myself, I used the equal lift method Vibrac mentions above when I timed my Shadow. I did however have the advantage that my pinions were off my camshafts. So I was able to set the timing marks to align and have equal lift at 5 degrees BTDC. Irving's book "Tuning for Speed" quotes Joe Craig as saying equal lift occurs between 4 and 6 degrees BTDC so I chose the middle ground. In the near future when I refurbish my Comet's engine I'll time it with equal lift and the marks aligning.
Steven

 

[chankly bore]

Just for the sake of detail: Mark a stroke on a tooth space of the large idler. Count 30 teeth anti- clockwise and mark that tooth with two dots. Return to the stroke and go clockwise 30 teeth and mark that tooth with one dot, then count a further 11 teeth clockwise and mark the next space with a "B" if you're lucky enough to own a Meteor or Comet. I believe because of the odd number (79) of teeth on the large idler the marks don't line up again for 158 revolutions. I could be wrong there, my memory is poor. The easiest way to understand the error in "Richardson" is to carefully compare the camshaft slot of the rear cylinder on page 115 with the camshaft slot on page 120. IF your camshaft is produced as per original the slot of the camshaft should point up directly between the pushrod tubes, i.e. in a direct line from the large idler centre to the camshaft centre. However, like the folks here say, best to get equal lift at about 4°. The camshaft slot trick does usually produce a fairly close starting point, though. Breather slot points down on a Comet, and ET98 goes INSIDE the cam followers, not outside as "Richardson" says.

 

[delboy]

500cc timing drawing is corrected in the Frank Griffin revised, Edition Three of Richardson's Vincent Motorcycles.
Delboy.

 

[ClassicBiker]

500cc timing drawing is corrected in the Frank Griffin revised, Edition Three of Richardson's Vincent Motorcycles.
Delboy.

Ahh, good to know. I just looked at my copy and it's revision 3. I'll make a note for that. Thanks.

Just for the sake of detail: Mark a stroke on a tooth space of the large idler. Count 30 teeth anti- clockwise and mark that tooth with two dots. Return to the stroke and go clockwise 30 teeth and mark that tooth with one dot, then count a further 11 teeth clockwise and mark the next space with a "B" if you're lucky enough to own a Meteor or Comet. I believe because of the odd number (79) of teeth on the large idler the marks don't line up again for 158 revolutions. I could be wrong there, my memory is poor. The easiest way to understand the error in "Richardson" is to carefully compare the camshaft slot of the rear cylinder on page 115 with the camshaft slot on page 120. IF your camshaft is produced as per original the slot of the camshaft should point up directly between the pushrod tubes, i.e. in a direct line from the large idler centre to the camshaft centre. However, like the folks here say, best to get equal lift at about 4°. The camshaft slot trick does usually produce a fairly close starting point, though. Breather slot points down on a Comet, and ET98 goes INSIDE the cam followers, not outside as "Richardson" says.

Looking at the drawings, I think the slots are inline with a line from camshaft centers to crankshaft center. The reason I say this is we know the camshaft slots are not inline with the dots on their respective pinions. The single dot is 159 degrees 57 minutes in advanced clockwise according to the instruction sheets. The timing marks appear to be inline with a line from the camshaft center to the large idler center, which would make sense as this would be the tangent point between the two pinions. So I don't believe the cam slot is inline with a line running from camshaft center to large idler center.
In fact the below diagram appeared some time ago on this forum or the prior version and it illustrates my point that the timing marks are on the tangents and the slots align with the main shaft.
Steven

 

[oexing]

Incredible drawing,must have consumed many hours. But it amazes me how people have faith in timing marks. They can never know how components have been fabricated and if they have been assembled from different batches. So not my logic at all, even with my original Andrews Mk2 that came with new gears pressed up, With this hunting tooth design it does not look practical to me to deal with marks on all gears in valve train. So maybe better go same road like mentioned and put two clocks on in and ex valve spring caps of one head, possibly with weak test springs fitted for timing operation only . Zero clocks on base circle of cam and then turn camshaft to equal lift both valves.
Now in this position mark one tooth of this gear and put a chisel mark aligned onto engine face like in photo. Do same with second cylinder on a twin with its equal lift mark on tooth and case in suitable place for checking alignment of second camshaft.
These marks and chisel lines of valve overlap will be perfectly accurate later with your cams - unless you get new sets or press up other components later. So only then you´d have to do fresh marks on new gears in that case.
Now you can find TDC of first cylinder via piston stop and degree disc and zero disc at TDC. For final assembly of the lot you turn rear cam to your new marks and keep it there. Turn crank to 4 degrees BTDC - or 0 TDC for best power - and put on the half time gear on crank after idler gear was shoved up between cam gears, no backlash. There are 5 slots in half time gear for finding best position to engage.
For front valve timing the crank has to be turned to 360 degrees plus 46 (50- 4) to get the front overlap TDC at 4 degrees BTDC . Or so I think after some time.
The best way to go is doing the cam gear marking with soft valve springs at the start of the job. Then take out the pushrods and put in all gears of valve train with marks like above and only then have valve springs fitted and assemble as usual. In later operations you save yourself a lot of time when you got your marks on gears and case. Funny timing numbers in handbooks are only confusing , go for equal lift and be happy.
Hope I did not fu** up my description from a distance . . . .

Vic

 

[ClassicBiker]

Vic,
When I timed up my Shadow as I mentioned in post #3, I timed the cams to equal lift at 4 degrees BTDC, I thought I did 5, but this photo I took shows otherwise. I purchased my new cams, cam pinions, and large idler and mounting boss from the Spares Co. The cams were not pressed into the pinions when I purchased them. Anyway, I did not disturb the 1/2 pinion at all. What I did notice is the timing mark on the 1/2 pinion was pointing straight up when I placed the rear cylinder a 4 degrees BTDC. Holding the rear cam at equal lift I aligned the mark on the pinion with the mark on the large idler, using and hammer and block of would I gave the pinion a sharp rap to start it on the shaft and used my hydraulic press to press it home. Using a surrogate for the front cam I aligned the double dots on the larger idler and front pinion, then rotated the crankshaft 410 degrees. I then placed temporary marks on the idler and front pinion. You can the front pinion one between the pushrod tubes in the photo. I then replaced the surrogate with the actual camshaft and rotated it to equal lift and aligned the temporary marks and repeated the pinion mounting process. When I rotated everything back 410 degrees, I didn't feel like rotating forward 100+ to get the rear marks to align again, that was then I noticed the rear cam slot was inline with a line running through the cam spindle and the crankshaft and the front cam slot was perpendicular and down from a line running through both cam spindles.
Myself I think doing equal lift at 4 degrees BTDC is the way to go. I would not trust timing marks on an unfamiliar engine. But I know that if I have all marks on all the pinions lined up and the slots are not close to being orientated as described above and/or the crank isn't at just before TDC or at TDC, then something is very wrong. I've read that the crank position is in the drawing in Richardson's book is at TDC and I've read it's at 4 degrees BTDC. I think when those slots align with a line from crank to spindle the cam is at equal lift. Which leads me to believe you could make a simple jig to spigot into the oil quill hole go, spigot into the cam spindle oil hole and drops a pin into the cam slot. But that assumes standard cams.

But that gets back to Tom's question. When Tom's Comet is at 4 degrees BTDC the slot in his camshaft should line up with the spindle and the crank and he can put his marks on it.
Steven