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alscomet with unmarked timing gears

alscomet

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VOC Member
Have a look at my previous thread, thanks for the two replys. What I could really do with is "how to do the timing setup, with the unmarked pinions" a line by line from start to finish,come on 66 people looked at the thread and only two replys surely someone knows how to do it other than by reading the Richardsons book. its not that clear. alan
 

stumpy lord

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VOC Member
timming vincent cams

Hi ,
Rather than spend ages typing out instructions, it is a lot easier if you have a look at the works instruction sheets[available from the club shop] where you willfind a comprehensive instruction for timming your cams.
hope this helps.
norm
 

Ken Tidswell

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VOC Member
Timing aComet

I assume all you have is a set of timing gears with timing marks , except the half time pinnion. Are you using a dial or dial and guages to measure the lift and opening /closing points ? The instruction sheets say use 4 thou nip on the on the pushrods to eliminate backlash.
What i do is to rotate the engine and establish TDC with a degree disk and a piston stop, set disk in place with the half time pinnion ready to slip on the mainshaft without removing the disk. turn the large idler until the inlet valve starts to open, slip in the half time pinnion , and select a key way the pinnion to give the best fit with the mainshaft and gently tap the key half way in.
now rotate backwards and recheck the opening position. Check overlap at TDC and opening and closing points of both valves, these will vary within the ranges given in PR's book. Check the opening point of the breather, closing is not too important, done
Tap in the key taking care not to score it , Some people then mark the pinnon with a carbide drill, or paint or a sharp punch.
If the timing is out you can withdraw the key and do it again, until you get it right. Ken
 

alscomet

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VOC Member
unmarked pinion

thanks ken for the information,its basically what i have done ,what i must do is make a piston stop to establish TDC properly and also make sure i have half time pinion ready to fit without removing the disc. then check the overlap and adjust.
thanks again. alan
 

timetraveller

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VOC Member
You could do what Mr Boggler suggests but that will only work if you know what cam profiles you have and if they have been made correctly. Many Vincent cams are not accurate. An alternative is to do most of what Mr B suggests but near TDC on the correct stroke accurately determine the lift profiles and arrange it so that the cross over from inlet opening to exhaust closing is about 4 to 6 degrees BTDC. That is degrees of inlet opening larger than degrees of exhaust closing. For my own purposes I always plot the whole lift curve of both cams and then draw a line at five thou. lift across the base of the curves. Determine the timing of these points and then find the best compromise with the figures given in Paul Richardson's book. This way you can overcome some of the deficiencies in Vincent cam profiles. I also suggest that you nip up 5 to 6 thou. before doing all this and check the base circle for circularity. I have seen cams with 20 to 30 degree flats on their base circles and if you set up the tappet clearance on that part you will have trouble later.
 

alscomet

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VOC Member
alscomet unmarked pinion

timetraveller,
Thanks again for the information, I am unsure what cam profile i have , it is a marked cam but the markings on my cam are 4 teeth away from the markings of
a cam which i compared it with, but that should not alter the inlet lift position.
Going back to your positioning of the camshaft when setting the timing how do you overcome the force of the valve springs via the pushrods trying to push the camwheel backwards? or doesnt that happen. alan
 

nkt267

Well Known and Active Website User
VOC Member
Thats interesting about the 4 teeth out as peter sprott's ( Suffolk section member)was the same.We sorted that problem out on the phone.He moved the cam 4 teeth,it is still a little out but he says the performance is now 'sparkling' .There is an article on his Comet in Real Classic this month
 

alscomet

Well Known and Active Website User
VOC Member
alscomet

Thanks again, i remarked my camwheel 4 teeth as my compared one to give me a starting point.something that should be easy seems to turn out relativly hard.
alan
 

nkt267

Well Known and Active Website User
VOC Member
What we did with Peters Comet was to put the degree plate on the drive side, line up TDC and turn the engine till the cam just took up the play in the push rod and took the reading.
Each tooth on the cam wheel = 15degrees. Compare your reading with the 40-42 BTDC.If your timing is way of that then you will have to adjust it.If your inlet opened at say 55-57 deg then you would have to turn the cam wheel anti clockwise 1 tooth.If it opened 25-27 degrees then you would have to turn the cam wheel clockwise 1 tooth.If this makes any sense then it should help you..Peters inlet valve was opening over 60 degrees early.
 

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