alscomet with unmarked timing gears

timetraveller

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OK Guys, do it how you want BUT is the cam a Mk I or a Mk II or even one of these 105 degree ones which are about now. (The Mk IIIs which I have measured no more have quieting ramps than I do.) I know that it is time consuming but I still recommend plotting out the whole lift profile of both inlet and exhaust valves and then plotting the numbers up either by hand or in a spread sheet. Many old Vincent cams have a serious flat either at the start or end of the lift and this makes timing difficult. With the full information one can make the best of a compromise on the timing if the cams are not what you think or are poor quality. It takes me about one hour on my own to take a measurement every ten degrees of engine rotation of both lobes on one cam. Nowadays I then always put those numbers into EXEL. I also have set the spread sheet up so that it shows the velocity and acceleration of both cams. That can be rather depressing. I did this years ago for some specials that (an engineer) had made for Roy Robertson with an extra 1 mm of lift. The acceleration was a factor of seven times greater than what is normally allowed and resulted in the valve heads falling off and wrecking the engine. If anyone wants a copy of the spread sheet then I can send them a blank version for them to play about with.
 

Ken Tidswell

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Timing

I forgot to say that you should get ahalf time pinion which has the least backlash against the large idler, before you start, Some sections carry a selection of half time pinions to enable this to be done
 

nkt267

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I agree with time traveller that plotting cam profiles is the best way to go about cam timing.I have rebuilt 3 comet engines in the past 4 years, 2 with Mk2 and 1 with mk3.I found that none of the cams were ground exactly to the figures stated for valve timing and a 'best compromise' setting had to be used.Alscomet seems to be in a bind and needs some practical guidance before he strips the timing case.It may be that he does not have use of dial guages to set his timing 'by the book',and any advise should be seen in this light. Surely there must be a member of his local section that can give some hands on help.
 

alscomet

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alscomet

nkt267,
thanks again for all the effort,what i intend to do later next week is to
take the quill out, fix my timing disc in with a solid pointer, find TDC ignition stroke ,stick the dial guage on turn the engine back, then foreward to see when the inlet valve is just starting to open, then I think I will post a new thread
and ask for all your comments on what i have. alan
 

nkt267

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Great Idea.Don't forget to nip the adjusters up (refer to earlier post by timetraveller) otherwise you will get the wrong readings.A couple of thou lift on the cam can be quite a few degrees .John
 
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