E: Engine Series ‘C’ Comet Camshafts

aciera

Forum User
Non-VOC Member
Hello, I'm restoring a Comet of 52, I'm not a mechanic, but in principle I'm doing pretty well.
When I stalled the engine, the rigging did not play, by trial and error I arrived at this result, which seems odd. Exhaust valve opening 46 degree, opening valve injection 29 degree, closing valve exhaust 34 degree, closing valve injection 90 degree. View the photo. I think this camshaft does not match this engine, or it possibly corresponds to a race version?
I bought this bike in 1987 from a person who was shopping.
I think I have to order a new camshaft, MK1 seems to me original? I'm not sure, is someone can help me? thank you in advance
Patrick
 

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timetraveller

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VOC Member
Hello Patrick, I do not understand some of the figures on your degree wheel. The value of the inlet closing at 90 deg and opening at 36 deg do not seem correct. The opening is about right but the closing should be about 64 deg whether it is a Mk I or a Mk II. If I take your figures of inlet opening, 36 deg, and exhaust closing at 34 deg then that gives an overlap value of 70 deg and that value for a Mk I cam should be in the range of 68 to 75. I think that you have a Mk I cam (or a Mk III which has the same timing but is supposed to have quieting ramps). The racing cam for Grey Flashes and Black Lightings have an overlap value of 105. You should know that over the years there have been some very poor cams made for Vincents and possibly you have one of those. Good luck with the rebuild.
 

aciera

Forum User
Non-VOC Member
thanks for the answer, I also think that this cam shaft is not correct, closing the intake valve at 90 degrees is much too late. I'm going to order a new cam shaft.
 

davidd

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VOC Member
Patrick,

I think you are doing the right thing, but the height at which you measure these openings and closings will cause the numbers to change a large amount. Often when a valve is late closing it is because it is down at 0.001-2", which is effectively closed (although it shows the the cam is not ground correctly.)

If you measure the events at 0.040" and 0.005" it will be easier to identify the character of the cam at the 0.040" and the correctness of the grind at 0.005".

David
 

timetraveller

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VOC Member
Patrick, David is correct and the figure of measuring at five thou lift is in all the books and instruction sheets on Vincents. If you do not have any of these then you will find it much easier to work on the bike with one of these books to hand. The book by Paul Richardson one is probably the best for a newcomer to Vincents and might be available from the Spares Company or other on line source.
 

aciera

Forum User
Non-VOC Member
The book KNOW THY BEST, I have it, the book of Paul Richardson I just ordered it. The problem the English language is not always easy to understand for me.
The measurements, I put two comparators on the valve head, and I start at the top dead center TDC, and two crankshaft lathes. I think it's the right method.
I am waiting to receive Paul Richardson's book before making a decision.
 

vibrac

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VOC Member
You learn so much on this forum years ago I found out about the valve equally open at 4 degrees before TDC and I have never worried about open and closing points since. Then only last month Bill mentioned the cam 'keyway' pointing between the rear push rods and the front camshaft keyway pointing straight down at TDC Ben actually used that last week to initally set up a new twin motor and when he got down to detail it was almost perfect
25833

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Bill Thomas

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VOC Member
I can't be sure ??, But I think on a Comet, That slot should be in a straight line between the pushrod tubes and the middle of the cam spindle, Slot at the top, Like the rear one on Vibrac's photo, With both valves OPEN !!.
TDC ish. Cheers Bill.
 
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