Comet Camshaft repair

champion

Well Known and Active Forum User
VOC Member
Hello,

As many of you are aware I am in the process of building a very early series C comet, I am now at the stage whereby I can time up the engine.

My father has a box of a dozen old camshafts and I decided to use the least worn of the lot rather than buying new at £415. However the cam did not time up correctly.

I have looked through the box and tried a second which almost as good but also did not work. I therefore have 2 questions:

1. Is there anybody who repairs Vincent cams now that Gary Robinson only manufactures new?

I have tried Newman Cams in Kent, who have said they maybe able to regrind the cams which are in good condition but will not do full repairs. I have also been given JOY motorcycle engineering email address by the owner of a company called Kent performance Cams, however they have not replied.


Any suggestions would be appreciated.
 

Rob H

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VOC Member
I would give Gary a call, I think he takes your cams in exchange. Definately a lot cheaper than £415. I just had a pair of cams and also followers for a twin done by Gary for about £500
 

Black Flash

Well Known and Active Forum User
VOC Member
If you look at my avatar you can see that I got damn close with only 2 thou difference in lift at 4 degrees BTDC. I always use this method and do not care about timing marks at all
Bernd
 

champion

Well Known and Active Forum User
VOC Member
Rob, Thanks for the advice!


Chris, I originally tried the timing marks, however found them not to be accurate.

From memory my process was as follows:
I put the cam in, without the large idler and nipped the tappet adjusters up a couple of thou.
Then rotated it until the inlet was about to open.
I then moved the crank until TDC, I then attached the timing disc and marked it at zero degrees, (top dead center).
I then moved the crank back 42 degrees and fitted the large idler and half time pinion.

I am using DTIs attached directly onto both valves and one which measures top dead center.

The best I have got so far is the exhaust opening 10 degrees early.
 

vibrac

Well Known and Active Forum User
VOC Member
My post #16 in the thread
identifying cams
explains how I do it, except after a recent enjoyable session with Bananaman and the chain drive cam Comet I am buying some digital 'dial' gauges, cheap as chips and sidesteps my original problem with contra rotating dial gauges
 

passenger0_0

Well Known and Active Forum User
Non-VOC Member
In the interests of preserving your finances I suggest you take up Robert's suggestion. The exhaust timing will take care of itself and what's 10 degrees anyway? The inlet timing is the one to get right.
 

davidd

Well Known and Active Forum User
VOC Member
Champion,

I would think that you could use a little worn cam and that it would time up properly.

I do not use the same method that you use. I don't use TDC in most cases, I use equal lift as the reference. This is handy for two reasons. First, the marks could line up at this position, but second, there is no dwell associated with this point and there is dwell at TDC. Most get rid of the dwell by using the piston stop method, which is what I use to find TDC. If the piston is in the engine I use both as references. I then adjust the gears to get equal lift to happen at 4° BTDC exhaust.

I set the valve lash at zero as if the engine were going to run. I usually measure the timing events on the cam at .050" just to compare them with modern copies. The Mk1 should be 30-44-44-30 and the Mk2 should be 37-51-51-37. They can vary quite a bit, but should be in the ball park and showing similar symmetry at this lift.

It is worth spending some time to come up with a method you like that will be a good reference in the future.

David
 
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