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E: Engine Camshaft



oexing

Well Known and Active Website User
VOC Member
Looks like any MK 2 cam. In my photo you see a new genuine Andrews Mk 2 cam, similar ? Can we have the cam lift for checking sizes ?

Vic
25947
 

Cyborg

Well Known and Active Website User
VOC Member
Definitely different from what I have. The ones in my bin are what I assume to be "normal" MK1 and MK2 and no idea what yours are. Don't recall my TP cams looking like that although it's been a while and my memory is not to be trusted.
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Bill Thomas

Well Known and Active Website User
VOC Member
The closing is very flat !!, I would have thought Mk 2 is nicer on the followers ??, Looks like something that would break a follower ?. Cheers Bill.
 

Bill Thomas

Well Known and Active Website User
VOC Member
If Vincent and Eric are right, I think Davidd has told us they fit bronze bushes, Which need more clearance!!,
Than the Oilite type we normally fit. Cheers Bill.
 

timetraveller

Well Known and Active Website User
VOC Member
Some of you will recall that a few weeks ago Swiss member Pat Patrik asked for help with his cams which did not seem to time up properly. He is new to Vincents and had enough sense to ask for help and advice. I cannot find the original posting so here is the latest. Pat set up a measuring system and sent me a value for the valve lift on both cams of his Comet at every ten degrees of engine rotation. We have had some discussions about this and the following graphs show what was found.
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You will see that although the cams time up quite well there is something wrong at maximum lift on the inlet valve. I got Pat to check that the valve collar was not hitting the lower guide, the valve hitting the piston etc and he tells me that there is still plenty of potential lift left at this point. He asked a retired competent engineer and was advised that this would probably not make any difference to cylinder filling etc. It is hard to explain to some people that there is more to cam design that just making the valve open and close. For example one cannot just weld a bit extra on to the nose of an existing cam, blend it in and then expect to have a trouble free engine.
So the next step was to calculate the valve velocity and acceleration. The next graph shows the velocity.
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Already one can see that there is potential trouble near the top of the lift on the inlet valve.

The next graph shows the acceleration figures.
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Now look at the mess in that area. It will, of course, depend entirely on whether Pat intends to potter around at 3,000 rpm or whether he intends to vigorously overtake and go up to 6,000 rpm on occasions but if it is the latter then there is every chance of a valve head being pulled off. Perhaps those who advocate just going ahead and trying the cam would like to work out what the G force would be at 6,000 rpm For those who wish to do the sum note that the engine rotation figures are exactly that, not cam rotation figures.
 

timetraveller

Well Known and Active Website User
VOC Member
I think that it is a Mk I but something has happened to it. I am assuming that nothing is clashing to cause the flat across the top of the inlet valve lift curve (Pat has checked that) and Pat assures me that there is not a deep groove across the cam follower base. What I don't understand is why the cam seems not to show some deformity. Note that we are talking a millimetre in round figures here. The reason I say Mk I is from the timing of opening and closing points. You will see that the cross over point is at TDC whereas there is a general view that 4 deg BTDC is about right. If I assume that Pat could advance the valve timing by 4 deg then the opening and closing points would be at the following values. The figures in brackets are the official Vincent ones for a Mk I.
Ex.O. 73 BBDC (70 - 72), Ex.C. 26 ATDC (28 - 33), In.O. 50 BTDC (40 - 42). In.C. 63 ABDC (60 - 64)
In addition the lift on the exhaust is about 8.8mm (0.346") which is more like a Mk I value than a Mk II.
 

oexing

Well Known and Active Website User
VOC Member
One could spare some speculation when having cam lift numbers taken by vernier from that unknown cam. As written above, the cams in my pictures are new unused Andrews Mk 2 , see stamps. I got three sets straight from Andrews in USA 30 years ago and copied one set on my cam grinder. So in case somebody is interested I could post them for copying , a few months is no problem.
Andrews was taken over by Megacycles some time ago , as far as I know. It will take some more months to get valve lift data from these cams but I guess Andrews were quite competent then to add decent quieting ramps to their version of Mk 2 .

Vic
copying my cams in youtube link:
HRD cam copying

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25954

25955

25956
 

timetraveller

Well Known and Active Website User
VOC Member
Hi Vic, I suspect that you know enough not to need any help but if you do then send me a table of valve lift against engine rotation and I will check out what happens with your cams. You mentioned quieting ramps, as are supposed to be on a Mk III. I have never found any evidence of such ramps on any copies of a MK III so it would be interesting to see what your cams give.
 

oexing

Well Known and Active Website User
VOC Member
Norman, these are Andrews Mk 2 cams, so I am confident they have added quieting ramps to them for optimised operation .

Vic
 

Bill Thomas

Well Known and Active Website User
VOC Member
Vic you want to try Somerton cams, Squareish with great round lumps on the followers, They run much better.
No Clacking !.
I think Norman meant, "Not seen on Mk2 "? Typo ?.
Cheers Bill.
 

davidd

Well Known and Active Website User
VOC Member
Andrews or Megacycle, they're Mk2's with quieting ramps. I've still got my Andrews' from 1976.
Megacycle bought the Andrews cams for Vincents, which they have offered for years. I have not spoken to Megacycle for a while, but they were offering only the phosphor bronze bush, which was unsuitable. I always ask them to leave the bushings out (they are installed after grinding) and they always have sent them without bushings. It is worth asking them if they changed to Oilite.

David
 

timetraveller

Well Known and Active Website User
VOC Member
No, it was not a typo. Years ago I was told that when the Mk III cam was designed they built in the quieting ramp by providing a ramp of about ten thou rising from the base circle over several tens of degrees. That sounds like it would provide a quieting ramp but having learnt a bit about cam design in a very amateurish way, I know that what might sound logical is not always correct. For example who would have thought that on the Swiss cam, a lower lift and flattish top to the curve, would have created more stress on the system? I just thought that is might be interesting to see what Vic's cams had in the way of a quieting ramp and what they did to the lift, velocity and acceleration curves.
Regarding the Tom Somerton copies of Picador cams, just remember that they have to be used with the correct radius curved followers.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Sorry Norman.

With the Somerton Cams, Mr Higgins once said , He thought they was being used with flat followers,
I would not Dare !, I don't understand how they work, But I like them, been in my Special since 1980.
Cheers Bill.
 


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