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E: Engine Camshaft


Bill Thomas

Well Known and Active Website User
VOC Member
I wonder what their Rocker Bearing looks like ?, And how it's fixed. Cheers Bill.
 

timetraveller

Well Known and Active Website User
VOC Member
David's photographs illustrate the point very well of how changing the radius of the follower requires a very different shape to the cams. Those are the broadest cam noses I have seen on a Vin. Isn't it remarkable that the centre axles of the rollers can be such a small a diameter without them breaking? Must be an interesting metal.
 

oexing

Well Known and Active Website User
VOC Member
Here are some photos of classics with roller cam followers resp. curved followers - which does not make any difference on cam shapes with same radius.
First is a Fifties Horex 400 standard cam, next my own designed and fabricated "sports" test cam with more lift, same acceleration, from computer calculated valve lift numbers from 40 curves in my bible. It had separate lobes for variation in spread, one lobe behind the indexing disc. I did the construction purely by graphical way, 10 times bigger drawing and follower plastic template plus degree disc, very laborious - you get the idea. No CAD anywhere near me 15 years ago.
I wonder if these Vincent roller arms have needle bearings inside, seem very small to me. If so, the outer race is very thin walled, would scare me a bit.
The prewar roller followers are Guzzi 1935, see Guzzi signed. And prewar Horex 600, modified for needle bearings by myself.
I do not see how there is a reverse rotation situation, a variation of rotation speed for sure. But so it is in the big end bearing due to the forward and backward swivelling of the conrod in one revolutiion at high speed ! That is why big end bearings have to be lightweight and I do not want rollers bigger than 4 mm in there. Alu cage or high tensile steel cage are acceptable, no brass as was used by some companies - that break after many decades from brass ageing.
Lastly still no advice from anyone on a slick way to design cam shapes starting from valve lift numbers and including all valve gear components ???

Vic

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Chris Launders

Well Known and Active Website User
VOC Member
If it's of any interest some ford engines (modern pinto ? transit) engines have roller cam followers virtually identical to the JAP ones in diameter, 1mm wider with needle rollers but the pin is 8mm. And cheap.
 

Grey One

Well Known and Active Website User
Non-VOC Member
earliest roller followers I've come across were these in a J.A.P engine. I was told it was of 1912 vintage, but have been unable to find what the complete engine was, and what it was used for.
 

Attachments

Grey One

Well Known and Active Website User
Non-VOC Member
Early cam design was very much a hit and miss affair, a shape was drawn up, converted to cam form, and the resultant cam tried out in an engine.
During the 1920/30's Rudge were quite prominent in competition, and one of their employees Jack Amott, rode a Rudge Ulster in the 1927 and 1928 TT's. Jack was involved in development, and a copy of one of his cam designs is attached, still a very basic way of laying out a design. The Rudge had a finger follower with a 0.53" radius pad.
Later Jack left Rudge and after WW2 he was working at BSA, where he designed all the cams for the Gold Star engines. When Phil Irving designed the Repco Brabham engine, he chose to use the Amott Gold Star profiles.

For comparison a drawing for an Ariel profile of 1952 is also included

Niether have any direct connection with Vincent, but should indicate how designers worked before computers, long hand calculations and larger than life drawings.
 

Attachments

vibrac

Well Known and Active Website User
VOC Member
It's a long time since I saw inside an ariel timing cover but on a single not only is there just one camshaft but I seem to remember both followers ex and inlet use the same cam track ?
 

Nulli Secundus

Well Known and Active Website User
VOC Member
VOC Forum Moderator
It's a long time since I saw inside an ariel timing cover but on a single not only is there just one camshaft but I seem to remember both followers ex and inlet use the same cam track ?
The earlier Ariel singles had twin cam lobes. I guess there were reasons to go to one wider single cam lobe on later models.
 

Bill Thomas

Well Known and Active Website User
VOC Member
If I was Clever, Which sadly am Not !, I would try and copy the Cams of the Velo' Venom, For our use.
When I was looking for " More Power", I bought a Cam, But it was much too big for our cases.
A standard Venom, Is a good match for most Vin' Twins.
It took me a few years before I was quicker than the Late Dave Houghton, On the standing 1/4 mile Sprint, Road class. I know the Bore and Stroke is not the same, But just my thoughts. Cheers Bill.
 

Grey One

Well Known and Active Website User
Non-VOC Member
Camshaft manufacture today is vastly improved over what was possible in the Stevenage era.
Today's CNC programmed cam grinders can grind profiles to a precision that was never possible with the old Berco and Van Norman type machines, which ground profiles from a larger than life size master. And this kind of accuracy is demanded by manufacturers who are involved in high tech racing, where valve control at elevated engine speeds is vital.

Some will say that beyond a certain degree of accuracy an engine cannot respond, but tests have proved otherwise, and have shown that even greater accuracy in terms of angular resolution is increasingly necessary. This is where the sub division of degrees is vital.
In checking a profile to ensure it absolutely matches the design, it is not sufficient just to note the cam lift per degree of rotation, but the need can be to determine the actual arc of a degree, and often in extreme cases, even further to seconds of arc.

So much for near enough being good enough!

What does this have to do with Vincent cams ?
Good question! The answer is that where new cams are to be ground by any of the leading shops who have the Landis, Schaudt or other CNC machines, the accuracy of the finished profiles will be exactly to the design, although of course this does not imply that the design is good to start with. You may never need to be concerned about the detail accuracy of the profile, but it would be there nevertheless.
To grind a profile by directly copying from an existing lobe is to copy all the errors, often making them worse, in the long run a most unsatisfactory method of working.
Has the VOC ever had a batch of cams professionally ground?
I would be interested to learn which profiles, and who the work was entrusted to if such has ever been done.

Just imagine what Phil Irving could have done had he had at his disposal all the design and manufacturing aids that exist today. Something a little better than a Mk2 I'll wager!
 

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