ET: Engine (Twin) Camshaft design

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oexing

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One can discuss this topic for ages, but fact is you cannot run a flat follower, be it a lever or flat cup (bucket?)tappets on a cam for roller followers. The duration would be extremely long but mainly you get almost a hammering mode from the nearly flat sides joining the base with the top circle. A flat type absolutely needs curved cam shapes all around the lobe for smooth operation. You may run a roller follower on a cam for flat followers but the performance would be less than poor.
Whenever a lever type follower is specified you will see a more or less asymmetric cam shape. With a curved lever follower this is not so obvious but in case of the flat Vincent type this is very pronounced. So for develloping a new cam you´d start with the valve motion file with lift, duration and acceleration from computer generated files that guarantee smooth operation without jerk.
Then you have to model the rocker design with its own changing ratio as the valve approaches full lift.
With that you go down to the flat follower and see what shape the motion from above via the flat follower produces as a cam shape.
I am no CAD freak and have no idea what software could help here. I´d have to cut cardboard templates ten times bigger than real and do hours on my drawing board with degree disc and good pencils , did that for a 460 Horex years ago as a trial.
Only later you can plot the valve lifting diagrams from an assembled engine and dials on the valves and paste your findings on paper charts to verify your efforts.

Vic
 
D

Deleted member 3831

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Time Traveller
my illustration of a Rudge cam has a feature which might be useful in explaining a point.
Because it has a radius that blends the tangent to the blending radius, the follower must also be of a radius type to properly follow the profile.
Now assume that there is no blending radius, there are two circles, base and nose, connected by tangents.
Starting with the base circle centred under the flat follower, as the cam rotates so the contact moves off the central position until the point is reached where for one brief instance, the flat of the tangent is in contact with the follower. The following instance sees the contact at the end of the tangent where it meets the nose circle, and from there the contact will come back to the centre of the follower as the cam is further rotated.
These sequences are then repeated in reverse as the cam further rotates until the cam finally ends up at the original starting position

My previous comments have assumed that in all instances a practical approach is made to the question of cam design, although as I have mentioned in an earlier post, it is actually incorrect to use the term 'cam design', the correct term is 'valve lift design', and following such design then a cam form must be devised that will enable that valve lift design to be realised.

passenger 0_0 gives an example based of Robert Norton's model that ends with something totally impossible to make, in simple terms, not practical. I wonder at the valve lift design that the model was meant to represent

Greg and David
if you go to Phillip Island to watch the Classic races, all the Winfield machines have my cam designs installed, and have had them for the last three years. These races though may see the winners laurels return to Australia through the efforts of the Horner Brother's Irving Vincents and their roller cam followers.
 
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Deleted member 3831

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oexing
you are pretty much spot on with your description of the design process, but I would like to add there is usually a reason for such a process to start, is it in order to obtain some increase in engine performance, or possibly better fuel consumption ?. Whatever the reason, it is usually sensible to first analyse as fully as possible before starting what the machines characteristics are, and how they have been obtained. From this analysis there will in all probability be areas that may be identified as having room for improvement.
 
O

oexing

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One good reason for a new cam shape would be a curved follower . That would cure some wear problems at the very pointy cam lobe. And regarding wear, the oil hole just in an area of high load is a very baaad (DT) idea. I will feed maximal oil flow into the cam bore and have welded all oilholes in the flat followers. Folks hope for oil supply from the pushrods down but in real life all oil wedge pressure disappears into these holes so there is most wear right at the holes. Same problem is seen with SR 500 XT 500 ohc which get oil feed into the hardchromed curved contact faces of the followers but nevertheless lot of wear around the holes. Honda does mostly oil supplly into camshaft bores and out by drillings in lobes right before start of valve lift - much better.

Vic
 
Martyn Goodwin

Martyn Goodwin

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greg brillus said:
The Horner brothers ran roller tipped lever followers on the Goodwood racer. I have seen pictures of them, but i don't have any to put on here.
Click to expand...
Not Horner Roller tipped followers but these ARE Horner experimental increased ratio rockers.

1516416556081.png
 
T

timetraveller

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A couple of questions David; What material was used as the pivot for the roller? That must have been a bit of good stuff. Secondly, that is a very interesting construction for the cam wheel. Are the threads in the holes in the camshaft part threaded for some sort of adjustment of the teeth to cam rotation? And why is it made in two parts, teeth plus pinion, unless that is to allow some rotational adjustment. Interesting posting that.
 
greg brillus

greg brillus

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Just remember these parts were used in the Goodwood bike not their Irving Vincent engines........I'm not sure I've ever seen any parts in these engines except when I visited their workshop back in 2015 and had a look at one of the heads off their 2 valve 1300 engine. The inlet port was massive, like you could stick your fist down it, all technology they've learnt from the V8 Supercar engines they play with.
 
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