ET: Engine (Twin) Camshaft design

[Bill Thomas]

Vincent cams are very small, When I was looking for more power, A cam expert up Cadwell way was making something special, It went on for years and he ran out of time, So he asked me to just put them in my motor and see how it ran, They were so big they would not go in the cases, So I gave them back.
I had a thought about Velo cams ,They always went well, Went and bought one, But I think that was too big also, My bikes went well on Mk2 s, So it was good enough for me.
Cheers bill.

 

[roy the mechanic]

G 50 cams are maybe not too far away, although it's o h c, single cam has rockers for valve movement and a vernier to adjust the lobes!

 

[BigEd]

, I know nothing of the inside of Gold Stars but if they do not have lever cam followers then it would be a time-consuming task, without the advantage of a computer, to convert their lift profiles so that they gave the same curve in a Vin. ..............

The link below to the ABSAF site shows the parts they make to go into the Goldstar timing case. The cams followers are flat "mushroom" type seen at the top right-hand corner of the photograph.
I had a BSA Clubman's Goldstar when I was a 17 year old apprentice. My £3 a week apprentice pay did not fit well with the Goldie's running costs.
ABSAF cam gear photograph

 

[Bill Thomas]

The link below to the ABSAF site shows the parts they make to go into the Goldstar timing case. The cams followers are flat "mushroom" type seen at the top right-hand corner of the photograph.
I had a BSA Clubman's Goldstar when I was a 17 year old apprentice. My £3 a week apprentice pay did not fit well with the Goldie's running costs.
ABSAF cam gear photograph

Me too, I sold it for £60 !!. Cheers Bill.

 

[eglijim]

"No doubt this has been done before by someone, it's too obvious not to have been." - exactly my thoughts when asking my question, an obvious (post MK2) first stage for development.
I would assume that the late great Ian Hamilton must have done something similar in his cam development journey, as he was just so meticulous developing his engines, using the dyno to validate each change - that is how he obtained his '105' cam.

Thanks Grey One for the info, are you aware there are some mantissa number errors and column ommissions within the number stacks?

From what I have been told the Mallows engine originally used cam events derived from Honda F1 engine tech, apparently the original cams were not included in the sale, so that info cannot be validated - did you do the cam work for his engine then?.

Thanks Phil, I worked closely with Ian through all of his racing career and as you say we learned early that meticulous note taking for each and every change bore results though not all changes showed an improvement, just proves the point of only one change at a time. We actually "broke" the development big bore (94mm) engine on the dyno the weekend before his final Cadwell accident. This engine was subsequently repaired and intalled in the BOTT chassis , I still have it. I run the 105s in my road Egli which we dynoed at 73 bhp/6250rpm at the gearbox sprocket, not really a touring engine. The later race bikes ran later 108 cams and 12:1 compression, not really suitable for a road bike.

 

[oexing]

Finding great smooth computer calculated valve lift curves to your desire is no big deal, there are 40 files in my Apfelbeck bible and surely some would fit in. When you look at just a few in my photos, the first line on top is "Hub" means valve lift, like 10.35 mm , 10.4 mm and so on.
Next number is 46 , 48 , 52 degrees, means the steepness of the curves left and right from max. lift,
and final number is "Verz." - acceleration like 2850 , 3000 .
You cannot possibly use extreme steep curves with accelerations/decelerations on a pushrod engine like with ohc bucket followers, the mechanics of all levers, rockers , pushrods are simply too heavy and no cam will take that for reasonable times without extreme wear or floating followers despite heavy springs.
So you choose your lift numbers and accelerations you believe your engine will accept for some useful times and from that chosen file you can start to work out the cam shape - - - and that is the real big job.
You´d have to know somebody good at that CAD business who would model all valve train components like rockers, followers, pushrods into his CAD to work out that cam shape that a CNC mill will use for producing cam lobes for copy grinding jobs. Only later you will find out on an assembled engine with dials on the valves if that CAD operation was correct to show these same valve lift curves that you started from . Deciding on overlap numbers is another thing you will have to decide from experience or comparisons.
The drawing shows from the bottom the lift curve of a beetle engine, the high lift curve is from a ohc racing engine, acceleration way too high for a pushrod design, 53 degrees steep , too radical.
So if somebody could provide good working crude valve lift curves for a Vincent valve gear and just likes to tweak them a little, I am sure there are files close enough among these 40 types that may provide perfect data down to tenths of a micron for smooth , no jerk basis to design a great new cam shape.
Certainly any change in the shape of the flat or curved contact pad on the follower will require fresh new CAD operations, no way can you use cam shapes from other engines that do not have exactly the same lever dimensions.

Vic

 

[Phil Davies]

Eglijim, to you (and Ian) I salute, as Ian (and you, it would appear) was (were) one of the very few tuners (and one of the microscopically small vincent tuners!) that could quantify what the outcome was of specifically changing something - proper tuning and he was a nice bloke as well!!.
Most of the rest (me included, back in the day) just 'felt' the outcome of a change.

As for me and cam forms, I am building what would have been my next development twin race engine if I had carried on historic racing (I stopped to go two stroke moderns) and that includes 'pusher' cam followers - so that I can use post 1948 development cam forms.
I am no skilled engineer (lots of people that know me will OK that statement!) but use lots of mechanical common sense (well sometimes). There is quite a range of modern workable materials that I can use to develop a follower radius and cam profile (possibly to generating a master that will do for me), its just a question of knowing what lift/rotation rate is acceptable (for the valve train) for each phase of the profile and a lot of time, but between them, old and modern BSA/Norton/AMC cams will no doubt assist me in that quest.
Having said all that did Eglijim and Ian secretly discover the holy grail in the 108s??

I mean, even PEI acknowledged that race cam form had moved on since his MK2s in 1948!

 

[eglijim]

Eglijim, to you (and Ian) I salute, as Ian (and you, it would appear) was (were) one of the very few tuners (and one of the microscopically small vincent tuners!) that could quantify what the outcome was of specifically changing something - proper tuning and he was a nice bloke as well!!.
Most of the rest (me included, back in the day) just 'felt' the outcome of a change.

As for me and cam forms, I am building what would have been my next development twin race engine if I had carried on historic racing (I stopped to go two stroke moderns) and that includes 'pusher' cam followers - so that I can use post 1948 development cam forms.
I am no skilled engineer (lots of people that know me will OK that statement!) but use lots of mechanical common sense (well sometimes). There is quite a range of modern workable materials that I can use to develop a follower radius and cam profile (possibly to generating a master that will do for me), its just a question of knowing what lift/rotation rate is acceptable (for the valve train) for each phase of the profile and a lot of time, but between them, old and modern BSA/Norton/AMC cams will no doubt assist me in that quest.
Having said all that did Eglijim and Ian secretly discover the holy grail in the 108s??

I mean, even PEI acknowledged that race cam form had moved on since his MK2s in 1948!

Thank's for that . I had been involved with Ian since joining the recently disbanded Avon Valley MCC in Strathaven when I was 16 till the time of his final outing at Cadwell , Ian and Vicky were at "ours" that Easter weekend as I live 30 mins from the circuit. There was an aim in the cam designs to try to extend the usable power band an extra few hundred RPM from the existing peak at around 6300, we had "enough"torque. This was why the bore was increased eventually to 94mm while staying with the 90 stroke with all of the extra diameter used to generate a circumferential squish band machined into the cylinder head by 172 thou. We had tried ratio rockers but the dyno showed no significant gains for the extra strain on the valvegear. We were also lucky to have had very good advice from people who knew what worked previously , Ted Davis initially and then Leon Moss at LEDAR whose dyno we used frequently and a few other friends and specialists who all pooled their knowledge without hindrance. Luckily we both had a scientific background and a mechanical bent, Ian had a Phd in Applied Physics and I had been a metallurgist with British Steel.
When Ian was elected "club captain" of the AVMCC there was a fine in place of 1 shilling for any member who overtook the captain on a club run. Many tried but few managed when Ian was on his Rap and pressing on over the moors, paying was seen as a major prize by any member quick enough to go by. We scared a lot of sheep on the unfenced roads.

 

[Deleted member 3831]

That's not the engine we were talking about. It's another! This one has plain big ends , look at the external oil pump arrangements. Or should that be derangements?

Going back through the photo's of the engine with the much modified cam followers and rockers, I discovered that after all the photo of the engine in the sidecar outfit that I posted was indeed the correct one.
The engine was fitted with a Nourish billet crankshaft with plain big ends, see attached

 

[eglijim]

Going back through the photo's of the engine with the much modified cam followers and rockers, I discovered that after all the photo of the engine in the sidecar outfit that I posted was indeed the correct one.
The engine was fitted with a Nourish billet crankshaft with plain big ends, see attached

Cannot now remember what happened to it but Ian Hamilton did have a one piece forged crank together with a pair of titanium rods. It was never built into an engine , the crank had not been finish ground, but it was used as a very expensive doorstop in the workshop for several years. It was another one of those ideas we never took to completion.