ET: Engine (Twin) New ESA Design

[oexing]

I would not spend much time pondering about spring types, don´t think you´d get a better action within the old ESA. I will keep those small springs but the only real flaw of the original design is the shape of the cams which is not steep enough and leaves too much backlash for the engine to bash the endplate with lethal shockwaves sent into the chain. I say , throwing out the complete ESA would be easier on the chain than an ESA with the present behaviour.
When studying the photo of the Maugham version I wonder what the mating cam shape will look like ? Is it the same fancy tapering curves that we see in the photo? Next mystery to me is, how do they machine that shape ? Possibly with a little help from full CAD/CNC programming . Compared to that my mod was simple enough for my old brain to produce exactly fitting male and female partners from the first try on the alu test pair up to the welded sprocket, and that on an old manual mill, just having two DRO for mill and dividing head. Thinking about it, one could feed my little steps that I worked out and wheeled in manually, into a file of a CNC mill that is wired to a CNC dividing head. So then the machining operation would be smooth and quick in a continuous cut, no big headscratching of will it match the counteracting part ? The male cams are simple 12 mm dia. cylinders, programmed on the mill in no time, using a simple dividing head for three positions. Just the female is more tricky and laborious when you have to machine without CNC.
So basically the whole assembly may clearly stay as it is, just the shape of the cams needs radical redesign. Below is once again a photo of the BMW ESA type in the gearbox that was troublefree for decades from the fifties up to all modern two valve flat twins . I am very confident that my mod will do its job no problems.

Vic

 

[timetraveller]

I thought that it might be instructive to calculate the path of a 12 mm diameter disc in a 36 mm diameter female semi circular hollow, Below I show the results of an ACAD series of drawings in which the male part was moved, one mm at a time, to the right. The crosses, which are connected with a smooth red curve (a spline function for those who care) shows the path of the centre of the 12 mm diameter disc.

I did consider also drawing in the angle of the contact point between the male and female parts but decided that there is enough on the drawing to cause confusion anyway. Clearly at the top of the movement the force between the two parts is purely lateral or sheer. If a linearly rated spring was used then the red line also shows the way in which the force applied would rise.

 

[Oldhaven]

has anyone done the analysis of this? Of course it would be 3X the amount required to shear one lobe. I believe the concept would also work with a larger male lobe if required. This is shown in the left assembly in the BMW photo. I wonder if the Vincent ESA cam shape was an attempt to avoid this type of stress :

 

[vibrac]

. I wonder if the Vincent ESA cam shape was an attempt to avoid this type of stress

Which Vincent ESA cam shape? the original? the one of up to 2 years ago (approximately assuming something changed ) or the newly designed one?

 

[Oldhaven]

OK, I know what you mean. You might throw in as another category the ones supplied as spares over the years after the factory closed and before some quality controls and drawings were available. I meant the original design, (PEI?) which seems to have some unwitting flaws in the design, but losing lobes would not be one of them. I twisted a mainshaft in my first Rapide shortly after I bought it when the cam lobes went end to end and locked up the bike. I guess the ESA nut had come undone enough to allow that.

 

[oexing]

When you add up all material in the triplex chain cross sections of one link , what do you think would snap first , the chain or three lobes ? There must be some info about the torque the crank delivers but I am not able to calculate what the lobes would take at their radius. My guess, the crank produces only a fraction of the max torque the lobes can handle.
Looking at the drawing above one can imagine the effect of the very steep curve. Theoretically you almost don´t need any springs at all when the big female radius goes all up to the centre line as the contact faces are almost vertical there. Add to that the enormous friction from the high pressure contact area plus spring forces and you will see the very progressive damping effect that a deeper cam shape will achieve. I did not go to vertical for the max lift on the test set, instead studied the BMW parts and concluded to copy their looks feeling that this should easily do.
I can add sizes of the BMW parts if needed, but they are a lot smaller in dia. and only two lobes. Sure , only max 300 cc with that originally from a R 69 S, but they had this type up to the R 100 two valve types - nobody never ever spent any thoughts on these items, there was never a problem there. Mind you, that shock absorber is the only one on the whole bike, no other chains anywhere , all gears from front to rear, so not even a minimal damping from chains that may help.

Vic

 

[Tim Kirker]

I'm afraid I don't often contribute to the Forum because I just can't find the time to keep up with all the threads I'm interested in, but my attention has been drawn to this discussion about the ESA profile. As draughtsman for the Technical Committee TC, I was insrumental in developing the latest cam design that is now available from VOCSC.

The first thing to emphasise is that the TC's terms of reference are not to develop new and improved designs, unless there is clear evidence that the current design is dangerous or clearly an error made by the factory. Our objective is to compile new manufacturing drawings that will allow new parts to be manufactured as close as possible to the original design intent.

In the case of the ESA, we came to the view that the then standard of ESA being made was not what PEI originally intended, and had all the faults observed by Vic. So I set out to reproduce a cam profile as close as possible to what PEI originally designed. We did not have original drawings but we did have drawings for the Velocette ESA, also designed by PEI. What I came up with is about the best compromise between that Velocette design and the slightly different surrounding dimensions of the ESA. (Like the amount of axial lift possible, the outer radius etc.) We also looked at some very early Vincent parts, which tended to confirm that the product then available had drifted a long way away from the original design.

All of this was written up, at some length, in MPH 808 in May 2016, together with photos similar to Vic's. I'm surprised and disappointed that nobody in this thread has referred back to that article, which I think you will find addresses most, if not all of the concerns raised by Vic and others. We may not have "solved" them in the same way as Vic proposes, but we have solved them pretty well within our terms of reference.

The BMW design that Vic is copying is very interesting but is only possible if you accept that the two cams will not be identical, and the drive will be through two lobes, not three - thus you can accommodate a much greater radius in the trough of one side, and a much finer radius for the lobe in the other side. The down side of this approach is that contact between the cams is restricted to two places (or three, if there are three lobes), whereas the Vincent/Velo design has contact in six places. Also, the Vincent lobes are much more robust than Vic's modified lobes. How long before one breaks off? As the Technical Authority for the VOC, the TC cannot take a punt on what might, or might not, work. Our Product Liability Insurance would be blown away.

Final thought, I seem to remember that Prof Higgins studied the movement of the ESA with strobe lighting years ago and concluded that it didn't need much torque/revs before the cam locked solid and it looks like the BMW design will effectively be solid under load. In the BMW case the limitation is that the cam faces effectively become vertical, in the Vincent case it is because the top plate stops any further compression of the springs. I'm sure the rider will not be able to feel the difference!

 

[Vincent Brake]

has anyone done the analysis of this? Of course it would be 3X the amount required to shear one lobe. I believe the concept would also work with a larger male lobe if required. This is shown in the left assembly in the BMW photo. I wonder if the Vincent ESA cam shape was an attempt to avoid this type of stress :

View attachment 18437

a lock up?

 

[Vincent Brake]

only thing one needs is a bit of rubber, for about 5 degree, to take out the max stresses....

 

[oexing]

Tim,
you have pinpointed some trouble spots and made clear the limitations of the drawing dept. , unforunately nobody here seems to have seen the new design so we have to draw guesses on the effectiveness. Sorry for repeating myself, the big point is to get some real progressive damping into the design to stop the EAS from bashing onto its stops, be that the springs or the end plate. No tweaking the basic shape as it still is - presumably- will help here so we will no doubt see more broken springs and broken chains with drastic consquences.
The BMW shape does not do a hard stop, there is definitely the very progressive deceleration of motion under high loads and you bet it does its job well since the fifties into the nineties I think. The BMWs have no chains in drives anywhere, all gears, so this ESA in the gearbox input shaft does a great job no doubt!
The bad thing with the flat lobes in the Vincent is really the shock impulse down the chain that breaks it. I bet it would break a belt drive easily as well if it was used there. NO ESA would be easier on the drives than bashing components ! When you look at my photos and see dimensions of BMW type and my modded HRD parts, BMW diameters a lot smaller!! , what do you really think: Do the three lobes break before the chain snaps ? Add up all cross sections of one chain link and add up the three lobes and compare . I would not be able to do the mathematics, was a bright 2 Watt bulb at that all my life, but my guts tell me there is not nearly a problem . Two lobes in the BMW on a smaller radius never ever had a problem , up into the 1000 cc Twins with 70 hp.
Vic