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ET: Engine (Twin) ESA upgrade

Bart

Website User
VOC Member
Speet & Speet have been on it today: a better curve for the ESA.
Let's see how this one will dampen those spikes in torque on the primary drive, as the original is't really up to the task.

Still only a demo in aluminium to get a feel for the shape of the cam. Also can be used in a superlight engine. ;-)

Will be used in combination with belville springs.

Cheers!
 

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Vincent Brake

Well Known and Active Website User
VOC Member
The design was eventually easy made: at any hight on the curve, a line on it (perpendiculair to the center axis), crosses the middle. Not so easy drawn though. So there is always a line contact at any height, and both sides are the same curve.
Made with ball mill R3 and CAM programm

and now for a question?
how much Tork does a twin deliver.?
say with a MKII cam and 1:8 tune?

so we calculate some springs. and an rubber end cushioning.

How would we test it? Other than trial and error.
We've got a molested primary cover, could do a piece of glass in it,
than on a dyno....
mabe there are better (easyer) ideas here?

Cheers

Vincent
 

Bart

Website User
VOC Member
Yes indeed, now we'll have to figure out the springrate & preload.
The ESA should move back and forth at least a bit to be functional, but shouldn't go to full lock too soon.

So to set ourselves some boundary conditions, we thought the maximum design torque is less than what the prim. chain will yield at or the crankshaft (ET17/2) will rotate in the flywheel from, i.e., other things will break before the ESA runs in it's maximum 'compression'.
And a value for the 'low end' of the peak torque we can find from engine torque.
Because the torque is delivered in a pulsating manner, the peak torque the ESA will encounter during typical driving will be two times the nominal torque of the engine.

Attached are 1) a picture with the cross-section of the designed cams, showing every 'surface' pointing toward the center of rotation and 2) the curvature of the cam profile, showing an initial ramp of 10 degrees, progressively increasing to 72 degrees at maximum curvature. The original is about 45 degrees, with no initial ramp angle (essentially, it's a round profile).

Any ideas, experiences or thoughts on this are dearly appreciated!
 

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oexing

Well Known and Active Website User
VOC Member
Hi Bart, Vincent,
compliments to your CAD skills, I guess this was quite some headscratching for designing something useful at the CAD place. My thinking you could have designed a bit more of range in the ESA for smoother operation on the road. There are two considerations I see with ESAs : Protection of gearboxes plus smoothing out the kangaroo ride with singles or twins at very low speeds.
The first aim seems not to be essential on Vincents as there are two chains in the transmission of power to rear wheel so not a harsh life for gear teeth anyway - unlike with all gears Guzzi or BMW twins. And Vincent gearboxes are designed extremely strong anway , I never have come across stories about gearbox wear even with the old non-working ESA. So this is not a point for any ESA on Vincents at all.
The second aim for smoother ride would require a bit more of range in the ESA to be felt so that is why I´d go for a bit more of range, so maybe keep your logic and reduce lobes to max. four of them and round out a bit more - bigger circle. 72 degrees at steepest spot seem quite a lot, I´d think 60 could be all you need. When going over 45 degrees at gradients you get some self-locking condition when having springs loaded onto the lot anyway, not so with the original design unfortunately, too shallow shapes there. But then I do not know, just thinking, tests will tell.
For some time I was thinking of suggesting you could find a business case here in new ESAs production as the Spares Co seems uninterested to go for real progress. But as expected when told about CAD activities at your place your design is not really great for economic machining - typical CAD ball nose cutter endless lines milling. My guess an hour or two rattling along in alu for each item, even longer for smooth finish.
Myself helpless in CAD I came to a different logic looking at the half century proven BMW ESA on all flat twins for machining both parts with standard straight end mill, using my dividing head plus encoder on it on the manual mill with DRO. That worked absolutely perfect even on the very first alu test pair. You´d do same today on a CNC lathe with milling attachment in 15 minutes for both parts and perfect smooth faces. These machines are so fast when having a standard end mill for roughing and finishing provided the part was designed for it - unlike the typical CAD line milling in small steps with ball end mills, unsuitable for mass production. In the BMW design you see two different shapes that go together, no benefit to have same shapes in an ESA, the effect will be you can machine this design at no time on a modern CNC lathe with milling head included, no mysteries about matching faces due to the logic in the design strategy. Just thinking . . . .

Vic
P1050188.JPG


P1050180.JPG


P1050216.JPG
 
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vibrac

Well Known and Active Website User
VOC Member
As always its not designing a superior item thats hard, its defining if a market is big enough to support it
If it were not so all Trains would be riding on 7ft* broad gauge now

(*never mind that extra 1/4")
 

Bart

Website User
VOC Member
About it being economical: probably not, but what's the volume of production anyway?
We're not so much interested in that. Cost of design far outweighs production anyway!

Machining time will be about 45 to 50 mins in hardened steel with insanely smooth surface. In aluminium it was done in about 30 mins and I can do something else. Load the machine with ten parts and go for a ride in the mean time! ;)

The shape, as symmetrical as it is now, has the (arguably small) advantage of two line contacts per lobe instead of only one, reducing wear.

I did draw a 60 degree steepest indeed, that's what we'll have to determine.
I think you're right about the function: smoothen out engine pulsations.

I'm guessing that... knowing the average engine torque at a certain engine speed, inertia of the crankshaft and the fact that only on one of four strokes per cylinder the torque is generated (and then even in a small part of the powerstroke itself), the angular movement of the crankshaft can be calculated -under the assumption that the primary drive chain rotates at a uniform speed-
Off to the white board!
 
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greg brillus

Well Known and Active Website User
VOC Member
Not to mention that a high proportion of twins and singles out there have crankshaft assemblies where the drive side mainshaft has already spun in the flywheel..........I have just replaced one last week on a single crank that had done this....... More common than you might think.......You only need to look at the mills pin and see if it still lines up.........They mostly don't........This might be the limiting factor you are looking for.
 

oexing

Well Known and Active Website User
VOC Member
Greg, what´s your way of repairing a crank when you find a snapped Mills pin ? Try to align a new mainshaft and ream an oversized pin ?
I wonder if one could do a mod on crank webs by broaching a parallel slot for a key and fit mainshafts like this prewar Horex below with slot ? It has a short taper fit, no great idea at all but the keyed shaft is allright and would be a fix for Vincent mains.
As to selling a few new design sets of ESAs, I would have spent my money on new sets for sure when reports about them were confirming their effectiveness. No question for me to have some peace of mind afterwards to avoid any risk of desaster from a snapped chain - got two engines with welded cases with same history thanks, but no thanks. So I´d think a supplier could sell 50 or hundreds of these new ESAs to the community when reports prove them working as intended.

Vic
P1070406.JPG
 
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greg brillus

Well Known and Active Website User
VOC Member
Hi there Vic........ I will say I'm a bit of a novice on these cranks, as I use to get them done by Laurie Binns down in Victoria.........he was a well known and respected machinist all his life and he generally replaced the main shafts in near all the many Vincent cranks he did over a long time. He explained to me that the stock Vincent flywheels where no more than boiler pate, and that their interference fit on the mains and big end was ok but not great.......The flywheel material has very little memory and so once the shafts have been pressed in they tend to loose a lot once removed. Because the shafts are only 1 inch in diameter the surface area is quite small for such a capable engine........I'm not sure if they rotate due to sudden stoppage, or just in long service and perhaps too much back and forth movement of the stock ESA........The shafts we use are stepped with the flywheel section at 30mm in diameter, then reduced back to the 1 inch from there. We decided not to pin this shaft, but a keyway is probably a good idea.......It is hard to come up with a fix for everything......Only folk with your skills can recommend what to do there. Cheers.........Greg.
 

Garth Robinson

Well Known and Active Website User
VOC Member
Hi there Vic........ I will say I'm a bit of a novice on these cranks, as I use to get them done by Laurie Binns down in Victoria.........he was a well known and respected machinist all his life and he generally replaced the main shafts in near all the many Vincent cranks he did over a long time. He explained to me that the stock Vincent flywheels where no more than boiler pate, and that their interference fit on the mains and big end was ok but not great.......The flywheel material has very little memory and so once the shafts have been pressed in they tend to loose a lot once removed. Because the shafts are only 1 inch in diameter the surface area is quite small for such a capable engine........I'm not sure if they rotate due to sudden stoppage, or just in long service and perhaps too much back and forth movement of the stock ESA........The shafts we use are stepped with the flywheel section at 30mm in diameter, then reduced back to the 1 inch from there. We decided not to pin this shaft, but a keyway is probably a good idea.......It is hard to come up with a fix for everything......Only folk with your skills can recommend what to do there. Cheers.........Greg.
Back in the 70's a couple of places in the UK ,I think Roger Slater and Mellors Motors or Hillgate Motors offered the service of "roller pinning' mainshafts. A quarter inch roller was fitted axially into a hole drilled half in the flywheel and half in the mainshaft.I never knew anyone who had it done,so don't know if it worked.The ads are probably in the back of old MPHs.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Yes Garth, I always did it, The next one I will do the same for timing side as well, Works 100%.
The shafts and wheels are not really strong enough, If Sprinting Drag Racing etc.
I sawed a mainshaft in half , For a special job, Some time ago, Did not know how soft they were !!.
Cheers Bill.
I think it was only a long 1/8" roller I used .
 
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timetraveller

Well Known and Active Website User
VOC Member
I did it on one of my engines when competing. The first time I took a twin apart the main shaft had rotated as could be seen from the angle of the hole for the original pin. It had not continued to rotate and as far as I know the bike had not been raced before I bought it. I used a quarter inch roller, half in the shaft and the other half in the fly wheel and, as far as I know, it never moved again.
 

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