ET: Engine (Twin) Shock Absorber

timetraveller

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and no amount of springs will prevent this
That is not quite right Vic. Several years ago Dick Sherwin fitted an Australian ESA to his 90 bore Black Knight which had a sidecar fitted. These ESAs have more springs than the standard Vincent one. After several months the ESA was taken apart and despite the fact that the bike plus sidecar had done several thousand miles there was only wear right at the bottom of the ESA cams. The ESA had not been getting anywhere near to the top of the cam profiles. A couple of springs were taken out and more movement was obtained. The cam profiles were very similar to the original Vincent ones.
 

oexing

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Norman, you may be right about that Australian special but I´d first want to see a picture of it before believing it. Must have been very different from original. I am quite sure you cannot have that spring preload from original Vincent ESAs so as not to slam the end plate , the cam shape is just not fit for purpose - as Neville once observed with bang/left-bang/right stops when playing the throttle. What makes matters even worse with unhealthy preloads on the poor ESA resp. the sprocket face is all loads from springs plus extra thrust from torque of crank acting on the cam slopes goes onto the inner race of the outer main bearing, wearing both the sprocket and the race. Only minimal area there for taking all wear and load, the radius on the inner race reducing it even more. Looking at the Vincent ESA the angles of the gradients don´t get steeper than 35 degrees when lifted. The BMW cams approach 60 degrees and this fact makes the progressive action almost self locking approaching that steepness, not much depending on springs near block length and not adding much extra load onto the bearing inner race. Self locking on steep gradients is well known from worm drives: You can turn a typical worm drive from the worm but the drive self locks when trying to turn the worm by the crown wheel. That was the reason Sunbeam inline twins had to have two start extreme pitch worms in the rear drive. Otherwise you would not have been able to push the bike with engine stopped when the crown wheel drives the worm.
Anyway, all efforts to get the old ESA do its real purpose by adding high spring forces are just bad engineering by not understanding - or ignoring - basics of face cam shock absorbers. Old habits and thoughtlesnesses die hard when engineers just take over from old times , accepting too fast all to be good enough - that´ll do - without thinking.
Just came to an idea for those poor souls running the stock ESA : Target is to prevent the ESA from bashing the end plate hard, the springs will not do it alone -as everybody knows. You could do a test with taking out maybe two or more springs and replace them with a length of hard rod, nice fit in the spring bores. In the bottom of the bores sink a short legth of a thick O-ring, a bit smaller o.d. than bore, maybe 1/4 " long. Do a test in a vice and compress the lot so you can see what length of o-ring you need to almost press the ESA to its stops. This would offer a softer sort-of- progressive stop and no more hard slam. Rubber gets steel hard when in a closed volume so some experiment with length and diameter of the rubber can help for feel. Don´t see any risk in trying on the bike, the rubber is in the bottom of the bore - unlike the broken coils of springs flying around in the primary.

Vic

Sunbeam worm drive:

p8_f5.jpg



BMW type ESA :

P1050216.JPG


Vincent ESA :

P1050185.JPG
 

vibrac

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Interesting to compare all that engineering complexity with a few pieces of special material on pegs in the electric start comet it doesn't take long to take the covers and sprag clutch off to inspect the drive so time will tell....
 

Peter Holmes

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Tim, apart from dispensing with the mechanical metal to metal contact of the standard ESA, how much movement does the new electric start ESA provide, it looks to be negligible to nil, I have no idea whether that is a bad thing or not, I have known people, very good engineers I might add, that have completely dispensed with the crankshaft ESA altogether and have the shock absorption elsewhere, especially when fitting a Norton/AMC gearbox.
 
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oexing

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Zero movement would not be a bad thing, if you just want protection for gearbox components. I´d think the Vincent gears are strong enough to not need any protection from an ESA taking into account that there are two chain drives on a Vincent - unlike all gears BMW or Guzzi transmissions. So some protection from harshness is there already. One thing I remember from the Alton ESA pictures is a non-existing bearing bush for the sprocket that one had to add on later or else I´d expect wear in there. But then in case you liked to reduce kangaroo drive mode at very low speeds by having an ESA with a lot more range the Alton will not provide this at all. So you are back at the questionable original - that I´d try to improve a bit with adding some rubber material in place of two or more springs in their holes. Somehow I like the idea now and hope somebody else will test this , can not do much wrong I guess.

Vic
 

Joe

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VOC Member
Now that would be another slap on that ESA, from me as you´d expect, once again: Could that knocking be from bashing the moving part of the ESA onto the end plate when all stroke of the ramps is used up - as is typical in this case and no amount of springs will prevent this ?

Vic
Hi Vic,
what You are suggesting seams something different from what I am trying to tackle - I am experience a little rattle only.
The behaviour you are explaining can be forced (and unintentionally happened to me) by quickly accelerated the bike from 2nd gear but rather then swithcing to 3rd engaging 1st gear instead. The ESA is doing it`s job by eliminating instant shock from rear tire to crankshaft.
What You hereby experience is like an inverted Automatic Breaking Systems (ABS). The rear tire oscillates at dry streets - I would say - at about 1/3 of the frequency you know from today`s cars. And Yes, You then clearly hear metallic sound of the ESA bashing to the end plate.
(Good, that the rear tire does not break out sidewise :). The oscillation frequency is mainly determined by the total ESA sping constant and difference in rear tire friction between tight grip and sliding grip)
 

Joe

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VOC Member
HI Guys,
I am surprised about the amount of feedback I am getting - thanks to everybody:)
To determine whether the little rattle comes from ESA I would need to spend half a grand to buy a new one which to me is not worth while the thing.
 

Martyn Goodwin

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Non-VOC Member
HI Guys,
I am surprised about the amount of feedback I am getting - thanks to everybody:)
To determine whether the little rattle comes from ESA I would need to spend half a grand to buy a new one which to me is not worth while the thing.
Fit a complete set of NEW ESA springs then go ride. If the noise is gone = solution.

If the noise remains then to rule our detonation/pinking set the ignitin full advance to 30 BTDC and go ride. If noise noise gone = solution (note with the standard ATD it may be a bit difficult to start with 30 full advance)
 

oexing

Well Known and Active Forum User
VOC Member
Joe, did you check the fit of all splines , on ESA that sits on the crank end, and the spline on the gearbox input shaft that holds the clutch center ? You described some not very loud noise when driving . Is this periodically even with constant speed , maybe not so loud but there ? Any difference in sound when accelerating lightly or decelerating lightly ? We are hunting for syptoms to understand but myself not competent in this, projects still a long way to go and never had a single meter on a living Vincent on the road, not to speak of yards or miles for sure.

Vic
 
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