ET: Engine (Twin) Engine Shock Absorber

greg brillus

Well Known and Active Forum User
VOC Member
The shock absorber is not only responsible to absorb power shock loads from the engine but reverse loads from the rear wheel forwards, like from a sudden stoppage like a crash or some other uncontrolled lock up. It absorbs torsional loads, just like the row of springs in a clutch plate center from a manual car. The issue with broken chains and so on is either poor maintenance, poorly fitting parts (wrong collection of parts assembly) and lastly the fact that over the years the availability of good quality chain has declined, remember what happened to the "Goodwood racer" of the Horner brothers......they could not find any decent chain, and were lucky it didn't smash out the front of their engine.........most users of these bikes should not concern themselves, it seems all too easy to "Overthink" these things.
 

Pushrod Twin

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VOC Member
I have just read the other post, directed to by the link. Like Cyborg, I am now understanding better the reason for Vic's insistence that the Vincent ESA is not progressive whereas the BMW one is. The steep sides of the female curve (for want of a better expression!) on the BMW style do not appear instinctively to be progressive, but when looking harder & adding that to Timetraveller's diagram, I now see it.
The Vincent one, visually, appears instinctively progressive, but is not, it the pressure exerted along the shaft would remain constant, it relies on springs progressively compressing to make the movement progressive.
I join Cyborg as convert number 2 and will go and stand in the corner. :(
 

Chris Launders

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VOC Member
I can certainly see what Oexing is saying about the ESA and I have to agree, but surely the shock loads are not generated by the engine, the flywheels should damp them out, and as regards breaking the triplex primary chains, that seems a ridiculous thing to happen in any sort of normal usage.
 

Simon Dinsdale

VOC Machine Registrar
VOC Member
VOC Forum Moderator
regards breaking the triplex primary chains, that seems a ridiculous thing to happen in any sort of normal usage.
It is common knowedge that the spate of breaking tripplex chains mainly occured in the 1970's & 80's when the quality of primary chain went through the floor with Reynolds stopping the manufacture of motorcycle grade tripplex chain and quitely replacing it with industrial chain, usually with cheap split rollers. Why is it you never hear of Comets breaking primary chains which use the same ESA but a single row chain? Could it be because the single chain was still available as motorcycle grade?
The biggest problem with the Vincent ESA is it rubs against the outer main ball bearing during movement and slowly wears away and so moves the engine sprocket inboard over time. This then puts side load on the primary chain due to sprocket misalignment which is not good and Vic's BMW design will suffer exactly the same problem. I have seen twin engine sprockets which have worn right through the hard surface of this contact area and caused the sprockets to be out of align by over 1/8" which is not good on a tripplex chain which is inherently stiffer against sidewards forces than a single row chain. That and low quality chain is most probably why they broke.
 

Albervin

Well Known and Active Forum User
VOC Member
I have come in late and only scanned most of the comments. However I did see a very graphic demonstration of the "old" type ESAs sold by the VOCS against the "new" type. The old ones were plainly riding up to a very thin shoulder due to poor machining practise. The manufacturer refused to change their design. It was only with Ian Savage's insistence that the new and more accurate ESA made it to the manufacture stage. Now the two parts of the ESA run perfectly in sequence and optimise the loads. One thing that did annoy me though was that when these new ESAs were manufactured the old ones were not consigned to the bin immediately. When you do your next major maintenance look closely at the way the ESA works, each cam should maintain full contact and not "ride up"; if it does then bin it and buy a new one.
A question. If you use an electric starter in the approved way, how does that differ from a roller or a run and bump or downhill clutch start? When I do a downhill start I am in two minds whether to use clutch or valve lifter. Again I absolve myself from cries of incompetence because I am a chemist and not an engineer.
 

Cyborg

Well Known and Active Forum User
VOC Member
The shock absorber is not only responsible to absorb power shock loads from the engine but reverse loads from the rear wheel forwards, like from a sudden stoppage like a crash or some other uncontrolled lock up. It absorbs torsional loads, just like the row of springs in a clutch plate center from a manual car. The issue with broken chains and so on is either poor maintenance, poorly fitting parts (wrong collection of parts assembly) and lastly the fact that over the years the availability of good quality chain has declined, remember what happened to the "Goodwood racer" of the Horner brothers......they could not find any decent chain, and were lucky it didn't smash out the front of their engine.........most users of these bikes should not concern themselves, it seems all too easy to "Overthink" these things.

Overthink is my middle name. Its a curse usually followed by a case of vapour lock. Don't disagree with anything you wrote there, but..... didn't I read some where that one of your fellow countrymen studied the ESA's movement with a strobe. He found that it was basically an on/off switch. So assuming I did actually read that somewhere and the ESA in question wasn't knackered, thats what makes me want to agree with Vic. Agreed that dampening is a good thing, its just that if the ESA isn't doing a good job of the "A" part and maybe at best it's delaying the inevitable shock by a nanosecond, then it isn't much of an improvement over just having a bunch of backlash in there. I honestly don't know, but I have an ESA installation coming up so find the subject interesting.
 

Bill Thomas

Well Known and Active Forum User
VOC Member
There is a lot of people who have put a lot of miles on the old ESA,
We now know not to use the washer that locates the spring ends the way it was intended, Some just turn it around, But there is a better washer we can buy now.
I think in over 50 years, 17 years Racing I had the nut come loose once, And had a few broken springs.
Not so bad ?.
 

erik

Well Known and Active Forum User
VOC Member
I would like to say that I have some experience with BMW gearboxes 5 speed from the seventies. I had never a problem with the esa ,but the rest of the gearbox was not very good engineerd.After less than 50000 miles the layshaft was for the bin and three idlers from the mainshaft ,too.Pitting on the pinions was although a problem.Changing gears was all the time very poor in relation to other motorcycles.BMW is not the benchmark to my mind.Regards Erik
 

Pushrod Twin

Well Known and Active Forum User
VOC Member
I would like to say that I have some experience with BMW gearboxes 5 speed from the seventies. I had never a problem with the esa ,but the rest of the gearbox was not very good engineerd.After less than 50000 miles the layshaft was for the bin and three idlers from the mainshaft ,too.Pitting on the pinions was although a problem.Changing gears was all the time very poor in relation to other motorcycles.BMW is not the benchmark to my mind.Regards Erik
True. I had an example of the reputedly "indestructible" 4 speed /5 box in my R90S powered Earles Fork side car rig. I guess it was the combination of R90S horse power & side car work that broke the gears!
The cush drive went back into service!

Another point which has occurred to me is that the rounded tips of the Vincent ESA do appear to lend themselves to binding together, like two tapered wedges driven together. The BMW type cannot do that.
 
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