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ET: Engine (Twin) ESA upgrade


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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.



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Vincent Brake

Well Known and Active Website User
VOC Member
Force did on standard D type hit the hard end.

Here not at all.
But maybe a bit more opening curve to say 55-60 degree would give bit more play.
Bellvile wachers machined to 1,5 mm


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VOC Member
ONLY ONE PROBLEM, It's going to take me about 50 to 80 years to wear out the "new" series "D" ESA's I fitted on the twins twenty years ago, old ESA's are OK for Comets. My great-grandchildren might be interested ! "Too late she said as she waved her wooden leg"
I also put a series D ESA on my twin two years ago thnik mine will last a tad longer as it has not been run for two years now and may be next year.


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VOC Member
It's 12 degree initially, 58 degree max slope.

And no, it wouldn't like this. The steeper angle drastically increases the rotational stiffness. Also, stiffness near zero angular deflection is already present, where it needs a significant angle to build up with the original one.


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VOC Member
The present design looks positive, a bit more of range now and possibly progressive enough. I am not so convinced about that locking in effect at zero position you wrote , at 12 degrees and a bigger radius snapping in there. I can imagine this could induce some chain vibration when overrunning this zero spot in certain conditions so I would not want to introduce this feature. But what do I know, just saying. Anyway, BMW or Kawasaki did not include this locking shape in the zero position and they had their ESAs for more than half a century with no troubles from them, only a smooth ending of overrun from either side on the ramps instead plus spring load and steep gradients.
Did you have some welding on one component while finding new shapes, in the photos it shows some rough edges like weld ?
When all is finished and case hardened I´d think no hard milling is required here, heat treatment deformation should stay negligible for the purpose.
Many years ago I had some Belleville washers for inspiration to avoid all those tiny springs. But later I came to keep them with my new design of ESA and am very positive to get no troubles , no spring blockages expected, so no breakages. But then I cannot tell much about your tests with Bellevilles , look pretty hard to me. Also I don´t know if there may be a limit of cycles with these, only had them in plastic injection moulding business - with numbers of broken washers too.



Website User
VOC Member
Hi Vic,
There was no welding.
The fact that bmw or Kawa didn't do it, doesn't say it's not better. ;) perhaps they were limited by their design or manufacturing capabilities in relation to the cost.
The zero spot itself actually does have a small radius to smoothen the curve of course, so it's not a hard notch really.

We'll see how it goes!

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