ET: Engine (Twin) ESA Upgrade

Bill Thomas

Well Known and Active Forum 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 Forum 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.
 

Bart

Forum User
VOC Member
Hi All,

So, again one iteration further, we settled on an initial slope of 12 degree ending at 65 degree at steepest
Milled it in some Maughans 'blanks' in under 30 minutes each (12000 rpm spindle helps).
The remaining 0,3 mm will be milled after hardening.
Saucer type springs with slightly increased bore.

Next: measure deflection under torque to fine-tune the springs.

Cheers!
Bart
 

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timetraveller

Well Known and Active Forum User
VOC Member
Nice project. I always like to see improvements being made to our old bikes. When oexing started discussing this and produced some figures I plotted a graph of the displacement against rotation on here. With linear springs the shape of that graph would have the same shape as the change in force. I could do that with the figures you have provided but I imagine that you have done that already. The question is what are the characteristics of those saucer springs? The characteristics of those have to be combined with the displacement. My memory is that when Norton moved over to a spring which I suspect has similar characteristics it was done to provide a large force to start with and then that would reduce with more compression. Good luck with the project.
 

Bart

Forum User
VOC Member
Yes, there is a slight non-linear relationship between force and compression, but it's increasingly less stiff.
Only ever so slightly, it's not a very strong effect! And it's compensated by the curvature of the cams.
Cheers!
 

Marcus Bowden

VOC Hon. Overseas Representative
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"
 

Bart

Forum User
VOC Member
Hi Marcus,
We're happy to provide you with adequate instructions on how to rapidly reduce your upgrade-cycle time. One of which is to try out this modern European style shifting pattern...
;)
 

vibrac

Well Known and Active Forum User
VOC Member
I guess there will be a bit of a glut on secondhand comet ESA from all us guys fitting 1/4" wide ESA for electric starts (plastic beats cad cam?)
 
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