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ET: Engine (Twin) Engine Shock Absorber

Bob P

Active Website User
VOC Member
I have looked at our stock of kickstart gears and the land at the top of the teeth is about 0.5mm so is much better that the one's in your photo. I have noted your comment for when we reorder.
I will raise the ESA profile issue with the technical team as I am sure this issue has come up before.
We are happy to get some made, but would require drawings.


Well Known and Active Website User
VOC Member
As I understand the situation
Suggested modifications or changes to Vincent designs should always be via the Drawings Comittee they are the source of drawings and it is the task of the VOC technical officer to liaise with them as he is a member of the comittee I would suggest your ideas about the redesign of the ESA should be addressed to him not The VOCSC
his address is inside cover of MPH


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VOC Member
VOC Forum Moderator
I think Tim Kirker had a modified engine shock absorber at an AGM a few years ago. I think this new improved profile was produced by the Drawing Committee. Is this used for the new shock absorbers sold by the Spares Co?


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VOC Member
I asked to see the new shock absorbers when I was at the Spares Company a year or so ago. What they had done was to go back to the original drawings and realised that over the years the machining quality had deteriorated in that the curved profiles were no long at the correct angle to the axis of the device. The new ones had this corrected but they were nothing like the one which Vic shows. Ian, or someone else there, can tell you if I have understood and remembered correctly.


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VOC Member
we had a discussion a while ago about the ESA, see link below. There are more details there and am afraid some did not get the point I was trying to make clear - instead trying to find excuses and making believe that the BMW type would not work on a Vincent. But they never found a real argument why it should not. BMW has sold millions of Bikes up to 1000 twins with that ESA in the gear box, and with a lot smaller size so the torque and loads are a lot higher than with the bigger Vincent parts - which has three lobes instead of just two in the BMW. To this day I have not seen a good photo of the current spares so must assume the design has remained basically and it cannot be modified to really do its job, no progressive action in there.
I am happy to send the alu test set to examine, the male side is simple to machine on any CNC plus dividing head. The female side requires a motorized dividing head with encoder for fast and smooth machining - any Mach 3 stepper motor CNC mills could do it but you had to pick a solid machine for milling that. I say any competent CAD and CNC guy should be able when I did it by pocket calculator and manual mill plus DRO on the mill and encoder on the dividing head - slowly but perfect from first try and two sets of ESAs welded and milled. I cannot provide a drawing, not easy with 3 D dimensions. But I can point to the logic how to find the data. We can go into details in PMs but for getting things done a public discussion may lead to results sooner than contacting the inner circle where all efforts may be dumped .
I do know Tim has redesigned the ESA shapes a bit and I am quite aware he will not be amused. But a working new design may produce a big sale and income to the club to compensate for remaining stock that will only be used for replacing some defect parts then.
There are some more photos of this type of ESA, some from modern BMWs , one in the Kawasaki 1300 four, so they really know . . . .


ESA new design

Kawasaki 1300 , one, maybe two ESA inside gearbox:


BMW R100 gearbox input :



Well Known and Active Website User
VOC Member
I am sure Bill Par will be very interested in your suggestions and if convinced I bet he could easily mock up your suggestions on his 3D printer, that's where I think you should direct your discussions.
PS I think this thread is drifting...