Grey Flash 2751

The history and restoration of a Vincent HRD Grey Flash

As mentioned in the post before last, there was something that we felt we needed to get to the bottom of. The image of this component, kindly sent to us by David Dunfey, featured a nut seated in a counter bore. This nut had been torqued into place and was held by the edges of the bore to stop it turning, enabling a bolt to secure the cranked plate from the inside of the inner primary chain case. We felt that this wasn’t perhaps what had initially been conceived… With the nut protruding, gearbox adjustment would have been practically nil.

Here we can see the countersunk nut.
Image courtesy of David Dunfey.
The “witness mark” of the gearbox adjusting slot is visible in the shot. If the gearbox were adjusted to move backwards, the slot casting would have come into contact with the protruding nut.
Image courtesy of David Dunfey.

We felt that The Works would have employed another solution, enabling full adjustment of the gearbox…

Solution #1.

First, Bert drilled and tapped a hole for the bolt. This looked better than the captive nut arrangement and would have allowed for full gearbox adjustment. I persisted with another line of thought though, despite Bert telling me it’d be good enough as-is… David’s plate was counterbored and this surely would not have been done so neatly when the bike was being used in anger on the track. I surmised that the unthreaded, counterbored hole had been for the fitment of a threaded “top hat” arrangement. I insisted and Bert set to work…

Solution #2.
Voila! The sleeve and bolt match those in an image that David kindly sent me – surely this was a better engineering solution?
Notice the beads of perspiration glistening on the freshly fettled alloy plate…
That’s what I’m talking about! Full gearbox adjustment is now achievable.

The end result is a part which is almost identical to David’s but utilises a different solution.

And the hole spacing appears very similar to David’s original component, visible in this shot.

We will never know the correct answer unless we are able to examine another original Grey Flash. Might full gearbox adjustment have not been deemed necessary? Or might a top hat threaded collar have once existed on David’s bike and been lost at some point? It could have dropped off and been replaced with the nut, or maybe it was always like this…

I could be barking up the wrong tree with this but we’ll stick with it. Once again, thanks Bert!

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