The Blog Oldracers posts - Grey Flash Diary June 2012

Grey Flash Diary June 2012

42 George Brown on the experimental 498 Vincent HRD, with Girdraulic forks, alloy cylinder barrel. Shortly to become the Grey Flash in the hands of John Surtees.

The workshop has been a busy place this month What with swapping of gearbox cogs in the Comet Racer, Angela’s XBR, and the Scott coming off its pedestal after a 3 year long fitful build things are a little crowded. So in the temporary restricted space I concentrated on turning some parts for the Flash.
The Comet races on a koni damper on the back, and for the last 5 years an AVO damper that I modified on the front. But as I am trying to stay true to the concept I have decided to try Vincent dampers to the Flash, when you think of what other British motorcycles (Douglas T35 excepted) were po-going about on in the late forties the Vincent dampers were a tour de force.
Way back in the sixties when I production raced the twin, before Konies were around (or perhaps they were, but I was too brassic to buy them) I modified and used Vincent dampers without any bad feedback., However there are 2 main faults I had to rectify.
Their perceived main fault leaking, is easily rectified. Modern seals should cure the leaks except under severe stress (I once had a front unit explode on me but it was the Comet Trials outfit and it was a very large rock and we weren’t hanging about). For the Flash I have modified the outer plug (D13), to take some nitride oil seals .43X0.93XO.24_R21 from Simply Bearings. There is plenty of space to bore the plug out and slip the seal in.
The other fault in the original damper, ‘aeration’ needs a little more work., So as before, I modified the Vincent unit to a ‘recirculating mode’ as suggested by P Hendra in MPH138 (or repeated in ‘40 years on’ page 11). Some of my metering holes are smaller than before since I am starting with fork oil (see below) rather than 20/40 filtrate, otherwise the ball in its hole and the plug were all made as described. Most fork oils are given as ‘weight’ (Wt) but one brand of Wt is not always the same as another’s so it’s a good idea to stick to one brand. My plan is to start with a small hole and heavy oil, and to work down the Wt’s and up the hole sizes. Of course these adjustments will only affect recoil damping. To adjust compression damping, the disc hole that resides in the assembly in the bottom of the unit would need to be changed (smaller=harder), needing to add hardness to a Vincent ride is unlikely, and since I doubt that item was changed twixt twin and single, initially I will ignore it. We will see the results in due course, If I fail AVO are just up the road.
I also turned up the parts for the foot brake I started on last month using the drawings from “obscure components”. It’s only when you hold the raw material like a steel bar in your hand, and you make the parts on contemporary machinery, (watching the pile of swafe rise and the clock tick), that you start to appreciate that Vincent’s were designed and built in another age. A time when function was king and cost was a secondary consideration. I worked as an apprentice in a similar engineering factory about 20 miles from Stevenage, and in the sixties I watched at first hand (and helped!) the bean counters move in, and redesign products wholesale. Economy of design was paramount, cutting material specification here, removing a machining operation there, and introducing proprietary components at every turn. The result today is that a motorcycle factory is just an assembly plant. Few factories making end products have a machine shop nowadays.
Because the design of the Vincent predates that wave of ‘efficiency’ the supposed lack of attention to economic design may well have contributed to its downfall. Thankfully, however, it is also the reason that that a Vincent is performing well after

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