Grey Flash 2751

The history and restoration of a Vincent HRD Grey Flash

The UFM

The Vincent Upper Frame Member (UFM) utilises the engine as a stressed member and also acts as the oil tank. It is attached securely to the cylinder head by a bracket (1). The rear of the UFM is attached similarly to the rear cylinder head on 1,000cc vee-twin models. The single cylinder Comet, Meteor and the Grey Flash models, however, feature a bracket/tie (2) that fills the void, where the rear cylinder would be, and connects the rear mounting point of the UFM with the engine plate, gearbox and inner primary chaincase.

The headstock is bolted to the oil tank and, on the Grey Flash, the headstock casting is extensively drilled for lightness.

On Grey Flash models, the vertical portion of the steering head, where the headraces are located, is covered by an aluminium plate where the headstock transfer is visible – this would have originally been polished but may be anodized on 2751.

Once this plate has been removed one is confronted by an extensively drilled area thus:

The UFM number is just visible.
The number RC/1A/4651 explained: ‘RC’ = Series C, ‘1A’ = Grey Flash (the design number) then the frame number. In this case, the frame number (4651) minus the engine number (2751) comes to 1900 – as was often the case with Vincent numbering.
Bracket welded to rear of UFM.

A bracket was welded to the rear of the UFM, by Terry Prince, to enable the attachment of a remote carburettor float chamber for a GP2 carb’. Once the UFM has been stripped of paint, the original dull chrome finish should still be in place. Then a decision will have to be taken whether to remove this bracket or not and how it might affect the external finish of the UFM.

The RFM

The triangulated Rear Frame Member (RFM) of the Vincent features a monoshock and was of a pioneering design. The origins of this feature go back to when Philip Vincent was studying at Cambridge and sketches he made from that time give an insight into his vision.

‘A’ is where the suspension connects the RFM to the UFM via two enclosed springs and a shock absorber. ‘B’ is where the RFM pivots – it’s sandwiched between the inner primary chain case and engine plate at this point. ‘C’ is the rear fork where the wheel is held in place.

Features of the Grey Flash RFM are a drilled and lightened pivot-bearing casting.

Image courtesy Peter Johnson.

I know that the RFM is dull chromium plated because I carefully removed some of the paint on the rear fork lug:

A bit fuzzy but the RFM frame number stamping is visible.

The lug on the opposing side features another less interesting feature though one common on Vincents:

Welded repairs are visible.

The axle is held tight by an “eared” or “lipped” nut on this side. The racing axle is of a solid waisted bolt type configuration not present here. Anyway, this nut features a tab that extends inwards into the chain adjusting slot of the lug. This enables the T-bar (on road-going models) on the opposing side to be rotated by hand whilst the nut remains immobile – a clever design. Unfortunately people unfamiliar with this feature often apply a spanner to this captive nut and attempt to undo it with brute force. The tab rotates, bears agains the lug slot and, if enough force is applied, will split it necessitating a repair by welding or brazing – as seen here… ⤵️

Brackets

The Cylinder head bracket of Grey Flash models was extensively drilled to a pattern that would be impossible to replicate without access to the relevant drawing.

But hang on…

30.10.2019: Actually, this bracket would truly be impossible to replicate; David Dunfey informs me that it’s not a Vincent HRD produced item… When compared to the drawings held by the VOC it’s plain to see the difference. A bit of a disappointment but one will have to either be acquired or fabricated.

The rear frame tie is of a special pattern unique to the Grey Flash as this model employed a different type of gearbox to those used by the road-going Comet and Meteor models.

The interface with the Albion racing gearbox is visible in this shot. On road-going Vincent singles the tie would have been of a different configuration to mate with the Burman ‘boxes fitted.
Detail of spacer and link.

The gearbox link is also visible in the below shot. I’m unable to state whether this differs from the regular production part or not, at present.

The gearbox link.

The engine plate (pivot bearing plate) is of a different configuration to match the mounting points of the Albion gearbox.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: