Flash Fork Blades

[Tom Gaynor]

I had the standard blades intended for my Comet "flashed" by Trevor Southwell, to dimensions taken from an original Grey Flash. I have a sketch somewhere. They are milled "above and below". The total weight of blades unflashed was 3.54 kg, flashed it's 3 kg. I doubt very much if it makes any difference at all to the stiffness, since the material removed is redundant from a structural point of view.
Which is a pity, because I have a gut feeling that it's the stiffness of Girdraulics compared with Bramptons that makes C twins (reputedly) handle less well than B twins. This is all very subjective, but while my twin handles well enough, it gives none of the feedback needed to find its limits, so I stay well the right side of them. (Captain Sensible...who'd have thought it...)
It would be ironic if PEI and PCV were both so intent on high lateral stiffness to serve a sidecar market that would disappear in a decade, that they lost sight of solo function - and fashion. When I became aware of Vincents in the 1970's, they looked like relics of a bygone age. The good news was that their performance was not at all bygone, but had I not been lent one for six months I doubt I'd ever have found out.

 

[Hugo Myatt]

I have always thought that the amount of consideration for sidecarring in the design of the postwar Vincent is under estimated. Perhaps PEI's experience of the Stuart Waycott ISDT Velocette outfit influenced his design of the Girdraulics. According to PEI's autobiography after testing the outfit somewhat vigorously he discovered that out of the four tubes in the Webb forks one was broken and two were cracked. It is certainly true that many of the competition outfits using girder forks sprouted all manner of extra bracing.

 

[Pushrod Twin]

I would have no hesitation about using lightened blades on a twin. Even 1/2 Kg reduction in unsprung weight must make the ride more compliant. And it will never be skittish, Bramtons are obviously lighter.
If you are concerend about fatigue in the alloy, you could have them chemically paint stripped, crack checked then shot peened. Ensure you use a reputable organisation, many aircraft companies have the facilities & can give you some form of paperwork to back up their quality. Just dont let some backyard grit blaster lose on them. If you wish to learn about shot peening process, visit shotpeener.com
Cheers, R

 

[vibrac]

In my opinion slotted blades are not worth the effort I never noticed any difference racing and the old girl has standard blades now as I sold the slotted ones years ago for good money when I needed an engine rebuild (and got some standard ones with the change!).
As for aluminium steering heads, that IMHO is a step to far and thats not just me thats from someone who knows more about the UFM and its stresses than most. Dont forget in the immediate post war period aluminium was more available than steel, if Phil could have done he would have done-certainly on the racers.
I have been looking to save weight on the Comet racer since 1965 best mod to save weight on the front end with safety is Eddie Stevens advice: change all the pad bolts and nuts on the girdralics to alloy. you can also lighten the brake cams and do some work on the bolts that have to stay steel.

 

[nobby]

...I have been looking to save weight on the Comet racer since ...

Don't forget to drink less beer, it saves weight too.
Unfortunately, I never had this option fully controlled

 

[Pushrod Twin]

Peter,

Better to go with an aluminum steering head. Saves 3 plus pounds! The pictures are great inspiration.

Tell me about the alloy steering heads, are they cast or forged? Where from & where are the pictures?
R.

 

[davidd]

I have seen two aluminum steering heads. They are cast replicas of the original. One, that a friend has, was made by Maughan & Sons. The other was made by Ted Davis and recently sold on Ebay. I wondered what alloy they might have used and we speculated that it was probably something like 713 Tenzaloy as the small foundries seem to like pour it. Maughan's supplied my friend's 25 years ago, but they may know what alloy was used. I do not know of anyone who has installed one. By the way, Maughan's has their name cast into the piece.

David

 

[vibrac]

Read about timetravelers tankslapper in the flywheel offset item in this forum (and elsewhere) then ask yourself do I want cast aluminium headstock in that situation?
Even steel ones fail as poor Lance Capon found to his cost all those years ago....

 

[Bill Thomas]

I Think the Alexanders had one on there spec' racer, Ian had a big crash, Late 80s ish, I was told it broke bad, Don't know if it was the cause or the result of the crash. Cheers Bill.

 

[timetraveller]

The girdraulic fork blades are remarkably strong. Many years ago, about 46 - 48 at a guess, I had an old child adult chair on the side of a Rapide. I did not have a car at the time and I used the chair for collecting fuel for the stove in the caravan in which I lived, the local coal merchant having refused to deliver to anything as humble as a caravan. One evening I was returning from the local Club night with a young lady in the chair and was chasing two friends on solos. All was well until I got to a left hander on which I drifted outwards until the handlebars snagged the thorn hedge on the wrong side of the road. I remember going upside down with my face dragging through the thorn hedge and ended up about 50 feet out across the field on the other side of the hedge. The lady in question was ejected straight through the body of the fabric and wood chair which had four inch nails in the frame holding it together. She also ended up about 60 feet down the road while all the spare nuts, bolts etc., which had been in the boot of the chair, were scattered about 100 yards down the road. It looked pretty much like an air crash in the dark Eventually the two solo based chums realised that I was no longer with them, came back, went and fetched another Vincent chum who had a van and got the bike back home and me and said lady to hospital. The impact had been so strong that the front wheel was jammed between the bike and what was left of the chair, roughly where the rear brake pedal is. The bottom link had given up the struggle completely and had bent so that it had allowed the bottom end of the forks and the badly damaged front wheel to take up their new position. Sometime later, I got round to measuring the fork blades, which seemed to be untouched, with a straight edge. The bottom hole for the wheel spindle was about 1/16 to 1/8 of an inch out of line and those blades were in use for many years after with no problems. Believe me chaps, those blades are strong.
As a happy end to this tale, the lady in question still speaks to me.