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For Sale Magnesium Girdraulics

Capt. Biggles

Website User
VOC Member
Not without having them X-ray tested first, and then only for racing (smooth circuits, so no pot-holes or kerbs, unlike riding on the road).
 

oexing

Well Known and Active Website User
VOC Member
These blades look like lasercut from magnesium flat bar, so x-raytesting not so critical I´d think. Unfortunately not suitable in EU as all is imperial.

Vic
 

timetraveller

Well Known and Active Website User
VOC Member
The pictures suggest that this is an unfinished project. The blades are nowhere near finished and there is an unpleasant mark on one side of the blades about 10" up from the lower end. It could be a mark from the casting or extruding process BUT!!! There would be a reductionin weight of about 30% but it would be hard to find a magnesium alloy as strong as the best aluminium ones. Caveat emptor springs to mind.
 

LoneStar

Well Known and Active Website User
VOC Member
Norman, that mark may be a step from reducing the crossection , made by lasercutting or waterjet cutting, possibly ?

Vic
Looks like it - but a sharp-looking edge, just what you want to avoid if you're concerned about a crack developing...
 

timetraveller

Well Known and Active Website User
VOC Member
Over fifty years ago I saw a set of girdraulics at Frank Shillitoes which had been lightened for racing. They were milled out on both inside and outside faces, both above and below the lower link spindle position. In addition they had been severly milled around the front where the F32 plate goes so that only enough metal was left to house the spindle, pad bolts etc. I doubt that 30% of the weight had been saved but my guess is that they would still have been stronger than the ones in the advert.
 

Mike 40M

Well Known and Active Website User
VOC Member
Why don't make the fork blades from carbon fibre, if you want weight saving? Works for telescopic forks inner tubes on MotoGP bikes. And titanium bolts. If you want to go light.
 

Pushrod Twin

Well Known and Active Website User
VOC Member
Why don't make the fork blades from carbon fibre, if you want weight saving? Works for telescopic forks inner tubes on MotoGP bikes. And titanium bolts. If you want to go light.
Yes, John Britten did. It was only the development bike that broke a leg :oops: .The weak point was identified & rectified, the next ones never gave any problems.
 

davidd

Well Known and Active Website User
VOC Member
The Girdraulic forks are not heavy. The twin drums are heavy and the spring boxes are heavy. The spring boxes are not necessary if you run a coil-over. Everything else can take a bit of lightening, but it is not essential. Lowering the unsprung weight is always the best. Everything else is just along for the ride.

There is not much reason to lighten the forks for street work and the way Girdraulic blades fail appears to be acceptable. I would be a little concerned about properly assessing the way the carbon fiber blades would fail. I think it might not be a good thing on the street. In racing, there is always some risk that you have to accept because you are pressing the limits of all the components.

Most carbon fiber is illegal in vintage racing. It is in AHRMA.

David Tompkins has been running titanium fork spindles for a few years and they seem generally up to the task. He also has run titanium axles for years. I have always advised against it, but the axles seem to work. The 1/2" titanium bolts have failed in the gearbox plates with great regularity. When replaced by a Grade 8 bolt, the bolt performs perfectly.

I like titanium, but it is not the best bet for parts that need to resist bending.

The Girdraulics were specifically designed for sidecar use in addition to solo use. I think the choice of materials was excellent.

David
 

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