Jake Robbins
Girder Forks Repairs & Manufacture

Jake Robbins talks about his girder fork engineering business, sharing his

insight into girder forks care, repairs, maintenance and manufacture.

(Part 2)

 

▲ Jake at his forge in East Sussex. The forge needs some attention to get it back into working order. It's a project that Jake is planning to tackle at some point in the future.

 

 

 

▲ Druid fork on a 1913 Zenith

 

 

 

▲ Chromed Girdraulic fork on a customised Vincent Comet.

 

 

 

 

 

Jake Robbins
- girder fork specialist

Telephone: 07986 254 144

Email: elkforks@aol.com

 

 


 

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Modifying girder forks

 

"Often, girder forks need to be modified in some way. I can help in replacing side-links with different sizes to suit various needs. Changing the length of the lower side-link alters the trail, which may be suitable for sidecars usage, or for trials riding or sprinting.

"Sidecar forks, incidentally, take a lot of abuse on the sidelinks, caused by the unbalanced riding and turning forces. It manifests itself in uneven spindle distortion, bent side plates, and fractures on one side of the forks. So these need special attention.

"Recently I had a works Royal Enfield in the shop that at some time had had its girder forks replaced by Montessa telescopic forks. The owner wanted to revert to girders, and I was able to build a pair from parts that I had around the workshop and extend them for extra ground clearance. That allowed the owner to use the bike in other categories.

"I also do a coil spring conversion that fits inside Dowty Oleomatic telescopic forks, as fitted to Panthers, for instance. You still want to keep the air system working properly, but Dowty forks can collapse when a seal blows, and the spring acts as a back up.

Generally speaking, I can sort out most problems without too much fuss. I look forward to helping out where I can."

 

Girder fork reproductions

 

"Recently I made a batch of 10 sets of Castle forks as fitted to Brough Superiors. The Castle design was “borrowed” from Harley-Davidson, and altered in minor ways. My forks are faithful reproductions, and accurate in every detail. The price was £1950, and all have been sold.

"But the demand is still there, which is why another batch will be ready soon. I’ll be happy to make batches of other forks for clubs. I was thinking of reproducing Speed Twin girder forks, but I have to be sure the demand is there because it takes a lot of time and a lot of investment in tooling to complete such projects."

 

Types of Girder Forks

 

"The earliest girder forks were built usually by motorcycle manufacturers. The designs varied considerably from company to company. Some were lower leading-link (meaning that the front axle is forward of the line of the front forks, much like a swinging arm reversed, while some had a parallelogram type system. There was also a cantilever system where the pivot action is up by the steering head.

"After about 1914 to 1915, almost all designs went over to the familiar top link systems with 4 spindles and a rigid girder. That, apparently, was the most effective way of doing it. It makes for a heavy fork, but a strong one. All the pivot action is kept well out of the road grime.

 

 

Druid, Webb and Brampton forks

 

"The early Druid forks have the four spindle system, but with side springs going from the lower yoke onto the fork blade—whereas Webb type forks have a single centre spring. The Webb system is better. You can vary the spring more and it gives a longer travel.

"Early Triumphs used a biflex system where the forks move not only up and down but backwards and forward, thereby dramatically shortening and lengthening the wheelbase, which is far from ideal in terms of handling. Such forks have a slider top link. They were around in the late 1920s.

"By the end of the 1920s-1930s, the three main types were Webb, Druid and Brampton. BSA, Triumph and one or two other manufacturers also made their own, but these were all broadly Webb-type forks.

"The triangulated fork tubes arrangement on each side of the wheel is called the fork blade. Tubes were, in many instances, tapered for both strength and elegance.

 

Fork damper systems

 

"Damper systems were introduced towards the end of the 1920s giving better control over the rebound and compression. The friction damper system was usually incorporated into the lower links and trimmed with damper wheels embossed with the marque or fork manufacturer’s name. But occasionally, the damper system is at the top of the fork on the side.

"Early HRDs and Vincents (pre war) had Bramptons. Post-war they went over to Girdraulics which was Vincent's own design.

"Webb forks are probably the best with high quality tubing and slightly better action. Velocette took it one step further with the last of the overhead cam bikes (post war). These forks had a hydraulic damper system.

"I’ve catalogues with 1000s of forks, and can usually help with identification where needed."

 

Girder fork care and maintenance

 

"The way to increase the longevity of girder forks is nothing other than simple routine maintenance. A light, modern, lithium-based grease is superior to the older grease that used to be common. Lithium grease has better water repellent qualities. Every 5000 miles or so is a suitable service period. But this will need to be increased if the bike is stored in a damp environment (which is generally bad news), or if a bike is being used for trials or racing.

 

Read Part 1 ►

In Part 1 Jake Robbins talks about identifying girder fork faults, repairs, frame straightening, girder fork retubing, modifications and replicas.

 

Jake Robbins

Girder fork specialist

Telephone: 07986 254 144

Email: elkforks@aol.com

www.jake-robbins-vintage-engineering.co.uk

 

 

 

Copyright: November 2009

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 




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