Girder Fork Repairs
Given that most manufacturers stopped using girder forks over 70 years ago, it is not at all uncommon to find forks badly worn or damaged. Worn bushes, spindles and stripped threads are common issues here we’ll show you how they can be repaired.
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Worn Bushes
Some manufacturers used bronze bushes in their forks from new. However many didn't, the Webb forks used for the images on this page and Norton forks are two examples. If bushes were used it is a simple case of getting the old ones out and pressing new ones in. A useful tip for getting the old ones out is to use a tap that's 1/16'' bigger than the spindle to put a thread in the old bush, then screw a bolt in and you have something to tap with a drift from the other side.
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When bushes were not fitted from standard the repairs are a little more involved.
Here’s one way of doing them.
Set up the machine
In this picture the top yoke is being set up on the milling machine using a length of silver steel in a collet to line the yoke up. It is important to use the correct size silver steel and run it all the way through. Any slight miss-alignment here will make the forks reluctant to move.
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It is important to bore, bush and ream one side before boring the other side. This makes sure you have the 2 bushes in line with each other.
Bore the end out
We'd recommend aiming to have a bush with a wall thickness of around 1/16''. In this example a 5/8'' cutter is being used in the yoke designed for a 1/2'' spindle.
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The longer the bush is the better, we usually aim for around 1''.
Make a bronze bush
Sintered and oil filled bronze bushes are available off the shelf in a range of sizes and are relatively inexpensive. However we have found these to not last that well. A proper bronze bush turned up from the solid, with the correct sized hole drilled and reamed, is a far better option. It also allows you to ensure a proper fit.
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About 0.002'' oversized on the outside diameter is ideal.
Press the bush in and ream to size
A fly press is ideal for this job, but if you don't have one, a piece of studding with a washer and nut on each end will also work.
Once the bush is pressed in you will need to ream it to size again as the interference on the outside will close the thin walled bush in slightly.
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Once this has been completed on one side, the yoke can be put back on the milling machine and lined up to bore the other side out and repeat the process.
Stripped or Worn Damper Thread
Turn old thread off and make threaded sleeve
This picture shows the link on the left with a badly damaged thread. The link on the right has been set up on a stub arbour in the lathe and the thread turned off. A sleeve has then been threaded and the inside bored out to give a 0.002'' interference fit on the link.
Press the threaded sleeve on
Make up a sleeve to use to press the thread on. It just needs to be a piece of aluminium tube that's a clearance fit over the turned down link and has both ends parallel.
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The threaded sleeve can then be pressed on with some Loctite retainer.
Repair the female thread
The damaged female thread can be built up with Sifbronze as shown on the bottom arm in this picture.
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As can be seen here, the top arm has virtually no thread left in it at all.
Bore and tap
The built up arm can be clamped down on a milling machine and bored back out to tapping size. A tap then needs to be used to re-cut the thread in the Sifbronze. Although not the strongest of materials to cut a thread in, it will be more than capable of the task here.
Refit the arm to the link
Due to the threaded sleeve being pressed onto the link with an interference fit you may need to use a thread chaser or thread file to get the final fitting. It can be time consuming but worth it for the good quality finish that can be reached.
New Spindles and Reassembly
Although not required on the forks used for this example, you'll often find the spindles to be badly worn as well. We produce fork spindles, nuts and washers for a range of girder forks.
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If you decide to make some new ones yourself that's fine but make sure you select the correct material. The fork spindles are a relatively small diameter and take a lot of force.
We use EN24T - EN16T would also be suitable. Do NOT use free cutting mild steel or stainless!
These forks are being used on the 1928 CS1 featured on this website. As such they were left unpainted to fit in with the 'oily rag' restoration being undertaken. If they were going to be painted we would complete all of the above work and have a dry assembly before getting them painted.
