dowty forks

[ERIC BAYLISS]

Hi Gammakieth you say that you rebuilt your forks, was it easy or was it a pig like I have herd some people say. I have a set that needs doing and its the one job I have never had to do even when I had Velocetts. thanks eric

[BRIAN MARSHALL]

Hi Eric, It is more than 30 years since I rebuilt a set of Dowty forks, but from memory it wasn’t too difficult, but I had to make a tool to unscrew the seal holders inside each top leg. The amount of wear on the sliders needs to be carefully measured as fitting new bottom bushes won’t achieve anything if the sliders are worn. They will probably need to be repaired by hard-chrome plating, and then grinding back down to the correct size, very much a specialist job. A word of warning… The hard-chrome plating process causes ‘hydrogen embrittlement’ of the underlying steel, which can snap like a carrot. The legs MUST be heat-treated to drive out the hydrogen from within the metal. Do discuss this with whoever is doing the work, and if they try and fob you off, walk away and take the job elsewhere ! Another point to watch is the need for scrupulous cleanliness when you reassemble the forks. Any dirt and grit inside them will rapidly ruin the new seals.
Brian

[Barrie]

The forks are difficult to strip sometimes,
in theory it’s quite a simple process ,
as has been stated everything has to be in perfect order and clean.
I myself converted mine to spring operation which means that they will never suffer from air leaks again!
This was a popular mod back in the day

[BRIAN MARSHALL]

I seem to recall that Sammy Miller does a conversion to conventional coil springs. Worth a phone call ?
Brian

[gammakeith]

Sorry about the delayed response but have just got back from holiday. Yes, it was a straightforward job and easier than on more modern forks though certainly an odd design. I didn’t have to make a special tool but rather “winged it”. However, I forgot how I did it 😛 . I think a tool design is in Technicalities. Brian gives good advice but the key thing to remember is that the main seal for the air springing is NOT against the chrome section. Rather, the sealing is against the inside of the leg so that needs to be carefully checked. Thus, the chrome does not need to be perfect.

I thought I would give a set of replacement seals a go first before converting to springs. However, all has been well since. The front end is lovely and plush and easy to adjust to taste. I suspect the modern seals are better than what was originally fitted.

I got the seal set from Graham Moag.

Keith

[ERIC BAYLISS]

Thank you every one, will have to strip mine and see what they are like before I make a final decision Eric

[BRIAN MARSHALL]

The inflation valve used to be very specifically a Kilner valve, but during the years I had my 1950 Flyer I used an ordinary tyre valve, and had no problem with it.
Brian

[Tman]

I think I would be reluctant to change my Dowtys to spring operation as the air ride is superb, though as it neither leaks air or oil appreciably I don’t (yet) have any reason to.
If the forks are changed to coil springs, is the damping lost?

[Barrie]

The damping seems remain the same , the seals are still used when rebuilding, and so is the oil in the correct quantity .
My intention is to change the oil every couple of years ,as you would with normal forks.
Dowty’s idea was filled for life, they might have been if they had been manufactured to the same specs as their aircraft components !
The inside of the outer tubes should of been plated , not left plain steel where corrosion can damage seals

[Steve Bowles]

I have the tool you need.
pm me your address and I will pop it in the post.
Just send it back when done.
Steve

[ERIC BAYLISS]

Tried Sammy Miller, he doesn’t do them now. eric

[Barrie]

There are plenty of springs available ,
I suggest you find a more modern common machine of about the same weight and see what the prices are like.
The springs I had were far too long so I made an estimate to get the ride height correct, (red dot ),
I ended up with the forks extended about 20mm longer at rest, I then used the cut off section of spring to make rebound springs so the forks will not fully extend when the machine is on it’s main stand

[ERIC BAYLISS]

Thanks Steve have sent you a pm. eric

[Roger Hulett]

Is there an article by anyone who has exchanged Dowty for springs. I did renovate mine but had trouble getting the right seals at the time,so have considered the conversion for some time.

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