Dowty forks

[Deleted User]

Evening all,

As part of a deal to obtain some new(ish) bits I am putting a pair of dowty oleomatics in the mix. From a scott, they obviously need rebuilding but appear to hold air. However I have no idea how much they are worth. Please could any one give me a rough figure on what I should ask?

Many thanks to my fellow Scott masochists in anticipation,

Jerry Hillman

29 Flying Mongrel (frame now done and engine not far off)

[Deleted User]

The Oleomatic design was a great idea but in many ways was almost designed to fail! Filled as they were with atmospheric air, inevitably containing water vapour, all contained in a bare steel tube, seal failure was almost guaranteed. The next time your plane is flaring out for a touchdown just hope that they managed a better job on the landing gear than they did on the Oleomatics!

It just happens that I’ve been working on a “cunning plan” to eliminate the problem for some time now and consequently have been collecting bits to play with. I’ve paid £50.00 for scruffy ones but they can fetch £150.00 or more for a really tidy pair with complete yokes.

If there is any scoring or rust pitting in the upper tubes then they are going to leak and/or destroy the piston seals as sure as God made little green apples. If you find the upper tubes to be anything other than perfect in the bore then replacement 1.875” inside diameter solid drawn steel tube with a perfect bore is almost impossible to locate – if you do let me know! I’d go so far as to say that if the seals need replacing then the upper tubes will want replacing too particularly after 50 odd years and the next pothole is just around the corner . . .

[Deleted User]

Just an idea, wouldn’t it be possible to use nitrogen instead of plain air? This is very commonly available these days at tyre fitters etc. and must be a lot cleaner than air….

[Deleted User]

Erik, don’t you dare start that hare running! I’ve already got to make it to July 2188 to stand any chance of realising all the schemes I’ve got buzzing around in my noggin!

In fact I’m slightly ahead of you, (great minds think alike, fools seldom differ?!!!), in that I did considered the possibility of a “Sparklets” soda siphon gas capsule, (do they make them anymore?), and a little regulator under the top yoke to keep things topped up. Then I took my pills and had a lay down in the dark ‘till the urge had safely passed!!!

I rather suspect that it is not just a bit of rust and worn/age hardened seals that is the Oleomatic’s problem. I rather suspect that the gauge and therefore the strength of the upper tube is marginal. I can’t think it was a question of weight saving either, the lower legs each weigh a ton and are unsprung weight into the bargain.

Also I am not over impressed with the fits of the internal components, there may be a reason that I have not considered but to my mind as things are, and I have measured several now, they do nothing for the location and control of the all important piston seals.

The result is, I suspect, that when the machine hits a pothole of any size the tendency is for the legs not only to compress but also for the top tubes to deflect backwards as well. The effect of such a deflection on any tube is to cause it to go oval to some degree; if then there is any weakness in the sealing such deflections could just be the last straw and cause a loss of pressure or a sudden deflation.

As I’ve mention before I do have a “cunning plan” that could just possibly entirely eliminate the problem. However the difficulties of obtaining the materials I wanted to use, the cost, (small pension, very limited funds!), and other calls on my resources have resulted in the idea going no further than a set of drawings so far. It is after all a highly speculative project needing a lot of time, testing and development. Even if it did work there is a very small market for the modification and so little chance of recovering the cost.

But that’s its love for your fellow man innit?

On the other had if anyone knows where we can get 15.125″ (384.17mm) lengths of 1.625″ (41.27mm) i.d. x 1.781″ (45.24mm) o.d. steel tube nicely hard chromed inside and finished to size for less than a king’s ransom then the existing design and seals would fine . . .

[Deleted User]

Maybe a path you already walked but from the days I owned a big pussy (a Panther M120 that is) I know the Panther owners club also has quite some knowledge on Dowty as they were also used on Panthers.
Below a link with some info.

https://www.pantherownersclub.com/PantherPage/p-tectip.html#Dowty

They also sell the Dowty seals.

Erik

[Deleted User]

The last time I was over at Holders, David had set up a bank of machines to manufacture a batch of new legs / stanchions for Dowty forks. David knows what he is doing and makes a good job at a reasonable price. If you are interested, I suggest you contact David, Matt or Ron at
The Velocette Motorcycle Company
Meriden Works
Birmingham Road
Allesley
Coventry CV5 9AZ

Tel (0)1676 522 066
email velocette.motorcycle@virgin.net

If they have a customer already for the batch, then ask who they are and you can buy from their customer. Hope this helps Roger

[Deleted User]

Well done, Roger, (again!), what a mine of useful information you are!

Just another thought; I know that most modern oils contain molecules that trap water but is there one that has an emphasis on this particular property?

In addition are there any new coating/surface finishing processes that might be employed to protect the bores? I’ve been out of the game long enough to be out of touch with the latest developments and it was only ever peripheral to what I did anyway so has anyone any thoughts?

After all, while buying new tubes will solve the problem for a time they will still be prey to corrosion unless protected.

Any ideas anyone?

[Deleted User]

We had a customer’s bike with Dowty forks here for a while. The forks were down to bottom position as all air had escaped. I decided that if there were slight air leaks through stanchion surface imperfections or seal wear, then air would leak more slowly if there was a thicker oil film. We put in SAE 90 gear oil and it worked fine and stayed up while we had it. Thinking more about this, I consider the Slideway Oils we used to use on machine tool slideways. In this application, a gear type oil was blended with an adhesive so that the oil would stick to the surfaces rather than drain off. This is a similar characteristic to Castor based oils where there is a molecular attraction to metal surfaces. If I had Dowty forks, I would put in this type of oil like Mobil Vactra 2 or if very worn Mobil Vactra 4. I put heavier oil in my Douglas 90 plus forks and as they are worn, it recreates the action of an unworn fork with lighter oil. It works for me! Kind Regards Roger

[Deleted User]

I’m sure I speak for a number of us with doubtful forks! Is it worth a straw poll to see how many people might be prepared to invest in a cure?
Add me to that list asap. Keep up the good work engineery types, we stupid owners need you!

A tutto gas

Paul

[Deleted User]

If a number of folks were interested in new stanchions, then tell Graham Moag and let him negotiate with David Holder about putting some in stock at a small batch price. He could stock some seals and sell with an instruction sheet, perhaps copied from Technicalities. Of course his time must be paid for. Only the rich can afford to be philanthopic! R

[Deleted User]

I can agree with previous contributors regarding the strength of the fork tubes. I set out on a long VMCC run to Stranraer in 2007. At the start , the forks were working perfectly. At the end of the run they were down, and no amount of pumping would bring them back up. After trying new seals etc , etc, all to no avail, I discovered that the fork tubes were very slightly bent , just below the lower yoke. I can vaguely remember hitting some big potholes on the run, and my theory, now backed up by others is that the fork tubes bent at this time.
After a fruitless search for replacements, I fitted internal coil springs. They work well, but damping is poor and I lose any oil quickly. Some work to be done here. I now have a choice of longer or shorter wheelbase, depending on which way I fit the tubes! The bend is so slight as to be unnoticable, but I am very careful over potholes now.

Jim

[dave bushell]

I’ve not had to dismantle my Brum forks that are Dowty but they have springs fitted as original. They are oil damped and do not leak. In the past, spring conversions were available. I know for the purists, doing the conversion is not acceptable but the appearance of the forks is unchanged and they don’t present any problems.
Dave

[Author]

Posts