Eddie Dow type damping on 1958 Huntmaster front forks.

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jj.palmer
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by jj.palmer »

David thanks again, trying to gather as much data as possible in an attempt to come up with something that is based on the ED unit but can be easily adjusted ie increase/decrease oil flow, with/without ball etc..

Can now assemble the unit into the stanchion from the top by removing the top yoke and the stanchion top screws, the screws being removed by a method suggested by Stan Coupland on AOMCC Facebook, thanks Stan.

John P.
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by jj.palmer »

Have been enjoying myself of recent, have made a pair of adjustable units for the front telescopic forks to provide damping when on the compression stroke. The flow rate or the area through which oil may flow is adjusted via a screw which gives infinite variance over a selected range. The range currently covers that which members' have referred to in respect to the various holes sizes used with the ED unit i.e. .125 inch, 9/64 inch and 7/32 inch.

I have tried to provide flexibility in the design so as to trial as many different settings as possible. For example it may be used with or without a non-return valve as per the ED units.

To adjust the units they are lifted upwards through the top yoke, the adjustment screw is marked with graduations to control adjustment and assist in recording performance relative to a particular setting.

It now remains for some trials to be carried out to determine whether it functions as intended and if so what are the most suitable settings and if not, back to the drawing board or into the junk bin.

I’m sure Eddie Dow made something similar to try various settings prior to arriving at the .125 diameter hole that he found suitable for the racing track surface.

John P.
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S6007200.JPG
jj.palmer
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by jj.palmer »

For attaching the Eddie Dow unit to the existing chromed top yoke stanchion bolts without having to drill a hole through the chromed surface this is one method, see attached.

John P.
Attachments
S6007292.JPG
S6007291.JPG
ED unit to top bolt.jpg
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paul.jameson
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by paul.jameson »

I like that and may well use it on my KHA. It has damped rear (plunger) suspension so improved forks may well be a good idea.
Paul Jameson
35 LG (project), 37 RH500, 52 ex ISDT KHA, 54 KH(A), 75 Healey 1000/4.
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist (but not Machine Registrar), Gauges and Clocks Spares Organiser.
jj.palmer
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by jj.palmer »

You are welcome, a small return for yourself and others for their dedication and contribution to the running of this excellent motorcycle club.

Hoping to complete the trialing of the adjustable damping unit, riding the same route at each setting, approx. 1/2 hour ride, going over the same bumps, grate covers etc. each time to get a reasonable comparison between each setting.

John P.
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by jj.palmer »

I have now finished the trials with the front fork Variable Damping Unit, the trials have proved
that it functions as intended and can be adjusted to achieve optimum damping on the front suspension compression stroke.

The units were fitted to my 1952 KH500 iron head.

The trials were ridden over a set route of approx. 30 minutes duration, I’d identified areas on the route where there were rough surfaces, grate covers etc.. I compare the ride over these areas at each setting of the damping unit, monitoring how the bike bounced, if that is the correct word, and particularly any bottoming of the suspension.

The operation of the damping unit is shown in the top part of attachment “A”, the non-return valve ball may be used or it may be removed. The unit is withdrawn through the top steering yoke for changing the settings, it takes approx. 20 minutes, also see pics. of the unit in a previous post.

At the bottom of attachment “A” is a list of planned settings that I had intended to use for the trials, each setting determines the total area through which the oil may flow, given in square mm, the total area being that through the centre holes and the outer annulus. Each setting is an increment of a quarter of a turn of the oil flow control screw.
Example setting number 1, only allows oil to flow through the outer annulus, an area of 42.2 mm^2 with nil oil flowing through the centre holes.
Example setting number 6, allows oil to flow both through the centre holes and the outer annulus, an area of 53.4 mm^2.
Added to this list, shown in red, are the equivalent Eddie Dow settings calculated from the hole sizes that members have referred to in previous posts. This will compare where I optimise my final setting to that of the Edie Dow unit.

Summary of the trials.
The oil used was ATF.
I started at setting number 6, carrying out trials both with the non-return valve ball fitted and also without the ball fitted, I could not perceive any difference in the damping whether the ball was fitted or not. The damping at this setting was not satisfactory.

I repeated the above at setting number 5, again I could not perceive any difference whether the ball was fitted or not. The damping at this setting was not satisfactory.

At this point I decided to remove the ball and not use it again.

I continued the trials without the non-return valve ball, setting number 3, total oil flow 45.4 mm^2, proved to be very satisfactory, this I decided was the optimum setting. This setting, you will note, is very near to the original Eddie Dow setting.
End of summary.

Prior to making the units a lot of work went into measuring the front forks, calculating the oil levels etc. this info. is available if required.
Having now tamed the front suspension it makes you realise how much the rear end is jumping about, Paul if you are reading this, you mentioned damping units fitted to your rear plunger suspension, could I trouble you for some pic’s, may be a winter project.

One thing that I did conclude was that without the non-return valve ball bouncing about these units could be made out of aluminium, much easier to machine.

John P.
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Variable damping unit..jpg
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by David Smith »

I have a set in my KH. I filled the fork leg, then dropped them in far enough to be just submerged. They work very well. Make sure the valve end is thread locked, mine loosened and fell off into the fork. My magnetic pick up thingy fell in half trying to retrieve the end, , also in the fork as well, finally managed to remove them with a claw type pick up without dismantling the forks!
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by jj.palmer »

Taken a long time to get around to it, have now wired the assembly together to avoid dropping any parts into the bottom of the forks, see previous post.
John P.
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