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 »

Thanks everyone, have now put the idea into the archive file, will no doubt pull it out sometime in the future and try it out.

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

Post by Simon.Gardiner »

simon.holyfield wrote: Thu Jan 20, 2022 10:13 am
simon.holyfield wrote: Wed Jan 19, 2022 7:23 pm The other idea I've been toying with is some kind of adjustable spring loading to dynamically restrict the damping according to the rate of compression...
I've been looking at this article. It shouldn't be too difficult to design a spring loaded valve into the Eddie Dow type rod, to provide less damping on sudden, sharp bumps - closing again to return to normal, higher, low speed /anti-dive damping...

https://racetech.com/page/title/Emulato ... hey%20Work
And for new readers this has almost moved round to the point of replacing Dow-type dampers with yer actual proper emulators, as per David Anderson:
viewtopic.php?f=21&t=61&p=1952&hilit=emulator#p1952 :twisted:
(Simes - I've had a set of the Racetech emulators for the Sprint for the last g.-knows-how-many years, however since I overhauled the forks and changed to a slightly thinner oil I've been happy enough with the 'factory' setup and not felt any particular need to do the mods, other than curiosity....maybe I just don't ride hard enough, although I do like to think my 'chicken strips' are respectable :mrgreen: )

SG
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'55 Huntmaster, '56 VH, ' 51 VH, '62 Arrow, '80 R100RT, '00 Sprint ST (now with a new Arrow project, and just now those 4-stroke Ariel parts can't even make one running bike...)
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by simon.holyfield »

I'd completely forgotten that thread... and I had commented on it!
cheers

Simes

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'58 Huntmaster,
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'30 Model A
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by Simon.Gardiner »

Time to lay off all that steam oil, me lad?!! :D

SG
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'55 Huntmaster, '56 VH, ' 51 VH, '62 Arrow, '80 R100RT, '00 Sprint ST (now with a new Arrow project, and just now those 4-stroke Ariel parts can't even make one running bike...)
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by jj.palmer »

Can someone please explain.

I'm trying to understand how the Eddie Dow unit creates damping on the springs rebound stroke when the ball restricts the flow of oil into the lower leg and the damping chamber, see attached diagram "B".

What am I missing ?

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

Post by simon.holyfield »

Ignore the damping chamber for the moment. As you have shown in your top picture, oil passes through and around the ED insert and enters the fork leg on the compression stroke. On rebound, the ball closes the orifice and the oil can only pass around the ED insert, to get back to the lower leg. It's that change in flow area that provides the rebound damping.

The damping chamber continues to provide the limited compression and rebound damping that Mr. Page designed it to do.
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'30 Model A
https://ariel-square-four.blogspot.com
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by david.anderson »

John
Don’t forget that your Ariel forks are rebound damped, although not very well. Forgetting the dow damper, on the compression stroke the leg rises on the stanchion. As the leg rises there is a vacuum created in the leg in the area that surrounds the stanchion between the top and bottom bush. Oil is sucked from inside the stanchion through the 2 orifices in it and into the expanding chamber outside the stanchion between the top and bottom bush. There is no damping as the oil movement is by suction but as the leg begins to extend on the rebound stroke the bushes move closer together and then the oil that has been sucked into that chamber is forced back through the orifices and that is where the rebound damping comes from. The problem with that system is cavitation ie air in the mix. The vacuum of the compression stroke was not enough to completley fill the outer chamber with oil so the initial part of the rebound stroke is undamped. And when you go to a heavier oil to increase the damping, then even less of the heavier oil is sucked into the outer chamber. Now when you add the Dow damper, on the compression stroke the oil in the centre of the stanchion is pressurised and some escapes through the centre of the Dow or around the Dow giving compression damping. But that pressurised oil is also forced from inside the stanchion through the stanchion orifices into the outer leg which also now forms part of the compression damping. But now the outer chamber in the leg is filled with oil (as it was forced in under pressure) so the rebound damping becomes more effective and is immediate.
David
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Re: Eddie Dow type damping on 1958 Huntmaster front forks.

Post by jj.palmer »

Simon, David thank you.

David, in simple terms cavitation is eliminated within the "damping chamber" by forcing oil into it rather than being sucked in by a vacuum, now understand.
I stilll have a copy, and often refer to it, of your writeup on the forum back in 2014 which starts "A little explanation on how your forks work".

One thing that I have noticed with the ED drawing is that there are no manufacturing tolerances stated. Comments have been made regarding increasing the centre hole for 1/8 inch to 9/64 inch to reduce the damping on the compression stroke, but, if you were to have made the .950 inch outside diameter slightly larger, even by .0022 inch, this would negate the increase in hole size. Accuracy I believe is quite important.

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

Post by jj.palmer »

Another question, can anyone help, why is there a ball within the unit to restrict the flow of oil from the upper stanchion into the lower leg ?

Question 1, on the rebound stroke, see diagram "B", the ball restricts the flow of oil from the upper stanchion into the lower leg, any partial vacuum created in the lower leg would have the effect of "sucking" the oil out of the damping chamber rather than it being forced out, thereby reducing the damping.

Question 2, on the compression stroke, see diagram "A", if there is a lack of oil in the lower leg, oil starvation, this could reduce the possibility of filling the damping chamber and also reduce the damping effect through the damping control hole.

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

Post by david.anderson »

John
The dampers were developed by Eddie Dow for his goldie. The effectiveness of these dampers on the track speaks for itself. However many find that the damping is overdone for the road, as our road surface is clearly not the same quality as the track. To overcome this, many such as myself use lighter fork oil. I use ATF. Others enlarge the central hole or remove the ball. Apart from the improved rebound damping through the outer chamber as a result of fitting the Dow damper, additional rebound damping is provided around the perimeter of the dow damper.
1/ yes the ball does restrict the flow of oil within the stanchion but forget about vacuum. As the 2 bushes move closer together on the rebound stroke, the oil within the outer chamber is compressed and has to go somewhere under pressure and that can only be through the 2 orifices and back into the stanchion. flow under pressure is much greater than flow under vacuum.
2/ yes if there is a lack of oil it will effect the damping. Fill the forks to the Ariel spec of 17” from the top of the stanchion and when fitting the dow ensure that the length of the rod immerses the damper fully in the oil when the forks are fully extended.
David
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