Author Topic: Front fork dampers  (Read 619 times)

Offline Rookie_V#60

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Front fork dampers
« on: 24.10. 2018 20:15 »
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1923 James Model 12 500ccm v-twin
1926 Douglas EW 350ccm flat-twin
1936 Motosacoche 500ccm single
1948 BSA A7 Longstroke 500ccm parallel-twin
1955 Ariel Square Four MKII
1960 C1, 1967 C2, 1979 C3-gone!

Online chaterlea25

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Re: Front fork dampers
« Reply #1 on: 24.10. 2018 20:43 »
Hi Rudol,
There are lots of topics here discussing the damper rods (including my own)
The early fork legs did not have the two oil holes that allow a certain amount of damping action by pumping oil in and out between the leg and slider,
this is one of the reasons early forks "clank" so much

John
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Re: Front fork dampers
« Reply #2 on: 25.10. 2018 12:15 »
G'day Rudy.
Easy to make your own with John's drawing. https://www.a7a10.net/forum/index.php?topic=2895.0
I made three sets, materials cost about $10 each.
A big improvement.
Cheers
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Offline Rookie_V#60

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Re: Front fork dampers
« Reply #3 on: 25.10. 2018 12:58 »
Thanks John,

yes there is much clanking in the fork on bad road!

And thanks Musky brining me on the spur of John's drawing and explanations! Great projekt for bad weather time! I'll try it also for my Ariel SQ4, I think it is a similar system!

Cheerio Rednose
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1923 James Model 12 500ccm v-twin
1926 Douglas EW 350ccm flat-twin
1936 Motosacoche 500ccm single
1948 BSA A7 Longstroke 500ccm parallel-twin
1955 Ariel Square Four MKII
1960 C1, 1967 C2, 1979 C3-gone!

Offline Rookie_V#60

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Re: Front fork dampers
« Reply #4 on: 02.11. 2018 18:43 »
Have now made 2 sets of dampers (one for the BSA and one for the Ariel). It was a simple, straightforward thing with John's drawings and explanations. Will now measure the oil level in the forks (and the inside diameter of the Ariel fork) to determine the length of the rods. I think I will choose the visible version with the dome nuts a la Eddie Dow  for the Ariel. For the A7 I welded nuts  in the top screws because they are a little bit bigger then the Ariel ones.


Rednose
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1923 James Model 12 500ccm v-twin
1926 Douglas EW 350ccm flat-twin
1936 Motosacoche 500ccm single
1948 BSA A7 Longstroke 500ccm parallel-twin
1955 Ariel Square Four MKII
1960 C1, 1967 C2, 1979 C3-gone!

Offline RogerSB

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Re: Front fork dampers
« Reply #5 on: 02.11. 2018 22:23 »
I have Eddie Dow dampers fitted to my 1960 Golden Flash.

I'm not an expert, engineer or mechanic like a lot on here but when I first got my GF the forks clunked on the return at full extension. This happened when going over a big bump or pot hole in the road.  I tried different oil without success but came to the conclusion it was because, with dampers, on full extension there isn't enough oil getting quickly enough between the bottom and top bushes and causing them to clash. I found the cure was to make sure the oil level covered the damper valves. I've not had that problem since.

Maybe others can throw more light on it?
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Re: Front fork dampers
« Reply #6 on: 03.11. 2018 10:40 »
G'day Roger.
The oil is supposed to cover the valve on full extension of the forks. The rods should not be long enough for the valve to hit the bottom of the sliders on full compression. So it may be a little juggling act to get both right.
The Dow dampers you have may have been made fot the A50/65 with shorter legs, hence having to add oil to cover the valve.
Cheers
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Offline RogerSB

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Re: Front fork dampers
« Reply #7 on: 03.11. 2018 18:06 »
Hi Musky,
When I first got this bike, and not knowing any better having not had dampers in any of my previous bikes, I added the manuals recommended 7.5 fl oz of fork oil. When I realised what was happening and to find out the right level to get rid of the clunking was this (rightly or wrongly):-

With my bike on the main stand and weight on the carrier to get the front wheel off the ground, I removed the dampers and aligned one of them alongside a fork leg to see where the valve would be when it was inside. I then added oil and used a steel rod to check where the level was, adding more until the level was just over the position where the valve would be when inside. With the dampers fitted again and the small amount of displacement - bingo! Not had a clunk on the rebound since.

However, I do get the occasional clunk on depression when I hit a pot hole or go too fast over a speed bump. I'm puttig that down to weak springs and / or worn bushes. My job this winter.  I did ask in a previous thread I started asking if anyone had experience of progressive springs: https://www.a7a10.net/forum/index.php?topic=13602.0

But no info forthcoming (edit: experience) with progressive springs  *sad2* .
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Re: Front fork dampers
« Reply #8 on: 03.11. 2018 19:29 »
Hi All,
When the full Dow kit was fitted to the forks, longer fork bushes were fitted, shortening and stiffening the forks
To restore the ride height the Super Leggera top yoke moved the stanchions downwards
Thinking this through it would also affect the length of the damper rods
I copied the dampers and rods from a set of originals
However I do not know if they were originally sold for standard or shorter length setup Or were there two different length rod lengths available back in the day *????*
If they were only sold as suitable for the shortened forks this may explain why (some) people find they do not reach the original oil quantity

 *conf2* *conf2*
John
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Offline RogerSB

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Re: Front fork dampers
« Reply #9 on: 06.11. 2018 13:18 »
Removed one of my dampers today to measure it and take photos.
Overall length of rod only including 1" of threads top and bottom is 16 5/16".
Assembled and from bottom of top nut where it butts up against top of stanchion to bottom of valve is 16 3/4".
Assembled and from bottom of top nut where it butts up against top of stanchion to top of valve (so is my oil level) is 15".
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Offline Rookie_V#60

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Re: Front fork dampers
« Reply #10 on: 07.11. 2018 16:43 »
Hi,
have mounted in the meantime, the dampers, 17 inches long are now with me the rods (old longstroke fork).
Have then made a test drive, there is a nasty railroad crossing nearby, was always associated with a loud "clank".
Well - now no more- the fork works perfectly with the dampers. Thanks again to the forum protagonists John and Musky

Cheerio Rednose
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1923 James Model 12 500ccm v-twin
1926 Douglas EW 350ccm flat-twin
1936 Motosacoche 500ccm single
1948 BSA A7 Longstroke 500ccm parallel-twin
1955 Ariel Square Four MKII
1960 C1, 1967 C2, 1979 C3-gone!