Fork mods?

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david.anderson
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Re: Fork mods?

Postby david.anderson » Tue May 22, 2018 10:50 am

Actually all forks can end up with pressure inside, however it is air pressure. As the forks function oil is pressurised as it is forced from one gallery to another, on both rebound and compression. This can cause a partial vacuum behind the oil flow which depending on the location may suck air into the fork through the fork seal. The fork seal by its design only seals in one direction which permits the ingress of air. Once pressurised, the damping may diminish a little, but is nothing to worry about under normal riding. I have noticed oil leaks around the top fork nuts when Dow dampers are fitted but no fork seal problems. And a little sealant stops the oil leak at the top nuts.
Even modern cartridge forks can be affected. My son has fitted aftermarket air bleed valves to his CRF250. After every race he depressurises the Showa fork before the next race.
David

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rschurr
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Re: Fork mods?

Postby rschurr » Mon Oct 29, 2018 5:17 pm

Had a discussion in the BSA forum aboutz "clanking" in the fork on my very early A7 (longstroke model). Have then got this drawing:

https://www.a7a10.net/forum/index.php?topic=2895.0

Will make this part / system for my BSA A7, but I think it fits also in the Ariel fork (which is much better than my A7 fork). It is indeed a replica of the "Dow dampers" how here in the forum several times were mentioned. I think the dampers of SRM and Paul Goff are similar in principle.

Please can anyone tell me how is the inside diameter of the Ariel SQ4 fork tubes, I can not get to this data without dismantling, what I wanted to spare now.

Will report on going work and tests.

Rednose
Last edited by rschurr on Fri Nov 02, 2018 6:46 pm, edited 1 time in total.
1923 James Model 12 500ccm v-twin -- 1960 Chevrolet Corvette C1
1926 Douglas EW 350ccm flat-twin -- 1967 Chevrolet Corvette C2
1936 Motosacoche 500ccm single --- 1979 Chevrolet Corvette C3
1948 BSA A7 500ccm parallel twin -- 1955 Ariel Square Four MKII :!:

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rschurr
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Re: Fork mods?

Postby rschurr » Fri Nov 02, 2018 6:41 pm

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 SQ 4. For my BSA A7 I welded 2 Nuts in the top screws, they are bigger as the Ariel ones.

20181102_191355 (Mittel).jpg

20181103_161208 (Mittel).jpg


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

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rschurr
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Re: Fork mods?

Postby rschurr » Wed Nov 07, 2018 5:00 pm

Hi,
have mounted in the meantime, the dampers on my BSA A7 (longstroke model).
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.

OK,
then I opened the top screws of my Ariel (the first time) to measure the oil level to determine the needed lentgh of the rods . What did I find?

Nothing!

There might be 1/2 inch of oil in the pipes. Damn PO. Have it filled up about 17 inches to the top.
Will now first make a test drive (see above) and then decide if I need the dampers or not.

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

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Re: Fork mods?

Postby tomwalker » Sun Nov 25, 2018 10:08 am

Hi rschurr
watching this thread with interest, as I am slowly working through servicing and checking over my new (to me) four piper.
Have you an update on the result of the correct oil level in the forks?
Thanks, Tom.

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rschurr
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Re: Fork mods?

Postby rschurr » Sun Nov 25, 2018 1:22 pm

Hi Tom,

it's about 17 Inches below the top face of the top bracket, motorcycle unloaded.

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

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Re: Fork mods?

Postby tomwalker » Sun Dec 02, 2018 10:12 am

I ve been looking at the drawing and dont understand how the oil returns past the valve on re-bound, because the ball bearing seals the 1/8" hole at the bottom of the valve,and there appears to be no other route for the oil to pass through? I cant see that all the oil passes round the valve itself?

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keith.mettam
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Re: Fork mods?

Postby keith.mettam » Sun Dec 02, 2018 11:57 am

Hi Tom, I am also interested in this fork mod and, after your observation, have just been reading through the replies in the above link to the BSA Forum and here is part of an answer from John O'Regan to one of the questions :-
'' The valve only has to sit in the oil, as the forks compress the oil is pushed up through the centre hole and out the radial holes, as well as up around the valve body,
on extension the ball closes the inner passage and the oil has to pass down around the valve body giving the damping effect
HTH
John O R ''

At the moment I am wondering what metal the valve bodies should be made in....aluminium ? I guess it is there somewhere and I have missed the obvious !
All the best, Keith

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Re: Fork mods?

Postby tomwalker » Sun Dec 02, 2018 10:16 pm

Thanks Keith. I wondered if that was the case.
I am still unsure over the basic design, because it would seem that there is less damping effect on extension than on compression, which I think is the wrong way round?
Again, I am probably missing something obvious!

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Re: Fork mods?

Postby nevhunter » Sun Dec 02, 2018 10:36 pm

Most shockers are set up to have more effect on rebound than compression but a motorcycle is different in so much as the tendency to dive is a factor that gets looked into. A hard compression cycle gives a harder ride feel and less "give" on the sharp bumps (The ones that dent your mudguard when you bottom out.). Nev


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