Front Forks Mk 1 Square Four

Singles, twins and fours.
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simon.holyfield
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Re: Front Forks Mk 1 Square Four

Postby simon.holyfield » Fri Apr 03, 2020 12:27 pm

Couple of questions then, given that I have my SQ4 in service with original forks (including springs) but new bushes, and I have my FH forks on the bench:
  • Should I fit new springs to both? The SQ4 is pretty soft on the front...
  • Is the two way damping modification worthwhile?
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

JohnnyBeckett
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Re: Front Forks Mk 1 Square Four

Postby JohnnyBeckett » Fri Apr 03, 2020 1:52 pm

if you need to get springs look up harlow springs they have them on the shelf look at my post in suppliers on this forum they are very good and made all my different types of springs and they have all the airel spring parts numbers :?: and a lot cheaper and a lot quicker because they are makers :!:

david.anderson
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Re: Front Forks Mk 1 Square Four

Postby david.anderson » Sun Apr 05, 2020 3:02 am

2 way damping is a major suspension improvement. Ariel forks are only rebound damped, and the design is such that the rebound damping does not work on the initial part of the rebound stroke. The standard damping relies on oil being sucked through the small hole(s) in the stanchion above the bottom bush on the compression stroke. The oil then floods around the outside of the stanchion, between the upper and lower bushes. On the rebound stroke the leg moves downward moving the bushes closer together and forcing the oil back through the hole(s) in the stanchion into the centre of the stanchion. It is the controlled flow of oil through those orifices that provides rebound damping. However, as the design relies on suction to pull the oil into place for the rebound damping, the outer gallery never completely fills, so there is no damping on the initial part of the rebound stroke.
Fitting the Dow type dampers not only provides compression damping, it also overcomes the inadequate rebound damping, as the oil is then forced into the outer rebound gallery which is then properly filled.
The only downside of the Dow damper is that the ride will become a harsher over potholes or rough surfaces potholes. But high speed stability is greatly improved and fork dive under braking is reduced.
The Dow dampers work best with a thinner oil. I use ATF.
It is also possible to adapt cartridge emulators to the Ariel fork which provides adaptive compression damping, giving the best of both worlds, but even when fitted (a tricky job involving some machining) numerous fork strip downs are required to get the damping setting correct.
The Goff springs are ideal for the 4.
David

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Re: Front Forks Mk 1 Square Four

Postby nevhunter » Sun Apr 05, 2020 6:52 am

Strictly speaking, the forks are damped on the last part of the compression stroke by the small finger sized projection going through the hollow bolt that holds the bottom bush in place on each fork stanchion. If you fiddled with it's dimensions you could vary it's effect. I never have and get damping using pretty heavy grade oil so far. I've always put a drain screw in the bottom of each fork end to replenish fresh oil now and again. A bit of extra fork travel would be desired if I was going to upgrade the forks much. They are typical "period" forks, so where does one stop? Once I have the springs about right I just put up with them and on the occasional BIG pothole, repair the front guard when it bottoms. (when (and IF) I get around to it). Nev


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