Fork 2 way damper drawing

[chaterlea25]

Hi All,
Hopefully the attached sketch will enable those of you who would like to make your own "Taylor Dow" type damper valves for their BSA's

The original TD valves used 3/8in. diamater rods threaded 3/8 BSF and a 9/32in ball bearing (try finding those now!!)

Pattern ones sometimes have 10mm rods and 8mm ball bearings,

On my Super Rocket the length from the underside of the fork cap to the end of the damper valve body is
16 and 11/16in.
The overall length of the rod will depend somewhat on the depth of the domed nuts you use on top of the fork caps
copper washers inside and on top of the caps will stop leaks

I intentionally did not draw the top cap setup, If you cannot see this in your "head" then this project is not for you
Some people either braze a nut to the underside of the fork caps (and rechrome) or make solid caps drilled and threaded to hide the fact that the dampers are fitted
Rather than drilling through and using a dome nut on top!!

**When fitted the damper valve must be submerged in the fork oil to work**

I found 20w oil made the forks too stiff and now use 10w fork oil enough to submerge the valve when the fork is extended

****NOW THE IMPORTANT BIT,****
This sketch is provided for information only
NO liability is accepted for its use or misuse or anything else either!!


Cheers
John O R

[MG]

Thank you John, great work, highly appreciated!

What's the diameter of the small hole in the bottom of the valve body? 0.125" as well?

[chaterlea25]

Hi MG,
Yes
1/8in as well

[trickytree]

Thanks John, much appreciated.

[dpaddock]

Well done, John!
Many thanks.
David

[muskrat]

THANKS John, another project starts.
Cheers

[dpaddock]

John -
Is the 16-11/16" length of the damper rod measured from the inlet end of the damper valve to the face of the fork nut hex where it engages the top yoke?

David

[chaterlea25]

Hi David,
The 16 and 11/16in. dimension is from the underside of the hexagon of the fork nut to
the bottom end of the valve body!

Put another way, the damper assembly sticks down the fork leg 16 and 11/16in

HTH
John O R

[dpaddock]

Thank you, again, John.
BTW, looks like you have a good stable going there!

David

[dpaddock]

John

Please check the overall length of the damper assy; 16-11/16" reaches only to the fork seal region. 26-11/16" seems more like it.

Thanks

David

[chaterlea25]

Hi David,
Think again!!
If the damper rod was that long it would go all the way down to meet the plug thats at the bottom of the slider and prevent any movement of the forks at all

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

[dpaddock]

With a fresh load (213 ml) of oil in the forks of my '57 Spitfire (8-inch single side brake), the oil level is 19 inches below the fork crown; hence my question. Consequently, I made the rods longer so that the valve would be immersed in the oil, as you have stated. I have no clue as to why the difference, but it works nicely.

One other modification I made was to enlarge the central hole from 1/8 to 7/32 inch to reduce the harshness on compression.

Thanks again, John.

David

[beezalex]

Good stuff.  Thanks.

[chaterlea25]

Hi David,
I was thinking about your "issues"
I took the measuremants from an original set of Dow dampers, I must compare the rod length with pattern sets!!

If one modified the BSA forks to full "Dow spec" this involved longer top fork bushes which reduced the travel
and also the overall fork length, there was some discussuion on the bushes here some months ago
This reduced the ride height if a standard top yoke is used, BUt if the "Superleggera" top yoke is fitted this restores the ride height as the front of it dips downwards,
Most pattern stanchions wont work for this!! the stanchions must be parallel between the top and bottom yokes (Tpieces) Also parallel stanchions required for mounting clip on's securely

My solution was just to add extra oil till it met the damper valve, 10w or medium fork oil
Remember the forks sit lower when off the centre stand (so oil is higher)
Anyway it works for me

Regards
John O R

[muskrat]

Just picked up the material, on my way to mates lathe to make 3 sets. Rods will be made to suit.
Again thanks John.
Cheers