The BSA A7-A10 Forum

Technical => Frame => Topic started by: chaterlea25 on 04.07. 2010 19:08

Title: Fork 2 way damper drawing
Post by: chaterlea25 on 04.07. 2010 19:08
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 *ex* *ex*
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
Title: Re: Fork 2 way damper drawing
Post by: MG on 04.07. 2010 19:20
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?
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 04.07. 2010 19:24
Hi MG,
Yes
1/8in as well
Title: Re: Fork 2 way damper drawing
Post by: trickytree on 04.07. 2010 19:31
Thanks John, much appreciated.
Title: Re: Fork 2 way damper drawing
Post by: dpaddock on 04.07. 2010 20:30
Well done, John!
Many thanks.
David
Title: Re: Fork 2 way damper drawing
Post by: muskrat on 04.07. 2010 22:00
THANKS John, another project starts.
Cheers
Title: Re: Fork 2 way damper drawing
Post by: dpaddock on 08.07. 2010 20:31
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
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 08.07. 2010 21:44
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
Title: Re: Fork 2 way damper drawing
Post by: dpaddock on 08.07. 2010 22:23
Thank you, again, John.
BTW, looks like you have a good stable going there!

David
Title: Re: Fork 2 way damper drawing
Post by: dpaddock on 09.07. 2010 21:41
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
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 09.07. 2010 22:27
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 *ex* *ex* *ex*

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
Title: Re: Fork 2 way damper drawing
Post by: dpaddock on 27.07. 2010 20:37
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
Title: Re: Fork 2 way damper drawing
Post by: beezalex on 28.07. 2010 13:41
Good stuff.  Thanks.
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 28.07. 2010 22:14
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 *ex*

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 *smile*

Regards
John O R
Title: Re: Fork 2 way damper drawing
Post by: muskrat on 28.07. 2010 23:02
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
Title: Re: Fork 2 way damper drawing
Post by: dpaddock on 29.07. 2010 00:04
OK, John; thanks.
BTW, I used threaded rod to ensure the valve was properly centered in the fork ID. Using a die on plain rod resulted in an off-axis thread, and my lathe needs to have its threading ability restored. Also BTW, I used 5/16 rod; seems to work fine.

David
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 29.07. 2010 21:19
HI All
David, a trick or 2 you can use to keep the threads straight is
1) hold the rod in the lathe chuck and use the tailstock hollow spindle up against the diestock to keep it square, advancing the tailstock as you turn the chuck by hand
2) make up a dieholder which has a morse taper that suits your lathe tailstock *smile*

A lot of the time I screwcut the required thread finishing a tad oversize and then clean with the die.
This gives the dies a much easier life especially on stainless

I found a photo of the complete "Dow" fork setup

"Enjoy the ride"

Cheers
John O R
Title: Re: Fork 2 way damper drawing
Post by: dpaddock on 30.07. 2010 15:08
Good tips, John; thanks.

David
Title: Re: Fork 2 way damper drawing
Post by: bonny on 30.07. 2010 16:00
just to say thanks for the drawing chaterlea , i have some nice 316 stainless steel bar and will turn up a couple . any other nice mods for the a10 ?
Title: Re: Fork 2 way damper drawing
Post by: muskrat on 30.07. 2010 20:33
G'day John O R,
                          Just fitted 1st set to the cafe, with 15 weight oil it feels great in the shed pumping up and down. Will have to wait to road test as I still can't get long pants on after last weeks little slide down the road. I made mine from duralium (high tensile aluminium) 19" O/A. Cost $30 and 3 hours to make 3 sets, the balls came from an old ball race.
 Fix one thing, find another. When checking the fork oil height on the '51 (2 1/2" on cafe) I was horrified. 8" of white GOOP. It's been a few years, lots of wash's and many wet rides since I looked at them. Water must get in on top of the seal and slowly work it's way in. Must be time for new seals and a small hole in the holders just above the seal.
Cheers
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 31.07. 2010 00:11
Hi All,
bonny, 316 is very hard on taps and dies!!!
Yup, lots more trick bits on my bikes!! (search for head steady)

muskrat, I believe most bikes will suck some water down the seals, I have gotten sealy which have a wee lip on top as well, this helps keep out the water!
I change the fork oil every year or so (or when I think of it  *conf*)

Hope your hide is mending well!!

Cheers
John
Title: Re: Fork 2 way damper drawing
Post by: bonny on 31.07. 2010 00:15
well i normally use the carbide tools in the lathe for cutting male threads and use taps for the female , and i have stacks of taps because we were supplied with them in my old job. so costs me nowt.
Title: Re: Fork 2 way damper drawing
Post by: muskrat on 31.07. 2010 08:23
Bonny, why add more weight when you don't have to. I also did away with the lock nut, just tapped and cut the threads to the right length and used loctite. Yes the alloy might wear faster but we would be talking many years.
Cheers
Title: Re: Fork 2 way damper drawing
Post by: bonny on 31.07. 2010 12:29
cos i simply don't have any on the shelf muskrat, i used to work as a fitter and turner for a company that made machinery for sewerage works all over the world , any stainless scrap was thrown into a basket under my bench and when full , dumped ! i started to feel sorry for all this stainless being dumped so decided to give it a good home ;)
Title: Re: Fork 2 way damper drawing
Post by: muskrat on 31.07. 2010 14:30
 *smile* No worries mate, I'm a alloyaddict. Less weight there, more weight here (pats tummy).
Cheers
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 01.08. 2010 00:22
Hi All,
I suppose I should have stated the valve bodies were/are made from alloy
I have seen a pattern set with alloy rods as well

Cheers
John O R
Title: Re: Fork 2 way damper drawing
Post by: Kees on 04.08. 2010 09:58
Hello John,

I have one question, I have a B31 do y outhink it also fits on my bike?
The inner diameter of my front tube is about 1" and the diameter of valve is .90" so the is a lot of space between those parts.
I think this will give no demping at all, maybe the inner diameter of your front tube is smaller?

Kind regards,
Kees
The Netherlands
Title: Re: Fork 2 way damper drawing
Post by: muskrat on 04.08. 2010 10:34
G'day Kees, Welcome to the forum.
                                                       I don't think John O R will mind if I answer.The OD of the valve is 0.950", giving 25 thou" clearance all the way round. Your forks would be similar to the A's and should work. Just check the length of the rod so that the valve is in the oil with the forks fully extended. Also make sure the forks have the correct amount of oil in them.
I just made 3 sets for my '51 and '57 and a mates '56 Goldie, they all work a treat.
Cheers
How many Karma's can I give John for the one post?
Title: Re: Fork 2 way damper drawing
Post by: bsa-bill on 04.08. 2010 11:17
You've just fired up my grey matter Muskrat.
I'm guessing the oil level should remain the same with the double damper installed, so would that mean the oil capacity should be the stated capacity (213 cc) less the volume of the damper valve.
Or maybe it's not that critical
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 04.08. 2010 11:20
Cheers Muskrat,
couldnt have put it better *smile*
"design" will work for  A, B and C models

One thing though The rod should not be too long or it will clash with the "spike" in the bottom slider on full compression of the forks *sad2*
I am sticking to the "Dow" length originally quoted and just add some more oil!!

BTY the damper makes a huge improvement to the early type forks that didnt have bleed holes in the fork stanchions
Cheers
John O R
Title: Re: Fork 2 way damper drawing
Post by: Tomcat on 31.12. 2015 01:14
I've just dug this old thread out to find out about two way damping. As buying them suits me better than making, I had a look around parts suppliers WWW's and have found SRM sell them but with hidden top threads. Does anyone know where I can purchase kits with the exposed acorn nuts? Thanks in advance TC
Title: Re: Fork 2 way damper drawing
Post by: BSA_54A10 on 31.12. 2015 03:24
Paul Groff does a couple of BSA forks
Title: Re: Fork 2 way damper drawing
Post by: Tomcat on 31.12. 2015 04:42
Yep, spot on Trevor. Exactly what I was after, and 20 quid less! Cheers TC
Title: Re: Fork 2 way damper drawing
Post by: KeithJ on 24.04. 2016 19:10
Hi, just been reading the posts as I am about to re-fit my dampers.  Can someone tell me if the dampers should touch the oil when the bike is off or on the centre stand?

Thanks

Keith
Title: Re: Fork 2 way damper drawing
Post by: Peter in Aus on 30.07. 2016 09:15
I have just made up a set of these dampers and one of the things I though I would do is to make the rods longer so as not to have to put so much oil in to cover the valve with the forks fully extended. But I soon found out that you can't, as when I checked to see if the valve would go right down (e.g. forks fully down) the valve hit on some thing, so had to make the rods so as the overall length was as the drawing, 16 1/4", I did  creep a bit I made mine 16 3/8" that gave me about 5" of movement before it would bottom out, not sure just how much movement there is  as I did not check that when I did the forks up some time ago, but I suspect that it is about 4" some one might be able to correct me on that?
One of the things that concerns me is the fact that the oil comes so far up the stanchion to cover the valve it leaves not much space for the oil when the forks bottoms out, I put 260ML of oil in to cover the valve,  adding a bit at a time (Fork oil 10W)and the last bit took only about 20ML to raise the oil level about 3"! (without the valve in there) so that makes me think that when the forks bottom out there can't be much space left at the top of the stanchion for the displacement of the oil, the pressure must be very high at the bottom of it travel, what do you think?
Haven't taken it for a test run yet, its been a bit wet and I'm allergic to water! but on all accounts it's makes a big difference.
Peter     
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 30.07. 2016 20:13
Hi Peter,
The length in the original post I wrote was 16 and 11/16in. (424mm app)
In reality the oil quantity and grade is a personal choice to some degree,
The valve does not need to be completely submerged,  once the end of it is in the oil at full extension it will work
most of the time the forks are compressed to some degree so the valve body is in the oil

John
Title: Re: Fork 2 way damper drawing
Post by: Peter in Aus on 31.07. 2016 01:05
Thanks John, yes that makes sense re valve not needing to be fully submerged in the oil.
And thank you for putting the post up with drawing in the first place *smile*
Title: Re: Fork 2 way damper drawing
Post by: Peter in Aus on 14.10. 2018 07:22
Had to take my forks out of my A7 Plunger for repairs (that's another story) so checked to see how far down the stanchion the damper valve body could go.
On my stanchions it is 19,1/4 Ins from the top of the top yoke to just above the top bleed hole of the two bleed holes in the stanchion, which is still well clear of the spike in the bottom of the slider. It could go down further but this would cover the bleed holes which may or may not affect its function? 
This adds just a bit over 2 Ins to the length so not having to put so much oil in to cover the valve body.
As far as I can see all the A from 1950 to 1962 are the same so 19,1/4 Ins should be ok for A7/A10 50 to 62.
Best to check thou.
Peter
Title: Re: Fork 2 way damper drawing
Post by: mikeb on 14.05. 2020 01:29
I’m eyeing up this mod – a question: the thread references making the valve out of various aluminium grades or 316 S/S whereas I don’t want to work with SS and don’t have the right aluminium lying around. As it’s bathed in oil, how about just mild steel? Any downsides (other than some weight)?

And I assume there is never significant vertical force on the valve/rod so mounting it under the fork cap hex doesn’t have to bear any load?

Thanks
Title: Re: Fork 2 way damper drawing
Post by: muskrat on 14.05. 2020 14:25
G'day mike.
I can't see why not use ms.
Cheers
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 14.05. 2020 19:15
Hi Mike,
It depends on how you go about attaching the rod to the underside of the top nut ? A paper clip won't work  *eek*
I have seen A65 nuts used or a suitable nut brazed into the standard nut but that ruins the chrome!
(It has to be dead centre)
The rod is under tension when the fork is extending , the ball valve is closed and oil is being forced to flow around the outside of the valve body in the small gap between both parts. This is what does the damping

John
Title: Re: Fork 2 way damper drawing
Post by: orabanda on 14.05. 2020 23:45
It's best to have dissimilar metals rubbing against each other; less liklihood of galling.
Title: Re: Fork 2 way damper drawing
Post by: Peter in Aus on 15.05. 2020 01:22
I used MS on mine no problems so far *smile*
Title: Re: Fork 2 way damper drawing
Post by: mikeb on 15.05. 2020 02:22
thanks for the comments guys.
Quote
A paper clip won't work
i was thinking blutak or hot glue John  ;) tho now you mention it, it hadn't occurred to me the A65 top nut would do. checking the specs it looks like the early A65 top nut will fit the A10 forks and has a 5/16 26tpi thread on the inside. I could put a 5/16 26tpi male thread on some 10mm threaded rod easy enough...

so checking the details- will the A65 top nut (41-5146) fit to the A10 forks, with similar-ish external dimensions eg across the hex?

cheers

65-5331 A10 (etc) - Thread: 1+1/16" x 20TPI
41-5146, 97-2652 – A65 66-68 Outer thread: 1+1/16" 20 TPI – CEI, Inside thread: 5/16" 26 TPI - CEI
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 15.05. 2020 11:29
Hi Mike,
I am not sure which A65's nuts work,
But, if you go that way you lose "street cred" *smile*
If observers see the dome nut on top of the A10 nut,  they go "OOOH"  "double dampers"
With A65 top nuts you will be told they are wrong *????*

 *smile*
John
Title: Re: Fork 2 way damper drawing
Post by: Jules on 16.05. 2020 12:55
Oh I'm using the A65 nuts too  *eek*, with 10mm threaded rod too  ;), just haven't got around to turning down and threading the rod to fit the A65 nuts, although I thought the internal thread of the A65 nuts looked smaller than 5/16" - interested in how you go Mike, thanks
Title: Re: Fork 2 way damper drawing
Post by: mikeb on 01.06. 2020 00:54
Job done!
Re top nuts. My slightly domed a10 top nuts were found to be quite tapered on the inside which prevents a nut easily sitting square against it on the inside (see pic). So no luck with John’s blingy street-cred dome nut look for me *sad2*. Instead, the early a65 top nuts (pn 97-2652) fit fine and have a 5/16” CEI thread into them (Jules: it is 5/16”, not smaller). Using 10mm threaded rod, I used John’s trick of starting to cut the thread in the lathe to get it dead straight, then finished it with a die.

Re the overall length of the dampeners. The original post using the Dow spec says 16 11/16 whereas other say 19” works. I made mine 19” (482mm) and measured as follows:
Using standard 22 1/2" length stanchions and with the fork leg fully compressed I measured 530mm (20.8”) from the top of the stanchion to the bottom lug. See the pic. So, there is no way these can bottom-out. This all fits with what Peter says above. In fact the dampener could even be a bit longer but there is probably no need and it may get in the way of the 2 bleed holes in the stanchions – I didn’t measure for this.

With respect to the oil depth, with 215ml fork oil and on the centre stand, the depth from the top of the stanchion to the oil level was 455mm (approx. 18”). But the top nut sits about 8mm higher than the top of the stanchion - due to the taper gap at the top of the top yoke, the speedo mount plate and the washer under the top nut.  So my dampeners should be immersed at least 482-455-8 = 19mm (3/4”). When I checked, the volume of the dampener valve also displaced some oil and it was well wet at least 2/3 the way up the valve body. Off the stand and on the road the valve will be further immersed.

So: early A65 nuts work fine and make threading easy. 19” overall length gives plenty of clearance.

I’m trying 10W oil and on one quick test ride it feels about right for me – much less spongy than without the dampeners. I’m looking forward to proper ride when it stops raining. Thanks again to John for this great thread. *thanks*
Title: Re: Fork 2 way damper drawing
Post by: Rocket Racer on 12.08. 2020 07:12
Mike,
 thanks for pointing me to this thread.
As Chaterley mentioned the difference between the 19" and the Dow figure is no doubt the Dow top yoke, which drops down compared to the stock BSA one. I need to investigate which stanchions fit a Dow top yoke  *roll* amongst other things
cheers
Tim
Title: Re: Fork 2 way damper drawing
Post by: RDfella on 12.08. 2020 11:14
"I used John’s trick of starting to cut the thread in the lathe to get it dead straight, then finished it with a die."
I have an old set of american dies - imperial - that have a pilot to keep the thread straight. However, they're getting tired now and chances of new inserts must be very slim.
Running a die down a rod always ends up running off to one side pretty quickly, hence John's starting off by threadcutting and finishing with a die. If the thread I'm doing isn't too long (say less than 1") I go straight in with the die - but always with the chuck of the tailstock pressed against it to start square and I continue to follow it up with gentle pressure which works pretty well in keeping the thread in the middle. Quicker than setting up a threadcutting tool in the toolpost and dialling in the tpi.
Title: Re: Fork 2 way damper drawing
Post by: chaterlea25 on 12.08. 2020 12:14
Hi All,
Tim,
The stanchions are all the same length, The Dow setup uses longer top bushes than normal to compensate for the dropped top yoke. I posted pictures somewhere on here
RD,
That's is the same method I use, only resort to cutting the base thread when using tough material or SS.
Luckily my big Colchester lathe has all the  thread settings in the gearbox so no need to mess with change wheels

John
Title: Re: Fork 2 way damper drawing
Post by: Jules on 13.08. 2020 03:20
how do you fit a long rod like this into a lathe to start the die please?? My old Myford inherited from Dad (I'm no toolmaker!) doesn't have a hollow chuck shaft nor does the moveable centre, so I guess I'm stuck with manually starting and cutting the thread  *sad2*??? any ideas on how to keep the die square appreciated, as I said I'm no toolmaker!! cheers
Title: Re: Fork 2 way damper drawing
Post by: mikeb on 13.08. 2020 04:22
Jules if no spindle bore I'm not sure how you'd do that either. tho maybe remove the tailstock, support the rod somehow and screw cut an inch of new thread near the chuck, then cut to length.

another way would be use the a65 top nuts and tap a 3/8 or 10mm thread into them, using that gauge for the rod. 8mm would be too close to the 5/16 to re-thread. if you could find 5/16 CEI  *eek* threaded rod that would work   *conf2*
Title: Re: Fork 2 way damper drawing
Post by: orabanda on 13.08. 2020 06:55
make a die holder; out of square stock, or plate. machine to accept the die. Tap the side and add grub screws to hold the die, and also allow you to open up the die to reduce the depth of the thread cut.
In the centre of the holder (below the die) drill a hole through the centre which is clearance for your rod.

Then hold rod in soft jaws in vice, and using a 12" - 15" shifter set to the outside of the holder, commence to cut thread. The hole in the centre of the holder will ensure a square thread.
Title: Re: Fork 2 way damper drawing
Post by: Jules on 15.08. 2020 11:08
Hmm, thanks for the thoughts, but I've just realised that since I cant get the rod into the lathe, I cant actually turn the end down to the die size for the 5/16 CEI thread anyway!!
So the options are either "phone a friend" and see if their lathe has a hollow spindle, in which case what diameter did you turn down to Mike before cutting the CEI thread please? OR....
Tap out the A65 nuts to 10 mm.....why didn't you take this course Mike, it would seem the easiest?? cheers
Title: Re: Fork 2 way damper drawing
Post by: mikeb on 15.08. 2020 11:17
Quote
Tap out the A65 nuts to 10 mm.....why didn't you take this course Mike
i didn't think of it until later.

Quote
I cant get the rod into the lathe
not even if held it the chuck and supported along the length of the bed on some v blocks of something, with the tailstock removed? that would not need a spindle bore.

EDIT: i can't recall the what size i turned down the rod to cut/tap the 5/16 CEI thread - i just measured it.