Author Topic: Fork 2 way damper drawing  (Read 9969 times)

Offline Jules

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Re: Fork 2 way damper drawing
« Reply #45 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

Offline mikeb

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Re: Fork 2 way damper drawing
« Reply #46 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*
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Offline Rocket Racer

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Re: Fork 2 way damper drawing
« Reply #47 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
A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Online RDfella

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Re: Fork 2 way damper drawing
« Reply #48 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.
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Online chaterlea25

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Re: Fork 2 way damper drawing
« Reply #49 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
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Offline Jules

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Re: Fork 2 way damper drawing
« Reply #50 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

Offline mikeb

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Re: Fork 2 way damper drawing
« Reply #51 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*
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Online orabanda

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Re: Fork 2 way damper drawing
« Reply #52 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.

Offline Jules

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Re: Fork 2 way damper drawing
« Reply #53 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

Offline mikeb

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Re: Fork 2 way damper drawing
« Reply #54 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.
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