Threadsize of an 1951 fork tube plug ?

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Raytag
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Threadsize of an 1951 fork tube plug ?

#1

Post by Raytag » Sat Jan 11, 2020 4:05 pm

Hi,

I`m sure it has been asked before and answered already and I searched the KB but I guess I missed it.

Anyone knows the thread size of a 1950-54 "fork tube plug" of an adjustable fork?
The metric size is ~ 34.83mm .
Is it 1 3/8-18 ?

Thanks for your time!
Ray



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Re: Threadsize of an 1951 fork tube plug ?

#2

Post by Bone Head » Sat Jan 11, 2020 10:19 pm

Raytag wrote:
Sat Jan 11, 2020 4:05 pm
Hi,

I`m sure it has been asked before and answered already and I searched the KB but I guess I missed it.

Anyone knows the thread size of a 1950-54 "fork tube plug" of an adjustable fork?
The metric size is ~ 34.83mm .
Is it 1 3/8-18 ?

Thanks for your time!
Ray
34.83 mm converts to 1.371259843".

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Re: Threadsize of an 1951 fork tube plug ?

#3

Post by RooDog » Sun Jan 12, 2020 12:12 am

You can not convert metric to US threads. It just don't work. If you are gonna work with a Harley you need the correct stuff....
....RooDog....

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Re: Threadsize of an 1951 fork tube plug ?

#4

Post by RUBONE » Sun Jan 12, 2020 12:15 am

RooDog wrote:
Sun Jan 12, 2020 12:12 am
You can not convert metric to US threads. It just don't work. If you are gonna work with a Harley you need the correct stuff....
....RooDog....
He is just giving the size of the hole, not trying to convert.

And 1-3/8 is 1.375, just .004 from 1.371 so his guess as to the correct US size is pretty good.

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Re: Threadsize of an 1951 fork tube plug ?

#5

Post by RooDog » Sun Jan 12, 2020 12:27 am

Lo siento, my bad.... What I read was: "Anyone knows the thread size of a 1950-54 "fork tube plug" of an adjustable fork?", There was no mention of a hole....

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Re: Threadsize of an 1951 fork tube plug ?

#6

Post by Raytag » Sun Jan 12, 2020 11:49 am

Here`s the background:
The tubes of the Pan are bent (sidecar usage? accident?)
It`s actually worse than the pic shows

Image

The bushings in the lower legs are surprisingly good. The lower one on the brake side is a tad more out. Not in forward direction but in 9 and 3 o`clock ?!?!
New china tubes of sad quality are U$370. There`s nothing else available here.
New bushings honed to fit the new tubes are U$320.

I have some used 4" over tubes here. They`re straight but the threads for the plugs are round, damaged. Beats me.
So the idea is to shorten these tubes and thread them new on the lathe.
If I can manage and the fork doesn`t clonk: Great. If not I have to go the hard way.
Gremlins have ransacked my internal threading bar so I still have to grind a new tool grrrr
I asked for the size because I must consider the major & minor diameter of the thread.
Thanks
Last edited by panhead on Sun Jan 12, 2020 12:35 pm, edited 1 time in total.
Reason: show picture

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Re: Threadsize of an 1951 fork tube plug ?

#7

Post by RooDog » Sun Jan 12, 2020 3:47 pm

So, why not measure the male threads on the fork top screw in plug and then cut the new internal threads to match? Can't the bent tube be straightened? I have straighten several of them in a press, it's not rocker surgery.
....RooDog....

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Re: Threadsize of an 1951 fork tube plug ?

#8

Post by Raytag » Sun Jan 12, 2020 5:43 pm

I can confirm that is 1 3/8-18.
Using a piece of mild steel I bored a 1.333" and cut that thread. The plug fits perfect.
(the vid doesn`t work in the newest firefox version )

Roo ..., course I meassured the outer dia of the plug however sometimes you guys over there have some really weird sizes

Straightening the tube ?
After sacrificing a bar for cutting internal snapring grooves and grinding it to a 60 degree angle, boring a piece of scrap steel to 1.333 you are telling me that? Now ? :? :shock: :lol:
OK .... I will give it a try

Thanks
Ray

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Re: Threadsize of an 1951 fork tube plug ?

#9

Post by RooDog » Sun Jan 12, 2020 7:39 pm

Atta Boy! Perfect fit.....
As long as the tube is not kinked or indented from the lower tree, then straightening is a viable commercial possibility.. If it's for you personally, a small indent from the tree may sometimes be overlooked especially if the fork tube is hidden by a cow bell.
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Re: Threadsize of an 1951 fork tube plug ?

#10

Post by panhead_kicker » Sun Jan 12, 2020 7:52 pm

If you try to re-use that tube, you may also want to ensure its still got a good sealing surface to present to your new upper fork seal. The travel area in the picture looks suspect.
Is there a reasonable cure for a few inches of grubby pitted surface?

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Re: Threadsize of an 1951 fork tube plug ?

#11

Post by Buddhahoodvatoloco » Sun Jan 12, 2020 8:07 pm

Mad Skills.... :lol:
Raytag wrote:
Sun Jan 12, 2020 5:43 pm
I can confirm that is 1 3/8-18.
Using a piece of mild steel I bored a 1.333" and cut that thread. The plug fits perfect.
(the vid doesn`t work in the newest firefox version )

Roo ..., course I meassured the outer dia of the plug however sometimes you guys over there have some really weird sizes

Straightening the tube ?
After sacrificing a bar for cutting internal snapring grooves and grinding it to a 60 degree angle, boring a piece of scrap steel to 1.333 you are telling me that? Now ? :? :shock: :lol:
OK .... I will give it a try

Thanks
Ray

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Re: Threadsize of an 1951 fork tube plug ?

#12

Post by RooDog » Sun Jan 12, 2020 9:15 pm

I like to use an additional seal in place of the felt wiper, but that is just a matter of preference. Now, if the tube is pitted where the seal rides then a replacement is in order. Taiwan Tedd's V-Twin has hard chrome replacement tubes cheaper than you could get your tubes chromed and then centerless ground back down to spec. Some things are not worth fixin'.....
....RooDog....

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Re: Threadsize of an 1951 fork tube plug ?

#13

Post by Excalibur » Sun Jan 12, 2020 11:14 pm

Ray, thanks for the super cool vid. Please keep stuff like that coming. It made my day. :wink:

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Re: Threadsize of an 1951 fork tube plug ?

#14

Post by Raytag » Mon Jan 13, 2020 8:19 am

I try straightening them and I guess it`ll work ... somewhat

As you guys are saying, suspecting: The surface isn`t too smooth and I`m not aware of any polish for chrome of this nature.
Rechroming is not an option over here anymore. Hardchrome tubes aren`t available here. ... NO I`m not too cheap for buying new tubes but not U$370 for showchrome with extremly loose tolerances in the bottom end of the tubes where the dampertube is traveling and so the dampertube is rocking along and scratching the valvekit damnit.

There are many nicks in these tubes but I need to look closer

A buddy with two left hands and ten thumbs is in IT. He is a good guy.
You want the sun to rise in the west ? He can program it.
But he`s always wondering what happened and when I`m messing with my toys I record something to show
him how things were done in the analogue age.

Some short shaky vids of preparing that tool



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Re: Threadsize of an 1951 fork tube plug ?

#15

Post by RooDog » Mon Jan 13, 2020 2:17 pm

If yo'll take a look in your Harley Panhead service manual, you do have an official Harley Man, or a reprint, don't you? There is a section on straightening forks. I recently straightened a lower tree bent from an easy head on. Anyway, the book shows a tube being pressed, note the use of close fitting pillow block to avoid deforming the roundness of the tube while applying the straightening forces. May not be totally necessary to use them, but certainly a good idea.....
...RooDog....

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