Author Topic: threads outside cush nut  (Read 797 times)

Offline coater87

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threads outside cush nut
« on: 10.10. 2018 00:17 »
 I have looked all over for a picture I can count threads on.

 I would like to make up a better system to mount a timing disk on my 58 GF. I dont own a SRM nut, I am going to make something up on the lathe.

 What I dont know (without taking my outer primary cover off) is how much threaded length of crank sticks out of a stock cush nut when its done up tight?

 In my mind its about 1/2 inch, but I better check before I do a bunch of work and find out I am wrong again. *conf*

 So if anyone has one open right now, or has a picture that shows the threads (should be 20 threads per inch) I would appreciate it.

 Lee
Central Wisconsin in the U.S.

Offline duTch

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Re: threads outside cush nut
« Reply #1 on: 10.10. 2018 02:12 »

 I can't say worth regard to Swing-Arm models,  but my Plunger nut has a couple of threads inside the pin-hole, enough to fit a 'safety shim' ~2mm, but keep in mind the nuts are slightly dished and similar,  but different.
 If you're planning to leave it in place I  think an outboard disc will clash with the cover.
 I put a dodgy ally 'degree-disc' behind the spring against the shoulder of the sliding bush,  but found after a while that as the shoulder is only half the thickness of the spring,  it started to deform so had to modify a hardened washer for the spring to butt up to (as a spring seat).
 ( slightly off topic,  I had a dodgy spring from a recently discussed supplier, that lost tension after only for years of use but found a better replacement at a swappie- better diameter & length so a good time to do the packer (spring still shorter than the original)
 And I took a pic...(nut is obviously not fully in place )
 Second pic is the crap spring
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Online Greybeard

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Re: threads outside cush nut
« Reply #2 on: 10.10. 2018 10:43 »
This is a picture I took of my cush-drive fully tightened but without the spring. Again, it's a plunger engine, but I'd have thought the swing-arm models would have the same parameters for that nut.

Online RDfella

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Re: threads outside cush nut
« Reply #3 on: 10.10. 2018 12:04 »
Greybeard - can't remember how much thread - if any - protrudes on my GF (and I'm not going to take the cover off just to see!) but your pic looks similar to the singles. On my race engines I used to use the extra thread to fit a locknut. Actually more of a back-up nut, as I've seen threads stripped by the tremendous force the cush drive puts on that nut. The camming effect of the cush drive should not be underestimated, and the twin lobe, due to ramp angles,  is probably more of an issue in that regard than the four lobe.
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Online RichardL

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Re: threads outside cush nut
« Reply #4 on: 10.10. 2018 12:29 »
The knicks on GB's cush nut (to be clear  *smile*), I believe are unintentional, but made me wonder why someone with an indexing head hasn't shown us an original nut with a graticule. Also makes me wonder why SRM doesn't include that on their nut. Cost, I guess.

Richard L.

NO. I KNOW WHY. SMALL DIAMETER OF CUSH NUT WOULD MAKE DEGREE DIVISIONS VERY SMALL.
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Online muskrat

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Re: threads outside cush nut
« Reply #5 on: 10.10. 2018 13:25 »
G'day Lee.
Mine's the same as duTch's and without the disc there is about 2mm of thread between end of nut and pin hole.
Cheers
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Online morris

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Re: threads outside cush nut
« Reply #6 on: 10.10. 2018 21:10 »
Happen to have the primary open on the SA. Here’s a picture from the cush nut.
The two threaded (BA 4) holes are for fixing a timing disc.
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Offline coater87

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Re: threads outside cush nut
« Reply #7 on: 10.10. 2018 22:30 »
 You guys are the best! *smile*

 There is enough threads there to make up a collar of some type and a threaded nut to pinch a paper disk.

 I am not going to set up anything permanent inside the primary. I will just install this and and bend up a pointer when needed.

 Richard, you hit it right on the head! TOO SMALL. I could "scratch" the marks in, or use a micro carbide mill/burr to do it. But either way, setting up a rotary table and than manually cranking 360 degree increments in a metal disk is honestly a lot of fidly work.

 I just print one out on the computer and glue it to some paste board.

 Lee
Central Wisconsin in the U.S.

Online RichardL

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Re: threads outside cush nut
« Reply #8 on: 11.10. 2018 00:54 »
You guys are the best! *smile*

 There is enough threads there to make up a collar of some type and a threaded nut to pinch a paper disk.

 I am not going to set up anything permanent inside the primary. I will just install this and and bend up a pointer when needed.

 Richard, you hit it right on the head! TOO SMALL. I could "scratch" the marks in, or use a micro carbide mill/burr to do it. But either way, setting up a rotary table and than manually cranking 360 degree increments in a metal disk is honestly a lot of fidly work.

 I just print one out on the computer and glue it to some paste board.

 Lee

Not to mention, everything is shaking around while you're trying to read pointer vs. disk. I set anchors for eye bolts in my garage floor to try to hold 'er down with cargo straps while revving up, and she still wanted to walk away. (Might not be best phrasing to refer to the bike in the feminine context here.)

Richard L.

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Offline coater87

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Re: threads outside cush nut
« Reply #9 on: 12.10. 2018 01:00 »
 Here it is. I had a small chunk of cheap, gummy aluminum- used that.

 Threads on end of crank with original cush nut still in place, other end threads in and pinches paper disk.

 Might need spacing washers or something.

 Threads are all 3/4 x 20 tpi.

 Lee
Central Wisconsin in the U.S.

Online Greybeard

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Re: threads outside cush nut
« Reply #10 on: 12.10. 2018 08:42 »
Here it is. I had a small chunk of cheap, gummy aluminum- used that.

 Threads on end of crank with original cush nut still in place, other end threads in and pinches paper disk.

 Might need spacing washers or something.

 Threads are all 3/4 x 20 tpi.

 Lee
Nice. I like the tablecloth.

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Re: threads outside cush nut
« Reply #11 on: 12.10. 2018 11:49 »
Is it a table cloth or a doily?
Lee says "What the heck is a doily?"
Nice work mate.
If only I had a lathe.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
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Muskys Plunger A7

Online Greybeard

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Re: threads outside cush nut
« Reply #12 on: 12.10. 2018 12:54 »
Is it a table cloth or a doily?
Lee says "What the heck is a doily?"
Might be an Antimacassar

Online ellis

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Re: threads outside cush nut
« Reply #13 on: 12.10. 2018 14:22 »
Are you also into coaches GB ?

ELLIS

Online RichardL

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Re: threads outside cush nut
« Reply #14 on: 12.10. 2018 14:35 »
The idea being that you remove the cotter key?

It's beautiful work. I assume you lathe-turned the threads yourself. Which thread profile did you use? I guess that means, "to what angle did you grind the tool?" I haven't run a lathe in over 35 years and I could basically turn diameters (making loudspeakers) and that was about it.

Richard L.
Plan on signing up for the world-wide 2020 DISTINGUISHED GENTLEMAN'S RIDEon September 27, 2020 (if it's not cancelled and we are free to move about by then). Watch website at https://www.gentlemansride.com for details.