Swing arm question

Norcoastal · Dec 26, 2019

I just noticed that the swing arm I got for my bike has two different adjustment threaded holes.

It seems like the guy I got it from must have tapped out one of the holes for a bigger threaded screw because maybe the original one stripped? I’m just guessing but that seems like a logical conclusion.

My question is, should I attempt to put a helicoil in the larger hole so I have matching threads, or just use two different size adjustment bolts?

maylar · Dec 26, 2019

Definitely make them stock threads. Counting turns is part of chain adjustment.

edit: If you do drill it out, take extraordinary measures to keep all axes straight.

jsnorton · Dec 26, 2019

I would think that as long as you can get proper adjustment it should be OK to use as is. Just make sure you can lock the adjustment once you have it.
Now if it's a show bike, then I would helicoil it and use an original adjuster.

Norcoastal · Dec 26, 2019

It’s going to be a rider not a museum piece, but now I have two conflicting options.

Hummm?

L.A.B. · Dec 26, 2019

Norcoastal said:
It seems like the guy I got it from must have tapped out one of the holes for a bigger threaded screw because maybe the original one stripped?

Norcoastal said:
should I attempt to put a helicoil in the larger hole so I have matching threads

If it's been tapped to take a larger diameter adjuster then it is probably too big to helicoil to standard size.

maylar · Dec 26, 2019

You would need to fabricate an adjuster bolt -

And I'm not sure the hex of a bigger bolt will clear the swingarm, it's close as is.

kommando · Dec 26, 2019

Its steel, so get the oversize hole welded up and re-drill and tap for the proper thread which should be UNF.

Norcoastal · Dec 26, 2019

maylar said:
You would need to fabricate an adjuster bolt -

View attachment 13752

And I'm not sure the hex of a bigger bolt will clear the swingarm, it's close as is.

Good point

Norcoastal · Dec 26, 2019

kommando said:
Its steel, so get the oversize hole welded up and re-drill and tap for the proper thread which should be UNF.

What does UNF mean?

L.A.B. · Dec 26, 2019

Norcoastal said:
What does UNF mean?

https://britishfasteners.com/threads/unf.html

Norcoastal · Dec 26, 2019

L.A.B. said:
https://britishfasteners.com/threads/unf.html

Got it, thanks.

I wonder if it would be cheaper to buy a new swing arm?

maylar · Dec 26, 2019

5/16-24 in this case.

maylar · Dec 26, 2019

how big is the hole?

texasSlick · Dec 26, 2019

You cannot hope to adjust the rear chain if the adjusters have different pitch, that is, a different thread per inch on each adjuster. Counting flats will be of no use ...... The pitch difference will yaw or cant the wheel.

Best to get back to stock either by welding, or inserting a threaded sleeve.

Slick

L.A.B. · Dec 26, 2019

texasSlick said:
Best to get back to stock either by welding, or inserting a threaded sleeve.

Shouldn't be difficult to make a new one.

Norcoastal · Dec 26, 2019

I’m an idiot.

Sorry folks.

My swing arm is in bad shape. All rusted and in need of repair.

last night when I was looking at it, one side was rusted and the other side was oily and gave the appearance of two different sizes.

When I just double checked them now, they are the same.

I’m happy but I’m sorry for wasting your time.

Merry Christmas

998cc · Dec 27, 2019

Norcoastal said:
I’m an idiot.

Sorry folks.

My swing arm is in bad shape. All rusted and in need of repair.

last night when I was looking at it, one side was rusted and the other side was oily and gave the appearance of two different sizes.

When I just double checked them now, they are the same.

I’m happy but I’m sorry for wasting your time.

Merry Christmas

No worries here. I learned a couple things from your post and the responses, so the effort by the group was not wasted.

Regards,
~998cc

MexicoMike · Dec 28, 2019

FWIW, I can't see why having adjusters of two different sizes would have any affect at all on alignment. You adjust the bolts so that the wheel is correctly aligned. How the bolts then align with the indices on the swingarm might be useful afterward for a reference but aligning the wheel by adjusting the bolts to the same indices position is a "rough" wheel alignment at best.

maylar · Dec 28, 2019

MexicoMike said:
FWIW, I can't see why having adjusters of two different sizes would have any affect at all on alignment. You adjust the bolts so that the wheel is correctly aligned. How the bolts then align with the indices on the swingarm might be useful afterward for a reference but aligning the wheel by adjusting the bolts to the same indices position is a "rough" wheel alignment at best.

What are "indices"? No gots on my 74. You get the wheel aligned once then when tightening the chain you count flats on the adjusters, an equal number each side. Aligning a 74 Commando rear wheel is a royal PITA any other way.

Mwood7800 · Dec 28, 2019

Never had much luck with my adjusters. They will get you close but that’s about it.

Swing arm question

Norcoastal

maylar

jsnorton

Norcoastal

L.A.B.

Moderator

maylar

kommando

Norcoastal

Norcoastal

L.A.B.

Moderator

Norcoastal

maylar

maylar

texasSlick

L.A.B.

Moderator

Norcoastal

998cc

MexicoMike

maylar

Mwood7800

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