where do I acquire replacement screws JIS for a 64 305

[paperslammer]

Ok now I get it. I do have JIS screws and JIS thread.

Then back to the original question - where can I get a JIS tap for the threaded hole that has been messed up?

[LOUD MOUSE]

The easist thing is to get a replacement for that part. ....................lm

Ok now I get it. I do have JIS screws and JIS thread.

Then back to the original question - where can I get a JIS tap for the threaded hole that has been messed up?

[paperslammer]

The easist thing is to get a replacement for that part. ....................lm

Ok now I get it. I do have JIS screws and JIS thread.

Then back to the original question - where can I get a JIS tap for the threaded hole that has been messed up?

Ah, so a new side casing?

[LOUD MOUSE]

I missed it is a DREAM.
If it's a later cover I'll look as I think I have one here. ............lm

The easist thing is to get a replacement for that part. ....................lm

Ok now I get it. I do have JIS screws and JIS thread.

Then back to the original question - where can I get a JIS tap for the threaded hole that has been messed up?

Ah, so a new side casing?

[jkv357]

Ok now I get it. I do have JIS screws and JIS thread.

Then back to the original question - where can I get a JIS tap for the threaded hole that has been messed up?

I don't think it will be called it a "JIS" tap. It will be a M5 tap with the same pitch as the screw - which is not the "standard" pitch.

If you look at the listing on McMaster-Carr (https://www.mcmaster.com/#standard-metric-taps/=172m1xf) you will see 2 choices of thread pitch for a M5 tap.

I'm not certain which pitch was used for JIS screws, but I believe it's the finer of the two.

EDIT: Looking at what I have, the .8mm pitch is the common size, so I would say the .5mm pitch is used on JIS M5 screws. That would seem right, considering it's 3x as expensive as a standard .8mm tap.

EDIT 2 - ^ Correction. The size listed is correct (5mm), but the pitch is .9mm - and is not available as an individual tap in the McMaster-Carr catalog.

[Tim Allman]

Ok now I get it. I do have JIS screws and JIS thread.

Then back to the original question - where can I get a JIS tap for the threaded hole that has been messed up?

Here's a set that covers all of the possibilities (i.e. JIS and ISO) https://www.craftsman.com/products/craf ... ap-die-set. There are other smaller sets on the site so it's worth checking out.

Bill Silver in his Restoration Reference Guide reproduces a service bulletin titled Change of Threaded Parts. It's dated 1967 so there should be few bikes with ISO (also called modified JIS) threads. Most of the sizes are unaffected by the change.

Here's the table from the bulletin showing the affected sizes.

Code: Select all

Diameter    Old JIS pitch    Modified JIS (ISO) Pitch
3mm          0.6                  0.5
4mm          0.75                0.7
5mm          0.9                  0.8
12mm        1.5                  1.25

It looks like there is enough old machinery out there to make the old-sized taps and dies desirable.

[LOUD MOUSE]

Just a simple question.
What's the big deal of staying with JIS threads?
The screws are rather difficult to find and when replaced with the ISO no one can tell the difference. ....................lm

Ok now I get it. I do have JIS screws and JIS thread.

Then back to the original question - where can I get a JIS tap for the threaded hole that has been messed up?

Here's a set that covers all of the possibilities (i.e. JIS and ISO) https://www.craftsman.com/products/craf ... ap-die-set. There are other smaller sets on the site so it's worth checking out.

Bill Silver in his Restoration Reference Guide reproduces a service bulletin titled Change of Threaded Parts. It's dated 1967 so there should be few bikes with ISO (also called modified JIS) threads. Most of the sizes are unaffected by the change.

Here's the table from the bulletin showing the affected sizes.

Code: Select all

Diameter    Old JIS pitch    Modified JIS (ISO) Pitch
3mm          0.6                  0.5
4mm          0.75                0.7
5mm          0.9                  0.8
12mm        1.5                  1.25

It looks like there is enough old machinery out there to make the old-sized taps and dies desirable.