Fixing Amal threads

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Coco

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Guys, I picked up a pair of new 930's for a Triumph I'm working on and one of the carbs showed up with lightly mangled threads in one spot.

It's the threads on the bell or mouth of the carb (?) where a velocity stack would thread on. Anyone know what thread size that is? I need to try to fix the threads so I can thread on velocity stacks.

Suggestions? I don't think I can simply go buy a die to repair the threads at the local hardware store.
 
I was going to go grab one but have never used them before. As silly as it seems I didn't know if the Amal had a strange thread pitch like Whitworth or something. Never had Amals before until now.

Since I've never used a thread file, I didn't know if a special thread file was needed for certain types of threads or if thread files are simply universal.
 
Amal Velocity stacks don't screw on. They're retained by three grub screws (and some epoxy if you want them to stay put because they fall off !) The grub screws will definitely damage the threaded section. The Velocity Stacks leave the pilot inlet s outside of the mouth.

Screw on inlets are bell-mouths which have the undesirable effect of placing the pilot air inlets on mk1 Concentrics in the fast air flow.

I would simply clean up a damaged thread like that with a small swiss file. Presumably you're only talking about de-burring ?
 
Get a used stock air cleaner adapter and make a couple hacksaw cuts in it to use it as a die.
 
79x100 said:
Amal Velocity stacks don't screw on. They're retained by three grub screws (and some epoxy if you want them to stay put because they fall off !) The grub screws will definitely damage the threaded section. The Velocity Stacks leave the pilot inlet s outside of the mouth.

Screw on inlets are bell-mouths which have the undesirable effect of placing the pilot air inlets on mk1 Concentrics in the fast air flow.

I would simply clean up a damaged thread like that with a small swiss file. Presumably you're only talking about de-burring ?
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They are not Amal velocity stacks but ones made by Maund and they thread on. A little more than deburring is involved but not quite much more. Those Amals look oke they'll crumble as they seem to be made from really poor quality pot metal. Disposable and plastic almost but that is another story for debate.

I'll buy a thread file. Looking at the carbs it seems like it is a standard SAE fine thread. I was told it was 24 TPI. Too bad no one in my city sells thread files if you can believe that.
 
Coco said:
I'll buy a thread file. Looking at the carbs it seems like it is a standard SAE fine thread. I was told it was 24 TPI. Too bad no one in my city sells thread files if you can believe that.
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It's certainly 24 tpi.

It could be SAE I suppose? But no other Amal Mk1 carb threads are SAE, as they are either BA or BS Cycle.

You could use the cutting edge of a 24 tpi tap to clean up the thread instead of a thread file?
 
L.A.B. said:
You could use the cutting edge of a 24 tpi tap to clean up the thread instead of a thread file?
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Good idea. :idea: I'll go with your suggestion first before racking my brain trying to find a proper thread file.

All I could find was a whitworth thread file from British Tools and Fasteners. There was no mention on anything in BA or BS threads.

I really don't want to have to buy a new carb body just becasue of some damaged threads.

This is my only option so far: https://www.bosstoolsupply.com/index.as ... odID=11858
 
Just google "buy thread file" and you'll come up with plenty. I don't remember who I bought mine from (if it will help you, let me know and I'll see if I kept the receipt) but I believe they were no more than ~$8 apiece (SAE and metric)
 
I've had a thread file in my toolbox for about 30 years. I believe I bought it at Sears - K-D with 8 different threads from 11 to 28 TPI.

Napa Online has the same file - SER2229, for US $15.29

Fixing Amal threads
 
Thread files are available over here in the UK, I might even have a spare one, they are essentially a crude tool for repair work only. I'm pretty sure the thread angle is 60deg through out the range but I've never found that a problem. LAB's idea using a tap with care will work as will a three cornered knife edged file.

Cash
 
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