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Carb Helicoil (insert) Help

londonboards

londonboards

Forum Sage
Past Site Supporter
You might remember, I am the one that had to drill out an air jet recently:

P1050750.jpg


P1050762.jpg


I went to a local bike show/jumble over the weekend and have got a supplier of helicoil kits from whom I am going to buy an insert for my stripped out carb air jet passage.

As most of the engineers amongst you will know, this requires some knowledge of thread sizes, inserts sizes and diameters.

On their website you get pages of stuff like this:

Inserts.jpg


So to start at the start. I bought a thread measure and a set of digital calipers and discovered that my little air jet has the following:

P1060143.jpg


and a diameter of:

P1060145.jpg


Now even I would know that a piece of carb would not be manufactured with a weird width of 5.73mm so I am assuming it's best to round it up to 6.00mm. Would that be right? Sorry about the grubby fingernails.

The only place I can find this combination of sizes is a listing in the "Coarse" section of metric sizes here:

Inserts2.jpg


So will my little job work with a "Coarse" 6 x 1 in a 1D length (1D length being 1 x diameter which looks about right to me)?

Am I a genius or a plonker?

Greetings
 
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m6 x 1mm is standard 6mm bolt thread size, so get a 6mm bolt and try screwing it in to the same place on a "good" carb. if it screws straight in lovely then you know its the size you need!
 
Why didn't I think about doing that? TBH "get a 6 mm bolt" is a bit beyond me. Where do I get one from? Yeah OK I know that sounds stupid. Any bolt that measures 6 mm diameter?

A bolt from the bottom gang bar screws nicely into a good jet opening. It measures 5.95 mm. Shall we call it 6 mm ?

I think I am getting there!

Greetings
 
try running a 6mm bottom tap down the threads and see how it feels when you screw the jet in. if its a reasonable fit then just refit with some thread lock. i dont think there will be enough metal there to fit a helicoil insert.
 
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Agemax said:
try running a 6mm bottom tap down the threads and see how it feels when you screw the jet in. if its a reasonable fit then just refit with some thread lock. i dont think there will be enough metal there to fit a helicoil insert.

P.S. sarcasm is not your strong forte Richard......
Click to expand...

+1
male threads measure just under, 5.73 mm is only .27mm (.0106in) under. Which depending on the class thread varies. In the Unified Thread system (US) there are class 1, 2, & 3, i.e. 1/4-20 unc-2b, class 1 tighter, less slop in threads, class 3 more slop (sometimes used when stainless screws are going into aluminum threads as well as other dissimilar metals).

Might be tough to get a helicoil in there..what about silver solder and retap?
 
Thanks for that. I now know that my measuring is OK and it makes perfect sense that the male thread needs to be slightly smaller.

I need to find out the external diameter of a 6mm helicoil to determine if I have enough metal to do the job.

But I also have some other options now (silver solder and retap).

Greetings
 
londonboards said:
Thanks for that. I now know that my measuring is OK and it makes perfect sense that the male thread needs to be slightly smaller.

I need to find out the external diameter of a 6mm helicoil to determine if I have enough metal to do the job.

But I also have some other options now (silver solder and retap).

Greetings
Click to expand...

Richard you need a 6.25mm drill for a 6mm helicoil
Tap size is 7.4mm
 
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Just thought I'd mention, this is for a carb jet, not a structural bolt holding anything together. All it needs to do is hold the jet in place, so drilling/tapping/heli-coiling might be overkill. Silver solder and a tap would be an easy, non-destructive route to try before taking a drill to your carb body.
 
The outside diameter of the air jet post is 9.5 mm (give or take) if I drill it out with a 6.25 mm drill and then tap with 7.4 then I should have 9.5mm - 7.4mm = 2.1mm of post left.

Should be enough eh?

Greetings
 
Thanks for your help with this. When you say "silver solder" are you referring to the solder that is used for soldering wires to a circuit board.

Just want to make sure I have the USA/UK terminology correct.

So you would fill fill the jet opening with molten solder then drill and tap to the 6mm size?

Greetings
 
have you tried just running a 6mm tap down it? there may be just enough material there to form a thread and with a bit of thread lock will easy be enough to secure the jet in there tight
 
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