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Old 01-19-2020, 02:45 PM   #1
TinCup
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Default Cap and Comp Jet Helicoil repair

Both of these are 5mm 75 pitch threads. Checked local auto parts and no luck there. Trying to repair Zenith 3 bottom that I found in a box at an antique store. All I can find is M5 .08.
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Old 01-19-2020, 04:36 PM   #2
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Default Re: Cap and Comp Jet Helicoil repair

Call Berts.. Brattons has it listed in its parts book..

Last edited by F.M.; 01-24-2020 at 02:47 PM. Reason: Found item
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Old 01-19-2020, 04:55 PM   #3
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Default Re: Cap and Comp Jet Helicoil repair

Can you find a SAE 10-34. It is only .00012 less in pitch and .007 smaller in diameter.
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Old 01-19-2020, 05:32 PM   #4
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Default Re: Cap and Comp Jet Helicoil repair

Go online found some on Amazon years ago .local club members
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Old 01-20-2020, 01:05 AM   #5
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Default Re: Cap and Comp Jet Helicoil repair

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Go online found some on Amazon years ago .local club members
No such luck spent all afternoon searching.
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Old 01-20-2020, 05:00 AM   #6
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Default Re: Cap and Comp Jet Helicoil repair

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Are you sure it is 5mm X 0.75 pitch? That is an odd thread. Metric coarse is 5 X 0.8 mm and metric fine is 5 X 0.5mm. A pitch of 0.75mm is very close to 34 tpi, again odd!
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Old 01-20-2020, 08:56 AM   #7
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Default Re: Cap and Comp Jet Helicoil repair

Try McMaster Carr
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Old 01-20-2020, 10:08 AM   #8
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Default Re: Cap and Comp Jet Helicoil repair

Braze them closed then drill and tap to the proper size. Be very careful that you get them straight.
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Old 01-20-2020, 11:16 AM   #9
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Default Re: Cap and Comp Jet Helicoil repair

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Are you sure it is 5mm X 0.75 pitch? That is an odd thread. Metric coarse is 5 X 0.8 mm and metric fine is 5 X 0.5mm. A pitch of 0.75mm is very close to 34 tpi, again odd!
Yes Zenith French Made!
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Old 01-20-2020, 11:21 AM   #10
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Default Re: Cap and Comp Jet Helicoil repair

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Both of these are 5mm 75 pitch threads. Checked local auto parts and no luck there. Trying to repair Zenith 3 bottom that I found in a box at an antique store. All I can find is M5 .08.
Sent email may be able to help you out,
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Old 01-20-2020, 11:56 AM   #11
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Default Re: Cap and Comp Jet Helicoil repair

https://www.snydersantiqueauto.com/P.../gaskets-parts


https://en.wikipedia.org/wiki/Zenith_Carburetor_Company
They are an American Co. The 2 jet design used was developed by the guy in the above posting and with more research would probable find that the two jet design was used under license, payed to the designer in France, so used some metric parts. The carburetors were made in the United States not France and used the same parts that Holley and Ford used in their carburetors.
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Old 01-20-2020, 05:35 PM   #12
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Default Re: Cap and Comp Jet Helicoil repair

Hmmm, Made in France - strange threads! I wonder what threads I will find in a Japanese copy I have. I'd like to get it going and I've asked before if anybody know of them and did Zenith parts fit. I received no responses so I guess I'm on my own. It looks to my (non expert) eye that it was a double venturi type. Do they even make the uniquely double venturi parts for those now?
BTW, it is branded KTK.
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Old 01-20-2020, 06:04 PM   #13
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Default Re: Cap and Comp Jet Helicoil repair

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Do they even make the uniquely double venturi parts for those now?
BTW, it is branded KTK.
Snyder's has the '28 twin venturi but it is any bodies guess if it fits your carb. Only you will know for sure when you buy one.
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Old 01-20-2020, 06:07 PM   #14
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Default Re: Cap and Comp Jet Helicoil repair

The one from Brattons fits and works just fine.. I think its the same one Snyders sells..
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Old 01-20-2020, 06:36 PM   #15
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Default Re: Cap and Comp Jet Helicoil repair

I use the tap all the time to chase threads I have used it for years. The challenge is the threads are worn away and even cleaning up what's there isn't enough to hold the jets.
All I can find is a 5mm .08 helicoil and not .75.
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Old 01-20-2020, 08:11 PM   #16
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Default Re: Cap and Comp Jet Helicoil repair

What about making some thin wall inserts using US thread but drilled and tapped for the 5m.75 thread.
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Old 01-23-2020, 04:45 PM   #17
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Default Re: Cap and Comp Jet Helicoil repair

Finally heard back for Steve at Bert's at as I was afraid they did not have a resource for the 5mm .75 helicoil for the repair. Because there is no way access the passage for the secondary well you cannot simply fill and retap. I had another old Zenith bottom that I tested using a 5mm .8 helicoil and it worked. It holds the jet and seals with no leak. Tends to chew up the threads a bit on the jet but is much better solution than JB Weld.
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Old 01-23-2020, 08:00 PM   #18
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Default Re: Cap and Comp Jet Helicoil repair

The secondary well is a different size then the 5M.75 jets. So you need more then just the jets thread repaired to refurb this carb?
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Old 01-23-2020, 09:23 PM   #19
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Default Re: Cap and Comp Jet Helicoil repair

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The secondary well is a different size then the 5M.75 jets. So you need more then just the jets thread repaired to refurb this carb?
The secondary well threads are not relevant here. Only the passage to the comp jet which cannot be reached if one was to fill the area with brass and cut new 5 mm threads.
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Old 01-23-2020, 09:41 PM   #20
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Default Re: Cap and Comp Jet Helicoil repair

Take the jets to a plating shop and have a copper or nickel flash put on the fittings. This will easily add .0002" to the surface of the threads. Make sure you put wax in the orifice of the fitting otherwise it will get plugged.
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