Carb pedestal stud bolt (TD978)

[Des N]

Having the carbs off again recently I've noticed that the carb pedestal stud into the inlet manifold was loose. Taking it out, the thread seems to have been helicoiled at some point and the insert thread just pulled out. I thought a new insert would fix the problem so got a packet of helicoil inserts off eBay. Got 3/8 x 16 unc but these seem too large for the thread. Question is -do I buy a complete helicoil thread repair kit (3/8 x 16 unc) and try and re-tap it, or get a longer stud made, with the thread extended by 1/4 inch? The thread seems ok further down in the manifold and it's only to hold the carbs tight.

Do you buy helicoil kits the same size as the thread or is it case of going up a size?

Ta

Des

[SGN]

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Hi Des

I've noticed on mine that someone has drilled & tapped for a larger diameter stud into the block,rather than helicoil,then re-drilled the manifold to suit the stud.
I only found out when planned to replace the original stud and nut the last time i had it apart.
Does the job though.

Cheers
Steve

[nib]

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Des I think I went for an M10 thread insert on one of my stags which is slightly larger,I just tapped out a new thread to take the insert,the tapwas supplied with the helicoil kit and there was no need for re-drilling.M10 threaded rod is commonly available,dont think you even need to run a drill down the manifold to take the new rod but might be wrong as it was a long time ago.

Mark

[Des N]

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Thanks for info

If I go for M10 thread, will that take the 3/8 stud thenas it's metric? Bit green on helicoil sizes etc. Also do you cut the thread by hand or attach to a slow speed drill?

[nib]

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Hi Des

Im sure 10mm is slightly larger than 3/8ths, someone with more engineering know how than me will clarify this.

If you put a 10mm insert in,you will need some 10mm threaded rod/stud which should be available from a good ironmongers and cut it down to size to suit.

If youve got a T shaped tap holder and go in nice and straight,keep backing off every half turn,bit of cutting oil and a hoover handy to suck the swarf out the pedestal.I used molegrips but you can easily go on the wonk with these so not recommended if can be avoided.

Mark

[stustag]

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Hi Des

I helicoiled mine when I refurb the carbs only takes 5 mins never a problem again

3/8 UNC got my kit off E bay really good value http://cgi.ebay.co.uk/THREAD-REPAIR-...item56368e6cd8

Just make sure all the holes are blocked and you have a vacuum cleaner handy to suck up all the swarf

Stuart

[whitestagman]

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I used superglue on mine - worked a treat!

Rodger

[twitchiwobble]

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Dear Des N

Thread Inserts,....A little knowledge is dangerous.

Repairing stripped threads with thread inserts(helicoils) can be tricky, especially on the Stag because the aluminium alloy is old and relatively "crumbly"

"Helicoil"thread inserts alsoknown as "Cross-Wire-Inserts" come in high tensile steel or stainless steel. They are available in various lengths and also, as "Free-Running" or "Locking",.................TIP, avoid locking inserts!

Forget molegrips, superglue and really, you should avoid mixing metric threads with the standard Unified threads used onthe Stag.

To do the job correctly, you need >

A quantity of3/8UNC thread inserts (Helicoils)

A set of two 3/8 UNC insert taps (Taper and Plug)also called ("Zone1", 2, or3)

These special taps will be marked as "Helicoil" or "Insert" and are quite a bit larger than anormal 3/8UNC thread

A Tapping drill of 9.8mmdiameter.

Ideally, you needa 3/8UNCinsert fitting tool, which looks elaborate, but makes fitting the insert easier (however, if you buy a "Thread Repair Kit", it will have a simpler tool AND the special sized drill)

Apropertwo-handled Tap Wrench(nottoo big)

A drop of oil to lubricate the tap

A vacuumcleaner withhose reduced down to "titchy"

A variable-speed electric drill.

For the thread insert to befitted properly, the topcoil of thread needs to be a full thread below the top surface.

If, after your best efforts,the "Helicoil" is perhaps a bit sloppy, then thoroughly de-grease and dribble in some Loctite241 or 242("thread-lock") and leave it overnight.

There is a "tang" on the helicoil which is supposed to be snapped off on completion, but I would leave it on, in this instance.

Going back to square one for a second,When I look down the threaded hole on my own Stag inlet manifold, I see that the 3/8UNC thread finishes a little way UP from the bottom of the hole, Inthis instance, you could maybe get away with just tapping the standard thread a bit deeper!!

Happy Staggering