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MG Midget and Sprite Technical - Stripped Thread

I have a stripped thread on bolting the air filter body onto the carbs on my 1970 midget 1275. Can anyone tell me the thread and the depth of helicoil I will need to repair the thread. If anyone has a reasonably priced supplier for heli coils that would also be helpful.

PJ
P.J young

Can't help with sizes (although it might be a 5/16"UNC) but when I needed to Helicoil the themostat housing I got my kit from these people:
http://www.cromwell.co.uk/static/publication/990/pages/1164.pdf
Which seemed a decent price at the time. Its not Helicoil (much more expensive) but the Kennedy stuff seems good too.
Good luck!
-Craig
C Robertson

Do what I did, and fit a bolt and stiff nut.

Dave
Dave Barrow

I don't know about Midgets, but the MGB carbs have a 5/16 UNF. Helicoils (and Recoil kits) come with coils that are measured in terms of bolt diameter (1, 1.5, etc.) I always get the 1.4 diameter coils. The coils can be trimmed off if they are too long. I just bend the excess coil up carefully and use a triangular needle file to cut a notch into the coil strand (about half way through the strand, then bend the excess strand at the notch, breaking it off. Cheers - Dave
David DuBois

Hi PJ,

I had the same issue with my HS2 carb, and Craig is right, the thread is a 5/16 UNC (coarse thread).

David, I bet that you had intended to say, "coarse", when you said, "fine"!

":oD
Norm
Norm Kerr

Might try the long set up time loctite weld (jb weld) and then drill and re-tap the hole.... Use the 24 hour set up stuff

Dont use the short time set up stuff, it dosnt hold up vary well


It does vary well esp if the parts are clean
Prop

Unless you are a perferctionist, and want absolute originality, just tap in a bigger bolt. Do both sides for even stevens sake. That's what I did, before changing to a single SU.
Lawrence Slater

I disagree with Lawrence, tapping the hole bigger is a sure way to eventually ruin the casting. If it strips again in the future then you're where you can't resore it to either size. Stick with the helicoil type repair and you'll be fine. Some brands have inserts of various lengths, I know that a brand I use here in the US, has those ranging from 3/8" up to 5/8" long for the 5/16" X 24 thread, the 3/8" should fit almost perfectly in the carb flange.
B Young

If you have never used a Helicoil type repair before, then take this as an opportunity to give it a go. When I first tried a Helicoil I found the experience strangely satisfying as an engineered solution. At one time I would have opted for the solution that Lawrence recommends, but having used Helicoils now I would far prefer that as a "proper job" solution.
Guy

I like heli coils also, but i also like pure gold coins...

What im saying is, a heli coil kit will cost you a good $20 to $30, and the kit is so small i doubt anyone will recall "that special place" to store it, 3 years from now.

SOOOOooooo... Why not just buy a good used carb body from someones junk pile.... Good classic brit shops normally have several boxes of spares like that

Prop....feeling cheap today
Prop

I like helicoils too, but as I didn't have one, and had a tap and bigger bolt to hand (not much bigger). I took the easy route, and in spite of the worry that some have that it might strip again, it didn't. It's still good today after 25 years of service, before I swapped for a single SU.

It probably stripped in the first place because it was overtightened by someone other than me before I owned it.

To me a proper method is anything that works and lasts.

But hey ho, use a helicoil it's certainly worth knowing how to install them that's for sure. Or as suggested earlier a nut on the back will do the job too, and is even eaiser. :)
Lawrence Slater

Helicoil kits are well worth the money as I have always had a policy that if I need a tool. then I buy it as over the years, it will pay for itself.
All my taps. dies and Kits lived in a Havana Cigar box until I retired and my wife bought me a Tool Trolley and Cabinet.
If you pull a Helicoil, then if you have enough wall thickness, you can fit a TwinSert which is a horrible American Helicoil in a Helicoil.
Geoff F.
Geoff Farthing

Another option if the damaged area is too large for a standard helicoil is to drill and tap to a pipe thread and install a pipe plug or nipple and then drill and tap that for the helicoil. Had to do that on one of the exhaust manifold bolts on my engine and it worked great.
B Young

Bill - I have to ask why you put a pipe plug in and then drilled and helicoiled that? Wouldn't it have been easier (not to mention expeditious to have just drilled the nipple and tapped for the original size? I have used that method on occasion myself. Cheers - Dave
David DuBois

Definitely 5/16 UNC.

You can normally pick up a recoil kit on ebay for mid twenties or less if you are prepared to wait.

Whereabouts in Hampshire are you, I think I may have a 5/16 UNC kit I can lend you. I'm near Petersfield.
Jeremy Cogman

Sorry, just checked and I only have UNF.
Jeremy Cogman

Thanks for all of your contributions. I shall be getting the 5/16 UNC helicoil set for the repair. Thanks for looking Jeremy, I am in Portsmouth so not too far from Petersfield. I will keep my eye on ebay.

PJ
P.J young

This thread was discussed between 05/09/2011 and 10/09/2011

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.