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MG Midget and Sprite Technical - Stripped captive nut for rack mount

Well, I'd cleaned out the paint in the rack mounting captive nuts (5/16". UNF) and checked the bolts would screw in well. The last of the front (longer) bolts was binding when fitting the rack and I probably should have back-tracked but kept tightening and it stripped. I re-tapped the captive nut but it wouldn't hold at close to recommended torque (with a good bolt).

So what are my options? I've never used a helicoil- they seem expensive but is that the best solution? I really don't want to cut into the square section mounting bar if I can avoid it but I suppose could drill it from behind and put a nut in behind the stripped one and use a longer bolt but that seems messy.

How about putting some weld into the captive nut, then drilling and re-tapping? Is that ok or am I likely to make things worse? A depressing afternoon really but there must be a solution!
Bill Bretherton

Helicoil. I was doubtful about them at first but they really are amazingly effective. First time I used one was for a front damper mount on which it worked very nicely. Easy to fit and has given no trouble at all considering the high stress application, and with probably 50k miles of enthusiastic driving since fitting!
GuyW

If a 3/8" UNF bolt will fit through the Rack mounting - even if drilled out a little, then tap the mounting out to 3/8 UNF and fit the larger diameter bolt.

Cheaper than Helicoiling which also requires tapping out to fit the coil.
Chris at Octarine Services

I would be inclined to try the 3/8" bolt approach.
Dave O'Neill 2

OK, I'll see if a 5/8" bolt will clear but, if all else fails, use Guy's helicoil solution. What's wrong with my weld idea - is it too imprecise?

Of course I blame the design using such piddling little nuts and bolts. But I am used to Volvos!
Bill Bretherton

I used the ‘Helicoil’ well actually ‘Uni thread’ brand on my front shocker mount as well - similar issue to you but I did tap it out or so I thought

I got my kit from Tracey Tools when they were in Dartmouth now in Paignton on an industrial estate. Still have a good mail order though.
Shame it’s not 3/8 or you could have used my kit - I’ve only used one insert !

R.
richard b

LOL I was using helicoil in a generic sense. Mine were also Uni-thread also from Tracey Tools.😊
GuyW

Another vote for a helicoil.
Bob Beaumont

I managed to tap the captive nut out to 3/8" UNF and the rack mount bracket hole only needed slightly enlarging. Tapping was difficult as no room to turn the tap wrench but I improvised - not my best thread but bolt tightened up ok so problem solved!
Bill Bretherton

Well done - I usually use a small open ended spanner on the tap flats in confined spaces so I can steady the top of the tap with one finger while turning the tap.
Chris at Octarine Services

This thread was discussed between 13/04/2020 and 15/04/2020

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