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MG Midget and Sprite Technical - How to repair this

The bolts holding the front near side damper should screw into the chassis. On my car these threads have been striped at some point and replaced with studding and nuts at either end. The threaded holes exit into the cone that locates the spring. To attach nuts to the end of the studs a P.O. has cut a section out of the cone, see pic.

How am I going to repair this?
My initial thought was to weld the nuts in place inside the cone to make them captive, and then repair the cone. I tried but the space is too limited to get the welder in properly and the first attempt failed.

There isn’t enough material left to retap the holes without going the next size up, but I can’t because the bolt size is determined by the holes in the damper.

I’m coming to the conclusion that i’m going to have to cut the cone off to get better access or at least make the hole bigger which i’ll then have to repair. This would give me access to what looks like a metal plate that would have the threaded holes that I may be able to replace.

Before I start chopping off more metal i’d welcome any other ideas?


C MADGE

That is a horrible bodge! Arghh!

I would remove the bolt and the damper and clean up the metal around the hole. Then fill the hole competely with weld, closing off from the bottom with weld and then filling in from the top until flush. Ensure you get a good fusion/ penetration as you do this and then trim the top smooth with a flap wheel.
Then, using the damper as a guide (or make up a steel template from the damper first) redrill and retap the fixing hole for that bolt. Clean it up and repair the cone with a welded in plate cut and shaped to fit.

Alternatively, if the bolt hole will still take it, fit a helicoil insert. This would normally be perfectly secure even for a damper mounting and certainly quicker and easier but you imply "there isn't enough material"?
GuyW

IIRC the normal tapped blocks are about 3/4" wide so there should be enough material for a thread insert. http://www.tracytools.com/helicoil-thread-repair-kits/unf-thread-repair-kits/3-8-x-24-unf-thread-repair-kit
David Billington

"...so there should be enough material for a thread insert"

Assuming that the bodgers haven't drilled through the hole with too big a drill.
Dave O'Neill 2

Dave, that is what I thought Mr Madge (is it Colin? - I forget!) that is what I thought he meant. Which is why I dived in to the weld up and redrill scenario. But on re-reading his words I think he means there is not enough meat to retap with the original size.

Its very likely that a Helicoil would work well to recover back to the original size and enable the use of the correct HT bolts.
GuyW

Could you weld the nuts onto a strip/plate which you could then tack weld through a small hole drilled in the plate midway between the nuts?
J Smith

When I built up my Heritage shell one of the damper threads did not clean up well so I bought the helicoil type kit from Tracy tools that David linked to and inserted a replacement thread.

I'm only down at Clevedon so if you want to give the 'Helicoil' type repair a try let me know as there are spare inserts in the kit.

R.
richard b

Thanks for your help gentlemen.

Guy - There isn’t enough metal to retap to original size, but can’t go up a size either because the mounting holes in the damper won’t be big enough.
Welding up the hole and retapping would be a good and cheap solution but the bolt goes into a 3/4 inch depth hole with i’m guessing the last quarter the thread in the plate at the bottom. Not sure I can get enough weld in there from one end.


David
I hadn’t considered an insert as I haven’t used them before, and assumed they wouldn’t be strong enough for this application. But it sounds like they would be. Is the link you posted the right size insert for these original bolts? They list a 9.8 mm drill, my hole is about 10 mm though.


The other two bolts are the same bodge. So first of all I need to get them undone, and the damper off to get a closer look.

Chris
C MADGE

Thanks Richard, I may take you up on that
C MADGE

Chris,

Worth checking the hole size accurately. I noted the 9.8mm drill listed and 3/8" is 9.5mm so hopefully the hole hasn't been taken out too large for that type of thread insert. The link I posted should be the correct one as from memory those damper bolts are 3/8" UNF, what you might want to check is the length of the insert supplied as you can get them in differing lengths so you may want a longer one. The inserts are the cheap bits though so extra longer should be cheaply available then maybe take up Richard's offer of the installation kit.

If the hole is too big then there are other type of insert which are larger but the kits are more expensive, Timesert springs to mind.
David Billington

Chris,
I realised you couldn't go up a size - I wasn't suggesting that. My preferred option was a helicoil insert. The wel option was an alternative if the hole is already too large to tap oversize to take the correct size of helicoil insert.

I used 2 helicoil inserts on one of my damper platforms some years ago and it has worked perfectly. Thase bolt holes had also stripped and wouldn't retap without using a helicoil
GuyW

Thanks Daviid and Guy, once I get the damper off i’ll measure the holes and explore the helicoil option.

C MADGE

As David has noted the thread is 3/8 x 24 UNF.

I have both the standard length inserts and the longer ones (noted on the packet as 2D).
Its noted in the packet that 'inserts will appear larger than tapped holes and cannot be measured by length or diameter in their free state'.

The drill is 9.8mm the tap is of course a special and its major diameter is approx 10.90mm, minor dia as best as my calipers can give is approx 10.5mm.

The insert is of high quality steel and it notes on the box 'due to the narrow and exact tolerance the new thread normally is stronger than the original one'.

If you want to borrow the set and give them a try you are welcome to pop down and pick up - tea can be suppied on request !

R.
richard b

The web site for the inserts is uni-thread.com and they also list an alternative self tapping insert - I've not seen these before and have no idea on pull out etc but they seem to be a bigger o/d so might be usefull if holes are bigger than suitable for the uni-thread inserts.

May be worth giving them a call

http://www.uni-thread.com/tr_baerfix_unf_inserts_detail.php?01552-3

richard b

not much to add with the fixings, seems to be pretty well covered, but AARGH what a bodge.
Rob Armstrong

Richard,

Those don't look like self tapping but quote M14 x 1.5 as the outer thread.

I saw these on ebay earlier https://www.ebay.co.uk/itm/UNF-3-8-thick-wall-thread-repairinsert-EZ-LOK-5-not-timesert-bigsert-319-624/121923259741 . 1/2" UNC given as the outer thread and they look to have a thread lock adhesive applied as standard, maybe a good option if the existing holes have been drilled too large for the helicoil type.
David Billington

In another bizarre BBS coincidence I was fixing that block on my car only yesterday!

When I undid the R/H damper bolts I heard a thud as something dropped off and it was that very block that had come adrift. It's not actually held on by a huge amount of weld and I think my shell has had some knocks which must have broken them. Anyway I managed to get it back in position by poking something through the bump stop hole, bolt up the damper and then I just blasted it blindly with the MIG welder through the hole. Luckily the 55 year old shell is still like new in that area so it was fairly easy to weld. It only has to hold enough to allow the bolts to be located but it would be a bummer if it came off again.

Anyway with yours I'd be tempted to try and remove the old block (even if it means making that horrendous hole bigger) and make a new one. Then just weld it back in place and repair the hole in the spring mount.
John Payne

David,

The instructions seem to mention tapping in some materials but also note self tapping - interesting option, especially if the holes are drilled oversize for the Heli type inserts.


http://www.uni-thread.com/instructions_detail.php?Installation-of-Baerfix-threaded-inserts---by-hand-1
richard b

Richard,

I stand corrected thanks. It wasn't evident when I viewed the original page you posted that they went in that way so the reason for the slots is now more apparent, they can act as cutting edges. If the block is 3/4" (19mm) wide as I recall then that still gives about 2.5mm each side. Yet another option for recovering the threads.
David Billington

Richard thanks for the information and your kind offer.

John I am thinking the same too. Whichever way I fix this i still have to repair the hole in the cone. So I may as well take the cone off and repair the block.

I really appreciate the responses and help, thanks.

C MADGE

Chris,
The only thing I would add is that when I repaired mine, using a helicoil insert, I found it extremely quick and easy. I am not an engineer and had some doubts about how secure an helicoil type insert would be. But in practice it is clearly a good engineering solution which I found neat and strangely satisfying to do.
GuyW

I'm a fan of Helicoils. They work very well in my experience, but a dab of Loctite 270 on the outside of the coil when installing it is an investment.
As to the length they are specced in multiples of the nominal diameter, so as an example M10 x 1.5D would have an installed depth of 15mm. Note that that is installed depth - it will be shorter than that when it's loose as they grow a bit when they're screwed in because the coils tighten up for interference fit.
I don't think I'd fancy getting in there with a MIG torch, but a stick welder ought to be OK so J Smiths idea still has merit I think, if there isn't enough metal to use Helicoils.
Greybeard

The pre-tapping clearance drill for the correct sized helicoil measures at 9.72mm whatever that is in English. Fractionally under 7/16"?
That's from my 3/8 X 24 Uni-Thread kit

GuyW

I have got the damper off. Although all three original bolts had been replaced with threaded rods and nuts, only one of the threaded holes is damaged. That hole has been drilled out to just over 10mm so helicoil isn’t an option as it stands.

The only alternative insert i can find is Uni-Thread Ltd Baerfix solid insert. The kit has a 13.25mm drill bit so that would work. However it’s a bit pricey at £67. I may try welding up the hole, drill, and tap first.

C MADGE

Chris,

I posted this link not that long ago and it only requires a 1/2 UNC tap from what is mentioned https://www.ebay.co.uk/itm/UNF-3-8-thick-wall-thread-repairinsert-EZ-LOK-5-not-timesert-bigsert-319-624/121923259741 .
David Billington

That does look like an interesting option.

Presumably fitted using a bolt and locknut.
Dave O'Neill 2

Dave O'Neill,

It does make me wonder whether one couldn't just take a 1/2" UNF or UNC bolt and drill and tap it 3/8" UNF in a lathe and screw the result in with some loctite to retain it after tapping the buggered hole out to suit. I would likely make a block with a hole drilled square to guide the drill and another for the tap so they went in straight, easy to do in a drill press.
David Billington

David
I clicked on the ebay link the other day and it didn't work for some reason so I missed it.

Those inserts look as if they might work, 1/2 unc needs a 10.7mm drill and then tap obviously. Those dont have a slot so would need to be inserted with a bolt and locking nut I guess.

The manufacturers website has them with slots for a screw driver. Part number 319-624

https://www.ezlok.com/assets/documents/dimensional_drawings/DimDwg_319Series.pdf


Thanks.
C MADGE

Back late from a jaunt down south to have Sunday dinner with some old friends, and I was confronted by Guy's picture. Sickening.
Nick and Cherry Scoop

Chris,

Note from the technical details that the insert has a modified thread form and the gives the modified minor diameter as 0.434" to 0.438" (11mm - 11.1mm) so would require a larger than normal tapping drill. Best check with the supplier or maker. Likely if you drilled 10.7mm and tapped 1/2" UNC it wouldn't screw in.
David Billington

"...and I was confronted by Guy's picture. Sickening."

You don't like courgettes?
Dave O'Neill 2

Dislike them, Dave. But I hate the yellow ones. I don't know how Guy knew this, but it's clear provocation.

Sorry, Chris.
Nick and Cherry Scoop

Nick, it was a fully justified retaliation for your choice of carpets.
GuyW

Chris,

Do you have access to a 1/2" tap? You will need ideally a 1st and 2nd tap, or just a 2nd. 1/2" UNF taps on Ebay for £5-10. If you end up buying a tap, avoid 'spiral flute', they are easy to break!

I have a selection of HT 1/2" bolts and setscrews, and from one of these I can make you a threaded insert with a 1/2" external thread and tapped 3/8" UNF internal thread.

The choice of 1/2" is UNF, UNC, BSF and BSW - which would you prefer? Standard tapping sizes are UNF 29/64" or 11.4mm, UNC 27/64" or 10.8mm, BSF 7/16" or 11.1mm and BSW Letter Z or 10.5mm.

What length does it need to be?

Insert as you said with a bolt and locking nut, with some thread lock on the external thread of the insert.

Richard
Richard Wale

Seems a lot of trouble to go to when a boxed set of clearance drill, tap, insertion tool and 10 inserts is less than £25.
http://tinyurl.com/ybk34uxv
GuyW

Guy,

The maximum size of the hole before tapping for a 3/8" UNF Helicoil is 9.9mm, and Chris says that the hole is already more than 10mm. It doesn't sound like a Helicoil is an option?

Making the insert is no problem (and no cost), and drilling/tapping the hole for it is much the same as for a Helicoil.

If Chris has, or can get the loan of, a drill and tap, then the total cost = £0.00! The solution is a strong mount for the damper.

Richard
Richard Wale

Ah, sorry Richard.
I had skipped Chris' post immediately after mine with the kit photo where l gave the clearance drill size as 9.7mm. l didn't realise his plate had already been drilled out to beyond that size.
GuyW

Richard Wale

That's a very generous offer, thank you. A custom insert would be a better solution as the ebay ones are a little short.

I have a pillar drill and the loan of some imperial taps, so I should be able to make my own insert, I'll need to source a 1/2 inch bolt and possibly some more taps.

I'm still thinking of the alternative solution, cutting the cone off, removing the threaded block, welding up the hole, drilling, and re-tapping. I have to repair the hole in the cone anyway, so welding it back on isn't that much more work.


What a great forum this is. :)

Chris



C MADGE

Chris,

I have a selection of 1/2" imperial thread bolts, a lathe and a 3/8" UNF tap. Would be very happy to make the insert for you - just tell me the length and which external thread you would like?

Even it you don't use it in the end, a choice is always nice to have!

Richard

Richard Wale

Richard if you are sure, then yes please.

Can I have a 1/2 UNC x 12 external thread, and a length of 3/4 inch?

If you can email me at chrismadge143 at hotmail dot com, I can let you have my postal address, and pay you for the postage and any costs you incur.

Its really appreciated, thanks.




C MADGE

sorry typo, I meant 1/2 - 13 UNC thread !
C MADGE

This is cheaper, the photo is metric but they deliver 50 UNF helicoils

Flip

https://www.hbm-machines.com/producten/apart/acties/hbm-unf-schroefdraad-reparatieset?gclid=Cj0KCQjwnqzWBRC_ARIsABSMVTP96ndfVYNhJTEi4_VyLcsNwxM1t78koDHIP7OvsU0O33EghuN4qVAaAiTCEALw_wcB#

Flip Brühl

Chris,

Your wish is my command - please see the attached photo.

1/2" x 13 UNC external, 3/8" x 24 UNF internal, 0.750" long.

Please make sure that you degrease the external thread thoroughly before applying the Loctite.

Have email you for your address. Zero costs.

Richard

Richard Wale

Great stuff, thank you !

I have sent you an email :)
C MADGE

To conclude this thread for anyone that’s interested, Richard’s insert worked nicely. I fixed it in with some thread lock and a bit of weld at the bottom where it protruded through the hole for belt and braces.

The cone was patched with some sheet metal formed around one of the wishbone cones and welded in place.

Thanks again for the insert Richard.

C MADGE

Tidy job!
GuyW

Look good, well done.
Nigel Atkins

Dazzling piece of work, Chris.
Nick and Cherry Scoop

Very nice Chris. Good work Sir!
Greybeard

Great news and a useful thread for the future.

Looks to be in suprisingly good condition under there as well.

Top job!
John Payne

I only just saw this thread, but I agree that the threaded insert idea is really good. As I have a lathe and not much money I have resisted helicoils. For some stripped holes, such as the timing cover, and where there is access from the back, I drilled out the hole and turned down the insert to an interference fit without threading it. With the engine in the car getting a tap into position is well nigh impossible. I left a small step on the end so that when it's pulled up tight with the bolt, and with a bit of Loctite, it's secure. For other problem holes I have drilled and tapped suitable bits of bolt, eg for the screen frame which is thin ally.

Les
L B Rose

This thread was discussed between 07/04/2018 and 17/04/2018

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