Seat Rails Nut Stripped?

Technical MGB discussion
nathan_f
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Seat Rails Nut Stripped?

Post by nathan_f » Mon Jul 13, 2020 12:50 pm

Has anyone had any experience replacing the front bolt that holds the driver's seat offside rail to the floor pan? I've noticed mine does not appear to be 'biting' like it should. I can wrench it down tight to the floor, but the moment any pressure is put on it, such as sitting in the seat and shifting your weight around, it pops back up. This is, obviously, not good from a safety standpoint. The other three bolts are in place and secure, but I don't want to trust 75% integrity in the even of an accident in my daily driver. I haven't pulled the bolt all the way out to check to see if it is stripped, but assuming the worst and either the welded nut has come undone or been stripped, does anyone have any advice for repairing or replacing without removing the floor pan? I don't have any welding gear and fear I'm not equipped to properly re-install it if I am able to get it out. Has anyone had any luck just putting in one or two self-tapping metal screws in lieu of the nut/bolt combo, or is the floor pan too thin to do that? I ordered some of the wooden shims and plan on pulling the seat to install them...when a previous owner re-did the seat coverings and installed new carpet, they appear to have failed to put the shims in place and it's riding directly on the floor.

Ian Fozzard
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Re: Seat Rails Nut Stripped?

Post by Ian Fozzard » Mon Jul 13, 2020 1:18 pm

Nathan,
is this the bolt which threads onto a welded nut inside one of the chassis box sections? If it is at all possible to reach the nut underneath you could always just add another nut to the bolt. Would require two people to do this of course.
If the nut is completely inaccessible, then I would suggest tapping out the hole and nut to the next size up. You then need to find the bolt for that larger threaded hole of course, and ensure it will fit through the seat frame etc.
Helicoil inserts are another option, they work very well but you are getting into fairly specialised work. They are DIY, and you can buy the specific kit you need for the bolt size in question.
Whatever you do, I would agree that you need 4 secure fixings for the seat.

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

Ian Fozzard
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Re: Seat Rails Nut Stripped?

Post by Ian Fozzard » Mon Jul 13, 2020 1:20 pm

P.s. if it is the bolt which is stripped, and not the welded nut, you may get away with just replacing the bolt😊😊

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

nathan_f
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Re: Seat Rails Nut Stripped?

Post by nathan_f » Mon Jul 13, 2020 1:32 pm

Yep, that's the one. I'm really hoping it's just the bolt, that'll make this easy! Just wanted to see if anyone has seen this before so I can start the mental checklist and be pleasantly surprised if it's the easy fix, hah.

Ian Fozzard
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Re: Seat Rails Nut Stripped?

Post by Ian Fozzard » Mon Jul 13, 2020 2:00 pm

One further possible solution (a bit of a bodge perhaps) is to drill down through the box section from inside the car, making certain that there are no cables/pipes in the way (some run under the car in that area) Once you have the pilot hole for alignment, enlarge the hole to permit a long socket and nut to pass through, and allow fixing of the seat bolt.
In general I believe any lightening holes should be on the sides/vertical faces of chassis members, but the MGB is so strongly built I would think one hole on the bottom surface would be acceptable.
Interested to hear what anyone else here might think?

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

Ian Fozzard
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Re: Seat Rails Nut Stripped?

Post by Ian Fozzard » Mon Jul 13, 2020 4:34 pm

A further post script:

If you are installing the wooden strips underneath the seat runners, don't forget that you will also need the 4 thick metal spacers which sit in the holes in the runners, if they aren't in place already?

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

Ian Fozzard
Posts: 436
Joined: Fri Mar 27, 2015 8:18 am
Forename: Ian
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Re: Seat Rails Nut Stripped?

Post by Ian Fozzard » Mon Jul 13, 2020 4:39 pm

These are: SEAT RAIL SPACER MGB
Product Code: AHH6939

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

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Tom Brearley
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Re: Seat Rails Nut Stripped?

Post by Tom Brearley » Mon Jul 13, 2020 8:44 pm

If the nut is still in place but has stripped then tapping it out to the next size up (5/16 from memory) seems the best option.

If it's come adrift perhaps the hole Ian suggests might be easier to make from the underside directly beneath the bolt hole? A new nut could then be offered up in a socket.

The seat rail bolts are surprisingly small (1/4" from memory) so I agree, I'd want them all doing their job too!
1973 MGB GT (Exeter) - currently shaking down after 3 years off the road

nathan_f
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Re: Seat Rails Nut Stripped?

Post by nathan_f » Tue Jul 14, 2020 1:51 pm

Thanks for the input all! Good to know that it's not a major issue to drill through the bottom plate to access the nut if needed.

On another note, has anyone ever tried using rivet nuts for an application like this? Seems like it could be a good fallback.

Ian Fozzard
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Re: Seat Rails Nut Stripped?

Post by Ian Fozzard » Tue Jul 14, 2020 5:30 pm

Not me... A bit new fangled for my workshop🤔🤔

Ian F
1972 BGT, Blaze, Navy trim, recessed grill
1961 Midget, 948cc, Clipper Blue, Blue trim and weather gear

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