14 replies to this topic

[lildeucecoop72]

Hi all,

 

last night I was 'working fast and tired', and wasn't using my head when torquing the 4 tower bolts on the front pre '76 subframe.

 

I very stupidly used the torque value (54nm!) meant for the 2 larger tower bolts for post '76 models.

The value for the type with 4 bolts didn't seem to be on any torque lists, but must be considerably lower, my guess is around 35nm.

 

Unfortunately  torquing them to 54nm stripped the thread on the driver's side outer tower hole, (The bolt thread was also damanged) and when this happened I immediately realized, snapped awake, and slackened the others off. The 3 others seemed to have survived. 

 

It is obvious that this is not ideal, and it will need to be repaired or replaced. The subframe is of course also fixed with 2 bolts at the front and 4 bolts in foot wells too

 

After much swearing, fist shaking, banging my head and a couple of biscuits, I found that bolt hole in question has a couple of good threads once I removed the spring washer and I tightened with a replacement bolt as much as I dared with some high quality lock-tight.

 

So, my questions are:

 

1) What should the right torque setting for thes 4 bolts be here be?

 

2) Is there a better way of shoring up the broken thread with a that new bolt whilst the subframe is still on the car?

 

3) Is it 'safe' to temporarily drive on 3 (or 3 and half!) tower bolts at the correct settings?  - What are the consquences here?

I have have spent literally hundreds of hours getting the car ready for the summer, and obviously avoiding that everything would have to come out again to repair or replace!

 

 

Thanks...from one exhausted and stressed mini owner, who will not work tired from now on!

Edited by lildeucecoop72, 09 June 2022 - 10:09 AM.

[Ethel]

The car sits on the subframe, so you could probably get away with no bolts - if you could find a bump free road.

 

Are you sure it's stripped? The threads would have to go somewhere - either the frame's are wrapped round the bolt or the bolt's are still in the frame. (Just asking to be 100% sure)

 

I'd expect the torque to be under 10lb/ft.

 

"engineers" fix - stick a stud in with thread lock, tighten it down with a nut instead.

[lildeucecoop72]

The car sits on the subframe, so you could probably get away with no bolts - if you could find a bump free road.

 

Are you sure it's stripped? The threads would have to go somewhere - either the frame's are wrapped round the bolt or the bolt's are still in the frame. (Just asking to be 100% sure) - I'll check, but I believe the thread from the frame was on the bolt.

 

I'd expect the torque to be under 10lb/ft. thanks

 

"engineers" fix - stick a stud in with thread lock, tighten it down with a nut instead. thanks, i'll look into that

Edited by lildeucecoop72, 09 June 2022 - 11:21 AM.

[sonscar]

Real engineers fix..Smother it in silicon sealer and place delicately in the hole.Seriously do not do this,Steve..

[EAVB]

It might be worth either getting a long tap or welding a tap to a piece of bar to see if you can run it through the subframe thread to clean it up. I don't have a frame to hand but you may even have room for a slightly longer bolt. Someone on here will know.

[Magneto]

Most 5/16" bolts torque to 18-25 ft lbs......3/8 are good to 45 ft lbs, you'd be safe at those numbers. I can't believe the others didn't strip at the amount of torque you put on them!

[Spider]

The threads here are only a 'soft' thread, they are tapped in to Mild Steel Plate and that's all.

 

The torque number is 18 - 20 ft / lb.

 

If you are only driving on the road, you'll get away with only having 1 bolt on that side, but if anything adverse may happen, it could be an issue.

You could try a thread repair, like a helicoil, which you should just be able to do with the subframe in place, but you'll need to extend the Tap for it. If it were me, I'd weld a bolt to the Tap to extend it, but if you do it this way, be sure the weld is good as you don't want it coming apart with the Tap in there. Be aware too, it's more or less a Blind Hole, so after cutting an initial thread if the Tap hasn't gone in deep enough, you may need to grind it back. 

 

There didn't seem to be a ryhme or reason but some models were fitted with Studs here that were 3/8" UNF on the bottom and 5/16" UNF on top. I will use these every time over bolts in this application. They seem to be NLA now, I think Swiftune have them, I make my own from Head Studs.

[Ethel]

Is the 18-20 from the workshop manual?

 

I allowed for the subby being mild steel & used a chart. Can't see pretension doing anything more than keeping it from unscrewing & didn't they have locktabs?

[lildeucecoop72]

Thanks for your replies. Very encouraging.

I’ll replace all the bolts just in case and gently torque them to around 18ft-lbs with thread lock.

I’ll see if I can engineer an extended tap and clean the thread on the damaged one. It’s possible the mild steel plate was pulled upwards under the pressure they were under but I guess if the held, they will keep holding at the correct torque and when locked.

Ref Ethel: Yes they have lock-tabs
Ref Spider: yes they have a blind hole

Thanks again.

[riktanius]

Can someone explain where the locktabs go? I just dropped my subframe and there was no locktab plate at all. I dont know where I am supposed to be the replacement. 

Between the body and the spacer? Between the subframe and the spacer? Between the bolt and the body? 

Tabs facing up? Facing Down?

[Spider]

Can someone explain where the locktabs go? I just dropped my subframe and there was no locktab plate at all. I dont know where I am supposed to be the replacement. 

Between the body and the spacer? Between the subframe and the spacer? Between the bolt and the body? 

Tabs facing up? Facing Down?

 

If you have studs and nuts, under the nuts and they are there to lock the nut in place, so tabs up, then bent over after tightening the nut, though, in 40 years, I've never locked them ever.

[riktanius]

 

Can someone explain where the locktabs go? I just dropped my subframe and there was no locktab plate at all. I dont know where I am supposed to be the replacement. 

Between the body and the spacer? Between the subframe and the spacer? Between the bolt and the body? 

Tabs facing up? Facing Down?

 

If you have studs and nuts, under the nuts and they are there to lock the nut in place, so tabs up, then bent over after tightening the nut, though, in 40 years, I've never locked them ever.

 

So I should see them from under the hood, right? IF that is the case, I have NEVER seen these on a Mini. Ever. Owned 2, and seen dozens in ITaly and the US. 

[Spider]

 

 

Can someone explain where the locktabs go? I just dropped my subframe and there was no locktab plate at all. I dont know where I am supposed to be the replacement. 

Between the body and the spacer? Between the subframe and the spacer? Between the bolt and the body? 

Tabs facing up? Facing Down?

 

If you have studs and nuts, under the nuts and they are there to lock the nut in place, so tabs up, then bent over after tightening the nut, though, in 40 years, I've never locked them ever.

 

So I should see them from under the hood, right? IF that is the case, I have NEVER seen these on a Mini. Ever. Owned 2, and seen dozens in ITaly and the US. 

 

 

They were only fitted on the UK made cars up to 1976 and Australian built to 81. In the UK they went to the single bolt (per tower) in 76. They didn't use these plates / tabs.

If the cars you saw were made before 76 didn't have them, then they were removed. The plates not on;t have the lock tabs on them but also retain a grommet that stops the trumpet filling with water and corroding from the inside out. It's for this reason that I fit these plates.

[Cooperman]

It would be entirely safe to drive it with only one bolt in one side. The twin-tower-bolt sub-frames are not rubber mounted, so there is no relative movement betwen sub-frame and body.

If it were me, I would fit the three bolts at a low nominal torque, then put some 'JB Weld' onto the bottom of the 4th bolt and try to 'nip' it up lightly into the frame.

An alternative would be to tap the damaged thread at the next metric size up which would be M10 fine. Then fit an M10 bolt in place of the UNF one.

Don't make this into a bigger problem than it need be as it's not a major issue. The loads are all compressive between tower and bodyshell.   

[lildeucecoop72]

It would be entirely safe to drive it with only one bolt in one side. The twin-tower-bolt sub-frames are not rubber mounted, so there is no relative movement betwen sub-frame and body.

If it were me, I would fit the three bolts at a low nominal torque, then put some 'JB Weld' onto the bottom of the 4th bolt and try to 'nip' it up lightly into the frame.

An alternative would be to tap the damaged thread at the next metric size up which would be M10 fine. Then fit an M10 bolt in place of the UNF one.

Don't make this into a bigger problem than it need be as it's not a major issue. The loads are all compressive between tower and bodyshell.   

 

Thanks Cooperman, What I ended up doing was using locktite on all the bolts, and tightening to nominal torque.

I will addresse this again next time the frame comes out, or go for one of your suggestions if one that has the stripped thread pops out.