Wrong Subframe Torque Settings - BOLTS OUT!

[Royalratch]

Can't find them in Bentley or Haynes.

M42/318iS.

[steviec_lj]

Hi mate,

Found this in the later 3 Series Haynes Manual on page 2A.3

Front Subframe Bolts* 105 Nm or 77lbf ft

*Use new bolts.

Hope this helps

[steviec_lj]

Oh, and thats the specification for M40, M42, M43 and M44 4cyl Engines

[Royalratch]

Awesome - cheers dude!

Luckily I do have new bolts!

[Royalratch]

Are these deffo correct - I just snapped off 3mm of subframe bolt deep IN the chassis rail.

Maybe my wrench needs to be calibrated but I have hardly used it since new. 100nm felt way too tight for this.

Now I've really got some shite to sort...

[DanThe]

How can you snap off 3mm of a bolt?

[Royalratch]

No idea. The top 3mm is now stuck deep inside the front chassis rail/cross member.

Will try to drill out.

[steviec_lj]

Yes, these are correct.

I'll attempt to scan the pages in for you mate

[Jhonno]

Did you use new bolts? Iirc they are the same dia as wheel bolts which are the same torque settings..

Maybe something a bit odd going on considering it only snapped the top 3mm

[DanThe]

Im guessing you used a short bolt in a deep hole

[Royalratch]

Im guessing you used a short bolt in a deep hole

But how would that snap off the top 3-4mm?

They are the correct bolts and brand new - checked part numbers against ETK and also checked against the old bolts.

I think I over tightened them and they 'spun off' in the hole.

The hole is not closed at the top (you can see them looking down into the cross member) so I should be able to push them through and retrieve.

Such an unnecessary waste of time tho...

[B7]

Strange one this. Are you sure there was nothing obstructing it. Those settings are not exactly OTT and for the size of bolt, I wouldn't expect it to sheer at those settings.

Right bummer tho.

[DanThe]

If the correct amount of threaded section was screwed in, it wouldnt have sheared off only 3mm, it would have sheared off most of the threaded section of the bolt

[Royalratch]

Barry has seen the bolts - strange indeed.

This is what happened. I hand tightened the bolts into the frame / chassis with light copper slip.
The subframe was supported by a jack underneath. I proceeded to torque to 100-105Nm and it seemed very very tight
but I kept going - long smooth motions, no yanking.

What I thought was the 'clack' from the wrench signaling correct torque I now know was in fact each bolt snapping in the chassis.

After I torqued the last one, the frame fell out the chassis, all 4 bolts dropped to the floor. Luckily the jack was still below it a few inched so it wasn't catastrophic.

But I now have 4 subframe holes with 3mm of threaded bolt buried deep inside.

Pished is not the word.

The weirdest things is, if the threads snapped off at their tip, why did they fall out? There was more than enough thread to keep them in?
Unless the weight of the engine pulled them out?

On top of all that, fitting the headlining, even with Barry doing the biz was stalled because of a few bastard plastic body nuts...!

[DanThe]

If the bolts fell out and they were only 3mm shorter they were not long enough to start with. If you had screwed them in properly there is no way 3mm could have broken off the end, even if it did the bolt wouldnt drop out.
They were too short

[Royalratch]

They were the correct bolts. Unless I was supplied incorrect bolts.

The other reason I know they were not too short is because they threaded all the way into the crossmember.
You can see them poking out the top of the hole from above so they were not too short.

[B7]

Got any photos? this is intriguing. Are they BMW supplied bolts? Certain steels have different tensile strength and would sheer if over torqued.

[steviec_lj]

Not been able to scan the pages from the manual, so I will need to dig out the camera tomorrow and photograph each page in sequence.

I assure you, the above is the correct torque setting for the bolts in question.

[DanThe]

Trevor, ratch is obviously talking crap again

If you screwed a bolt in to a threaded hole 20mm how can the end 3mm break off? It cant...

Even if the bolt bottomed out, it would break between the start of the threaded hole and the head of the bolt

[Brianmoooore]

What are the markings on the bolt heads?

[e30topless]

that's awful, how you going to get them out ?

[bss325i]

There seems to be some confusion.

There is only 3mm or so left on the bolt, ie 3mm of thread left from the head of the bolt with appox 30mm left in the chassis rail. On all four!

It doesn't look like they have bottomed out as you can see the end of the bolt from the top of the chassis rail as there are holes on top.

[DanThe]

Well that explains it

Cant beat 'feel' (common sense) when tightening bolts

[Royalratch]

@DanThe - do you feel a little like a complete arrogant knob or a lot like one?


@e30topless - Tap and Die set? EasyOut type gadgets? Drill? All ideas welcome - gotta do it damn sharpish tho before I set the thing on fire...

[bss325i]

I think its bloody strange tbh as 105Nm isn't that tight for the size of bolt.

[e30topless]

buy a set of easy-outs, that should get them out, are the bolts high tensile ?

could be hard to drill,

[Royalratch]

Easy out / drill outs will be sorted for Tues. Faulty bolts or badly calibrated wrench who knows...

[Brianmoooore]

If it's new bolts in clean, bottomless threads, they should be impossible to drill out. Applying a normal drill bit should just spin them out the bottom of the nut.
A left handed drill bit is what's required.

[Rav335uk]

You'll need something like this.

http://www.screwfix.com/prods/20084/Van ... t%208%20Pc#

[B7]

I've had a couple of those sets Rav and I've never succeeded with a set yet . And at 9.99, I would expect the quality of a BMW bolt to be of a far higher quality that this kit. Good luck Ratch if this is the kit you've bought!!

So I'm getting a better picture now (as we don't have photos). The bolts have gone in, locked short of tightening the part and sheered.

I reckon the new bolts are 3mm longer than the old ones. the threads are congeeled with paint and / or other at the top down to where the old bolts were. The very slightly longer bolts have gone in with no issues then locked 3mm short of where they need to be and bang. off comes the head.

Chances on all 4 are very slim but no impossible I suppose.

[DanThe]

@DanThe - do you feel a little like a complete arrogant knob or a lot like one?

You tell me ratch, your the expert

Looking at the BMW tightening torque specs (sticky in tech help) it seems you exceeded the maximum setting
Those screws wouldnt be anymore than 10.9 = 75NM max

[Rav335uk]

I've had a couple of those sets Rav and I've never succeeded with a set yet . And at 9.99, I would expect the quality of a BMW bolt to be of a far higher quality that this kit. Good luck Ratch if this is the kit you've bought!!

So I'm getting a better picture now (as we don't have photos). The bolts have gone in, locked short of tightening the part and sheered.

I reckon the new bolts are 3mm longer than the old ones. the threads are congeeled with paint and / or other at the top down to where the old bolts were. The very slightly longer bolts have gone in with no issues then locked 3mm short of where they need to be and bang. off comes the head.

Chances on all 4 are very slim but no impossible I suppose.

That was just an example of the tool Trev, I have a much better set, but having said that, i've only used it twice in the last 10 yrs or so, and that's to extract broken spark plugs from the head.

[bss325i]

@DanThe - do you feel a little like a complete arrogant knob or a lot like one?

You tell me ratch, your the expert

Looking at the BMW tightening torque specs (sticky in tech help) it seems you exceeded the maximum setting
Those screws wouldnt be anymore than 10.9 = 75NM max

To be fair Dan, he posted a question in this section and got an answer which has caused this possibly caused this problem.

[simonsimoff]

In the Bentley manual it's got subframe anchor bolts listed as:

M10 @ 42Nm
M12 @ 77Nm

Section 13, page 47.

[DanThe]

I know what your saying Barry but this is only words on the internet, you cant take it all as gospel

If you remove the subframe there might be enough of the bolt poking out to grip with a proper stud remover