sub frame up grade - MG-Rover.org Forums
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post #1 of 24 (permalink) Old 09-04-2017, 13:04 Thread Starter
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sub frame up grade

Hi all
Well this Wednesday my 04 TF is going to get s/steel front sub frame mounts and new 12.9 bolts. Just hoping the frame is not too rusty
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post #2 of 24 (permalink) Old 09-04-2017, 14:32
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Originally Posted by helsbyman View Post
Hi all
Well this Wednesday my 04 TF is going to get s/steel front sub frame mounts and new 12.9 bolts. Just hoping the frame is not too rusty
Have you soaked the existing bolts thoroughly to give them the best chance of coming out in one piece?

Does the person doing the work understand the problems often experienced with this job?

Good luck.

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post #3 of 24 (permalink) Old 09-04-2017, 14:37
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Why not stainless bolts?
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post #4 of 24 (permalink) Old 09-04-2017, 14:58
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Why not stainless bolts?
I thought that Grade 12.9 bolts were not available in SS?

And isn't SS weaker for 'structural' bolting purposes?

Of course I might have been dreaming though

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post #5 of 24 (permalink) Old 09-04-2017, 16:22
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Judging by the trivial size of the 3 bolts MGR used there ain't much loading there to worry about!
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post #6 of 24 (permalink) Old 09-04-2017, 17:59
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Judging by the trivial size of the 3 bolts MGR used there ain't much loading there to worry about!
But as I am sure you are aware, bolts are sized using their csa (cross sectional area) and shear strength.

Therefore if you are using 'softer' bolts (even with the same csa) they will be under far higher load and therefore more likely to fail.

Its not a chance I would be taking on a sub frame...

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post #7 of 24 (permalink) Old 09-04-2017, 19:20
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The four bolts that hold the rear subframe brackets to the body of the car and two for the front mounts would be fine in stainless as they are not in shear load, The larger longitudinal bolts that fix the brackets to the subframe would be better as spec. I thought they were rated at 10.9 though.


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post #8 of 24 (permalink) Old 09-04-2017, 20:00
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Of the four available rear mount bolt holes even MGR only fit 3! As Sundance says they are not under any particular stress other than the bolt's own torque setting for tightness.

When I sheared several sub-frame bolts on my car I fitted larger bolts and all four of them...because I could. I have to say that it always worried me how an MOT tester knows that MGR only fit 3 out of 4 bolts.
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post #9 of 24 (permalink) Old 09-04-2017, 21:22
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Quote:
Originally Posted by TipperMG View Post
Of the four available rear mount bolt holes even MGR only fit 3! As Sundance says they are not under any particular stress other than the bolt's own torque setting for tightness.

When I sheared several sub-frame bolts on my car I fitted larger bolts and all four of them...because I could. I have to say that it always worried me how an MOT tester knows that MGR only fit 3 out of 4 bolts.
When I replaced mine all four bolts were present. Not sure when they began to use three bolts in the rear brackets, but my car is a Jan 04 build.
I cannot for the life of me find a logical answer to why they would not fit all four bolts, not like they cost anything and the time taken to whizz one in with a torque gun is negligible....
Were the cost savings that tight, or the bosses bonuses not big enough?


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post #10 of 24 (permalink) Old 10-04-2017, 12:07
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On of the concerns with using stainless steel hardware is galling of the threads. The other is stainless steel's strength.

Last edited by mowog73; 12-04-2017 at 12:09.
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post #11 of 24 (permalink) Old 10-04-2017, 17:41
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I only mentioned the bolts as I knew that someone would bring up the tensile strength issue, as would I. I would never use stainless bolts in load bearing situations.


The reason I ask is that not many people would use stainless bolts, but they seem happy to use stainless subframe mounts. Nobody has ever answered my concern about using stainless mounts, which take all of the weight and stress of the subframes, from braking to acceleration and suspension bottoming/shock loading.
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post #12 of 24 (permalink) Old 10-04-2017, 21:04
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Hi all
Well this Wednesday my 04 TF is going to get s/steel front sub frame mounts and new 12.9 bolts. Just hoping the frame is not too rusty
Is this an upgrade per say or maintenance using alternative parts?
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post #13 of 24 (permalink) Old 11-04-2017, 07:31
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Haven't dealt with stainless steel much but it's strength is something to be noted, especially as it varies quite a bit on the property class used (50,70,80)

A stainless steel M24 bolt for example with the highest class of 80 will have a shear strength of 135kN and tensile of 158kN

Whereas a M24 mild steel grade 8.8 (commonly used in construction) will have a shear resistance of 136kN and 203kN (depending on design codes used)

So while the shear is similar (when using a 80 class stainless steel bolt) the tension capacity is significantly less.

If using a lower class stainless bolt then you can see the resistance becomes much worse...

Stainless capacity.


Grade 8.8 Steel

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post #14 of 24 (permalink) Old 11-04-2017, 08:33 Thread Starter
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Hi T/C
It is because some TFs seem to have a rust problem at 04 reg which mine is, so I thought a little look to see if mine were rusty and while looking put new mounts on So maintenance I did this to the hoses also last year they were 12yr old so I got silicon ones front and rear and I also put wheel bearing on all 4 wheels as it was costing me money at mot time as the bearings on two wheels had gone and damaged the flanges on those wheels

Last edited by helsbyman; 11-04-2017 at 08:42.
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post #15 of 24 (permalink) Old 11-04-2017, 10:03
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they seem happy to use stainless subframe mounts. Nobody has ever answered my concern about using stainless mounts, which take all of the weight and stress of the subframes, from braking to acceleration and suspension bottoming/shock loading.
Judging by the condition a lot of sub-frame mounts get to (almost totally rusted away) I think mounts made from papier mache would be strong enough

Peter
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post #16 of 24 (permalink) Old 11-04-2017, 21:33
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The inboard mounts on the 2002 TF I recently broke are good, the smaller out board ones are almost completely gone.

All the ones on my 1999 mk1 VVC are VGC.
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post #17 of 24 (permalink) Old 12-04-2017, 07:30
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Judging by the condition a lot of sub-frame mounts get to (almost totally rusted away) I think mounts made from papier mache would be strong enough

Peter
This.

I feel lots of the problems/belief we have on these forums could be proved wrong.
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post #18 of 24 (permalink) Old 12-04-2017, 08:01
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All the ones on my 1999 mk1 VVC are VGC.
That's because they are rubber filled mounts on a F and simple steel fabrications on a TF. Water collects in those on a TF and that's why they rust away! If only MGR had thought through rust protection coatings properly...
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post #19 of 24 (permalink) Old 12-04-2017, 16:40
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Quote:
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That's because they are rubber filled mounts on a F and simple steel fabrications on a TF. Water collects in those on a TF and that's why they rust away! If only MGR had thought through rust protection coatings properly...

A proper coat of paint rather than just showing the mounts the paint can would have helped as well
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post #20 of 24 (permalink) Old 12-04-2017, 16:56
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The mounts on my '95 F appear to be the originals.

Would early F mounts fit a TF? - if so, are they still available anywhere?

I notice that they are not available from Rimmer Bros.

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