Crappy bolts...

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Originally Posted by langy

try some M12 coarse thread HT (grade 8) bolts 125 mm long with nylocks.

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There is no such thing as a Grade [X] Metric bolt.

Imperial bolts have grades, metric bolts have classes.

A CLASS 8.8 Metric bolt is roughly equivalent in shear and tensile strength to a GRADE 5 imperial bolt of equivalent diameter (3 radial lines on the head). A CLASS 10.9 metric bolt is roughly equivalent in shear and tensile strength to a GRADE 8 imperial bolt of equivalent diameter (6 radial lines on the head).

For recovery points, or bullbar fixing, an absolute minimum of grade 5/class 8.8 should be used.

As a VERY ROUGH guide, a Class 8.8 bolt can safely handle about 80kg/mm2 for a tensile load and 2/3 of that amount for a shear load (use root diameters of the thread for calculations).

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Originally Posted by Rosco

To be pedantic, it's Grade 8.8 which has a Tensile Strength of 800 MPa and a Yield Strength of 640 MPa. On the other hand mild steel bolts are Grade 4.6 with a TS of 400 MPa and a YS of 240 MPa. As you can see 4.6 are much weaker than 8.8. Bear in mind the weakest link in the chain would usually be the chassis rail, which would most likely fail in bearing due to being the thinner of the two sections connected (elongation of the bolt holes).

Bolts would be readily available at any reputable bolt shop.

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As above - just substitute Grade with Class.

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Originally Posted by incisor

thats my point exactly, bolts for a sheer comression and bolts for recovery should be a totally different grade :P

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I agree that recovery points SHOULD IDEALLY be bolted straight to the chassis. But don't know what you mean with the statement above - there is no difference in a bolt you would use for a recovery point and a bolt you would use for any other shear OR compressive load application.

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Originally Posted by isuzurover

There is no such thing as a Grade [X] Metric bolt.

Imperial bolts have grades, metric bolts have classes.

A CLASS 8.8 Metric bolt is roughly equivalent in shear and tensile strength to a GRADE 5 imperial bolt of equivalent diameter (3 radial lines on the head). A CLASS 10.9 metric bolt is roughly equivalent in shear and tensile strength to a GRADE 8 imperial bolt of equivalent diameter (6 radial lines on the head).

For recovery points, or bullbar fixing, an absolute minimum of grade 5/class 8.8 should be used.

As a VERY ROUGH guide, a Class 8.8 bolt can safely handle about 80kg/mm2 for a tensile load and 2/3 of that amount for a shear load (use root diameters of the thread for calculations).




As above - just substitute Grade with Class.



Not sure what you mean? Recovery points SHOULD IDEALLY be bolted straight to the chassis. And there is no difference in a bolt you would use for a recovery point and a bolt you would use for any other shear OR compressive load application.

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With the utmost respect I would beg to differ .. :angel:

AS 4100 Steel Structures Code, which has been Metric since the early '70's clearly refers to bolts by Grade viz 4.6 & 8.8

Cheers

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Originally Posted by sam_d

Okay, fairy nuff :)

But, my point is that if it was installed like that and at least three people who have vast amounts of off road experience all said it was okay then who am I (as a newbie) to argue? :)

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i am not having a go at you or anyone actually, i just dont understand the logic of the industry these days, it is common practice to do what they did to you, that doesnt mean it is right...

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Originally Posted by Rosco

With the utmost respect I would beg to differ .. :angel:

AS 4100 Steel Structures Code, which has been Metric since the early '70's clearly refers to bolts by Grade viz 4.6 & 8.8

Cheers

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Doesn't mean it is correct - they probably kept the wording the same when they switched from imperial to metric:

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ISO metric fastener material strength property classes (grades). As given in ISO 898-1, ISO metric fastener material property classes (grades) should be used. For example, fastener material ISO property class 5.8 means nominal (minimum) tensile ultimate strength 500 MPa and nominal (minimum) tensile yield strength 0.8 times tensile ultimate strength or 0.8(500) = 400 MPa. (In a few cases, the actual tensile ultimate strength may be approximately 20 MPa higher than nominal tensile ultimate strength indicated via the nominal property class code. Consult Table 10, below, for exact values.) Many anchor bolts (L, J, and U bolts, and threaded rod) are made from low carbon steel grades, such as ISO classes 4.6, 4.8, and 5.8.

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AND

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Standards for metric bolts are set by the ISO. In metric bolts, a grade is called a “property class.” A property class designation consists of two numbers separated by a decimal point.

* The number before the decimal point is one-hundredth of the nominal tensile strength of the bolt in newtons per square millimeter.
* The number after the decimal point is the ratio between the nominal yield stress and the nominal tensile strength, times ten.

Bolts in property classes 4.6, 5.6, and 8.8 and above must have the property class marked on the head of the bolt. Property class 6.8 roughly corresponds to SAE grade 2; 8.8 to SAE 5; and 10.9 to SAE 8.

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For many years I have used socket head cap screws & bolts ( SAE Grade 12) & hardened washers with Nyloc nuts on tow bars, bull bars, and recovery points.

As to using a bull bar as a recovery point, many heavy trucks have a tow pin in the centre of the bull bar. I have seen plenty of semi-trailer and roadtrain units debogged or recovered from off-road excursions using this fitting, and using a gin pole, towed hundreds of kilometres. I always felt, though that a bridle of steel plate from behind the tow pin back to the chassis rails each side would be a wise option.

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Originally Posted by incisor

i am not having a go at you or anyone actually, i just dont understand the logic of the industry these days, it is common practice to do what they did to you, that doesnt mean it is right...

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I didn't think you were having a go - I was just re-itterating my point that if there is something is put there to supposedly to do a job it should at least be able to do it even under the very easy situation that was the case on the training course :)

I've spoken to ARB today to ask about bullbars and recovery points - they are keen to talk about bullbars but don't want to even discuss recovery points. When I asked them about being able to install a recovery point at the same time as installing a bullbar (not install a recovery point on the bullbar but a separate recovery point) they got kind of arsey and rude about it...

Sam_D Thats because it's ARB. They are expensive and often anti Land Rover.


My front recovery points are part of my bull bar and I often use the winch that is mounted in the bull bar. I always thought it was the correct thing to do.

Mechanical properties of metric used to be designated in Grades but was changed quite a few years ago to Property Class. This is inline with the ISO standards for mechanical properties of bolts and nuts, which Australia adopted.

Hexagon head bolts can be readily obtained in class 8.8 and some sizes can be obtained in class 10.9. Class 12.9 hexagon head bolts are almost unobtainable in Australia.

Unbrako socket head cap screws are class 12.9. Not SAE grade 12 as Brian posted. Other brands of socket head cap screws may be a lesser grade.

Imperial bolts designated by SAE Grades. As Ben posted Grade 5 is similar to ISO. There are no SAE grades above 8.

There is one bolt manufacturer (their name escapes me at the moment, but I have their catalogue somewhere) that claims to manufacture the strongest production bolts in the world. They refer to them as strength grade _9 (substitute their initial where I have shown _ ). They claim that the mechanical properties would be equivalent to grade 9 if the SAE standard were to include that grade.

Getting back on topic.

My disco had a TJM bar fitted when I bought it. The bolts fixing it to the chassis were only M10. Upon investigation I found that the holes did not line up properly, which probably explains why this size bolts were fitted.

After some filing and jacking, I managed to fit 1/2", SAE grade 8 bolts. 1/2" (at 12.7mm) is the largest size that will fit the holes in the chassis.

Because of the eccentricity of the recovery point, the shear load on the bottom bolt is approximately twice the load on the recovery point. To address this, I extended the recovery point to pick up the bolt for the panhard bracket.See pic which i just took.

The angle that this pic was taken from does not show the extent of weld on the other side.

The other point to be noted about the bracket for the TJM bar is that there is another plate on the other side of the chassis rail. But the way that it is made (so that a winch can be fitted), does not improve the strength much. And it is important that the bolts be fitted from the outside. So that the bolt threads are not in the shear plane, on the side that will see most of the load (the shear strength is reduced at the section that is threaded).

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Originally Posted by sam_d

I didn't think you were having a go - I was just re-itterating my point that if there is something is put there to supposedly to do a job it should at least be able to do it even under the very easy situation that was the case on the training course :)

I've spoken to ARB today to ask about bullbars and recovery points - they are keen to talk about bullbars but don't want to even discuss recovery points. When I asked them about being able to install a recovery point at the same time as installing a bullbar (not install a recovery point on the bullbar but a separate recovery point) they got kind of arsey and rude about it...

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I have a TJM bullbar on my disco, and that is the same make that the original poster has/had. The recovery point on mine is not a part of the bullbar.

Although I was not present, I doubt very much that the snatch strap was attached to the bullbar - I believe that the description in the post was not precise regarding that point.

The recovery point is part of the bracket used to attach the bullbar to the vehicle. You can see this recovery point in the pic in my previous post, along with some of my comments.

It appears that it was not a fault of the bullbar that contributed to the failure.

I have a rangie (same Chassis) however i have an ARB bar fitted and it uses the hole under the body mount all so with 4mm plate either side so i have 6 bolts holding my bar on an i have shock loaded the crap out of it over the years and never had it come loose how ever i do chk the bolts from time to time and have changed all 6 twice in 6 years as they started to look a bit ratty. But you guys know that the hole on the front of a bull bar is not a recovery point!! it just somewhere to hook yr winch on when not in use! I have seen those rings ripped out on a few occasions! if you look at a new arb bull bar they stopped putting thise rings on as ppl were using them as recovery points! if you want to recover using yr bull bar get some Jate rings (sp)

Mick