good quality tow hooks

[flyingbrick]

OK, so we know the deal about tow hooks- but what about eye bolts and pintle hooks and stuff?

They are fine as long as they have a rating stamped on them?

[DaveM]

OK, so we know the deal about tow hooks- but what about eye bolts and pintle hooks and stuff?

They are fine as long as they have a rating stamped on them?

Eyebolts for recovery? Hopefully not, pintles are strong, but its the pressure you are putting on other areas, or someone elses vehicle, as the rated hooks will open when overstressed as pointed out, where pintles won't.
I have seen a pintle on the rear of a Safari just about torn off its mount, as the frame where it was mounted (where the factory loop on the rear attaches, above the alloy step) is not as strong as some would like to think.
In fact, I'm sure I've seen a pic on here from a similar thing (think Doddzee posted it?)

[flyingbrick]

OK, so we know the deal about tow hooks- but what about eye bolts and pintle hooks and stuff?

They are fine as long as they have a rating stamped on them?

Eyebolts for recovery? Hopefully not, pintles are strong, but its the pressure you are putting on other areas, or someone elses vehicle, as the rated hooks will open when overstressed as pointed out, where pintles won't.
I have seen a pintle on the rear of a Safari just about torn off its mount, as the frame where it was mounted (where the factory loop on the rear attaches, above the alloy step) is not as strong as some would like to think.
In fact, I'm sure I've seen a pic on here from a similar thing (think Doddzee posted it?)

that loop is actually exactly what i was thinking of. A workmate has that loop (its an eyebolt?) on his 97ish GQ. Mine has the tow bar come up and attack to that location instead.

[coxsy]

i made a 10mm plate half box mounted a tow hook on it bolt it with 8.8 bolts on to the stock middle of the rear xmember step thing used it a few times till notice it was bowing outward by 5mm , then bolted two hooks on the the chassis instead , threw it in the scrap bin, x member to thin welded nuts on inside , not stenghtened at all for towing

[flyingbrick]

well this has answered my questions exactly. thanks all

[T-Boon]

ok, so on a surf, if you ran a decent size Steel sandwich plate, on both sides of the chassis and ran the tow hook bolts all the way through with nuts etc, would that be suitable mounting ?

Alternately where is a good place on a VZN130 (non winchbar fitted) Surf/4runner to fit hooks ?

[curly12]

ok, so on a surf, if you ran a decent size Steel sandwich plate, on both sides of the chassis and ran the tow hook bolts all the way through with nuts etc, would that be suitable mounting ?

Alternately where is a good place on a VZN130 (non winchbar fitted) Surf/4runner to fit hooks ?

This thread may help with mounting pointers

http://www.offroadexpress.co.nz/Forums/viewtopic.php?f=49&t=3731&hilit=+roof+hook#p34720

[coxsy]

sandwich idea is the best way to do it,

[T-Boon]

ok, got two of the 4x4 bits hooks, there are strong points on the shassis at the front of my surf, only problem is they are the wrong size/thread, so i have 2 options, use the bolts that came with the hook (High Tensile imperial bolts), and re thread the hole (there's plenty meat to do so), or buy new M12x2.5 that will go straight into the chassis, only problem being there will be a fraction of play with the bolt in the hook (by fraction i mean 1/4 of a mm if that).

Or do i fab up different mounts elsewhere, can take photo's if that dont make any sence.

Idea's ?

[KiwiBacon]

ok, got two of the 4x4 bits hooks, there are strong points on the shassis at the front of my surf, only problem is they are the wrong size/thread, so i have 2 options, use the bolts that came with the hook (High Tensile imperial bolts), and re thread the hole (there's plenty meat to do so), or buy new M12x2.5 that will go straight into the chassis, only problem being there will be a fraction of play with the bolt in the hook (by fraction i mean 1/4 of a mm if that).

Or do i fab up different mounts elsewhere, can take photo's if that dont make any sence.

Idea's ?

All bolt holes are supposed to have clearance, it's not a problem. The load is taken by friction between the chassis and the hook, the bolts are just there to hold them together tight enough.
Get the bolts that fit your chassis. Never heard of M12x2.5 threads before though.

[Bulletproof]

ok, got two of the 4x4 bits hooks, there are strong points on the shassis at the front of my surf, only problem is they are the wrong size/thread, so i have 2 options, use the bolts that came with the hook (High Tensile imperial bolts), and re thread the hole (there's plenty meat to do so), or buy new M12x2.5 that will go straight into the chassis, only problem being there will be a fraction of play with the bolt in the hook (by fraction i mean 1/4 of a mm if that).

Or do i fab up different mounts elsewhere, can take photo's if that dont make any sence.

Idea's ?

All bolt holes are supposed to have clearance, it's not a problem. The load is taken by friction between the chassis and the hook, the bolts are just there to hold them together tight enough.

I disagree with the comment about clearance because if it is too great ,the shear factor of the bolt is greatly increased if the torque of the bolt is not tight enough.

If a person does a snatch tow at 30 degrees and then then next snatch is 30 the other way the bolts will shear straight off .

You will say you shouldn't do that ,and I agree but that is what happens in the real world.

I have seen it happen.

Richard

[KiwiBacon]

I disagree with the comment about clearance because if it is too great ,the shear factor of the bolt is greatly increased if the torque of the bolt is not tight enough.

If a person does a snatch tow at 30 degrees and then then next snatch is 30 the other way the bolts will shear straight off .

You will say you shouldn't do that ,and I agree but that is what happens in the real world.

I have seen it happen.

Richard

As you've said, that's because the bolts aren't tight enough. You need enough support through (crush tubes) or around (plates) your chassis to get enough tension on the bolts.
If the bolts are loose enough to move, then they're doomed. It doesn't matter how much or how little clearance they have.

Standard clearance for a M12 bolt is 12.5-12.8mm

[Smurf]

ok, got two of the 4x4 bits hooks, there are strong points on the shassis at the front of my surf, only problem is they are the wrong size/thread, so i have 2 options, use the bolts that came with the hook (High Tensile imperial bolts), and re thread the hole (there's plenty meat to do so), or buy new M12x2.5 that will go straight into the chassis, only problem being there will be a fraction of play with the bolt in the hook (by fraction i mean 1/4 of a mm if that).

Or do i fab up different mounts elsewhere, can take photo's if that dont make any sence.

Idea's ?

For bolts that fit the thread in the chassis you want metric fine.

[flyingbrick]

The load is taken by friction between the chassis and the hook, the bolts are just there to hold them together tight enough.
Get the bolts that fit your chassis.

I am interested as to how you came to this conclusion.

[Bulletproof]

The big problem is that most hooks have a half inch hole which is 12.7mm.

Therefore the clearance is nearly .75 mm which is miles too much if you use a 12mm bolt.

You need a hook to suit the bolt.

Cheers Richard

[T-Boon]

After talking to the Jeep trainer today, i'm going to make a mount, that uses the 2 factory holes (with suitable metric HT bolts), and also mounts further back, through the chassis, bolt the hook to that, using the high tensile bolts and nuts that came with it. rather do it right first time, that way i can also mount them poniting up instead of down.

next qestion is, how thick should the steel i use be?

[KiwiBacon]

The load is taken by friction between the chassis and the hook, the bolts are just there to hold them together tight enough.
Get the bolts that fit your chassis.

I am interested as to how you came to this conclusion.

It's not my theory, it's the way bolted connections work.
The bolts are only there to provide the clamp load, all the forces are taken by friction where the two parts meet. if the joint moves then it has failed and you need bigger bolts or more torque.

Clearance in bolt holes is largely irrelevant.
I have two hooks which are close to identical, one has 12mm bolts, the other 1/2 inch (12.7mm).
The 1/2" version is fitted so I can't measure, the holes in the 12mm version measure 13.2mm
The 12mm bolts themselves measure 11.7mm at the shank.

[flyingbrick]

It's not my theory, it's the way bolted connections work.
The bolts are only there to provide the clamp load, all the forces are taken by friction where the two parts meet. if the joint moves then it has failed and you need bigger bolts or more torque.

The hooks come supplied with bolts which have an un threaded portion (the shank). The shank is designed primarily to take shear forces. A quick google comes up with plenty on bolt shear strength calculations and theory.

I was always taught that the nut or clamping force is only there to ensure that the surfaces stay close enough together and parallel to ensure the bolts shank works correctly.

Please feel free to farther educate me. I'm an apprentice atm and this is all a part of it.

[vvega]

if the bolts holes are sized correcly and bolt is at the correct tension for the grade of bolt you have then sheer is not a factor
however if you requite a "saftey" backup to you engineering solution(i.e bolts come loose) then your bolt must be sized correctly for sheer

in ETHIER case if you holes are to big ... then you need to resize the bolt or hole... or both

sheer only works if the bolts are "neat" in the holes otherwise they will just rip apart
how do i know this ... i work with hydraulics .. and we have rams sheering 4" 4130 pins because they have sloppy bush's


and nathan the point of the shank is to minimise bolt streach witch... is the only way to ensure a bolt is tightend correcly ...unless its a t to yield bolt

so who here used a streach guage to do up there hi tensile bolts......
i find it amusing that clubs say that you need to have a rated hook .. but there is no requirement for fitting other than they need to have a 8.8 bolt ...

personally i think that a RATED hook needs to be fitted by a suitable qualified person to be effective
in my industry we work to a factor of 3
that means the bolts would need to take 3 times the sheer of the maxium load of the hook

just my thoughts

[vvega]

#### that is unreadable... ill fix it tomorrow

[KiwiBacon]

if the bolts holes are sized correcly and bolt is at the correct tension for the grade of bolt you have then sheer is not a factor
however if you requite a "saftey" backup to you engineering solution(i.e bolts come loose) then your bolt must be sized correctly for sheer

in ETHIER case if you holes are to big ... then you need to resize the bolt or hole... or both

sheer only works if the bolts are "neat" in the holes otherwise they will just rip apart
how do i know this ... i work with hydraulics .. and we have rams sheering 4" 4130 pins because they have sloppy bush's

Can you expand on these points a little?
A bolted connection is very different to a pinned joint and clearance makes no difference to the loads taken by the bolt if they loosen.

Regarding safety factors, I ran a 10,000lb rated hook through my FEA program, the results were posted earlier in this thread.
The results, they will yield and straighten before their 10,000lb load is reached. Safety factor of 1.

[flyingbrick]

if the bolts holes are sized correcly and bolt is at the correct tension for the grade of bolt you have then sheer is not a factor
however if you requite a "saftey" backup to you engineering solution(i.e bolts come loose) then your bolt must be sized correctly for sheer

in ETHIER case if you holes are to big ... then you need to resize the bolt or hole... or both

sheer only works if the bolts are "neat" in the holes otherwise they will just rip apart
how do i know this ... i work with hydraulics .. and we have rams sheering 4" 4130 pins because they have sloppy bush's


and nathan the point of the shank is to minimise bolt streach witch... is the only way to ensure a bolt is tightend correcly ...unless its a t to yield bolt

so who here used a streach guage to do up there hi tensile bolts......
i find it amusing that clubs say that you need to have a rated hook .. but there is no requirement for fitting other than they need to have a 8.8 bolt ...

personally i think that a RATED hook needs to be fitted by a suitable qualified person to be effective
in my industry we work to a factor of 3
that means the bolts would need to take 3 times the sheer of the maxium load of the hook

just my thoughts

This is why I have so much respect for you from an engineering standpoint vvega
What i had been taught (by a tradesperson too) was incorrect...

I'm off to buy 3 of these hooks today.

[vvega]

if the bolts holes are sized correcly and bolt is at the correct tension for the grade of bolt you have then sheer is not a factor
however if you requite a "saftey" backup to you engineering solution(i.e bolts come loose) then your bolt must be sized correctly for sheer

in ETHIER case if you holes are to big ... then you need to resize the bolt or hole... or both

sheer only works if the bolts are "neat" in the holes otherwise they will just rip apart
how do i know this ... i work with hydraulics .. and we have rams sheering 4" 4130 pins because they have sloppy bush's

Can you expand on these points a little?
A bolted connection is very different to a pinned joint and clearance makes no difference to the loads taken by the bolt if they loosen.

Regarding safety factors, I ran a 10,000lb rated hook through my FEA program, the results were posted earlier in this thread.
The results, they will yield and straighten before their 10,000lb load is reached. Safety factor of 1.

your right a bolted connection is very different to a "pinned join"
once the bolts losen it is no longer a bolted connection .. it is now a pinned joint hence why as bulletprrof stated "if you pull at 30 deg one way the 30 deg oposite they snap" if it was a "bolted" connection it woudlnt not matter because the hook would not move and there woudn be no sheer apllied to the bolt because .. as you have said the friction holds the hook in place so in that case the bolt in not in sheer it is in tension

you have to know what forces your working with with bolts or you pissing in the wind
a bolted connection relys on tension to work
a pinned connection relys on sheer and clearances are a issue, i can quite happily give you a demonstration on what 500 tonnes of sheer can do to a incorectly toleranced pin ... because if its loose it then bends the pin and puts the pin in tension, sheer and twist at the same time hence why you get a catastrofic failure

a engineered joint relys on both because you then incorperate a saftey factor of 3

i know you know all this so im not digging

[Bulletproof]

It might be off topic but I am saying it any how.

I have mentioned on here before that hooks are only half the story when it comes to sheering tow hook bolts.

The equally important thing is the type of rope used, it has to be like bungy cord.

On a snatch recovery a person needs the stretch of nylon rope to stop the sheer factor.

Most 4 wheelers use polyester because it is cheap and it greatly increases the sheer factor .It doesn't cut the mustard.

The snatch straps as well do not have the stretch of nylon. Every accident I have witnessed involves one of these and I have seen a few.

That is my opinion and I am sticking to it no matter what any one says. At 62 I have seen most things used.

Cheers Richard

[DieselBoy]

It might be off topic but I am saying it any how.

I have mentioned on here before that hooks are only half the story when it comes to sheering tow hook bolts.

The equally important thing is the type of rope used, it has to be like bungy cord.

On a snatch recovery a person needs the stretch of nylon rope to stop the sheer factor.

Most 4 wheelers use polyester because it is cheap and it greatly increases the sheer factor .It doesn't cut the mustard.

The snatch straps as well do not have the stretch of nylon. Every accident I have witnessed involves one of these and I have seen a few.

That is my opinion and I am sticking to it no matter what any one says. At 62 I have seen most things used.

Cheers Richard

You mean shock loading eh

[KiwiBacon]

your right a bolted connection is very different to a "pinned join"
once the bolts losen it is no longer a bolted connection .. it is now a pinned joint hence why as bulletprrof stated "if you pull at 30 deg one way the 30 deg oposite they snap" if it was a "bolted" connection it woudlnt not matter because the hook would not move and there woudn be no sheer apllied to the bolt because .. as you have said the friction holds the hook in place so in that case the bolt in not in sheer it is in tension

you have to know what forces your working with with bolts or you pissing in the wind
a bolted connection relys on tension to work
a pinned connection relys on sheer and clearances are a issue, i can quite happily give you a demonstration on what 500 tonnes of sheer can do to a incorectly toleranced pin ... because if its loose it then bends the pin and puts the pin in tension, sheer and twist at the same time hence why you get a catastrofic failure

a engineered joint relys on both because you then incorperate a saftey factor of 3

i know you know all this so im not digging

Very true about keeping a pinned joint tight to prevent pin bending. However there is no way you're ever going to get a bolted connection to act like a pinned connection. Even with your bolts clearance so tight it resembles a press fit. You're also never going to be able to share those loads evenly across two bolts. In direct tension you can only rely on one. With side loads you're loading the front bolt of a hook with far more than your strap tension (the hooks protrusion becomes a lever).
Which is why I maintain that bolt clearance is almost always irrelevant.

When you do attempt to get a bolt clearance really tight (like size for size) you'll usually be damaging the bolts on the way in and greatly reducing their strength. I've yet to meet anyone who can drill two holes through a chassis with better than 1mm accuracy. I've seen CNC mills with bad operators being 0.3mm out on about 30mm spacing.

BTW safety factors aren't always a good way to work. If you can shear a pin off because the clearances are out then I'd think the stresses are much higher than 1/3 of uts.
Would you like to engage my services as a mechanical engineer to solve your breakage problems?

And yeah, shock loading is a biggie.

[T-Boon]

next qestion is, how thick should the steel i use be?

And after all that, no-ones answered my question yet

I`m thinkin 5mm steel should be plenty..

[LOLYF]

I used 10 mm on my mounts, and they bent!! my new ones will be stronger!

[KiwiBacon]

next qestion is, how thick should the steel i use be?

And after all that, no-ones answered my question yet

I`m thinkin 5mm steel should be plenty..

That question cannot be answered with the information you've given. A photo or drawing showing the size and gometry is the minimum needed to give you any advice.

[vvega]

so nathan bought me over some tow hooks yesterday ... and they were black .. and came with grade 5 bolts
http://www.akrongear.com/bolt_head_identification.htm
if you dont have numbers on the heads of the bolts... this well help you tell what they are