Al-Ko Trailer Tongue failure

On Thursday, July 7, 2016 at 5:21:21 PM UTC-4, Dave Springford wrote:
On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture he

http://www.foxonecorp.com/images/20160703_154501.jpg

In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.

The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.

These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.

I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.

So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.

A few dollars in bolts might save you thousands in repairs!

Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.



Piet---check your jockey wheel mount weld. Last picture shows a crack developing. Are you towing with the jockey wheel retracted but in place? I remove mine for travel.

While this is a thread I've done in an automotive forum, it gives some good basic engineering/hardware info......

http://www.newtiburon.com/forums/new...g-engines.html

Basically, it's about the plastic/elastic deformation of the grade/size hardware you're using and why a torque value is "approximate" based on many outside influences.

Without having seen in person any of these failed bolts I am therefore guessing a bit -- and at some point in this long thread this may already have been said.
1. it is unlikely that the initial failure of these bolts was in shear. They actually came apart at the end in shear, but the initial failure was fatigue. When the growing fatigue cracks (typically growing inward from each side of the threaded section normal to the load) reduce the remaining unbroken area of the bolt to around the level of the load limit of the steel the bolt busts.
2. The first and most important thing when trying to avoid the problem is to buy decent quality bolts where the shank of the bolt is longer than the outside measurement of the tongue. The thread adds a notch factor which reduces the fatigue limit of the steel being used. Depending on how badly the threads are made (many are pretty rough at a microscopic level and the surface actually has what amount to many many small microcracks) the fatigue limit of the steel in shear is seriously reduced, easily by a half in many cases. Make sure the failure inducing threads are well outside the area where shear loading will occur. Preferably do not use washers to fill in the gap, but a proper spacer.
3. Do tighten the bolts to the correct amount as specified for the steel in question. As has been said in this thread often, an insufficiently tightened bolt is asking for the thing to break, even if of proper shank length -- as for different reasons is an over-tightened bolt.
PS: From personal experience the round tube tongue is clearly inferior to the square one when it comes to serious road overload, as in a sway that gets out of hand and ends in ugliness.




On Thursday, July 7, 2016 at 3:21:21 PM UTC-6, Dave Springford wrote:
On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture he

http://www.foxonecorp.com/images/20160703_154501.jpg

In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.

The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.

These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.

I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.

So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.

A few dollars in bolts might save you thousands in repairs!

Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

If memory serves me ( 64 years since A&E school) to be considered airworthy; threaded portion of a bolt must never rest on the components of the joint, one washer under the nut is always necessary with a maximum of two washers, or use a shorter bolt. USAF A&E school, Witicha Falls, Tx 1952.
JJ

On Wednesday, July 20, 2016 at 10:31:52 PM UTC-4, Dave Springford wrote:
Hi Tom,

Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).

After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.

I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.

I just checked my new trailer (delivered this year), it has bolts 10.9.

On Thursday, July 28, 2016 at 2:59:28 PM UTC-6, Andrzej Kobus wrote:
On Wednesday, July 20, 2016 at 10:31:52 PM UTC-4, Dave Springford wrote:
Hi Tom,

Very doubtful that the nut came off from vibration. Nylock nuts are used and they are not prone to this. My trailer is towed behind a motorhome with a large axle to tow ball distance resulting a bending moment on the tongue and shear load on the (front) bolt (in particular).

After my post, another motorhome owner checked his trailer and found that the same bolt on his trailer was broken - shear plane through the threads, bad design - but fortunately the rest of the bolt was still in the tongue so he was able to take pictures of it. It was certainly a failure due to shear.

I question why AL-KO switched from 1000 MPa bolts to 800 MPa bolts at some point. I checked several other older trailers than mine and they all had 10.9 bolts. Mine had 8.8, as did the other trailer that failed.

I just checked my new trailer (delivered this year), it has bolts 10.9.

To follow up on my earlier post. My trailer, as many know, is towed behind my motor home. Its on a 6 foot tow bar which goes under my motorcycle lift which then attaches to the bottom of the lift. This whole system does allow for movement as its subject to bouncing/flexing around when traveling. But I never have seen the trailer sway thru my rear view camera.
I again checked my bolts(10.9) and their is a washer then self locking nut installed. I did take my torque breaker bar to check. The head of the 2 bolts are really tight( I never went for a max torque reading), but both nuts had less than 25 pounds of torque applied.
I did tighten both nuts down and it appears the nylon used in the nut has worn allowing them to loosen(become looser or maybe that is what they were originally torqued to?).
My trailer is a 2006 and has around 80,000 tow miles on it. Have gotten new bolts,washers, nuts to carry with me.

Thanks again to Dave for bringing this to our attention.

Best. #711.

The bolt which sheared on my trailer was also a 10.9. As Howard noted above and I have stated earlier in the thread the threads were in the shear plane which I believe is the starting point for the troubles as the threads become distorted due to trailer tongue stresses during towing allowing the bolt to loosen which creates move movement which eventually ends in shearing.

David Martin
ASG29E BV

Just to clarify what I tried to say above:
The failure in metallurgical terms was caused by fatigue. The load was in the shear plane. Threads in the actual load area do serious damage to the fatigue limit of the bolt. (Looking at a microscopic level at most threads, especially ordinary commercial ones, can be frightening.) The fatigue cracks originate in the bottom of the threads, typically diametrically opposed to each other and normal to the load plane. When the fatigued area gets to be large enough and the load exceeds the properties of the steel the bolt breaks.
If you have a failed bolt of this sort look at the fracture surface. There will typically be smooth area(s) that in moist circumstances are a bit rusty, or at least darker from oxygenation, and the final failure is much brighter in color. If it is clear from just looking that the fatigued area has tended to rotate and not just propagate in a symmetrical fashion, that indicates the bolt was not tight enough and was actually rotating slowly.
Since this particular failure is not happening once a month in the US, it suggests that the original bolt specification (as in 10.9) is adequate. The problem is that the bolts are not of adequate shank length. An easy thing to fix. Those lucky enough to have monster RVs (as in 711!) should just change the bolts at some regular interval.




On Thursday, July 7, 2016 at 3:21:21 PM UTC-6, Dave Springford wrote:
On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture he

http://www.foxonecorp.com/images/20160703_154501.jpg

In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.

The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.

These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.

I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.

So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.

A few dollars in bolts might save you thousands in repairs!

Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

Preferably do not use washers to fill in the gap, but a proper spacer.

Hi Howard,

Could you elaborate on this? By spacer, I assume you mean a cylindrical block with similar diameter to a washer, but with the height of the cylinder equivalent to the stack of washers?

Why is this preferable to a stack of washers?

Thanks,

On Thursday, July 28, 2016 at 8:20:29 PM UTC-6, howard banks wrote:
Just to clarify what I tried to say above:
The failure in metallurgical terms was caused by fatigue. The load was in the shear plane. Threads in the actual load area do serious damage to the fatigue limit of the bolt. (Looking at a microscopic level at most threads, especially ordinary commercial ones, can be frightening.) The fatigue cracks originate in the bottom of the threads, typically diametrically opposed to each other and normal to the load plane. When the fatigued area gets to be large enough and the load exceeds the properties of the steel the bolt breaks.
If you have a failed bolt of this sort look at the fracture surface. There will typically be smooth area(s) that in moist circumstances are a bit rusty, or at least darker from oxygenation, and the final failure is much brighter in color. If it is clear from just looking that the fatigued area has tended to rotate and not just propagate in a symmetrical fashion, that indicates the bolt was not tight enough and was actually rotating slowly.
Since this particular failure is not happening once a month in the US, it suggests that the original bolt specification (as in 10.9) is adequate. The problem is that the bolts are not of adequate shank length. An easy thing to fix. Those lucky enough to have monster RVs (as in 711!) should just change the bolts at some regular interval.




On Thursday, July 7, 2016 at 3:21:21 PM UTC-6, Dave Springford wrote:
On my way home from Nephi (towing my trailer with the RV) I stopped for fuel and found one of the bolts that holds the Al-Ko trailer tongue together was gone as can be seen in the picture he

http://www.foxonecorp.com/images/20160703_154501.jpg

In the picture you can see the front hole that has been vacated by the bolt. Fortunately, the second bolt didn't fail before I stopped for fuel and also fortunately, five minutes down the road was a well stocked hardware store. So I was back on the road an hour later.

The original bolts are M12 x 100 with an 8.8 rating giving a tensile strength of 800 MPa (116,000 PSI). The holes in the tongue will accommodate a 1/2 inch bolt so I installed 1/2 x 4 inch grade 8 bolts with a tensile strength of 150,000 psi.

These imperial bolts are about .02 inches larger in diameter than the M12 and also about 30% stronger, not including the added effect of the extra diameter.

I emailed with Alfred Spindelberger and he indicated there is no harm in using stronger bolts.

So... my suggestion to those that tow their trailer with an RV is to check the bolts on the tongue, and maybe just go ahead and replace them before yours fail. It also might be a good idea to replace them every 4-5 years if you tow a lot with your RV (my trailer was new in 2012). Then, keep a spare set of 1/2 x 4 grade 8 bolts in the trailer just in case.

A few dollars in bolts might save you thousands in repairs!

Now, at every fuel stop, as well as visually checking tires and wheel hub temperature on the trailer, I'll also be checking the bolts.

Yes, Howard I hear you. Late this afternoon I removed the bolts and both bolts on the head side of the shaft showed excessive wear. Both bolts where the threads were riding in the holes showed excessive wear.
Went down to our nuts and bolt supplier and ordered new bolts with longer shafts so now both sides will ride on the shaft.
A regular inspection/replacement, along with having several spares, as we do with trailer tires, is a great idea.

Best. #711.