Zinc-plated wheel bolts

[RogerL]

During yesterday's annual service, the technician said that the zinc-plated wheel bolts need replacing according to a NCC bulletin - I asked if this was to fit WSL bolts, he said no but couldn't identify what specification was needed.

I've contacted NCC but unhelpfully they just refer me back to a AWS technician or workshop.

I've searched the internet and found no references to this - does anyone have any info on this?

 

[Jcloughie]

In my opinion, if he made a statement he should be able to support it. Surely the decision had to be made on some factual examination.

Bolts can fail if overtightened as they loose the elasticity needed to stop them from coming loose. My understanding is that WSL bolts are a better quality steel than the norm, and have a greater elastic range.

Since suffering a detatchement in 2015, my last two vans have been retro fitted with WSL bolts.


John

 

[RogerL]

In my opinion, if he made a statement he should be able to support it. Surely the decision had to be made on some factual examination.

Bolts can fail if overtightened as they loose the elasticity needed to stop them from coming loose. My understanding is that WSL bolts are a better quality steel than the norm, and have a greater elastic range.

Since suffering a detatchement in 2015, my last two vans have been retro fitted with WSL bolts.


John

He's sent me a copy of the NCC bulletin, I'll ask him if I can copy it on the forum - essentially it's a widening of the Bailey issue covering all makes and is an alternative to the WSL bolts.

The specification is :- 10.9 grade wheel bolt with a 60 degree conical head and low friction coating.

According to the NCC bulletin, most NCC-approved caravans are now being manufactured with the new bolts so the replacement only applies to older caravans but there's no cut-off date given. The replacement is only recommended, not mandatory, and the bulletin confirms there isn't an issue with the older bolts when they're torqued up properly.

My AWS technican is charging £38 for a set of 10, including fitting, so cheaper than a set of the WSL bolts.

 

[otherclive]

He's sent me a copy of the NCC bulletin, I'll ask him if I can copy it on the forum - essentially it's a widening of the Bailey issue covering all makes and is an alternative to the WSL bolts.

The specification is :- 10.9 grade wheel bolt with a 60 degree conical head and low friction coating.

According to the NCC bulletin, most NCC-approved caravans are now being manufactured with the new bolts so the replacement only applies to older caravans but there's no cut-off date given. The replacement is only recommended, not mandatory, and the bulletin confirms there isn't an issue with the older bolts when they're torqued up properly.

My AWS technican is charging £38 for a set of 10, including fitting, so cheaper than a set of the WSL bolts.

But why then did your AWS technician say that the bolts needed to be replaced which seems at odds with the NCC advice in the bulletin. If it’s only a matter of correct torque then I’m sure that both you and he are very capable in ensuring the specified torque is achieved.

 

[RogerL]

But why then did your AWS technician say that the bolts needed to be replaced which seems at odds with the NCC advice in the bulletin. If it’s only a matter of correct torque then I’m sure that both you and he are very capable in ensuring the specified torque is achieved.

He did say it was optional.

 

[Lutz]

Zinc plating reduces friction between the bolt and the mating surface. It therefore increases the tensile force in the bolt for a given torque and hence the clamping effect. Presumably the advice to replace with new zinc plated bolts was to ensure that if the recommended torque is applied there is less of a chance of the bolt loosening in service if the bolts were corroded.

 

[RogerL]

Zinc plating reduces friction between the bolt and the mating surface. It therefore increases the tensile force in the bolt for a given torque and hence the clamping effect. Presumably the advice to replace with new zinc plated bolts was to ensure that if the recommended torque is applied there is less of a chance of the bolt loosening in service if the bolts were corroded.

No - the recommendation is to replace existing zinc-plated bolts with a new specification which has a "low-friction coating" but doesn't specoify what that coating is.

 

[Dustydog]

My 15 year old was serviced in February and no mention of this. Are we to believe such a radical nationwide change will become mandatory on all caravans? The first series of Bailey Unicorns had problems as did swift but that was resolved via Al-ko and WSL bolts. No bulletin was ever issued then about earlier models.

 

[Jcloughie]

It is my opinion that it is the fact that AlKo UK vans use 2mm smaller diameter bolts than continental vans using exactly the same hubs. That contributes to wheel the number of detachments. our bolts are living on the edge.

John

 

[otherclive]

My 15 year old was serviced in February and no mention of this. Are we to believe such a radical nationwide change will become mandatory on all caravans? The first series of Bailey Unicorns had problems as did swift but that was resolved via Al-ko and WSL bolts. No bulletin was ever issued then about earlier models.

I think from what Roger quoted in #3 it doesn’t seem as if it’s any more than a recommendation for vans fitted with what I would call older style bolts. But that doesn’t mean that it may not be made retrospective if failures start appearing. But given the large number already in satisfactory service that would seem unlikely. But good practice would be to change bolts that appear visibly corroded and then new spec would be appropriate or WSL.

 

[Lutz]

No - the recommendation is to replace existing zinc-plated bolts with a new specification which has a "low-friction coating" but doesn't specoify what that coating is.

That would be something upon which only the chassis manufacturer, presumably AlKo, can issue a recommendation, not the NCC. It would be vital to specify the nature of the "low friction" coating or else there would be a danger of the bolt suffering from tensile failure if the torque or the steel is not matched with the type of coating

 

[Martin_E]

I would suspect they are the same as Swift started using for 2012 vans onwards, along with one or two other makes, I think the WSL bolts use the same coating.

Geomet 321 plus L coating

I think they were delta protect wheel bolts

 

[RogerL]

I found this leaflet, promoting WSL bolts, which shows the difference in clamping force between standard zinc-plated bolts, low-friction coated bolts and WSL bolts - in figure 3 the clamping force is 20, 40 and 70 Kn respectively with a tightening torque of 130 Nm

https://www.foxcounty.co.uk/wp-content/uploads/2015/11/WSL-Caravan-Wheel-Safety-Bolt-leaflet-inner.pdf

 

[otherclive]

I found this leaflet, promoting WSL bolts, which shows the difference in clamping force between standard zinc-plated bolts, low-friction coated bolts and WSL bolts - in figure 3 the clamping force is 20, 40 and 70 Kn respectively with a tightening torque of 130 Nm

https://www.foxcounty.co.uk/wp-content/uploads/2015/11/WSL-Caravan-Wheel-Safety-Bolt-leaflet-inner.pdf

Thank you an interesting article. There’s no doubt that if I was still towing I would probably go for WSL bolts as the extra cost is peanuts compared to the other outgoings. I wonder if modern caravans with them as OEM still advise retorque after 25-50 miles ( as per cars) but not before every trip?

 

[Dustydog]

Thank you an interesting article. There’s no doubt that if I was still towing I would probably go for WSL bolts as the extra cost is peanuts compared to the other outgoings. I wonder if modern caravans with them as OEM still advise retorque after 25-50 miles ( as per cars) but not before every trip?

My bolts have served me well for 15 years . Is there really a true benefit changing them now?
Retorque? Absolutely yes and usually before each trip.
Some people undo the whole bolt and then torque it up. I just don’t see the point of doing that🤔

 

[otherclive]

I was always of the view that slacking the bolts and retorque was a no no.

 

[ProfJohnL]

My bolts have served me well for 15 years . Is there really a true benefit changing them now?
Retorque? Absolutely yes and usually before each trip.
Some people undo the whole bolt and then torque it up. I just don’t see the point of doing that🤔

Do you mean Retorque? or do you mean "check the torque"?

There is an important difference. Retorque means to undo the fastener so it is loose and then retightening it, where as a check only requires the torque to be reapplied without loosening first.

If a fastener is loosened off completely then retightened it resets the the checking process from the beginning just as if the wheel had been changed.

 

[Dustydog]

Do you mean Retorque? or do you mean "check the torque"?

There is an important difference. Retorque means to undo the fastener so it is loose and then retightening it, where as a check only requires the torque to be reapplied without loosening first.

If a fastener is loosened off completely then retightened it resets the the checking process from the beginning just as if the wheel had been changed.

If you read my post you will see I clearly differentiated retorque and undoing and tightening again. Retorque means checking the torque not undoing and starting again.

 

[Dustydog]

I was always of the view that slacking the bolts and retorque was a no no.

You’ve got me thinking now.
We all agree undoing the bolts and doing them up again to the correct torque is a no no .
In my book retorque is merely checking the already torqued up bolts ensuring they haven’t slackened.

Is that what you mean ? Maybe it’s a foible of the English Language😉

 

[otherclive]

You’ve got me thinking now.
We all agree undoing the bolts and doing them up again to the correct torque is a no no .
In my book retorque is merely checking the already torqued up bolts ensuring they haven’t slackened.

Is that what you mean ? Maybe it’s a foible of the English Language😉

Dusty to me retorque is slackening the bolts and then tightening them to the correct torque. Whereas what is done after service and 25-50 miles, or before a trip is to check the torque. The torque wrench is used just to confirm that the bolts are at the specified torque.

 

[Dustydog]

Dusty to me retorque is slackening the bolts and then tightening them to the correct torque. Whereas what is done after service and 25-50 miles, or before a trip is to check the torque. The torque wrench is used just to confirm that the bolts are at the specified torque.

Thanks Clive.
Strange , the dictionaries say the opposite! Irrelevant to us as we know what is right and wrong🤪🤪

 

[Martin_E]

The only issue with keep torquing a nut/bolt repeatedly is that each time you do it your actually inadvertently increasing the torque slightly each time you click

 

[Dustydog]

The only issue with keep torquing a nut/bolt repeatedly is that each time you do it your actually inadvertently increasing the torque slightly each time you click

Even if the torque wrench is correctly set?

 

[Martin_E]

Yes.

It won’t go up by huge amounts but each check/click increases it slightly.

The ten things you should know about your torque wrench

Torque wrenches are common place across a variety of industrial processes, commercial garages and even homes wherever there is a precision assembly process utilising threaded fasteners. Considering their widespread use however, there remains a number

www.norbar.com

 

[ProfJohnL]

Yes.

It won’t go up by huge amounts but each check/click increases it slightly.

The ten things you should know about your torque wrench

Torque wrenches are common place across a variety of industrial processes, commercial garages and even homes wherever there is a precision assembly process utilising threaded fasteners. Considering their widespread use however, there remains a number

www.norbar.com

There are several factors at play here some may allow the fastener to relax a little as the compressed materials settle, and other mean once the fixing has torqued, to move it any more requires several percent more torque to over come the static limiting friction to actually get the fastener rotating

In the context of wheel fasteners these differences are insignificant and we can in practice ignore them. and checking the torque settings should make no practical difference to the safety or effectiveness of the fasteners.