Changing simple bobbins

[i think it goes]

Hey everyone, I'm trying to change over my petzl simple bobbins as they're now pretty worn. I have two spanners and am giving it my all but the bolts seem pretty stuck in place. Anyone have any tips for getting them looser?

I'm aware they're glued in place so can see why they won't budge but its unhelpful at the moment. Also any advice on what glue to use when reassembling it would be appreciated too. Thanks!

 

[Pitlamp]

If no-one on here knows the answer, maybe ask Petzl what solvent would soften the thread sealant?

(I presume you're using a ring spanner or box spanner, rather than a less secure open ended one?)

 

[Pitlamp]

If you do speak to Petzl ask what thread sealant to apply on reassembly.

Might be worth sharing the answer on here for anyone else with the same problem.

 

[i think it goes]

Yes am using two ring spanners but they're not super long so that's possibly the issue - I know that they're tightened to 20kN supposedly. Good idea about petzl, will get in touch and see what they say.

 

[Fjell]

Decent socket set and bars. I would try a torque wrench set to 30Nm, which is about 10 above the tightening torque that Petzl recommend I believe. At some point you will need to consider new bolts if you abuse them. My biggest breaker bar could easily shear the head off a bolt that size.

You’ll need the torque wrench to reassemble it. Do not even think of not using thread lock. 20 is not a high torque, but you putting carbon steel into alloy. 30Nm is the normal torque for M8 8.8 bolts (steel to steel).

 

[Chocolate fireguard]

You mention 2 spanners, but IIRC from when I did this some years ago you only need one.
The shouldered nut comes off, but I am almost certain that the bobbin is threaded so after that nut is gone (yes it was tight) the screw then undoes.

 

[Mark Wright]

And if that doesn't work, a blow lamp will usually break the thread lock seal.

 

[i think it goes]

Decent socket set and bars. I would try a torque wrench set to 30Nm, which is about 10 above the tightening torque that Petzl recommend I believe. At some point you will need to consider new bolts if you abuse them. My biggest breaker bar could easily shear the head off a bolt that size.

You’ll need the torque wrench to reassemble it. Do not even think of not using thread lock. 20 is not a high torque, but you putting carbon steel into alloy. 30Nm is the normal torque for M8 8.8 bolts (steel to steel).

Managed to get them off with a not-so-decent spanner! But thank you very much for the advice! Is regular bike-style thread lock good enough or is it something special?

 

[i think it goes]

You mention 2 spanners, but IIRC from when I did this some years ago you only need one.
The shouldered nut comes off, but I am almost certain that the bobbin is threaded so after that nut is gone (yes it was tight) the screw then undoes.

Yep you were right! Only the one spanner needed. I'd heard two were required which is why I tried that first but now I know

 

[Fjell]

Managed to get them off with a not-so-decent spanner! But thank you very much for the advice! Is regular bike-style thread lock good enough or is it something special?

Red or blue. Red is stronger. Blue is easier to undo……….

Not purple.

 

[Ian Ball]

To get the thing moving I used a soldering to heat it up as I don't have a blow torch.

I may be courted embarrassment here but I didn't use any thread lock when I replaced the bobbins, I just tighten it up when I give it a look over the next time I go caving, which is not very often. I don't think I've ever actually tightened it up though, nothing more than maybe half a minute turn.

 

[i think it goes]

Here's a picture of my old simple bobbins vs the new about to be put in. Out of interest, when are other people replacing theirs/getting new descenders?

I decided to replace mine because I found there was actually too much friction at times on fat ropes, the edges were beginning to get very sharp and I didn't want to hit the bolt in the centre.

 

[Fjell]

Are there people who really use a blow torch on a bit of aircraft alloy they intend to commit their life to? It’s possibly hotter than the original manufacturing process which was a careful multi-step process of quenching and tempering. It’s not steel.

 

[langcliffe]

Out of interest, when are other people replacing theirs/getting new descenders?

If you can use the bobbins for cutting pizzas, it's time to change them.

Like Ian, I don't use thread lock, and never had a problem., although I do check it when cleaning.

 

[Fjell]

I read recently on this forum about someone whose descender with no threadlock fell to bits after replacement. Can’t remember who, but it is clearly a “has happened in industry” frequency. Threadlock and 20Nm is in the instructions I had with mine, and I imagine this is how Petzl build them.

 

[Chocolate fireguard]

View attachment 16279
Here's a picture of my old simple bobbins vs the new about to be put in. Out of interest, when are other people replacing theirs/getting new descenders?

I decided to replace mine because I found there was actually too much friction at times on fat ropes, the edges were beginning to get very sharp and I didn't want to hit the bolt in the centre.

My ropes were 8 or 9mm, and I worried about the different curvatures generating sharp edges and damaging the bigger ropes, especially if I used 10.5 mm club rope. So I suspect I changed over/got new bobbins more often than most people would.
I remember getting a stainless bobbin from Tony at Starless River, and that significantly reduced the rate of wear. But I can't swear it was for my Simple - I did sometimes use a Stop.

 

[i think it goes]

My ropes were 8 or 9mm, and I worried about the different curvatures generating sharp edges and damaging the bigger ropes, especially if I used 10.5 mm club rope. So I suspect I changed over/got new bobbins more often than most people would.
I remember getting a stainless bobbin from Tony at Starless River, and that significantly reduced the rate of wear. But I can't swear it was for my Simple - I did sometimes use a Stop.

Stainless would be nice! I got my bobbins from Up and Under and are the standard petzl ones. Anyone know why they're ali and not stainless in general?

 

[alanw]

Anyone know why they're ali and not stainless in general?

Thermal conductivity, perhaps? Aluminium is ~240 W·m−1·K−1, stainless is approx 14 to 20. Aluminium alloys can be lower, however.

Better heat dissipation, less risk of glazing the rope.

List of thermal conductivities - Wikipedia

en.wikipedia.org

Metals, Metallic Elements and Alloys - Thermal Conductivities

Thermal conductivities of common metals, metallic elements aand alloys.

www.engineeringtoolbox.com

 

[traff]

Thermal conductivity, perhaps? Aluminium is ~240 W·m−1·K−1, stainless is approx 14 to 20. Aluminium alloys can be lower, however.

Better heat dissipation, less risk of glazing the rope.

List of thermal conductivities - Wikipedia

en.wikipedia.org

Metals, Metallic Elements and Alloys - Thermal Conductivities

Thermal conductivities of common metals, metallic elements aand alloys.

www.engineeringtoolbox.com

I've forgotten far to much physics but I suspect it's not that straight forwards. I should imagine specific heat capacity, bobbin mass and friction coefficients will play a factor.

I would suggest they are typically aluminium due to weight, ease of machining and material cost all being preferential over stainless steel.

 

[ChrisB]

The new model STOPs have stainless friction surfaces.