Seat collar exploded!

rumbataz

I bought a new Thomson seat collar to go with my new Thomson Elite seat post. The collar requires a torque wrench set to 2.8Nm. As I was tightening it carefully, the damn bolt in the collar literally exploded! It shocked me.

Luckily I still had my cheap old one that was going to be replaced so I ended up using that, which works fine.

Now, ordinarily this would be a minor inconvenience but the Thomson collar cost me £18 which wasn't cheap.

It's going to be difficult to return this as the obvious response from the supplier would be that I overtightened the collar so I'm going to have to write the £18 off.

Has anyone had issues with Thomson collars exploding?

arlowood

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19740508#p19740508]rumbataz[/url] wrote:

I bought a new Thomson seat collar to go with my new Thomson Elite seat post. The collar requires a torque wrench set to 2.8Nm. As I was tightening it carefully, the damn bolt in the collar literally exploded! It shocked me.

Luckily I still had my cheap old one that was going to be replaced so I ended up using that, which works fine.

Now, ordinarily this would be a minor inconvenience but the Thomson collar cost me £18 which wasn't cheap.

It's going to be difficult to return this as the obvious response from the supplier would be that I overtightened the collar so I'm going to have to write the £18 off.

Has anyone had issues with Thomson collars exploding?

I think you've got a good case to argue that the bolt was faulty and ask for a replacement bolt or a complete collar.

Ordinarily if you had over-tightened the bolt, my expectation would be that the threads on the bolt or the collar would be stripped first. The fact that the bolt disintegrated suggests to me that there was some fatigue fault with the bolt.

I would take pics of the bolt or bits thereof and the collar threads (if you can) and send those to the supplier with a demand for a replacement

crankycrank

Your first step should be to contact Thompson or the place you bought it from and then post here if you get no satisfaction. No sense jumping to conclusions about their customer service.

rumbataz

I'll contact the supplier (it was an online retailer) and see if they can help. I'm fairly certain there was a manufacturing defect in the bolt.

I used exactly the same torque wrench and tightened the cheap, old collar to the same torque just to verify the torque wrench wasn't playing up.

dj58

By exploded do you mean the socket cap head sheared off leaving the threaded portion in the clamp?

rumbataz

It looks like the middle of the bolt snapped and flung out the top of the bolt. Yes, the lower threaded portion remained in the cylindrical nut inside the clamp.

bbrap

If you examine the ends of the broken bit (with a magnifier), does there appear to be anything amiss with the structure (e.g. a bubble or crack)? I'm assuming the actual collar is intact and its only the bolt that has fractured.

rumbataz

I'll take a careful look at it in the next couple of days. The actual collar is intact.

term1te

I had exactly the same problem with a Thomson seat collar. It didn't explode as such, but did snap very easily, and I was using a torque wrench. I found another bolt the same size in my box of useful bike bits, and managed to remove the broken end of the bolt by screwing the new bolt in the other side until I could get purchase on it with some pliers.

I got the collar off ebay, so didn't bother contacting Thomson. The new - old - bolt has held perfectly for a couple of years now.

on-yer-bike

I use one of these and tighten it to 4.5Nm as 2.8 isnt enough. I know they say dont but nothing has happened in 3 years. The post is very tight in the steel frame and ive used carbon paste.

sungod

2.8Nm ? leaving aside the ambiguity of whether they meant dry or lubricated (assume dry), even with an accurately adjusted torque wrench you probably are looking at up to 25% error, with small bolts you could easily go way over the limit

if the collar is otherwise ok i'd just fit a new bolt, but go for a grade 10 or 12, then you should have some margin for error

make sure the threads are clean, no oil etc., use carbon paste on the post to reduce required clamping force (i suggest the tacx one, it's finer than some others), as a plus it'll also help reduce the risk of corrosion which could cause the post to get stuck

rumbataz

It was for my old bike which isn't carbon - I think it's an aluminium frame but I'm not sure. I followed the instructions to the letter - including lubing the thread of the cylindrical nut inside the collar and the outside surface of the seat tube where the collar fits.

One thing I did notice was that it took a long time to tighten the collar although hardly any effort was required.

Frustratingly, I can't get hold of anyone at the e-tailer via their chat window as their chat is always busy, yet when I don't need to chat to them I get popups asking me if I want to chat to them!

rumbataz

I've just re-read the installation instructions for the Thomson clamp and I'm wondering whether I may have caused the issue. To explain, the slot on the frame faces forward. It's a metal bike so the instructions for the clamp say that the opening on the clamp should be oriented in the same way as the slot on the frame (it's 180 degrees for carbon seatpost or carbon frame).

The existing clamp on my hybrid had the clamp opening at 180 degrees from the slot on the seat tube. I am pretty sure that when I came to attach the Thomson clamp, I used the same 180 degrees orientation.

Could this have snapped the bolt even before 2.8Nm of force was generated by the torque wrench?

bbrap

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19742171#p19742171]rumbataz[/url] wrote:

I've just re-read the installation instructions for the Thomson clamp and I'm wondering whether I may have caused the issue. To explain, the slot on the frame faces forward. It's a metal bike so the instructions for the clamp say that the opening on the clamp should be oriented in the same way as the slot on the frame (it's 180 degrees for carbon seatpost or carbon frame).

The existing clamp on my hybrid had the clamp opening at 180 degrees from the slot on the seat tube. I am pretty sure that when I came to attach the Thomson clamp, I used the same 180 degrees orientation.

Could this have snapped the bolt even before 2.8Nm of force was generated by the torque wrench?

I would not think this has anything to do with the bolt shearing. The tube the clamp is going round is circular, as is the inside of the clamp. The actual clamping force on the seatpost may be a bit higher if the slot in the seat tube is aligned with the join in the clamp but not by much. 2.8 is bugger all and I don't think anything you did will have any bearing on the bolt giving up. I still think the bolt was substandard.

rumbataz

Okay, so I think it might actually be my new torque wrench! I fitted the old collar back and it clicked once. I went to adjust the seat height today and loosened the old collar and adjusted the seat height by a few mm.

I wasn't aware that the torque wrench was set to the minimum torque and I started to tighten the bolt on the collar. I could see it tightening but no click at minimum torque. I wound up the torque to maximum and then back to minimum again and tightened the bolt and I knew it was already very tight but the torque wrench did not click and would have carried on tightening the bolt until that one snapped too.

I resorted to hand tightening using my hex key multi-tool to be on the safe side.

Now, I bought this torque wrench from the same retailer as I bought the Thomson collar from. It's obviously developed a fault already (worked fine on the couple of times I used it on my road bike). By developing a fault it has damaged a new collar.

Luckily (for me) this fault happened when I was working on my old hybrid bike so not very costly issues that could have happened on my carbon bike.

Do I have any recourse with the retailer as the torque wrench set cost me £28.50 and the Thomson collar cost me £17.99. The fault in the torque wrench caused the collar to be damaged. I'm not overly keen to write off almost £50!

I'm really disappointed in the torque wrench developing this fault as I was about to use it to check the torque settings on my road bike and it could have caused huge issues.

sungod

at torque values near the low end of a wrench's range there may not be a click, just a slight 'give' and then the wrench will keep on tightening

if it is new at least you can get it swapped or get a refund

cycleclinic

You should not need a torque wrench do tighten to 3 Nm. Do that by feel as torque wrenches even the good ones are jot always accurate at the minium setting. You should use carbon fibre grip paste to increase friction and that minimises the torque needed on bolt. I put that stuff to stop posts slipping all the time.

bbrap

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19742913#p19742913]thecycleclinic[/url] wrote:

You should not need a torque wrench do tighten to 3 Nm. Do that by feel as torque wrenches even the good ones are jot always accurate at the minium setting. You should use carbon fibre grip paste to increase friction and that minimises the torque needed on bolt. I put that stuff to stop posts slipping all the time.

Agree with the above. Over the years you develop calibrated fingers and it is surprising how accurate they become. For 2.8 I would use the long bit of the hex key in the bolt and turn the short bit, that way you will not be able to over tighten it (unless you have gorilla tendencies :P ).

Regarding torque wrenches, I've always found the bar type (rather than ratchet type) better to use as you can see the torque building and tighten accordingly. You can get them in 1/4" drive that go from 0 - 7 Nm which is ideal for a lot of bike stuff.