Towbar mounted bike rack problem

[Murmansk]

I have a Witter bike rack that attaches to the towbar.

You put it on and at first it?s all loose and of course will lift off, then you tighten a big bolt which at first is really easy as it goes round for quite a few turns without much resistance, then as it grips the towball you give it a couple of really firm turns with the spanner to make it fully grip the ball.

Removing the rack is the reverse of the above where you apply big force for a couple of turns to loosen it, then lots of relatively easy turns to make it loose enough to actually come off the towball.

The problem is that once I?ve loosened it enough to make the rack sag but not actually come off, the bolt starts to feel really tight again ? almost as tight as it normally does at the last stage of attaching it ? so much so that I feel as though I need to apply so much force as to damage the thing.

I?m now left with the bike rack attached and sagging but can?t remove it and I?m wondering if anyone has any experience of this?

[Fredxx]

I'm tempted to suggest that the bolt thread has been damaged so it can't be unwound fully.

I'm not sure what to suggest apart from more welly.

[Michael Chare]

I suspect that something is getting in the way perhaps of a part that moves when you losen the bolt. Maybe moving the rack when it is loose will help. Alternatively phone Witter and ask for advice.

[williamwright]

Could be damaged threads or contamination. A grain of sand or small grit can do this. Would it be possible to get some light oil into it? Maybe apply oil then tighten and untighten a few times to work it along the thread. Then untighten as far as you can before the resistance starts, then go just a bit further, then back off, then go again, try to go a bit further still, and so on. I've had exactly the same problem with other things and this has usually worked, but it needs patience.

Bill

[Brian Gaff (Sofa]

Could it have become bent or as you say, damaged. I'm not sure how these things are supposed to actually work myself, but it sounds pretty crude. Brian

[soup]

Sounds very like a bolt with a damaged thread (possibly a bent bolt). Can it be economically replaced? Alternatively you could take it all the way out and 'hand chase' the threads. This may involve mounting in a lathe (local light engineering firm for the cost of a couple of pints) and running a chase along it.

Just realised you 'say' you can't move it out at all. Maybe try oiling and working the bolt in and out eventually freeing it (be prepared to cobble up a hole new looking system as if the bolt is harder than the threaded part it may well cut its own thread thus knackering any holding function).

[soup]

Whole not hole. Locking not looking

Note to self :- Think, have you said everything and proofread before clicking 'send'.

Use a chaser NOT a die to clean the thread (looks and operates rather like a die but doesn't cut so much as 'clean'.

You can use a hand chaser (rather like a file with a thread pattern on the tip) That way you only ,really. have to concern yourself with the thread profile not, within reason, the actual diameter

[Murmansk]

OP here

Well, the bolt would only turn a quarter turn, I flooded it with oil and worked it for half an hour but no joy so with the help of my neighbour and a metre long bit of scaffolding pole attached to the spanner I eventually got the bolt out.

Every turn of the bolt took a huge amount of effort even with the scaffolding pole, the thread is knackered. Only question remaining is what the thread in the nut that's welded to the mechanism is like - probably knackered too!

I'll have to see if Witter will sell me a new mechanism

[Fredxx]

Sometimes the intention is for the bolt to be captive, but still give the necessary amount of movement to pinch and release the ball.

Hopefully it's still in guarantee.

[newshound]

Not surprised to hear that this is your problem, from the original description. If Witter are unhelpful nut condition can be estimated by trying with a brand new bolt. I would strongly suggest using moly disulphide grease on it, as that will reduce the risk of further damage. If nut threads are bad, worth buying a tap and seeing if they will clean up. Chinese carbon steel taps from eBay are available in a wide range of sizes, much cheaper than "proper" HSS ones and OK if you only need to use them a few times. I've bought a few for "odd" things (e.g. when I wanted to fit "seat belt" threaded screw eyes into some angle iron). Invest in a tube of Trefolex or similar "cutting" compound for tapping.

And use Moly grease on the bolts in future.

[Fredxx]

Or copper grease, a very good suggestion.

Most greases stop pick up and balling of the material from two sliding surfaces.

[newshound]

But nothing does it so effectively as Moly Disulphide. Copper and graphite do not come close.

I once ran an experiment with a mild steel pin in a mild steel bush, about 3 inches length and diameter, under ten tons load. (This had rolling element bearings as slaves, for those interested in the detail). Flooded with oil from a pressure feeder, it turned about ten degrees before seizing solid from galling. Although I was pretty sure it would never turn again, out of interest I swapped the oil supply for one with a high concentration of moly disulphide powder in oil, and it became relatively easy to move freely and repeatably through about 60 degrees while still under load. If I had not done it myself, I would have had difficulty in believing it.

While mild steel is not quite as prone to galling as austenitic stainless steel, it was a very dramatic demonstration.

Changing the subject slightly, if you use the type of Rivnut tool that uses a cap head screw rotating in the nut to provide the tension that collapses the gripping part, it is well worth using a high moly paste on the screw. If you don't, they typically wear out after you have done a handful of nuts.

[newshound]

Sadly, not without fishing mine out and taking a picture. I've lost its leaflet, and have forgotten the name of the manufacturer. Mine is a sort of variant of this

but it does use the threads in the rivnut to do the jacking.

Otherwise Google seems dominated by pliers and lazy tongs types.

There is another very compact type that uses a wedge to apply the strain.

[bert]

In article [e-mail], Murmansk [e-mail] writes

Have you cross threaded it putting it in?

[Murmansk]

No danger of having cross threaded it as it's never been taken out - it just goes up and down through the nut which is welded to the mechanism.

Anyway, a call to Witter revealed that I can get a replacement bolt and the associated nut and its metal support for £15 including postage so I've ordered one.

[soup]

Buying stuff, PTOI This is D-I-Y. Mine some ore, smelt it , cast it into ingots bite ; support, nut and bolt shapes with your teeth... voila a replacement nut, support and bolt. FTAOD ;O)

[Chris Holmes]

lol

My brother once borrowed a tow ball mounted bike rack when he went to Europe.

His son insisted he take it off the car once they arrived. There was suddenly a profusion of pingfuckits and he couldn?t get it back together.

A foreign Jonny came over and offered to help. And couldn?t do it either at first, but he was persistent and insistent. And after about an hour and a half it was back together.

My brother didn?t remove it again until he was at the lenders house lol.