On 05/06/2021 16:17, Fredxx wrote:
On 05/06/2021 15:58, newshound wrote:
On 05/06/2021 11:08, Murmansk wrote:
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


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.

Or copper grease, a very good suggestion.

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

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.