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Re: [TowerTalk] HAM IV rotor / mast slipping / Slipp-Nott

Subject: Re: [TowerTalk] HAM IV rotor / mast slipping / Slipp-Nott
From: John Becker <>
Date: Thu, 05 Apr 2012 21:41:20 -0500
List-post: <">>
>> Looks like a good solution and easy to install !
> I never tried one of these but they get good reviews,

I had a similar slipping problem with a HAM III and a KT34XA. I tried a 
Slipp-Nott but had a VERY bad experience. It seemed to work fine for 
about a year, but then after a very windy day I found the beam totally 

Apparently the Slipp-Nott itself was holding fine to the mast but the 
mast was still slipping in the rotor clamp. As it moved back and forth, 
the brackets from the Slipp-Nott completely unscrewed the nuts from the 
upper U-bolt. The lower U-bolt snapped and was pulled out of the rotor 
on one side.

I have a video on my webpage showing what was found:
Note the piece of mast clamp hanging from one side of the broken lower 
U-bolt, and the unscrewed upper U-bolt on the rotor shelf where it 
landed. Note also the bent Slipp-Nott brackets.

A photo on my webpage shows the damaged U-bolt and an undamaged U-bolt 
for comparison. Note how the damaged one is snapped off on one side and 
bent on the other:

The Slipp-Nott manual is also on my webpage so you can see how it is 
supposed to look when installed:

The tower is Rohn 25 and there is a Rohn thrust bearing above the rotor. 
The KT-34XA is mounted only two feet above the thrust bearing. In order 
for the lower U-bolt to be pulled out as it was, the mast must have been 
tipping. I don't know how this could happen with the thrust bearing in 
place, but I can't figure out how else this could have happened.

Because I no longer climb, I had to pay someone to make this emergency 
repair. He removed what was left of the Slipp-Nott and apparently 
tightened the new U-bolts much tighter than the originals had been 
because the mast has never slipped again in the 2 1/2 years since this 
happened. I guess I hadn't tightened them enough due to fear of snapping 

The Slipp-Nott at first seems like a good idea, but as I found it can 
put too much stress on the rotor U-bolts. If I had thought to double-nut 
the U-bolts, that should have prevented the nuts from being unscrewed, 
but it might have caused the upper U-bolt to fracture instead. If the 
mast is slipping in the rotor clamp, that force is transferred through 
the Slipp-Nott brackets to the rotor U-bolts, which are not intended to 
withstand that kind of load. BTW, I know of another ham nearby who also 
had a Slipp-Nott failure, but I don't know exactly what happened to his 

My suggestion is to use a torque wrench to tighten your rotor U-bolts to 
the maximum torque allowed and see if this helps. See


John, K9MM


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