A 47' Tri-Ex crank up I rebuilt had Boeing surplus sheaves in it from
the factory. I think they were designed to guide flight control surface
cables so quite nicely made. The ball bearings were Boeing specials,
not in any catalog, but amazingly I found what I needed on ebay! The
Boeing sheaves were perfect for the job since the wide race bearings
were held in with upset sheave flanges on the outer race to lock them
centered. Those needed a Dremel and carbide burr to remove so the
bearing could be pressed out.
The bearing is marked Fafnir K6. Dimensions are 0.375 bore x 1.437 od x
0.470 wide race x 0.619 wide inner race. I see K6's on ebay that are
very different. No guarantees that this is the bearing in your tower.
If Tashjian doesn't have replacements, then you might temporarily get
going with an lightweight oil soak to loosen the dry grease, but if they
are rust locked up not much choice but making new sheaves, probably with
a sintered bronze sleeve bearing. Ideally a flanged bearing on one side
and a bronze washer on the other to keep the sheave centered in its holder.
Grant KZ1W
On 9/17/2017 12:29 PM, Joe K2UF wrote:
I have 4 sections of an old tri ex 7122 tower with my 40 yagi and tribander
on. I cranked it down a few days ago for antenna maint. Now I am having
trouble cranking it back up and I think one or more of the pulleys (shives)
have finally given up. Anyone know where these pulleys are available.
Thanks es 73
Joe K2UF
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