A better fix for stripped threads than a new casting is to use a
stainless steel Helicoil (+ other brands) insert. The correct metric
kit (M8 x 1.25) is available at most auto stores/amazon etc. Kits
include the inserts (many lengths available), correct drill bit, and
insert installing tool, and perhaps the drive tang break off tool. The
insert removal tool is usually separate. Helicoil taps are the same
thread pitch, but a larger major diameter than the hole being fixed and
are marked "STI" + thread size & pitch.
In aluminum the Helicoil-ed hole is much stronger than the original
threads. Obviously, don't drill too deep into the casting. You might
also need a bottoming STI tap to have enough threaded depth. Drill on a
drill press if possible to get the hole perpendicular and start the tap
the same way.
When reinstalling make sure the bolts aren't bottoming in the hole
before tight on the tower plate. Yaesu supplied different length bolts
but probably now lost into the ether. To reduce the chance of slipping,
I'd coarsely sand off the powder coating around the bolt holes and make
sure both plate and this area were clean. Use a torque wrench. If the
bolts are also stainless, use some NoAlox or similar to prevent galling.
Console yourself that it was the prior installer that damaged the
threads. ;)
Grant KZ1W
On 5/29/2021 19:14, Rob wrote:
Hi Group,
A couple questions. I installed a G800 in a 25G tower with a thrust
bearing top plate, that turns a JK Navassa 5 beam for a friend. At the
beginning and end of rotation, the torque from the beam was causing the
G800 to twist slightly on the plate, most likely from the bolt holes
being larger in diameter than the bolts. Apparently the grinding sound
was a bit unnerving to the operator. So with a short wrench so as not to
be able to easily strip the bottom casting, I incrementally and
carefully started tightening the bolts to get to the point where it
would not slip. So, you are probably smiling as you know what happened
next. Yes, I stopped after stripping the first bolt hole in the casting.
Fortunately, a new bottom casting is not that expensive from Yeasu and
is on its way. So my questions are:
1. How difficult is it to replace the bottom casting on a G800?
2. Any thought on how to install the rebuilt G800 and not have it slip
on the plate? Maybe something as simple as putting a star washer on each
bolt between the plate and the bottom casting?
Thanks,
Rob K6DQ
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