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Mark Borgerson

In article ,
says...
"Wayne.B" wrote in message
news
On Fri, 12 Nov 2010 11:21:39 -0500, "Flying Pig"
wrote:

Nice pix.

I'd be worried, however, about all the washers for depth. Not possible to
build in a bend to the tightening arm to bring it flush to the alternator?

It's possible but I'd need to disassemble part of the heat exchanger
to remove the adjusment arm, bend it and reinstall. What I've done
since the pictures were taken is to replace the washer stack with a
solid steel spacer. I've also replaced the original bolt with one
that is longer so that it now projects all the way through the
adjusment tab on the alternator, backed up by a grade 8 steel washer,
lock washer and nut. The whole assembly is extremely rigid with no
hint of vibration or flexing.

Reply:
I would watch the grade 8 for looseness. May be to high of grade bolt, may
need a grade 5. To keep a bolt tight, you need to stretch it a little. In
the elastic range and not the plastic range of the metal. Grade 8 bolts are
hard to get a good stretch on. I would at least go with a nyloc nut.

That's a good point. One reason for lock washers on high-grade bolts is
that they compress so you don't have to stretch the bolt.

Another reason for a lock washer is differences in thermal
expansion/contraction. If you tighten a steel bolt against an aluminum
flange when both are hot, the flange will contract at a different rate
than the bolt as it cools. The aluminum will contract at almost
twice the linear rate of the steel bolt. Conversely, tightening
the bolt when things are cool will increase the bolt tension when
both are hot as the aluminum expands more. This is probably
a good thing----especially as it lets you work without burning
your hands! ;-)

Balancing out all these factors is how mechanical engineers earn a
living. The rest of us use LocTite! (Note, LocTite may keep you
from losing the nut---it won't keep the belt tight in this application
if the thermal factors aren't accounted for.)

One thing that might help keep the belt tight is to use 60-grit
sandpaper across the adjustment arm on the side facing the aluminum
alternator flange. WHen you tighten down the bolt, the arm should
press some grooves into the aluminum to act as interlocking 'teeth'.

You should also be careful about overtorquing the bolt. Depending
on the thread size, you could strip out the threads in the aluminum
flange.

Most of these issues are things you learn over the years as
you maintain your boat. It sometimes helps to list the
issues just to make sure something isn't being overlooked.

Mark Borgerson