Date:         Sun, 15 Oct 2006 17:22:52 -0400
Reply-To:     Dennis Haynes <dhaynes@OPTONLINE.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject:      Alternator brackets! Why they break.
In-Reply-To:  <71d9cdf90610151213j1beb782sec6e9603f3389e6d@mail.gmail.com>
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The Water Boxer Alternator Bracket is one of those parts that can cause a
lot of grief. The problem with replacement is that the cause is often not
determined and corrected. To make matters worse, failure usually breaks the
studs and the moving bracket destroys the mating surface on the case so a
proper fix is difficult.

Failure can be the result of mechanical fatigue or corrosion of either the
bracket or the mounting studs. Improper belt tension, (too loose) or a bad
rear bearing can create shock waves or vibrations that put the mounting to
the test. After rear bearing fails, the rotor can hit the stator windings
taking chunks out of both. Rebuilds often use these damaged components.

Many folks leave the bottom alternator bolt just loose enough to allow belt
adjustment. This is a no-no. Any vibration will cause some movement at this
joint and now you get a little velocity. The alternator now becomes a high
speed hammer. Keep in mind that little alternator is spinning at some 2.5
times the engine speed. Yes, that 4,500 rpm hill climb is spinning that
thing at almost 10,000 rpm and that belt you left loose trying save the
bearings is flapping all over putting all types of cyclic harmonic loads on
the mountings.

So the bracket finally gives out and we have the broken studs. We some
drill, prey, curse whatever and get them out. We restore the threads and get
new studs, nuts, and a bracket. Is the mounting surface on the case flat? It
needs to be. Get a big file before installing the studs. Where did you get
the studs? Most studs are property class 5, (grade 5.8)or lower. These are
OK for crushing that exhaust gasket, maybe. Not to be used here. You need to
Property Class 10, (grade 10.9) or better. The nuts and washers have to
match. These can be hard to come by. A set screw can be used as a stud. I
myself like to use grade 12.9 hex bolts, hardened washers, loctite and a
torque wrench. Think CV joints at 32 ft/lbs.

That bottom alternator bolt also needs to be tight. Both sides of the
alternator should be true and the hole should not be worn into an oval. If
you can adjust the belt, the bolt is too loose.

Looking at Larry's picture, I see thread impact marks and corrosion in the
mounting bolt holes. It came loose before it failed. I also see some wear
marks where the alternator sits. It was probably moving there also. There
may be a problem with the alternator but it looks like the fasteners failed
first (lost preload and loosened) and the hammering caused the final
failure. Additional supports or braces probably will not help this. Get rid
of excess vibrations and improve the fasteners and all will be good.

Dennis