Drain Bolts one more time

["Tom Brown" <tbrown@xxxxxxxxxxx>]

Listen guys:

I didn't come to this drain bolt thing by thinking I know more than
engineers.  (I knew this was was gonna get out of hand.)  I just wanted to
let people know about this in case they were changing oil out on the road or
something and were imagining drain bolts falling out while riding or, if
they didn't have the specs at hand etc....   Your practices in your garage
are your practices.  I've got no quarrel with anyone who wants to follow the
book.  I follow the book too for most everything....but.... I've been
changing oil for many many years before I ever had a torque wrench.   I've
had numerous high buck German cars with the same drain setup as oilheads...a
lot more expensive engines, byt the way.   It's because of this experience
and the fact that not one of these drain bolts has ever come loose in 25
years of oil changes that I brought this up.   We had a list member asking
about the factory spec for these bolts and recently, I changed oil in the
rear case of my RT and, just for grins, looked up and used the factory
torque.  I was shocked at how far the crush washer squished down using
factory specs.

Now, for the mechanical engineer....I've got two mechanical engineers
working for me.   I'm not one myself, but I play one on TV, as the saying
goes, and I supervise them.   I'm able to avoid a lot of disasters in my
business and a lot of runaway cost situations by not listening to every word
that comes out of mechanical engineer's mouths.   Often I find these guys
using their calcuations for the wrong situation.  Right answer to the wrong
question.  They don't see the forest, if you know what I mean.  No one is
always right, no matter what degree they hold.

I am not, by the way, the guy who said that the threads would be stripped if
the factory specs were followed.  That was another guy with a Japanese bike.
I've seen some pretty soft bolts on some of them, so maybe he has a point
there...not my point, however.

The drain bolt does not stretch when tightened to factory spec.   This is
because it is steel and the engine case is aluminum.  If you tightened
enough to stretch the steel bolt, you would have some thread issues in the
aluminum case.   So, if it's not the bolt that's stretching, what holds the
bolt in?   The crush washer!  It acts as a lock washer for this fastener by
squishing and having elasticity.

As to the guy who took assembled his brake caliper using factory torque
specs and stripped the alan bolts, I'm guessing he either had worn out allen
wrenches or the bolts were actually star or torx bolts instead of Allan
bolts.

Anyway, I meant no harm here and I'm not encouraging anyone to ignore torque
wrenches in general.  They're great inventions and it's very good practice
to use them.  Just giving a little confidence that the drain bolts on
Oilheads are made to work with a variety of torques, probably in
anticipation of many differnent people with and without accurate torque
wrenches tightening them.   I'm sure a lot of engineering went into the
design of this drain bolt system and it's like it is for this very reason.
My point is that it's not necessary to get all anal about this particular
bolt and if you're in a situation where you don't have everything you need
to do the perfect job, the bolt will still hold.   Make sure you have clean
surfaces.  Make sure you compress the crush washer.  Don't overtighten.
That's it.   To my mind, overtightening is much worse than tight enough but
under factory spec.   In fact, 25 years of practice tells me that I'm right.

As an example of the kind of engineering BMW uses, (yes, I do respect
engineers and good design) the newer BMW engines have their cartridge (not
spin-on) oil filters under the hood in an upside-down position.   You can
stand and remove a bolt and pull out the cartrige assembly and replace it
without getting under the car.   Only the oil drain bolt needs access under
the car.  Why did they do this?  Because they sell a lot of cars in Arab
countries and they were complaining that sand gets in the filter area when
they change oil outside!!!  No kidding.   By the way, this car uses the same
drain plug as our bikes.

- -TB

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