[SEL] semi-OT: oil drain plug ideas

[Richard Allen]

Wow! There sure were some good educational stories about oil drain
plugs! 

My old 1972 Caterpillar D4D tractor has both an oil pan drain valve and
a plug to seal it off. The plug is a one-inch cast iron pipe plug with
an itty-bitty 5/8-inch square wrench grip to turn it, which won't
transfer enough torque to damage the threads because the corners will
become rounded over before that point.

The same kind of idea needs to be used for automobile drain plugs to
prevent damaged threads. A very large diameter plug with a very long
thread engagement and very small head, say 5/8-inch diameter bolt by
3/4" long thread reach with a 1/2-inch hex head (16mm dia x 20mm long
and 12mm hex), would be ideal to keep from getting damaged threads. The
plug would also need a guide nose to keep the plug from being inserted
cross-threaded, with a large round shoulder under the hex to take the
bite of a chisel point to unscrew it with a hammer and chisel in case
it somehow got too tight.
 
To prevent a gorilla with a wrench from destroying drain plug threads,
I have often thought about designing another kind of drain plug with a
free-turning wrench grip with an ordinary 1/8-inch cotter pin through
it to act as a shear pin. If a wrench-wielding gorilla tightens it too
hard then the pin simply shears, which can be easily replaced with
another ordinary mild steel cotter pin. In case it is stuck then a
piece of 1/4-inch steel rod or drift punch tip can be inserted into a
blind hole to lock it up to unscrew it. The unscrewing pin hole would
need to be blind to keep the stupid wrench-bearing gorilla from leaving
a 1/4-inch pin through it permanently, which would defeat the purpose
of having a protective shear pin.

If you look at new car 50,000-70,000 mile warranties, the oil drain
plug is mentioned specifically as a non-covered item! 


Work and play safely!

Rich

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