Excessive heat that was not carried away by the cooling system at a fast
enough rate of exchange.
403 engines have cylinders in pairs, like siamese twins. They are
joined side by side with no water jackets between them. In hard water
areas, where tap water is used instead of distilled water, minerals in the
coolant can turn to hard scale around the hottest parts of the engines.
Hard mineral scale is an excellent insulator, and is very difficult to
remove from internal surfaces when using modern hot tank chemistry. The
days of using caustic (toxic) lye solutions are long gone. I quit using my
hot tank over 10 years ago because the chemistry is no longer available,
and dish washing machine detergents just don't get the job done.
Media blasting will remove it, but if so much as a teaspoon of the
stuff gets left behind, bad ju-ju.
Steel shot blasting, same deal.
S &J uses a super hot oven, heats the castings very hot for 24 hours, and
turns the stuff to ashes. Then, follows up with water based cleaning
solutions.
If your 403 block was not de-scaled when it was overhauled, that MIGHT
be one of the causes of overheat, along with ignition timing, crappy
gasoline, lean air fuel mixtures, vacuum leaks, higher combustion
temperatures from overbored cylinders, tightly fitted pistons, and the beat
goes on.
Jim Hupy
Salem, Oregon
On Sat, Jul 6, 2019, 1:12 PM Ray Erspamer via Gmclist <
> Yes, I just replaced it 2017, it had 6500 miles on it and burned a hole in
> #8 piston. Still trying to figure out what caused it.
> --
> Ray Erspamer
> 78 GMC Royale
> 414-484-9431
>
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