I'm changing engines because the old one crapped out - blown head gasket I'm told. Was told it'd be more expensive to go in and repair the old engine. We don't know exactly why the head gasket went and the engine wound up shot, because we haven't had the car in our possession. Maybe it was driven around on a leaking gasket for some time, then allowed to sit (it was allowed to sit).
Sit too long and water in the cylinders would rust it beyond easy redemption. Something like my endless genset project in other words. Silly to contemplate when good used engines are as relatively cheap as they are, versus rather expensive repair parts, etc. For my genset, of course, Hercules G3400 engines are _not_ like OM617's so far as availability goes.
-- Jim
