[Vwdiesel] GM V-8 diesels of the '80s

[Kurt Nolte]

I really, really, really wish folks would stop calling them "converted 
gas engines," because they flat out -weren't.- I found someone who puts 
the differences, and the problems, quite plain and simple, so I'm 
spreading this:

--
The Olds diesel blocks were entirely different castings. Main bearing 
webs are 3/4", and the main bearing journals on a diesel 350 measure 3" 
(big-block sized) while the gasser 350s are 2.5" in size. A 350 diesel 
crank is the only small-block crank that won't directly fit in your 
gasser 350. Cylinder walls are 0.4" thick - a lot of extra iron around 
the cylinders to the point where the diesel blocks can be bored 0.125" 
over (stock = 4.057") WITHOUT sonic testing if you're using a diesel 
block as a performance gasser buildup. Match that overbore with a 425 
crank, and you end up with a 437 CID V-8 gasser. Bore that same diesel 
block out to 4.25" (WITH sonic testing required), match to a shaved 425 
crank and a 3.975 stroke to end up with 451 cubic inches for a V-8 gasser.

Head gaskets kept blowing for a variety of reasons. Mainly, diesel fuel 
in the 70s was crap and contained a bunch of water. GM built the cars 
without a water separator, and water would rust the steel internals of 
the fuel system. Rusted injectors would result in erratic operation. Too 
much fuel injected prior to TDC causes "pre-ignition" and the water 
injected also causes some hydrolock. Water in the fuel hydrolocking 
coupled with injection pump timing that was way out of whack (from 
rusting of precision injection pump parts) resulted in extreme cylinder 
pressures WAY above what GM ever designed the engine for. The head 
gasket or head bolts were thus the weak link. If the head gasket leak 
didn't cause major hydrolock to the point of bent rods and bent 
crankshafts, the mechanics (untrained on diesels) would REUSE the 
STRETCH head bolts when they just shotgunned a new head gasket in the 
engine. I say shotgunned in that they just fired random parts at the 
problem, and 99% of the time never diagnosed the causally related 
problems to fix the problems with the fuel injection pumps. Hence, you'd 
end up with multiple head gasket failures or multiple head bolt failures 
because the mechanics would never fix the underlying problems - and the 
hapless owners would just swing in a replacement gasser engine and blame 
the problems on the diesel engine. These owners would just never 
understand the causes of their problems, and they'd never take the 
proper care necessary to prevent the problems in the first place.
--

The "350 Diesel" blocks are /highly desirable/ in the high performance 
Chevy 350 world, owing to their much stronger webbing and bottom end 
coupled with head bolt, coolant and oil holes that all line up with 
whatever your favorite SBC head happens to be. Stronger alloys, the 
ability to use a stronger big block crankshaft, and the more robust 
design of the block itself all make the engine quite strong.

Weak dealer training, gas engine maintenance practices, and poor quality 
fuel were the death of far too many 5.7 diesels. :(

-Kurt



William J Toensing wrote:
> I note that "Photo Bug" has a1982 Cadillac diesel. This converted Olds gas 350 GM diesel is the diesel that gave diesel a bad name in the USA. However, I heard the latest "GM Goodwrench" replacement diesels were reliable engines but the engines came too late to stem GM's bad diesel reputation. Perhaps Photo Bug can share some more info on his Cad diesel & what modifications, if any, he has done to make this a reliable engine. If some of the others out there have made some mods to make this a reliable engine, please share the info. I am not looking for one of these GM diesels but it is possible I might stumble on one & reject one I shouldn't.
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