Thread: Diesels in America

Originally Posted by JDNSW

Meeting the demand by imports across the Atlantic is by and large illegal, so keeping the price up for the few that are there.

John

25 year import rule AFAIK.

So early 110s and 90s have been trickling in for a couple of years now. As have TD5s and TD4s that have been (illegally?) altered to become much older (at least on paper). Some may have been fitted with older chassis.

The Americans also had a very bad introduction to light duty diesels with the olds 350 Diesel V8 which was bad enough to deter buyers from purchasing a diesel powered vehicle for many years.
From Wikipedia....Oldsmobile V8 engine - Wikipedia, the free encyclopedia
Head bolts

GM used "torque to yield", commonly known as "stretch" or "angle torque", head bolts. This allowed the bolt pattern to remain the same as the gas powered counterpart with an increase in clamping load when compared to standard head bolts. A total of 10 bolts per head were used, four per cylinder with the center three pairs shared. This permitted the use of the same tooling and reduced setup costs. This design did not provide adequate clamping force under the severe conditions to which these engines were subjected. Overheating or excessive cylinder pressure could breach the seal of the head gasket and in severe cases break the bolts.

High strength aftermarket head bolt sets are now available to make the engine more reliable in this area.
[edit] Pump timing

The Stanadyne injection pump was driven with the use of a short stubby shaft with a built in helical gear which meshed with a gear on the front section of the camshaft. With high mileage,the timing chains tended to stretch a little (like any other timing chain) and the injection pump timing could become less than perfect. The pump timing can be adjusted dynamically with the use of a Snap-on MT480 analog diesel timing meter or with one of the more modern meters used today.
[edit] Water in fuel

Arguably a major portion of the LF9 engine's problem could have been simply avoided by using a water separating fuel filter. The lack of water separators was a fuel system deficiency across GMs' light duty diesel lineup into the late 1980's.

Water will rust the steel internals of the fuel system. Rust will damage the precision parts in diesel fuel injection pumps and high pressure diesel injectors causing erratic operation. Injecting fuel too much prior to TDC on the compression stroke will cause pressure conditions similar to pre-ignition / detonation in gasoline engines. Water in varying amounts will also be injected with the fuel charge. Any rust in the steel fuel lines, fuel filter, pump etc can damage replacement parts and continue to cause injection cycles out of time.
[edit] Consumer created fuel problems

Water in gasoline fuel systems can be addressed by adding anhydrous alcohol [drygas] to the fuel. This technique does not work with diesel fuel. Some consumers used drygas in their diesels to combat the water, but the Alcohol in drygas accelerated the wear of the governor flex rings inside the early Stanadyne DB injection pumps. These pumps included an ignition advance mechanism based on pump housing fuel pressure. The housing pressure was affected by fuel return flow. Pieces of a damaged governor flex ring lodged in the fuel return check ball assembly. The sometimes intermittently blocked return line combined with a damaged governor caused erratic ignition timing. The flex ring governor was replaced, by Stanadyne in 1985, with a much improved Elastomer Insert Drive Governor Assembly commonly referred to as an EID. The EID is a service replacement part that eliminates the disintegrating flex ring.[19]

The above mix of conditions originating with water in the fuel contributed to creating extreme cylinder pressures far exceeding those foreseen by the LF9 engine designers. These pressures would damage the head gasket and sometimes break head bolts.

A head gasket leak effectively quenched ignition in the affected cylinder. This allowed unburnt fuel and coolant to leak into the crankcase, and would thin the lubricating oil. It also combined with combustion byproducts to make mild acids that attacked the copper/babbitt bearings and aluminum pistons. A head gasket failure can be particularly damaging in a diesel. A diesel engine has effectively no piston to head clearance at TDC on the compression stroke. The introduction of coolant into the cylinders can cause hydrolock. Hydrolock typically results in bent/broken crankshafts, pulled threads on main bolts, and bent connecting rods, effectively destroying an engine.

Because the various failures these engines encountered were causally interrelated, and dealership technicians were unfamiliar at best with passenger car diesel engines, recurrent failures were possible because only the most obvious symptoms of trouble were addressed. The "one use only" head bolts were commonly re-used and symptoms in other interrelated systems ignored. Thus, cars could suffer multiple head gasket/head bolt failures from re-use of head bolts or a damaged injection system.

The Oldsmobile Diesel V6 engines, although sharing much of the same production history, were produced on different tooling, where it was feasible to upgrade the head bolt pattern to what is arguably a superior design capable of withstanding more consumer abuse. However, the fuel system suffered from the same deficiencies.

Regards,
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