8v92 6v92 two stroke basics

[Gregory OConnor]

The 92-series Detroits are two-cycle engines.

All current production diesels are 4-cycle.

Detroit stopped production on the 2-strokers due to EPA
requirements - and for no other reason. They simply would not meed
EPA emissions requirements on or off-road, no matter what they
tried - and try mightily they did, with their DDEC and then DDEC-II
(electronic control) systems.

Ultimately, they were forced into 4-stroke production.

It is true that modern electronic engines get better fuel
efficiency. However, there is a LOT to be said for a basic engine
design that goes back to WWII!

I have 6V92s on my boat (two of 'em.) Detroit's basic design was
simplicity itself, and ingenious. The supercharger on these engines
is necessary; they will not run without them. There is no intake
valve system at all. The valves are all for exhaust; as the piston
moves down on a power stroke, the exhaust valves open and at the
same time the piston uncovers a port, much like a 2-stroke outboard
motor, that leads to an airbox that is pressurized by the blower.
The clean air forces out the exhaust. When the piston moves back
upward the valves close and the ports are covered; compression
occurs, and fuel is injected at the appropriate time. Injection is
performed by a cam-driven unit injector. The design is extremely
simple - ingenious, really. The emissions problem comes from being
unable to perfectly scavenge the exhaust. However, these engines
tend to run very low EGTs compared to 4-stroke turbodiesels due to
the overabundance of air that flows through them on a given power
cycle.

The nice thing about Detroits is that there is no high-pressure
injection pump or electronics. They will run, once started, so long
as they have fuel and compression. You can also replace the entire
fuel system (the injectors) for about $100 a hole and the low
pressure fuel lift pump for a couple hundred bucks - these are unit
injector engines. With under $200 worth of special tools you can
keep a Detroit running in tip-top shape for a loooong time, and
properly maintained they are great motors. They have a reputation
(somewhat earned) as oil leakers, which is due to the fact that
Detroit made the blocks so they could be "doubled" - thus, you have
6V92s, 8V92s, 12V92s (two 6V92s end-to-end) and 16V92s (two 8V92s
end to end!) This, however, means there are oil ports and such on
the ends of the blocks that have plugs in them and thus they tend to
leak oil....

The other thing to be aware of is that Detroits are quite
inexpensive to get parts for. A cylinder kit, for example, is about
$600 - that's the liner, piston, con-rod, rings, etc - the whole
shot. One new hole, coming up. So for about $5k in parts you can do
a complete kit replacement, and it can be done "in-frame" - without
pulling the motor.

Detroits have no glow plugs and "off the shelf" no starting assist.
They are ENTIRELY dependant on engine compression to start. They
also require (not recommend, REQUIRE) straight weight 40 grade Cx-II
oil. Multigrade oils are strictly forbidden due to the high shear
strength required by the injector followers - you WILL destroy cams
if you run a 15W40 in them, for example, and you'll also get
incessant low oil pressure warnings and probably a spun main to go
with it. Unlike "modern" diesels its not uncommon (nor a problem) to
have oil pressure readings as low as 10psi at idle when fully warmed
up! Normal oil pressure at power (1800 rpmish) is in the 45-50psi
range though, just like modern engines. What this means is that in
cold weather you need STOUT batteries or you will not be able to
roll them over at a high enough RPM to get 'em to light. Block
heaters are strongly recommended for the winter months. Ether is
very dangerous to use on these engines; I know people who have and
do, but my recommendation is "never" on a Detroit.

The nemesis on the 92 Series Detroits is overheating. This is a wet
liner design with elastomer (O-ring) seals at the top and bottom of
the cylinder liner. If you overheat these engines, even just a bit,
the liner seals will be compromised. The result will be oil to
cooling system leaks, and if not caught very quickly, damage to the
mains or even worse, a spun main and damaged crank. Cooling system
maintenance is THE big deal on these motors. Keep them running cool
and all is well. Let them get hot and you will be rebuilding them.

Also, later versions of these engines in "turbo" trim used
aftercoolers, which are under the blower. That needs to be kept
clean; getting to it requires removing the blower, which requires
disturbing the governor and fuel rack. Its not a tough job, but it
is a pain in the butt. Thus, its important to avoid exhaust leaks
and use a good air cleaner so that becomes an infrequent problem
rather than a frequent one.

Finally, there is the matter of airbox drains. The airbox on a
Detroit is where the blower "accumulates" the charge for scavenging
and the new combustion cycle. The blower seals, as the blower ages,
and turbo seals will eventually leak small amounts of oil, and the
compression and then cooling of the air charge causes water to
condense. The airbox drains allow this accumulated crud out of the
airbox instead of having it sucked into the cylinders where it will
cause abnormal wear. On turbo motors there are check valves located
at each drain; these must work properly. If they stick open or
closed its bad news; many people neglect these service items. They
should be pulled and cleaned at every oil change, and if you have
motors where Detroit routed them back to the oil pan (they did on
some motors, as the EPA had a kitten about the original design which
just allowed the slop to go onto the road) you will do your engine a
huge favor by removing that and routing them to a "crap can" that
you then empty once in a while (at oil change intervals is a good
choice.)

I'm very much "up" on the 92-series engines, since I own two and
maintain them myself. Set up for reasonable power levels (500HP from
an 8V92TA is reasonable) and proper maintenance they provide
extraordinarily good service. The 8V89TA CAN be "hot-rodded" to as
far as 750HP quite cheaply just by changing injectors and a few
other things - don't be tempted, as the service life in that
configuration can be as short as 1500 hours or less between
overhauls!

The DDEC and DDEC-II versions of these engines replace the
mechanical fuel rack with electronic control of the injectors and a
bunch of sensors in an attempt to get cleaner and more fuel-
efficient operation from them. Its mostly successful, but now you're
into the computer-controlled realm and simple mechanical maintenance
procedures go out the window.

If I was going to own a Detroit-powered coach, I'd want one with
mechanical injection - if I'm gonna buy an electronic engine, I want
one of the new design ones, as if I'm gonna get the warts I want the
benefits too. With a handful of parts and a few tools on board I can
fix these things by the side of the road if necessary so long as I
haven't spun a main or something equally catastrophic - something
you simply won't be doing with "today's technology".

Repost form JimS

GregoryO'Connor
94ptRomolandCa