You have probably heard that a DD will leak oil no mater what. I have even heard the castings are porous, allowing oil to actually seep through. That is completely untrue. It is no more prone to leak oil than any other engine. With a good engine, the only place that will normally expel a few drops of oil is the air box drains.
Air Box drains explained
The 2cycle DD has exhaust valves, but compressed combustion Air enters
the cylinder through Ports just above the top of the piston when at the
bottom of the stroke, forcing the remaining exhaust out the valves.
The Ports are surrounded by the Air box, which is pressurized by the Super
charger, normally referred to as a roots blower. During normal engine operations,
water vapor from the air charge, as well as a slight amount of fuel and
lubricating oil fumes, condense and settle on the bottom of the air box.
Air box pressure through air box drains tubes mounted on the sides of the
cylinder block removes this condensation. These tubes may be routed
to a collection tank, for periodic draining.
If the amount of discharge exceeds a few drops, it can be an indication
of engine wear, or leaking blower seals.
The 53, 71, 92, 149, is the Cu In Per Cylinder. The 71cylinder has a bore of 4.25 and a stroke of 5 inches, hence 71CI. The 71 is a dry sleeve engine, meaning the sleeves are surrounded by the steel of the block. The early series did not have water below the ports, and are referred to as dry block. The later model had “WBP” or Water below ports. The visible difference is in the air box covers being oval on the dry and the WBP with bone shaped covers. There is also freeze plugs below the ports on the WBP. The 6-71 is an inline 6 cylinder with 426CI. The inline is made in 2,3,4 and 6 cylinder versions. The 6v71 is the same 426Ci In a V configuration. The V is made in 6, 8, 12 and 16 versions. The Detroit is a two-cycle engine and requires a blower to force the exhaust out the valves and fresh air charge in. The pistons are cooled from the bottom with a drilled oil port from the rods.
When I first started looking at buses, I knew very little about the
Detroit engine, even though I had been around and drove Trucks with DD.
I thought the 6-71N was a 238HP and the 8v71N were 318HP. Detroit has two
ways of measuring HP. One is the Max Rated, measured at 60F and (29.92
in Hg) Sea Level, and the SAE, which is measured at 85F and (29.00Hg)
500Ft Elev. The SAE is the standards by which the HP is federally certified.
It is also the HP you will find in DD Tune up manuals. Almost all of the
HP ratings for the 71 & 92 are given at 2100RPMs. HP is arrived by
the following formula “HP= (Torque * RPM) /5252”.
An 8v71N W/ N65 Injectors & A timing has 304 SAE HP @ 2100. The
Max Torque is 800Ft# @ 1600. From 1600 through 2100 the torque will
decline slightly. You can find the torque with this formula. “Torque
=HP * 5250 /2100”, So, 304*5252=1596608/2100 rpm =760Ft#. Even though
the torque is down some, the HP is up because of the increased rpm. With
this rate, the same engine produces 326 SAE HP at 2300rpm W/Torque at 744Ft#.
When comparing engines, it is important to compare all at the same conditions
and RPM, preferably SAE and 2100rpm.
Detroit also shows some HP on coaches with #1 Diesel. Examples
I have given are with four valve heads and #2 Diesel.
The 8v71N W/65 Injectors, and Advanced Cam Gear timing, produces 304
SAE HP @ 2100. Most coaches have 55 or 60 Injectors. The 60s produce 280
SAE HP @2100, W/ Standard Cam Gear timing. To change the Cam gear
timing, you must remove the bell housing and everything attached to it.
Some Overhaul Shops put in 65’s With Standard Cam timing and use a
1.460 Injector timing, instead of the 1.484. This allow you to run N65s
with std. Cam timing, but it will not give the most out of the engine,
and it will smoke a great deal more.
You can turbo an 8v71 and get 370 SAE HP @2100 with N75 Injectors.
The pistons must be changed to lower compression from 18.7:1 to 17:1, The
liners changed from 1.05 port height to .95, and the blower ratio changed
from 2.05:1 to 1.95:1.
The blower seals have to be changed too. An oil port would have
to be drilled and taped for the Turbo supply oil. And if you want to get
the last 20 Hp, you will have to install an after cooler, if your block
is designed to accept one. And of course install the Turbo, and the connecting
exhaust and intake pipe.
You will find a few turboed 71s in buses, not many are original.
The 92 has a 4.84 bore and a 5-inch stroke, to get 92CI. It was only
made in the V configuration, with 6, 8 and 16 cylinders. The 92 is a Wet
sleeve engine, meaning it is in direct contact with coolant above the ports.
The pistons are also cooled from the bottom with a drilled oil port from
the rods.
The 92 was made in turbo and normally aspirated, however almost all
92s, 6 and 8 cylinder, in Bus use, were Turbo. The 6v92TA With 90
Injectors, has 335 SAE HP @2100. The 8v92TA with 90 injectors is
440 SAE HP @2100.
As with the 8v71’s Max rating of 318hp, the 6v92TA is Max rated at
350hp and the 8v92TA is Max rated at 475HP, remember this is not SAE ratings.
The V71 and V92 are almost identical in appearance and weight, with the 6V at about 2,000# and the V8 at about 2,400#. The serial and model numbers are stamped on the block, just below the air box covers. Looking from the front, either on the right side, uper front, or on the left side, upper back.. Some engines will have a tag attached to the valve valves with the engine configuration.
T = Turbo with conventional HP
TA= Turbo Aftercooled with conventional HP
TT= Turbo with constant HP
TTA= Turbo Aftercooled with constant HP
I = Intercooled, as with marine engines
C = California Rating