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9 August 2006Andy CassidyPart 2 of 2
Turbo Chargers
Canadian Pacific General Electric AC4400CW number 9838 in the diesel shop - 9 Aug 2006 Andy Cassidy.

Part 1 of this article on the Turbo change in CP 5915 (GMD SD40-2), stirred up a few comments. So I thought it worthy of note to go a touch further on a couple of different fronts.

First, to expand on the operation of the General Motors (GM) 2 cycle locomotive engine, it was pointed out to me I should have touched on the fact that not all GM engines have a Turbo. I never gave it a thought at the time, but yes the GM engines in the lower horsepower ranges get their breathing air from mechanically driven Roots Blowers. I thought I had some Roots Blower internal workings photos on file, but not the case. However, here's a good explanation about a Roots Blower. These blowers are very reliable devices and virtually never need replacing for the most part, so one doesn't see them on the shop floor that often.

In any event some years ago we had a flat car in the yard with two GM engines on board that give a good view of the external workings. The first two shots are of a 12 cylinder roots blown engine.

Figure 7 - GM 12 cylinder roots blown engine - 9 Aug 2006 Andy Cassidy.
Figure 8 - GM 12 cylinder roots blown engine - 9 Aug 2006 Andy Cassidy.

One can see the two Roots Blowers mounted at the back of the engine on top of the Air Ducts that feed the air to the Air Box along the length of the engine (top hand hole covers). Above the blowers are the Air Filter Holders, minus the filter media. The Roots Blowers don't need Aftercoolers like the Turbo equipped engines as they don't generate the heat a Turbo does compressing air. You'll note there are no Exhaust Manifolds on the top of the engine, as they're not involved in the air intake system.

Now as a comparison, the other engine (part of a Gen Set) on the flat car was a 20 cylinder Turbo charged engine.

Figure 9 - GM 20 cylinder turbo charged engine - 9 Aug 2006 Andy Cassidy.

As you can see, the Exhaust Manifolds are attached together and direct the exhaust past the screen and into the Turbo at the back of the engine. The Stack outlet is covered with a tarp to keep the rain out. The big box above the generator is for the air filters at the inlet to the Turbo. And finally, the Turbo Outlet Air is directed through an Aftercooler on each side before being fed to the Air Box. The Aftercooler has that blue water pipe attached to it, and the water from the cooling system provides the cooling. Basically it's a small radiator.

Finally, back in 2013 they were changing out the Turbo on CP 9838 (GE AC4400CW). As noted in the previous message, GE's employ 4 cycle engines that don't need any mechanical drive from the engine other than the exhaust. As such they are a pretty easy repair but still expensive though. Shown here in the final photos are shots of the removed Turbo from this units 7FDL engine.

Figure 10 - GE Turbo Exhaust Inlet - 9 Aug 2006 Andy Cassidy.
Figure 11 - GE Turbo Exhaust Inlet - 9 Aug 2006 Andy Cassidy.

In the these shots it rests on the shop floor, and you are looking at the Exhaust Inlet side of the unit. The outlet is at the top with the lifter attached.

The third shot is about a month later and the same Turbo is sitting outside the Stores Department waiting to be shipped out. In this view you are looking at the Air Inlet side and the two Outlet Scrolls that feed each cylinder bank. The overall size is about the same as the GM Turbo, but without the gear train, and all the nut and bolt connections.

Figure 12 - GE Turbo Air Inlet and two outlet Scrolls - 9 Aug 2006 Andy Cassidy.

The next photo shows the Exhaust Stack/Spark Arrestor that sits atop the Turbo when applied to the engine. This is the part you see sticking out of the roof on these locomotives. The newer GE EVO engines have a similar Turbo, just a bit more compact and with different Scroll Outlets.

Figure 13 - GE Turbo Exhaust Stack / Spark Arrestor - 9 Aug 2006 Andy Cassidy.

That's it for mechanical lessons for now.

Andy Casidy.