Saturday, April 6, 2019

Power Assemblies for Locomotive Diesel Engines

I have already written some notes on the history of the diesel engine. The share below of a 2007 incident in Louisiana motivated me to learn more about the "power assemblies" used in off-road diesel engines.

Stephen Grief shared a post of a GE power assembly that had shot out of a diesel locomotive. Note the tracks at the top of the first photo. That gives you an idea of how far this assembly went. The piston went even further. It went through the roof of a house (6 and 2), down through the ceiling (3) and embedded itself in a wall (4).




This is what a power assembly looks like if it has not been shot across someones backyard.
Richard Wineman commented on a share
should look like this
John Corum Richard Wineman Alco??
[Richard "liked" John's comment, so I assume this one is for an Alco engine. Even though Alco no longer makes locomotives, their engines are still made for other applications such as marine (boats).]
Smaller engines such as those in cars and trucks have a head that goes across the top of a cylinder bank. When a valve burned out in my Honda CRV, they had to uncover all of the cylinders just to fix one cylinder. Since it had close to 100,000 miles, I also had them change the timing belt. That repair cost $2000. Can you imagine removing a head from a V20 engine that would be about 20' long?
EMD/Winton 201 [DeBruler]
Engines are typically covered so that you can't see how they are built. But the screenshot below of an experimental engine shows that GM used power assemblies from the beginning of their development of a two-cycle engine for the locomotive application.
This video lists the components of a power assembly: head and valves, liner, piston and rings, piston carrier and bearing, piston pin, thrust washer, snap ring, connecting rod, basket on fork rod assemblies.

A comment on this video explains the expected life of a power assembly:
BilgeDweller1 month agoI ran the engine room on an 8000 hp towboat powered by two 16-710's; we went 28,000 hours between overhauls. At about 14,000 hours, each engine got rebuilt cylinder heads and the piston thrust washers replaced. We ran the snot out of those things...
To replace the cylinder head and piston thrust washers, I assume they just swap all of the power assemblies to get a boat or loco back into service and then do the replacement work in a shop so that the power assemblies can then be used in another boat or loco that needs repair.

The cause of the "blown power assembly" at the top of these notes was improper torquing of
the nuts that held the power assembly in the block.  I read in one of the comments, which I now can't find, that they need 1,400 ft-lb of torque. I gave away my half-inch socket torque wrench, so I can't go look at its scale now. It was a beam wrench with an 18" handle similar to the one in this photo. But I think its scale topped out around 200 ft-lb. Given that spark plugs and lug nuts use a torque below 50 ft-lb, it was fine for my use.
EncMstr [CC BY-SA 3.0], via Wikimedia Commons
To get 1,400 ft-lb, even with a very long wrench handle, would be hard. Then I discovered there are hydraulic torque wrenches that can be used to turn the nuts. (An EMD 710 engine needs 2,400 ft-lb of torque. [video])
It is easy to envision how the power assembly chassis is blown out of the top of the locomotive if the nuts were not torqued properly. If they were too loose, they come off. If they were too tight, the bolts break. And the next power stroke blows the top, and sides, up and out of the locomotive. But a power stroke blows the piston down, not up. However, if the piston pin is broken, then at the end of the next compression stroke the piston would keep going up out of the hole already made by the power assembly.

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