If it is any help, export Alcos had the same characteristic "hunting" at idle.
I was told this was caused by a low oil level in the Woodward electro-hydraulic governor, such that the governor did not react quickly enough to maintain a steady idle speed, but was able to keep the engine running. This affected both 244 and 251 engines.
(Edit) The oil served as a damping medium to even out the changes in power, and with a low oil level, the governor oscillated between a setting higher than wanted and one lower than wanted, hence at idle, the engine sped up and slowed down in a continuing cycle.
I feel confident that neglect of minor maintenance details such as this occurs equally all over the world.
M636C
That is not what I heard. It is as if the fuel were shut off to shut down the engine. It sounds just like an engine that is being shut down. The engine coasts down in RPM, but then at the very last instant, it surprisingly comes back to life and rises back to full idle RPM. The engine slows down to probably within 1/4 second of being stopped. It does this over and over in cycles lasting maybe 20-30 seconds each.
JoloSee my reply to Euclid and let me know what you think.
I am no expert on 539 governors, but many of the ones I saw 'remaining' on PC in the early '70s exhibited this condition, and I attributed it to poor adjustment of the mechanism, not some method of 'fuel saving' or avoidance of critical speeds, which shouldn't matter 'that much' during the idle range (or any 'overshoot' when correcting from a lag).
One of my reference books references a 'carbonstat' with attached systems that could produce engine hunting (and gave some procedures for correcting the issue). They specifically indicate that the governor itself is much more likely to produce hunting, and nothing I have heard so far described is outside what a mis-adjusted governor would produce.
Now, idle on a 539T is not exactly a smooth thing even at best. I have read descriptions of a brand-new DL-109 on ATSF (or whatever finicky technical model number of this general nose style they bought) shaking the dining car so badly through the tightlock couplers that coffee was slopping out of cups.
I strongly suspect that posting this over on RyPN, where there are several participants that actually work on these engines, would produce a great deal of precise technical information relatively quickly.
Air compressor kicking in?
Norm
I don’t think that what the OP described was a defect. It sounds exactly like what I have witnessed, which was a perfectly regular, repeating cycle. The engine did not speed up from an idle. It slowed down from an idle to the point where anyone would conclude that it would die, and then it speeded back up to normal idle RPM. There was no “coughing” or other indications of something wrong.
I assume it was normal function, but it was not there for all Alcos of that era. Maybe it was an option with the governor and fuel system. The only reason that I can think of would be to save fuel by creating a lower than average engine RPM. Maybe that average engine speed can be lowered by letting the engine almost die and then come back; as opposed to maintaining a constant speed as low as possible. But that is just a wild guess. Whatever the reason, assuming it was intentional, it must not have been deemed a good enough reason to make it universal practice.
I always figured the momentary increase in speed was because some electrical device needed more power than was being supplied by the idle speed and when that device turned on, the Diesel had to speed up to supply the power.
I suppose the cycling could also be due to the throttle control "hunting" for the quesient spot... sticky linkage possibly causing the engine to not respond as fast as the control circuitry was calling for to speed up or slow down trying to find the "sweet spot". Maybe too large of a fuel resevoir between the throttle and the cylinders causing a lag between the control calling for a change and the change being implemented and thus over reacting to too much or not enough speed.
Semper Vaporo
Pkgs.
I must be getting old. I remember when just about all eastern
railroads had Alco S1 and S2 switchers. The un-even idle of
an Alco 539 was quite normal.
Thank you for your reply. See my reply to Euclid and let me know what you think.
It wasn't being worked on, it was in use, just parked. My first thought was the B/O governor but because I heard this idle from multiple engines including a marine engine, I figured it was 'normal' in this case. (I gather that Alco did also use their engines for marine purposes.)
That was my question too. I thought for something that uncommon that there would be some reference to it's unusual idle written up somewhere. Just taking a less than educated guess, I wondered if it might have something to do with avoiding harmonic vibration problems. (The sounds of this engine compared to the smooth idling larger engines did sound a bit unrefined and that it could conceivably start rattling apart at some point.)
I have seen Alcos idle like that on a couple occassions. I believe they were RS-1s. Each time the engine would slow way down, it seemed like it would shut off for sure. But at the last possible second, it would come back to life. It was quite intriguing. Assuming it was operating properly, why would an engine be set up to idle like that?
Jolo I worked for Southern Pacific in the Ogden Locomotive shops. I remember hearing an old switch engine idling outside the shops. It would rev up to a certain RPM then it would die down to a low RPM. It then repeated that cycle nonstop. I am thinking it may have taken about 10 seconds per cycle. I think it may have been an Alco switch engine. I have also heard this type of engine in an older industrial boat. Just curious, does anyone know why these types of engines would have this variable idle?
I worked for Southern Pacific in the Ogden Locomotive shops. I remember hearing an old switch engine idling outside the shops. It would rev up to a certain RPM then it would die down to a low RPM. It then repeated that cycle nonstop. I am thinking it may have taken about 10 seconds per cycle. I think it may have been an Alco switch engine. I have also heard this type of engine in an older industrial boat.
Just curious, does anyone know why these types of engines would have this variable idle?
Alco 539 based switchers had very variable engine speeds at idle. They would slow down to almost stalling, then rev up and repeat the cycle.
Especially considering this was at a shop could it have been caused by a mechanical problem, like a B/O governor or fuel pump, or perhaps stuck injectors?
Greetings from Alberta
-an Articulate Malcontent
Our ALCO (MLW) RS18u's idle down after a certain amount of time. I've never noticed them idling back up - probably by then we're making a move.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
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