Symptoms of Worn Out Throttle Linkage on Low-Speed Diesel

On a ship with a low-speed diesel when the ship was heavy, going from slow ahead to half ahead the engine would get stuck in critical speed range and the alarm would go off. The cure was to give a full ahead bell till the engine pulled out the critical range and then drop back to half ahead.

Ahead bells only, Ok astern and didn’t happen when the ship was lightly loaded.

I discussed this with the chief a few times and he insisted it was just because the ship didn’t have enough power, which didn’t make sense. A few years later, after I got off I ran into the chief and he told me they replaced/adjusted the throttle linkage on the main engine and it solved the problem.

Later I ran into a similar thing on two different ships. Any comments or experience with this elsewhere?

On a slow speed other then electronic controlled there are several hemi joints from gov outdrive leaver till you get to the fuel pump index. Those do wear out and can be a pain to balance a load out amongst the different units.
I just changed out all of mine on my engine for the same reason. a little bit of wobble can add to a lot of lost stroke on the rack with the size of those systems.
I keep our third on regular greasing rounds on or rack bearings and hemi joints as well as making sure both the first and myself are regularly feeling the rack for slop.


That sounds like the same thing.

I recall being shown a table the engineer filled out for the port engineer. It must have been measurements taken at the gov outdiver and the corresponding measurement at the fuel pump index for each cylinder.

That’s another part of the same question. On one ship it seemed like we kept going slower and slower, but it’s hard to be sure because of the various factors, hull condition, trim, load, weather etc.

One chief kept telling me it was not the engine but when the opposite chief showed up he told me that what was happening was the previous chief was balancing the load by always turning down the “hot cylinder” resulting in a gradual reduction in power.

Does that seem plausible?

With out a performance reading and a test bed performance reading to compare to that can be a tough one for the internet.

I’ve delt with a counter part that treated the main the same way. Unfortunately all he was doing was hiding the issue and creating new ones by not providing enough fuel when it was needed.

Exhaust temps only tell part of your performance, you really need to see temps, pressures and compare to baseline readings.

This answers the question. I didn’t know how plausible it was that the chief might be making that error.

Did any of the chiefs take indicator diagrams? Analysis of the computer generated cards would have revealed poor fuel timing.

AFAIK injector timing was not an issuse. What is the reason to think it might be?

I dare say it wouldn’t. Injection timing, commonly defined as start of injection, is not influenced by the rack, which only controls end of injection. Indicator cards might show differing duration if you somehow could indicate all cylinders at once, but that’s not how I was taught to do load balancing.

Anyhow, my hands on experience doesn’t go beyond medium speed, so someone more qualified will have to chime in.

How is that? It would be based on the amount of time required for a given volume of fuel I assume?

Strictly speaking, it’s about the length of plunger travel before the pump unloads. There’s a helical cut in the plunger, and a port in the sleeve bore. Rotating the sleeve decides how far the plunger travels before the port lines up with the helical cut.

Surprisingly, I wasn’t able to quickly google up a good animation, but I found this:

EDIT: There are of course numerous alternatives, but this is how the Bosch PE pump works, and every large engine that I’ve seen with mechanical injection control use variations of this working principle.


its all about the helix…