Possible damage from high speed shift?

[Bob England]

Gordon,I enjoy reading your informative posts. The diesel engine is the "mysterious" and (financially) scariest part of my boat to me, and having your advice available makes me feel better.My question is about transmission damage from shifting at high RPM. Last weekend, after changing my engine oil and filter, I was testing to see what maximum RPM the engine would reach in neutral gear. (As an aside, new oil added a 100 RPM or so it seemed.) While the engine was turning about 3700 RPM, there was a bang, and the transmission dropped into reverse gear. The engine is a Yanmar 2GM20F, about 11 years old. Everything seems OK subsequently, but what is the possibility that there is hidden damage? Oh, and if I may ask another question, is there a way to make the neutral gear detent more noticeable? It's hard to tell when mine is properly in neutral.Thanks,Bob England

 

[Gordon Torresen]

Shifts and detents.

The reversing gear builder state that high speed shifts can be tolerated. That bang when shifting puts a jolt on a lot more than just the reversing gear. The entire drive train is jolted from the fly wheel to the propeller. If it hasn't happened too often, you are probably safe. Not being able to feel the shifting detent could be the result of several things. Stiff cables are the greatest offender. Over time the cables just slowly tighten up so that you have to apply greater force to overcome the stiffness and can feel the shift less and less. Misadjustment can also be the culprit. If your control has a detent it must be adjusted to coincide with the detent on the gear. The best way to check this is to disconnect the attachment at the gear, put the control detent in neutral, put the gear shifter in neutral and adjust the end of the cable so that the pin slides into the hole without having to move anything. The support (or lack of it) of the cable outer jacket is also important. If the outer jacket can wave in the breeze there is no way to maintain a proper adjustment involving two detents. If you determine that your cable needs replacement, determine that the old one is as short as possible and then consider the purchase of a Morse Supreme cable. Costs a bit more but are they ever smooth.

 

[Bob England]

Thanks, Gordon

This has only happened once, and I will be very careful that it does not happen again. I will check the shift cable adjustment as you described.Thanks again,Bob.