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Old 25-06-2022, 03:57   #1
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Yanmar SD60 Max Props Neutral Engine Jarring Knock

Happy weekend everyone!

As the title suggests, we have twin yanmar 80s with SD60s and max props. Iíve owned the cat for coming up on a year with no event (w the SDs). I will try to explain in enough detail below so hopefully someone can chime in on what is happening.

Yesterday while under sail or using the other motor as propulsion to gain forward flow (I say this so you understand this is not while sitting stagnant) over the feathering max props there was a loud banging knock coming from the STBD saildrives! (I may get an award there for longest run-on sentence). Anyhow, this banging/knocking happens when engine is on, boat is propelled forward, water is flowing past the max props. The volume of the knocking can be heard easily from anywhere on the boat and cadence of the knocking is about 120 knocks per minute (about the pace of singing ABCDEFG song to a child). Itís violent enough to shake the engine on its mounts!

Troubleshooting - When it happened and when it stopped - all while forward momentum

- If we turn the engine off - the knocking continues until shifting transmission into reverse (normal ops w Maxprops to bring to feather)
- if we shift into forward or reverse while engine on - the knocking stops - only happens in neutral
- SD fluid/oil is at normal levels - no milky or seawater issue
- I do need to swim the prop to verify proper and free movement of the feathering system - but intuition tells me itís working - and I just greased and serviced weeks ago and they worked fine - and even if it wasnít - itís no different than having a fixed pitch - it shouldnít BANG when in neutral

This tells me when moving forward - in neutral - the maxprops not feathered - so spinning the SD hydrodynamicly (sp?) - it causes this shutter?!? Stumped here.

Hoping one of you may know what this is or could be.

We are continuing on up the east coast from
Brunswick GA to Charleston so will have another 20 hrs or so to see if it continues to happen and further troubleshooting.

Thank you for reading and in advance for your wisdom.

Coy
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Old 25-06-2022, 04:10   #2
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Re: Yanmar SD60 Max Props Neutral Engine Jarring Knock

It will be the props not feathering, happens when there is some growth on the mechanism. A simple cleaning should fix. Putting into reverse and then neutral normally can fix it temporarily.
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Old 25-06-2022, 04:46   #3
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Re: Yanmar SD60 Max Props Neutral Engine Jarring Knock

Thank you Clownfish.

What doesn’t add up is - if the maxprops aren’t feathering - which they shouldn’t feather in neutral - they are spinning same as fixed pitch in that moment - why would a then “fixed pitch prop” cause a jarring banging shuttering?
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Old 28-06-2022, 10:30   #4
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Re: Yanmar SD60 Max Props Neutral Engine Jarring Knock

Difficult one, anyway I'd check if anything is entrapped in the propeller. Also check if prop is steadily attached and tightened to the S-Drive shaft and engine's silent blocks are OK
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Old 28-06-2022, 11:00   #5
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Re: Yanmar SD60 Max Props Neutral Engine Jarring Knock

Since you just serviced the prop, that would be where I would look first.
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