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Old 07-07-2020, 15:10   #1
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Yanmar RPM issue

A couple of Months ago on a very low tide I found a rock in my canal with my port sail drive (Yanmar SD60) while returning home. Note that I hit the rock 20 minutes before high tide so note to self, don't come into my canal system on a North wind. In any case I bent one blade of my autostream propeller pretty badly. The engine stopped abruptly, but immediately restarted. I was around 1000 rpm when I hit. I ordered a new blade from OZ and put the prop back on. I did a quick test going into both gears at the dock and all seemed well, but didn't run the rpm up. I took it out the about 10 days ago and the port engine would not go above 2200 rpm in gear. This is a 3jh3ce and should turn up about 3600 RPM. The fuel system was cleaned and that tank drained and fuel replaced last August. New filters at that time. I've been doing boat projects and did not take the boat out until April when I found the rock. The engine ran normally on that trip, at least until I hit the rock. I probably only have about 10 hours on the filters and no evidence of contamination is visible in the Racor bowl. Today I dove on the prop and found that the port engine had about .5 inches or about 12-13 mm more pitch angle than the starboard prop so I took the pitch adjusting screw out and checked it for damage. None found. I adjusted the pitch screw so that the blade angle of the port prop was the same as the starboard prop at least within a mm or so. I then did a static rpm test and the port prop would still only turn up 2200 rpm while the starboard went up to about 3100. I rechecked the pitch after the static test and they were still the same. I was guessing that something in the governor got bent or broken when it stopped abruptly but it turns up 3800 when in neutral. It's not putting out smoke of any kind when under full throttle in gear, but still only 2200 rpm. I would have expected black smoke if it was really a prop pitch issue. I'm thinking that maybe it's coincidental that I've got an injector that has failed during the down time since April, but it seems to idle smoothly. Before you ask, yes both props are clean. Does anyone have any suggestions besides cracking the injectors to see if I've lost a cylinder.





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Bill
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Old 07-07-2020, 15:17   #2
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Re: Yanmar RPM issue

Can you transpose the props fairly easily (to confirm it isn't a prop issue)?
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Old 07-07-2020, 18:33   #3
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Re: Yanmar RPM issue

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Originally Posted by Wotname View Post
Can you transpose the props fairly easily (to confirm it isn't a prop issue)?

These props are a major project to reassemble in the water. There's no practical way of swapping them easily.
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Old 07-07-2020, 19:11   #4
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Re: Yanmar RPM issue

Can't imagine how an abrupt stop would damage the governor, and that it revs up to max high idle out of gear kinda eliminates that anyway. The smooth idle seems to rule out a bad injector; so does reaching max high idle speed, though neither rules out the under-load problem completely.

Do you have struts? You might want to see how easily one shaft turns by hand, compared to the other.
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Old 07-07-2020, 20:08   #5
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Re: Yanmar RPM issue

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Originally Posted by jimbunyard View Post
Can't imagine how an abrupt stop would damage the governor, and that it revs up to max high idle out of gear kinda eliminates that anyway. The smooth idle seems to rule out a bad injector; so does reaching max high idle speed, though neither rules out the under-load problem completely.

Do you have struts? You might want to see how easily one shaft turns by hand, compared to the other.

It's a sail drive so no struts. I did spin the prop by hand while it was in neutral and it moved freely in both directions. I also didn't wobble so I don't think the shaft is bent.
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