I had that same question many years ago from then, our senior DD guy.
He was not sure but did mention, a wood plant he worked at when he was young, the engine was brought down to a near dying idle when engaging/dis-engaging a manual gear to drive the PTOs and blades.
Didn't mean hunting for idle.
You ever hear the engine want to rev up a little just for a half second, then return to good normal idle, when you return to neutral?
This is what I was trying to refer to.
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Re: Idle rpm for 50 MY with 8V71n's seems high.
Last edited by Captain Ralph; 12-04-2021 at 10:50 AM.
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12-04-2021 12:55 PM #13
Re: Idle rpm for 50 MY with 8V71n's seems high.
Idle is supposed to be 550 I thought. My boat with the OEM wheels can also be a handful with the amount of thrust produced at idle. I have had to explain more than once that I can't go any slower. It does 5+ knots at idle. There are a bunch of anchored sailboats that are liveaboards on your way out of the ortega river, and they all seem to be self-appointed traffic cops who complain up a storm about a 1' wake that didn't hurt anything.
My engines when the governors are set properly have maybe a 10-15 rpm difference in gear vs. out of gear, if even that much. If you're getting a 50 or 100rpm drop going into gear then your governors need adjusting, that's not normal.
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12-04-2021 02:43 PM #15Registered Member
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Re: Idle rpm for 50 MY with 8V71n's seems high.
Mine definitely idles just shy of 700 with a very slight change if any when in gear. Luckily my boat came with a DD service manual the size of an old telephone book. I think I have one maybe two more boat rides until I winterize. I'm gonna record the drive pressure at all rpm ranges next time I'm out.
Also Giving it a rev doesn't change anything. I'll peak at the linkage. everything is so butterly smooth on mine I didn't think of that.
I love everything analog but any recommend a digital display system they like? I'd like a small screen on the port side of the helm giving me digital read outs.
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12-04-2021 02:55 PM #16Registered Member
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Re: Idle rpm for 50 MY with 8V71n's seems high.
I'm from the Lake of the Ozarks and we have our fair share of wake whiners here. I agree some of the Sea Rays need to get up on plane or slow down, don't just plow. It's the people that buy a house two lots off some of the busiest spots on the main channel, then freak the f out when you come in making a ripple.
On my Carver 440 Aft I watched guy fishing in the first slip off the sea wall in a condo dock. He see's me coming, intentionally reeled in his pole, walked all the way out to the end of the dock, and dropped his line in the water as I idle by so he could throw his hands up like what the hell. My reply "If you don't like boats, go to the (insert frustration word ending in ing) library."
That's my rant on that topic. lol
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Re: Idle rpm for 50 MY with 8V71n's seems high.
I think you may like the Aetna tachs.
https://www.aetnaengineering.com/aet...ring-products/
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12-05-2021 10:11 AM #18Registered Member
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- Jan 2019
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Re: Idle rpm for 50 MY with 8V71n's seems high.
detroit diesel has a 550 minimum speed engauged spec on that engine. first confirm the tach is reading correctly at idle and go from there. 600-625 should be good if the props are sized correctly. the engine should turn 2350 at wide open throttle. if the engine is running correctly and not turning up then the prop size either pitch or diameted is oversized and should be adjusted. idling too low can cause a stall to occur and in some cases the engine can kick backwards and restart and get full of seawater from breething in from the exhaust and exhausting out the air silencers. seen that happen many a time.
pat
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12-05-2021 07:13 PM #19
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12-07-2021 01:26 PM #20Senior Member
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Re: Idle rpm for 50 MY with 8V71n's seems high.
Mine idled high when I purchased it, and then I learned the previous "mechanic" did not properly set the idle machinery (it is a little complicated).
You should have a good DD mech fix it.
In my case, the high idle would drift downwards as I drove the boat, eventually going below 475 RPM and thus dying when I was maneuvering, which is hair-raising.
I would make sure the high idle is not to cover up another issue like broken buffer spring or other. preventing hunting and rolling, etc.
FYI.
DAN