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Go Back   SailNet Community > Boat Builders Row > Pacific Seacraft > HIgh RPM in neutral
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Thread: HIgh RPM in neutral Reply to Thread
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Topic Review (Newest First)
02-14-2007 08:46 AM
RickBowman BTW guys... it was read by an optical tach check so we do know that the 4K is an accurate number. Good to know it it probably just a governor adjustment.

Cam,
Thanks for that info. It's an involved and technical proceedure to set the adjustment of the Fuel Injection Pump and Govener; way to much for this discussion, and quite possibly not even necessary as the injection pump appears to be operating without complaint. The motor appears to be operating ok, there are no reports of any other issues except high rpm's in neutral, which is what the manual calls for; verification at no load test. Why not break the wire on the Maximum speed adjustment bolt to lower the no load RPM's to 3600. Then rewire the maximum speed adjustment bolt. The wire I would asume is an antitampering concept. Another alterenative as Ed pointed out in an earlier post is to not run the engine at full throttle, which imho is as easy as it can get to solve this issue.
02-14-2007 12:44 AM
hellosailor Rick, if you follow quantum and string theory and all the wierd science that suggests there are 11 dimensions and now *confirms* there are five states of matter, including one that can radically slow down the speed of light...

Hey, it could happen.<G>

I suspect that physics as we "know" it may soon be remembered with the same laughter as "everything is made of earth, wind, water, and fire" and there is a mysterious aether permeating the universe. Well...the aether may actually be true, the stuff they are suggesting about dark matter and dark energy fits the bill closely enough.<G>
02-13-2007 08:40 PM
camaraderie BTW guys... it was read by an optical tach check so we do know that the 4K is an accurate number. Good to know it it probably just a governor adjustment.
02-13-2007 08:38 PM
RickBowman ... First off I don't really think that running your engine at wide open throttle in neutral is a very good idea..

Ed,
Thanks for posting that. You may have just saved or at least extended the lifetimes of a few engines.

I have an additional question that I will post as a new thread. Please chime in if you have an opinion.

Fair Winds,

Rick
02-13-2007 08:25 PM
Edwright105 Your right Rick, if 3400 RPM is rated then yeah that is high, I am still wondering what it will rev up to when loaded? I would be willing to bet that this problem lies with a misadjusted governor, if it's an electronic governor, I would be questioning the rpm signal going to the governor... you may have a faulty sensor there. Unfortunately one of the only ways to diagnose an electronic problem is to plug it into a computer which you will be charged for, the computer will then give the technician an error code and tell them exactly what's wrong.
02-13-2007 08:11 PM
RickBowman
HelloSailor

Quote:
Originally Posted by hellosailor
Rick, it could be that the boat was permanently deformed by sailing in the Bermuda triangle. A simple residual 10% time/space compression distortion would leave the boat, um, 30.6 feet long now, with the engine operating 10% too fast simply because the ring gear had now been permanently reduced in size by 10%.

That kinda stuff happens all the time, right? <VBG>

So, using a new tape measure that's never been on the boat before, first we measure the boat...<G>....
Is that possible deformation anything to do with the time/space/continum? Have we watched way to much star track or played space invaders to often or what?
02-13-2007 07:58 PM
RickBowman
Loaded RPM

Quote:
Originally Posted by Edwright105
Ok, I am a marine engineer so I thought I would weigh in... First off I don't really think that running your engine at wide open throttle in neutral is a very good idea.. Diesel engines do not respond very well to this kind of treatment. Diesel engines run best under loaded conditions (rated full load is optimum but not realistic that you will run at that load all the time). Likely the rpm of 3600 that you are reading about is under loaded conditions... if not you could have a slight problem with your governor, a difference of 400 rpm is however not anything you need to worry to much about. As for having bad rings, and blow by I don't think that is very likely because once a diesel starts firing on an external fuel source ie. lube oil blowing by the piston rings... which is very unlikely, the engine will usually run away and you will have a very big problem on your hands (a catastrophic failure) In any case a difference of 400 rpm's is not a huge deal, don't sweat it
take care

Ed,
I picture this engine being run at open throttle as only a test, and it was discovered that it was actually able to reach 4000 RPM by using two different tachometers. But just suppose that the tachometer sensor is faulty? Cam was right in suggesting eliminating a possible error with the tachometer setup and using an independant electronic rpm tester. The 3600 RPM is a one hour rated output at the flywheel. The continuous rated output for the 3JH2 is 3400 RPM at the flywheel. If I remember correctly on this particular diesel the adjustment for the high speed setting at the govener is wired off by the factory to proper specs. The low speed idle adjustment was left as end user adjustable. So, if 3400 RPM is the factory continuous rated output, and this engine is purported to be able to run at 4000 RPM wouldn't that make it as 17% above redline condition in continuous operation mode?
02-13-2007 06:22 PM
Edwright105 Ok, I am a marine engineer so I thought I would weigh in... First off I don't really think that running your engine at wide open throttle in neutral is a very good idea.. Diesel engines do not respond very well to this kind of treatment. Diesel engines run best under loaded conditions (rated full load is optimum but not realistic that you will run at that load all the time). Likely the rpm of 3600 that you are reading about is under loaded conditions... if not you could have a slight problem with your governor, a difference of 400 rpm is however not anything you need to worry to much about. As for having bad rings, and blow by I don't think that is very likely because once a diesel starts firing on an external fuel source ie. lube oil blowing by the piston rings... which is very unlikely, the engine will usually run away and you will have a very big problem on your hands (a catastrophic failure) In any case a difference of 400 rpm's is not a huge deal, don't sweat it
take care
02-13-2007 02:44 PM
hellosailor Rick, it could be that the boat was permanently deformed by sailing in the Bermuda triangle. A simple residual 10% time/space compression distortion would leave the boat, um, 30.6 feet long now, with the engine operating 10% too fast simply because the ring gear had now been permanently reduced in size by 10%.

That kinda stuff happens all the time, right? <VBG>

So, using a new tape measure that's never been on the boat before, first we measure the boat...<G>....
02-13-2007 11:15 AM
RickBowman
3JH2 Tachometer

Quote:
Originally Posted by gc1111
First make sure your RPM readings are correct. With diesels, unless you have a mechanical takeoff, there can be lots of errors. Most tachs operate by measuring the frequency of the AC generated in the alternator. This requires calibration by an external reference. Best option is an optical tach. These operate by putting a reflective patch on the flywheel, shining a light on it and counting the returning light pulses. I got one off EBay for about $40.

If your RPM measurements are correct, fire the mechanic. You most likely have a problem with the govenor.

The 3JH2 Yanmar tachometer uses a magentic pickup sender that converts the rotary motion into an electrical signal by counting the number of teeth (127) of the ring gear that is connected to the flywheel. PP 9-42 Yanmar Service Manual.
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