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Old 19-02-2006, 11:55   #1
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Operating RPMs

I am guilty as can be of running a diesel at too low of rpms and this boat is no exception. The engine is a 1985 Universal 5424 (24 hp model) with a two bladed fixed prop. I had a three bladed Sailprop feathering prop but removed it last year when I replaced the cutlass bearing. The reason I removed the feathering prop was that it appeared to need a rebuild and it is a German product with apparently no US reps. The manual calls for 80% of the maximum engine speed for average cruising. Max engine speed is 2800 rpm; if my math is correct I should be running the engine at around 2240. I have been running it at around 2100. Think that extra 140 rpms will help this old engine or just wear it out sooner?

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Roger
SV Tin Cup
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Old 19-02-2006, 12:21   #2
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I doubt that the engine has been ‘desanguinated’ by the previous slight (operation @ 75% vs recommended 80-% full-load) under-loading, but the higher RPM will certainly stop any further bleeding.
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Old 19-02-2006, 12:31   #3
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Revs

You should be able to reach maximum revs at WOT with the prop that you use. You do not have to run at those revs, just be able to reach them in forward gear. When I sold moemcycles I just told the guys to shift when there fillings or glasses started to vibrate. Which prop ran smoother ?
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Old 19-02-2006, 14:16   #4
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When you're proped corectly you should be able to reach hull speed at or just before 2800rpm. Cruise speed should be between 2000 and 2500 that's 70 to 90 % ish. This all assumes your tach is correct.
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Old 20-02-2006, 05:47   #5
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Thanks Guys. Actually the 2-bladed fixed prop is a bigger wheel than the 3-bladed feathering and more efficient going forward (not astern). It is easy to reach hull speed and maintain a cruising rpm in the ranges that you described. I was only concerned about operating at a higher rpm (considering the age of the engine) when it really is not necessary to achieve and maintain hull speed. We hope to be on the move again by the end of next month and have a few engine maintenance chores to accomplish once the weather gets a little nicer. Thanks again...
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Old 20-02-2006, 05:53   #6
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Great point on the tach accuracy Pat. I know that the tach/hour meter was replaced on this boat several years ago (before I bought the boat) and I never thought to check the accuracy of the meter. How would you go about this Pat? Would I need to buy a timing light? This thread reminds me that I still have a handheld laser temperature gun on my list of "wants". Roger
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Old 20-02-2006, 06:59   #7
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Rippy,
I use a phototach available at Grainger for about $300.00 you addd a small piece of reflective tape to the front crank pully rim and count the times it goes by.
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Old 20-02-2006, 11:51   #8
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re: photo tach

the only way to get a true reading.
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Old 20-02-2006, 11:52   #9
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I highly recommend you get the RPM checked. It could be waay out and give you all sorts of erroneouse thoughts.
Just to strengthen Pats advice. The engine HAS to be able to reachmax RPM or darn near close to it. Nothing to do with what you will normally run the engine at under normal crusie conditions. It has everything to do with your engine lasting. Over loading an engine at low RPM is death to piston tops and main engine bearings. You will "run" a bearing waaaay before it's time. The high load at low RPM means excessive loads and thus "shock" thumping down the conrod onto those wrist pins or gudgeon pins and the main's every stroke and causing them to wear out early. Excessive loads at low RPM will cause the Piston tops to over heat and it is possible to melt a hole right through them. Then there is the incorrectly burning fuel producing smoke that will eventually carbon up exhasts and other parts of the engine.
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Old 21-02-2006, 05:26   #10
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Thanks again guys. I guess that I will need to take the boat out on a flat day and open her up. If I understand you, if the boat has the correct propellor, I should be able to reach near 2800 rpms and hull speed. I will need to find a way to check the tachometer accuracy short of buying a $300 piece of gear. Wouldn't the old fashion timing lights do the same thing? I see there is a piece of reflective tape on the main engine pulley.... Also have the problem of measuring hull speed since the knotmeter impellor is on the fritz and GPS might give me enough data to interpolate the true speed.

Another related question: I have not set the valve clearance since I bought the boat several years ago. The engine is not excessively noisy, starts well, runs well, etc. Any rull of thumb on checking valve clearances. Probably should order a valve cover gasket and get to it before we take off again.

Thanks,
Roger
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Old 21-02-2006, 05:40   #11
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Seems to be a bit of confusion happening here. The manufacturer will specify a no load speed for your engine. This is the speed it is governed to in neutral with the throttle fully advanced. If it does not achieve this then it needs to be repaired. Next is establishing the revs it achieves at maximum throttle with a clean hull, normal weight and calm sea conditions. This also is set by the manufacturer and if it can't be achieved then there is a problem with engine, drivetrain or propellor. Once this has been repaired only then can you establish if it propelling the boat at hull speed. Visitor, got to go.
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Old 21-02-2006, 07:02   #12
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Sorry for the abrupt departure, it's the time of year for farewells here.
Valve clearances. Yes, check them. Simple job and will help to prevent burnt valves amongst other things. Valve clatter indicates they are too loose or unevenly adjusted. Quiet valves can indicate the clearance is correct OR they can be too tight. Manufacturer's guidelines should be used as engine temperature is the critical variable. Valve clearance is used to account for thermal expansion as well as a final setting for valve timing.
Timing lights for diesels are not readily available in NZ, the best method of checking tacho calibration is the tool Never Monday suggested. You may possibly be able to borrow or rent one.
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Old 21-02-2006, 12:54   #13
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Rippy,
Where in the world are you located?
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Old 22-02-2006, 05:29   #14
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Pat We are currently in North Carolina near New Bern. Should be leaving here in late March or early April for the Brunswick, GA area.
Roger
SV Tin Cup

PS Guess I will check those valve clearances. No reason for putting it off. Last time I did it was on a small Yanmar and it was easy. This Universal seems a little more intimidating since it has a viewing window on the flywheel case for locating top dead center marks and then you have to set the decompression lever adjustments for each cylinder after setting the valves. But at least the manufacturer calls for setting the valves cold. Small engine room/access makes everything something of a challenge!
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Old 22-02-2006, 05:59   #15
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Roger,
Get with Stanley at Beta Marine in Arapahoe. I think he has a photo tach you can borrow. If not I can work something out with you to ship mine up there with a deposit.
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