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-   -   Universal M25 losing power (http://www.sailnet.com/forums/diesel/92290-universal-m25-losing-power.html)

eherlihy 09-20-2012 02:45 PM

Universal M25 losing power
 
I posted earlier this season about the low in oil pressure, and a subtle loss in power on my Universal M25. Briefly; after running for an hour or so, the oil pressure would drop to < 10 PSI on the dash mounted gauge. I also noticed that at WOT that she would rev to 2600 RPM, and not 3K. I believed that I addressed the problem with a quick oil & filter change, as well as changing both the primary and secondary fuel filters.

Since then, I have added 10 gallons of fresh fuel, yet noticed that I am still not achieving the full 3K RPM at WOT.

I was on the boat last night, and had the chance to take a close look while she was secured in the slip. After warming up the engine in reverse, I pressed the throttle to the stop, while still in reverse. I was shocked to see that she would now only reach 2100 RPM at WOT.:eek:. I don't normally motor at more than 2K RPM, but this is not good. When she starts (cold) I usually get a puff of white smoke, then it runs clean. There is a little soot on the transom, under the exhaust port, but not much.

I think that I may have to break out the wrenches, and start fixing stuff. The question is, where to begin. One theory is that it could be the mixing elbow blockage. Another is that it may be the injectors are getting fouled.

Under the assumption that it is the injector, I found this;

<iframe width="480" height="360" src="http://www.youtube.com/embed/EbjDH7fr_J8?rel=0" frameborder="0" allowfullscreen></iframe>

and this:
<iframe width="640" height="360" src="http://www.youtube.com/embed/hP-0mpkoom8?rel=0" frameborder="0" allowfullscreen></iframe>

And lastly, this which is my exact engine (Kubota D850);
<iframe width="480" height="360" src="http://www.youtube.com/embed/XJn2kDnWQPU?rel=0" frameborder="0" allowfullscreen></iframe>

Any other comments, or theories?

Thank you in advance.

Faster 09-20-2012 03:01 PM

Re: Universal M25 losing power
 
Have you ever been able to rev to 3K?

Different max revs in fwd/rev could be tied to the gear ratio differences, together with perhaps an overpitched or oversized prop (assuming you've never reached 3K).. also (maybe more relevant) max revs when trying to tow a secured dock away would be different than underway, I'd think....

eherlihy 09-20-2012 03:23 PM

Re: Universal M25 losing power
 
It will hit 3K in neutral.

Over the summer I know that it hit 2600 while underway.

MarkSF 09-20-2012 03:25 PM

Re: Universal M25 losing power
 
I have the Universal 5424, which has a max RPM of 2800 but on my boat only reaches 2400. This is due to the large pitch 3 bladed propeller.

There is a misconception that you have the correct propeller if the engine just about reaches max rpm. This is based on a misunderstanding of how an engine works. Peak power is not necessarily developed at max rpm. This varies from engine to engine, as the plot of torque vs. rpm varies and power is a product of torque and rpm.

Optimum performance will be reached when the propellor is selected such that the engine just reaches it's maximum POWER, not rpm. I've seen numerous posts on fora where people say that if you can't reach max rpm, you are overpropped or the engine is faulty. Not necessarily.

Should you be selecting the prop based on performance of the boat through the water, or on reaching the rpm spec? There was a recent post where someone followed the forum advice concerning the boat being overpropped, put a lower pitch one on, and now achieves max. rpm - at the cost of 1 knot maximum speed and increased fuel consumption due to cruising at higher rpm.

Stop obsessing over getting it to 3000rpm and instead concern yourself with the boat's performance. If you're getting to hull speed at reasonable rpm with good fuel consumption, all is good.

PS, when my max rpm starts dropping I know it's time to get the boat dived. A dirty prop makes a BIG difference.

PPS, You'll get less rpm when the boat is stationary that when it's moving.

PPPS, sounds like the one thing we're sure of is that your dock cleats, docking lines, and boat cleats are all in good shape.

PPPPS (gosh), diesel tachometers are only as accurate as they were adjusted to be. Don't take any rpm reading as gospel without confirming it with a strobe.

eherlihy 09-20-2012 04:03 PM

Re: Universal M25 losing power
 
Part of the problem that MarkSF points out is this statement from the owners manual;
http://i188.photobucket.com/albums/z...psabc687f0.jpg

Also, I did confirm the accuracy of the tach when I installed the new alternator last year.

Faster 09-20-2012 04:27 PM

Re: Universal M25 losing power
 
.. so now the question is.. are you achieving a decent/appropriate boat speed at a comfortable RPM? (which need not be max RPM). If so methinks you may be worrying too much..

We motor at a relatively quiet smooth 6.4/6.5 knots, but at an RPM several hundred below max. Pushing it gives us over 7.0, but at a higher consumption and greater discomfort/noise.

Maine Sail 09-20-2012 04:32 PM

Re: Universal M25 losing power
 
Quote:

Originally Posted by MarkSF (Post 924484)
I have the Universal 5424, which has a max RPM of 2800 but on my boat only reaches 2400. This is due to the large pitch 3 bladed propeller.

There is a misconception that you have the correct propeller if the engine just about reaches max rpm. This is based on a misunderstanding of how an engine works. Peak power is not necessarily developed at max rpm. This varies from engine to engine, as the plot of torque vs. rpm varies and power is a product of torque and rpm.

Optimum performance will be reached when the propellor is selected such that the engine just reaches it's maximum POWER, not rpm. I've seen numerous posts on fora where people say that if you can't reach max rpm, you are overpropped or the engine is faulty. Not necessarily.


For Universal and Westerbeke engines, as well as Beta the manufacturers want to see max rated RPM or as close to it as you can get. we don't make this stuff up the MANUFACTURERS DO.... This is not where you need to run the engine all the time but where it needs to be able to get to so that the HP curve is appropriate across the curve.


This is a direct quote from the Universal M-25 XPB spec sheet. The engine is 3000 RPM rated..


"Universal recommends a propeller that will allow the engine to turn 3000 RPM underway at full throttle."

Quote:

Originally Posted by MarkSF (Post 924484)
Should you be selecting the prop based on performance of the boat through the water, or on reaching the rpm spec? There was a recent post where someone followed the forum advice concerning the boat being overpropped, put a lower pitch one on, and now achieves max. rpm - at the cost of 1 knot maximum speed and increased fuel consumption due to cruising at higher rpm.

Stop obsessing over getting it to 3000rpm and instead concern yourself with the boat's performance. If you're getting to hull speed at reasonable rpm with good fuel consumption, all is good.

Really? Is it all is good? Many of these manufacturers, Universal/Westerbeke included will void a warranty if the engine can't attain the specs they say needs to be hit. Joe Joyce of Westerbeke called it "lugging" the engine with a prop too big or over pitched so the engien can't attain its max rated RPM. The farthest off Westerbeke likes to see a prop is 100 RPM but they prefer closer to max if possible.

Quote:

Originally Posted by MarkSF (Post 924484)
PS, when my max rpm starts dropping I know it's time to get the boat dived. A dirty prop makes a BIG difference.

Exactly all this is predicated on a clean bottom and prop. Even a small amount of slime can hinder performance.

Quote:

Originally Posted by MarkSF (Post 924484)
PPS, You'll get less rpm when the boat is stationary that when it's moving.

Again very true. You can't test for max RPM attainment with the boat tied to the dock. Also many gear boxes have different ratios for forward and reverse.

Quote:

Originally Posted by MarkSF (Post 924484)

PPPPS (gosh), diesel tachometers are only as accurate as they were adjusted to be. Don't take any rpm reading as gospel without confirming it with a strobe.

AMEN! This was a recent deviation card I left for a customer after measuring it with a digital photo tach: Engine manufacturers often show up to warranty "issue" claims with a digital tach and they do test for max RPM.

Tach Actual
1000 - 1025
1500 - 1400
2000 - 1900
2200 - 2100
2400 - 2275
2500 - 2375
2600 - 2450
2700 - 2525
3200 - 3050
3600 - 3350


Even with our engine looooong out of warranty Joe Joyce of Westerbeke flat out told me I was damaging my engine by running it 275-300 RPM off max rated with the prop we had. In the short time we ran the boat that way the soot on the transom was considerably more than with the right prop. I hauled the boat, sent the prop back and had it re-pitched. It now sings within 25-50 RPM of max rated just as it had for the previous 2700 hours..


PLEASE consult your engine manufacturer on this issue if you have doubts. They have these guidelines for a reason.

eherlihy 09-20-2012 06:18 PM

Re: Universal M25 losing power
 
I knew I had this ferreted away somewhere...

Here are the power curves for the Universal M25XP

http://i188.photobucket.com/albums/z...ps86567829.jpg

To MS' point, you can see that HP increases - almost linearly - with increased RPM.

Good point about scrubbing the prop. I will do that next chance that I get.

What concerns me is that the max RPM at WOT have dropped far more than I had expected over the summer.

MarkSF 09-20-2012 07:15 PM

Re: Universal M25 losing power
 
"Even with our engine looooong out of warranty Joe Joyce of Westerbeke flat out told me I was damaging my engine by running it 275-300 RPM off max rated with the prop we had. In the short time we ran the boat that way the soot on the transom was considerably more than with the right prop. I hauled the boat, sent the prop back and had it re-pitched. It now sings within 25-50 RPM of max rated just as it had for the previous 2700 hours.. "

The suggestion that you're going to damage an engine by loading it such that it will only reach 90% of max rpm does not stand up to scrutiny. This is a tractor engine!. I hope no-one will be connecting any kind of heavy load to their tractors.... last time I checked the manual for my diesel car, it did not forbid driving up gentle gradients.... or putting some luggage and passengers in the car.... or driving into a headwind...or just driving on the freeway in 6th gear.

If the Universal in my Bristol (3 bladed prop, only reaches 2400rpm) is being damaged, it's taking a while for that damage to make itself obvious... it's 28 years old, the hourmeter broke at 3700 hours years ago, and it shows no signs of wear.

Mechanical wear rises rapidly with rpm so the lower your cruising rpms, the better (with reason, of course).

eherlihy 09-20-2012 07:40 PM

Re: Universal M25 losing power
 
And I am still wondering if anyone agrees / disagrees that I may have an issue with my injectors, or restriction in the exhaust....


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