Twin diesels - unequal power

[Carioca]

I "DIY marinised" a pair of MWM 4- cylinder lorry turbo diesels rated at 145 HP @ 2600 rpm. The injection pumps were re-calibrated to generate 170 HP @ 2600 rpm to avail of the added benefit of the after-coolers (sea-water cooled).

The problem: Starboard engine is fine but port is definitely underpowered over the whole rpm range, say by some 15 - 20 %.

I have made the following observations:

1. Port engine temp. gauge goes up quicker than starboard´s ; identical cooling systems, raw water pumps, raw water flow etc. and both heat exchangers were recently refurbished and cleaned.

2. Port engine turbo boost is some 10 - 15 % LOWER than starboards - at 2300 rpm, for example, port turbo makes 0,6 - 0,65 bar versus o,75- 0,8 bar on starboard; both turbos went through a complete overhaul recently.

3. Port engine sounds rough and nosier, while starboard is smooth.

4. The props were recently examined and nothing odd was found.

Extrapolating to my (limited) experience with petrol engines in cars, could it be that the injection timing on the port engine is retarded ?

Would welcome help on this subject.


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[tr7v8]

Someone on the forum had a similar problem last year turned out to be head gasket weeping between cylinders. This would bear out the rougher and noisier.
It could be pump timing but I'd find someone with a compression tester first.
Anything which reduces the overall efficiency will lower the boast pressure.
Are they raw water cooled or fresh water, if the later do they use fresh water/coolant?

Jim
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[Carioca]

Thanks for your help.
The engines are fresh water cooled (50/50 glycol/water mix), using sea-water-cooled heat exchangers.
The head gaskets - individual cylinder heads on these MWM´s - on the starboard
engine were replaced recently as coolant was being spewed out of the overflow pipe at 2000 + rpm. Since then, starboard engine is OK.
Port engine spews out a litre or two after topping up and getting underway, but after that coolant level keeps within normal limits.
Could it be a head gasket or two or three or all four ? !
Wish it were a simple timing problem !

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[byron]

<font color=blue>Not wishing to detract from what tr7v8 has said because I know he knows his onions. I see you had the props checked but did you check that they are equal in pitch etc. ?

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[david_steward]

The overheating and lower turbo boost could be a symptom of restricted airflow.

Check the air flow through the Port engine. Is the exhaust arrangement causing excess back pressure? Is the exhaust much different from the starboard side?

What about the air filter, is it plugged?

Is that engine smoking more than the other? If so this would suggest overfueling, either from restricted airflow ofr an injection problem.

Good Luck

<hr width=100% size=1>We don't want a sports cruiser, totally impractical. Err ok then.

Dave S

 

[omega2]

Are your fuel tanks independant? if yes take a look in your water separators our twin set up was like yours till we found that one was running on dirty water. Also if both engines are identical I presume the exhaust pipe runs are different ie one must have an extra bend in it this also could upset the power output. If you can pull Max revs on load on both then run at 200 below that see if that helps. Hope I am not trying to teach you to suck eggs. On our 180's we even out by the boost gauges not the rev counters, and generally all is sweet at about 7lbs, our boost pressure is not as high as yours granted but 50 percent of max is good for us. I was writing my tome whilst others were exploring and posting, having heard that you are pressurising the system I would suspect head gasket/s, leave the cap off the header tank and watch for bubbles going round, or borrow a presseure tester and see if the sytstem is holding. I wish you good fortune.

<hr width=100% size=1>J HAMER<P ID="edit"><FONT SIZE=-1>Edited by omega2 on 03/03/2003 16:06 (server time).</FONT></P>

 

[Carioca]

Blade angle of port prop just by the hub was - so claimed the prop shop - "letting in too much water" but that was sorted out and both props are now matched.
Even when just idling, port engine attains operating temp. much quicker than starboard.

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[Carioca]

The underpowered port engine has been in existence since commissioning the boat in 1999, after replacing all the original systems.
Trial runs with the engines uncovered gave the same results. Air filters are metal-screen (mesh) types. These were immersed in solvent, sloshed around and re-installed.
Starboard exhaust-hose run is S-shaped.
Port exhausts straight out to transom, excepting for short section which bottoms-out a little.
Starboard exhaust sounds "throatier" - port is (considerably) less noisier

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[tr7v8]

Umm, see what others have posted but it wouldn't generally cause rough/noisy running. Using coolant normally is a head gasket leak, try running with the header tank cap off and see if you get a stream of bubbles. Another thought is intercooler leaking but I'd assume that when they were cleaned they were pressure checked as well. Other possibility could be an exhaust leak as this would cause noisy/rough running or a faulty injector that could create knock.
As someone said are the exhaust roughly equal in appearance uch as excessive steam or smoke?

Jim
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[yoda]

Could you clarify a few things please. You say the engine is under powered across the rev range but since power is a function of output revs and prop size and pitch I assume you are applying more throttle to achive a given RPM on the port engine than on the Stbd? Do the turbo chargers have any control mechanism on them? If so are both operating in the same way. Loss of boost will cause lack of power and therefor you will input more fuel to achieve the same output RPM. Exhaust restrictions could cause a similar problem, is one old and blocking up or are they the same age? Check the air filters for cleanliness, Exhaust fumes going back into the air filter can quickly reduce power. Will try and help more once you can clarify these things.

Yoda

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[Carioca]

Are bubbles in the coolant header tank conclusive (or strong ?) evidence for a possibly blown head gasket ?
I always thought the purpose of the overflow oulet in the pressure cap was to vent bubbles (vapour) to the atmosphere, given that HOT spots within the circuit could generate vapour even with a 50/50 glycol/water mix and - pukka (perfect) head gaskets.
My exhaust manifolds are in the coolant circuit - more heat to soak up.
Port exhaust puts out "whitish" smoke, but not always, as for instance yesterday when all went fine, excepting for the lack of power. It could be due to steam - I am unable to check if it is unburnt diesel.
Hope am not being stubborn, especially that Byron warned earlier on that "you know your onions", but I want to know the facts before resorting to surgery.


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[Carioca]

1. The throttle lever on port is (and was) generally further forward than Stbd to make for equal revs on load. I have not checked this at idling, but could do so. What is obvious, is the power differential as perceived between the wake from port and Stbd.
2. Both turbo chargers are waste-gated that SHOULD cut-in at 1,3 bar. APPARENTLY, both operate in the same way, but have not checked, neither know how to.
3. Both exhaust systems are NEW, no restrictions or other impedimentos to the flow.
4. Test runs with the engines totally uncovered, 100% ventilation, but noted no difference.

Hope you have the patience to keep up with me !



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[mtb]

I just looked to see your a long way away. Shame cos I have the correct diesel compression testing kit. My money is on a leak re head gasket or cracked head.
Get the engine compression checked then a coolant system pressure test .
If you are getting air in the system ( bubbles to you ) but steam to me the engine is both pressurising the water side of things then at some point, re heat, causing steam .
If you cant get the right kit to check , a basic yet easy thing to do is to crack each injector to see if it makes the engine rev's worse or no change.
Re the timing do a spill port test but I dont think it's retartded timing !!
cheers
Mick

<hr width=100% size=1>smile you'l be on your boat soon ;-)
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[yoda]

Ah good more info! Smoke is a good indicator of things going on. Black smoke is unburnt fuel, blue smoke is burning oil, white is normally steam. Given the work you have had done I would follow MTB's line of thought and try checking each cylinder in turn. May even be worth the investment in a compression tester given the cost of major surgery. Do make sure that your control levers are set up to apply equal movement on the fuel pumps for the same movement. I know how difficult they can be to set up having spent most of yesterday inside the stern locker getting mine right (and I only have one). Final thought is to check the thermostats are both operating in the same manner and that both pairs of water pumps are working in equal measure. Lack of power and the more rapid rise to operating temprature could be 2 different problems. Check thermostat operating temp by placing in a pan of water and observe temp at which they open.

Food for thought

Yoda



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[saturn]

yes i agree with you,also imo faulty injector would cause a lot more smoke and rougher running.

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[richardandtracy]

I have limited experience of running a diesel car with the wrong timing. The cam belt was one tooth off. Did no damage, the power was down by quite a bit at higher revs, but the torque at low revs was phenomenal - fantastic for towing at speeds up to 5mph.

This may not be appropriate if you've checked the timing, but may be worth remembering for the future.

Regards

Richard


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[tr7v8]

Ah slightly different, yes retarding the cam timing will increase the low end power, but timing in this context was the injection pump timing. If this is out it gives effects similar to a petrol engine ignition timing, eg knocking and poor power.

Jim
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[Carioca]

Today´s test run aided by GPS.

1. Outbound leg, both engines at 2200rpm, speed 14,5 - 15 mph ; engine temps. port = 83°C, Stbd = 79-80°C; turbo boost differed by 0,15 bar.

2. Return leg, both at 2200rpm, port temp started rising non-stop and engine shut down at 95°C, Stbd steady at 80°C; turbo boost differed by 0,3 bar; limped back with Stbd steady at 90°C / 2200rpm, speed 10,5 mph.

Thanks for the timing tip-off Richard.
TR7V8 no knocking on the port engine but miserable power for 400+ kg mass.
Additional test tomorrow will decide how much to open up.

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[david_bagshaw]

Looking from another perspective


perhaps the load imposed on the port engine is less, are the prop pitches correct in relation to the gearbox ratio?


Boost pressure is directly related to the power output of the engine at that moment.

try

1 running port engine at whatever revs to achieve the same boost pressure, does it run smoothly then?

2 swapping the boost sensors round , then the gagues, to check one does not incorrectly read.

3 finding out the gear box ratios & prop pitches, to see they are matched correctly, as often there is a ratio difference between the handings.

Run each engine on its own, under power with the other ticking over just in gear, gives a good idea about engine total available power output. (indisplacement craft)

the whole idea of boost pressure indication is to run an installation on equal power outputs, not equal rpm.

hope that helps



<hr width=100% size=1>David
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[Carioca]

Unable this morning to put the port engine on load and let Stbd tick-over in gear. As both sustained load at 2200rpm, masses of hot coolant spewed out of the port header-tank overflow, etc. obliging me to shut it down.
Stbd engine did this until two weeks ago when the head gaskets were replaced.
Port engine to have new head gaskets by end of week, which will solve PART of the overall problem. Skeptical if this refurbishment alone will see port power on a par with Stbd .
For your information, gear box ratios, prop diameters and pitches etc. identical on port and Stbd.
After replacing head gaskets on port and doing a test run or two, would be interesting to swap injection pumps betwen port and Stbd to see if the power imbalance shifts accordingly.
The idea of running engines on the basis of equal turbo boost was ventilated by another "pbo regular" in a previous post concerning this subject - sounds to me as "if you can´t beat ´em, join ´em", unless I have made a terrible gaffe on this one.

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