sulzer rta engine

[armat]

this is a 9rta 76 engine. i am having problem with one of the showing low compression pressure. the peak pressure is normal.fuel valve and exhaust valve operation is ok.what can be the resons for low compression pressure

 

[itsmoked]

In order of likelihood:
head gasket leak
worn rings
leaking exhaust valve
loose spark plug
leaking spark plug(internally)
holed piston

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[armat]

this is a 9rta76 engine on a sailing ship(2 stroke engine). all piston rings have been renewed and cylinder head gasket has been renewed.still same problem of low compression pressure with one unit exists. the piston crown and cylinder head are re-conditioned ones. i was wandering, could that have some problem.

 

[IRstuff]

There are only so many places that a cylinder can leak. However, just because you "renewed" some items, it doesn't mean that they might not be the culprit. Additionally, there's still the spark plug and any valves, if it has any.

TTFN

FAQ731-376

 

[armat]

there is no spark plug. it has fuel valves and i have renewed them with new spare after testing them

 

[waross]

After looking at the following web page I decided I was out of my league.

http://people.bath.ac.uk/ccsshb/12cyl/

But, from general problem solving principles, have you checked or swapped your pressure sensors?
respectfully

 

[itsmoked]

On later looking back I realized that you were talking a large compression ignition engine. Sorry.

The pressure of course is very, very, very, closely linked with the compression ratio. If in the process of reconditioning, the top of the piston or the head had much material removed you would see a large shift in pressure. How hard would it be to "cc" the cylinder at TopDeadCenter? Compare it to a cylinder you're happy with. That would eliminate that possible issue.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[rob768]

It seems hardly possible that, if the low compression pressure is related to a leakage, you'd get normal pressure from combustion. compression 13-14 bar? combustion 150-160?
Any leakage would certainly interfere with resulting combustion pressure. As mentioned in previous post, I'd check or swap pressure gauges.

 

[HEC]

itsmoked's suggestion is the best one so far if you believe all other sources of leak have been addressed. The compression pressure (ratio) is very closely linked to the clearance volume at top dead centre.
cheers

Mark Hutton

 

[waross]

Do I read the specs correctly? Is this a cylinder big enough for 3 or 4 or 5 men to stand in and not be able to reach the top at bottom dead center?

I have seen problems with compressors, but the areas from which metal is typically removed during a rebuild generally results in a greater compression ratio and pressure, not less.
A couple of suggestions from first principles;
1> An air restriction during the intake cycle.
2> A new compression (head) gasket installed without removing the old gasket. This is easier to do by mistake than you may think.
3> Too much cooling. Possibly a baffle or diffuser was left out of the cooling circuit for this cylinder.
4> Instrumentation errors. Check your pressure transducer.
respectfully

 

[aquatica]

If i get it right you are mentioning that the peak pressure in the same cylinder is fine but somehow its compression pressure is less. Peak pressures will probably not vary much since it is a function of the amout of fuel that goes in. Which cylinder number is it? have you done any compression test after the maintenance was done? Loss of compression can have several reasons but can be found systematicaly. If you give more details I coud help!
AM

 

[BrianBT]

Spark plugs? Hmmm

The rta engine has been in production for a large number of years nad as such has been subject to continuous development. Without more information it is difficult to nail down but I would add the following to those made earlier by Waross

The engine has both VIT and VET both of which if not operating correctly will affect peak pressure. I would check for slippage of the fuel cam and lift of the fule pump. I would check the condition of the cam followers ( I have seen a number of failures), the condition of the pump espcially the anti dribble device. I would check that no bespoke fule limiters of pump lift devices have been inadvertently activated.

Apologies if this has been mentioned but some korean built rta's suffered from excessive bore cooling and porr scavenge demisters resulting in huge wear rates in the cylinder ( I know of a batch of engines running liners out in 5000 hours with piston ring packs lasting as little as 250 hours. Yes I do mean two hundred and fifty.

Operating the enginer with one unit significantly underperforming leads to extremely serious torsional vinbration and critical speed issues and you should consult the manufacture for advice on operating the engine in a degraded condition.

I like the idea of a sensor failure.

 

[Sierra701]

Whoa! I am assuming that you have a digital readout instrument to measure the peak pressure, and that you are using the same on another cylinder where you have same readout at different different running condition.
First thing I would like to investigate is the instrument: I was accustomed by an old fashioned Chief Engineer to use Digital to quick check, then the usual spring loaded paper ribbon MAIHAK recorder to have a GRAPHICAL readout of the pressure transient. It gives a lot of Hints

It is my direct real experience that on another marine engine the use of reconditioned piston rings caused a lot of problems. If someone fitted one of the compression rings upside down nobody notices until compression is too low.

What about exhaust gas temperature? maybe ten to twenty degrees below the next cylnder?

Do you have original testbench readouts, the one stamped by Classification Society?

I do agree that a misfiring condition is a definitely limited time, limited power takout situation, while I have a very limited experience with 2stroke engines.

If you have a "spillable" oil mist detector sample piping, you may check for abnormal oil mist from the obseved cranck section.

Any way, if you are the Chief, report to the Superintendent and limit the power out: you may be in a dangerous situation.

Let us be informed....