Lack of power

[Keithleask]

Hi , I posted a thread several weeks ago about a lack of power on my twin volvo kad 42 B engines, I had quite a few responses which I have followed up but have still not got it sorted yet. A re cap on the issue, the boat gets up to 26/27 knots then the power drops off the bow settles back down and the revs drop off. Easing back on the throttles and it picks up again but flattens out again either at or just before the turbos are supposed to come in. I changed all the fuel filters. They looked pretty good, no crud etc, cannot hear or feel any leaks anywhere on the pipe work . Have checked in side the fuel tank and removed and checked the fuel pick up pipes for the eberspacher nothing bug looking or anything.Thing is on the port engine the pipe from the supercharger to the turbo is steel but the one on the starboard engine is rubber , I have noticed that when I throttle the engines from the engine bay the rubber hose contracts a lot and there is a real screech, not sure where this is coming from but I stripped the air filter box assembly ,the pipe work and took off the exhaust elbow and inlet sides of the turbo housing. The impellers spin very freely, so nothing jammed or seized. Unfortunately I did not have any feeler gauges to measure the radial gaps but having looked at other turbos that have been removed for overhaul the ends of the blades looked pretty good, no missing bits , or serious sloping gaps etc. Just wondering if this collapsing of the rubber pipe to the turbo could be the culprit? Should have tried each engine separately I suppose when I had the boat out but hindsight again! Would be grateful for any feedback, thanks,

 

[GAMPortsmouth]

Hi, can you give me a few more details - what rpm are the engines doing when this happens, and does one engine suffer more than the other (drops off first). Also, have you tried the single engine run up test (each engine independently run up at full throttle - allow vessel speed to stabilise, record speed and engine figures (temps & rpm) and then repeat with other engine and compare data). If both engines are producing similar power, the results should be similar. This test can help to identify the 'trouble' engine in a twin vessel where sometimes one engine can compensate for the other.

 

[Keithleask]

Gam, hi thanks for replying so soon!, not tried the single engine test as I said in the question, I should have tried when I was last out but never thought about it! I would need to check the revs again from memory it was around 3000, I know the superchargers should drop out at around 2800 then the turbos pick it up , but that's when it goes flat , I hope to be down at the boat this week so I could try it then and let you know, many thanks ,

 

[GAMPortsmouth]

A couple of things to check when you are out - check the air diverter valve between the supercharger and turbo is not stuck open - this would allow the turbo boost pressure to escape out the air filter and would give the symptoms you have. Also, make sure your air filters are clean to eliminate these as a possibility, you can remove them for the duration of the test if unsure (just remember to replace these afterwards). Check those and do the single engine test, once you have done these I can help you with next steps.

 

[spannerman]

The screech is most likely the main belt which has to drive the circulation pump, the alternator, (power steering pump on starboard motor), and then when the compressor cuts in it loads up even more causing the screech.
Are you certain that the main belts are adjusted corrctly as I have had it where the load as the compressor clutch engages causes the main belt to slip, which in turn meant the alternator wasn't producing enough charge and then the compressor clutch tripped out due to low voltage.

 

[Keithleask]

Gam hi, I forgot to mention I also replaced both air filters, the divertor valve / flap that is housed in the plastic air filter box assembly and that was moving quite freely , I had all of that out when removing the elbows etc,

 

[Keithleask]

Hi, I checked all the belts and slightly re tensioned them just in case , would you expect the rubber hose from the supercharger to contract a fair bit when the engine is throttled up? Just thinking the solid pipe on the stud engine is obviously an upgrade ?

 

[GAMPortsmouth]

Hi, I checked all the belts and slightly re tensioned them just in case , would you expect the rubber hose from the supercharger to contract a fair bit when the engine is throttled up? Just thinking the solid pipe on the stud engine is obviously an upgrade ?

Yes, solid pipe is an upgrade kit for the KAD42 to quieten the supercharger noise - standard from the 43 onwards. The rubber hose may contract a bit when the turbo cuts in, but for me it is important to know what rpm the engine is doing when these happen so I can understand better.

 

[spannerman]

The rubber hose goes from the compressor to the diverter valve then to the turbo, it will 'expand' when the compressor kicks in then 'relax' when the compressor cuts out. It has nothing to do with the turbo cutting in as that then breathes directly from the airfilter and the airflow through the diverter valve closes off the rubber hose to the compressor.
If it contracts when the turbo is working then that would indicate a restriction in airflow to the turbo, and that can't get air via a compressor that isn't rotating as that would completely block any airflow.

 

[KevB]

I read that you checked the pickup pipe from the eber but did you do the same for the engines? The eber pipe doesn't generally go to the bottom of the tank to stop you using all the diesel for heating and having nothing left for the engines. The reason I ask is I had the same problem as you a few years ago and at the bottom of the engine pick up pipes on my boat had wire gauze for some reason. This was partially blocked. I removed the gauze and it solved the problem

 

[Keithleask]

Spannerman, thanks for pointing that out, will take another look at the belts , tensioners again, I think there is an upgrade kit for the tensioner and pulleys now?

 

[Keithleask]

Kevin, hi thanks for the input, no , I only looked at the heater pick up, not sure how difficult it will be to get to the fuel line trappings, will check it out this week, thanks again,

 

[Portofino]

Long shot slightly left of field -= props

If they are not spinning fast enough cos .....

1-are they clean .?
2-damaged ?
3-hub splines ok ?
4- other friction inductive wear in the drives ?

 

[Keithleask]

Portofino, hi, thanks for the response, pretty sure the props are ok, had a lift out in June and all cleaned jet washed etc looked ok, I have another problem with water getting into the drive pump on the stbd leg, so it's coming out next week to get this sorted. Will get the legs, drives looked at once it's out , good fun this boating !!

 

[aquatom]

Did you get any photos of the gap between the exhaust turbine and the turbo housing?

 

[Keithleask]

Yes I did, they are a bit difficult to judge on the images but I am going to check out the clearances next time,

 

[Pendana]

Did you get any photos of the gap between the exhaust turbine and the turbo housing?

I suspect Aquatom is on to your problem. That radial clearance between the the turbine blades and the housing should be 0.42mm (about 16 thou). It was nearer 3mm on mine when I replaced both turbo's.

Good Luck

Eddie

 

[Keithleask]

Eddie, am going to check the clearances out at the weekend will let you know, I still feel it is something else though because the power dropped off so quickly. I am still looking at fuel starvation , blocked pick up pipes, diesel bugs perhaps ,

 

[jamie langstone]

I don,t know if you have tried this already but i have had a fuel pipe collapse when under load and the faster the engine goes the more fuel is required hence the suction increases and the pipe collapses.But as soon as you back off the throttle less suction and the pipe returns to normal and the engine runs like a dream.
regards
Jamie

 

[Keithleask]

Interesting point Jamie,thanks