Question for the diesel engine specialists

[BartW]

some on here might remember that I had a complete overhaul done on both my MAN diesel engines,

both engines run very smooth, with little but normal smoke for these old mechanically injected 12cyl. engines,

One engine gets to normal 2300rpm max,
BUT the second engine only gets max 2170rpm.

We had the boat lift out, clean hull and props,
difference was the same,

Yesterday a team op 3 ppl spend the whole day swapping the injection pumps from the two engines.
and this morning again sea trial,
now the lower rpm is on the OTHER engine,
so its the injection pump that creates the difference for max rpm.

a year ago, both pumps have been send together to Bosch (in Koper Slovenia) for refurbishing, so actually it is their responsability.

but the MAN service Guy's are a bit in doubt if its worth finding the last
130Rpm ???
also as the pumps are really old, (its cam shaft might suffer a bit of wear)
the two engines run perfectly smooth up to that speed, and I will never ever run the boat above 2100Rpm... and its a big job to get that pump out one more time.

any advice from the specialists on here ?

 

[omega2]

Not up on bosch pumps but with our equally ancient simms pumps we were advised to "open" the regulator screw a little at a time and whilst running at wot look for black smoke from the exhaust, and close a little if it is excessive, or open if no wisps of black appear. Seeing that you have narrowed it down to one pump then you are halfway there. Or could it be the pump timing out a fraction? or the throw of the throttle lever. I would expect your "engineers" to have checked all that though. Something silly maybe a fouled prop.

 

[NormanB]

I am not familiar with your engine or fuel pumps.

Well the fuel pump calibration that should have been done at the Bosch facility is part the issue

Of course there is always a tolerance on these things +/- 'something' and I would have thought you would have received the calibration charts for both pumps. On the face of it we are talking 5% difference at top end - what is the difference at idle?

Is it possible the pumps were delivered to the test and calibration facility at different times? Or the facility was not aware these pumps were for the same installation. I would have thought that if they were aware then they could, within the permitted tolerances, provided a better outcome.

I would demand the calibration charts (which should show fuel pumped per element throughout the range) otherwise demand that it (the calibration) is redone.

The other part of the issue is the the on engine setting of the fuel racks and I would have thought there would have been some adjustment - of course you need absolute confidence in your instrumentation (tacho) to ensure you have equal idle and top end condition, but as you say the low performance follows the pump.

If it was on my dollar though I would probably leave it as it is. 5% at top end is not going to have much impact on speed through the water.

 

[Deleted User YDKXO]

I dont pretend to be a specialist Bart but isn't the key factor whether this deficit in max rpm is stable or increasing. Has the 2170rpm been exactly the same since the engine rebuild or is this figure reducing year on year? If the former, I would be tempted not to do anything but if the latter you will be forced to do something

 

[WFA]

If you assume the fuel pump phasing calibration and injector delivery is equal on both engines you should then consider engine variations such as swept volume, bumping clearances, valve timing and tappet clearances,cam and fuel pump shaft wear and timings. Despite living in a precise world of expectations, engines performance is the sum of all the minute adjustments we make to correct original design tollerances, friction, accumulated wear and tear and control adjustments. Suggest you keep working through and comparing the basics on each engine and their controls. Also check each prop shaft for restistsance to further is alignment, true or bent and glands.

 

[ROW]

I read your original engine rebuild thread with a mixture of fear and admiration. I've been asking brokers how you get the engines out on the boats we've looked at!

My view would be to get Bosch service to get it right if you aren't footing the bill. Whilst I note you won't use the last 130rpm, you don't know that is the only problem - there may be other problems that aren't obvious. Those other issues could manifest themselves later when it is your problem again, particularly if they cause consequential damage.

As an example we had an "expert" recalibrate a machine for us and it was producing accurate components when he finished. However when we changed steel strength, the components were no longer accurate. Upon examination we found the method used only resulted in an accurate calibration for a particular thickness and grade of steel. In this case there were undetected issues that caused the calibration to be useless. We ended up having to reset the machine to factory base settings and then calibrate from there. My point is that something can look right but there can be errors in getting to the answer.

In your case, you know it's not right and you don't know the under rev is the only issue, you need to know they are working properly throughout the rev range including achieving the last 130rpm. As NormanB suggests you definitely want the calibration charts and the calibration certificates for the test machine at both dates. I suspect the answer lies there.

The issue I mentioned had just cost me a mid five figure sum in lost and defective production as well as customer problems. So I may be over.cautious but I wouldn't let them off! At the moment it's someone else's minor problem, it could
soon be your major problem.

 

[Seastoke]

I read your original engine rebuild thread with a mixture of fear and admiration. I've been asking brokers how you get the engines out on the boats we've looked at!

My view would be to get Bosch service to get it right if you aren't footing the bill. Whilst I note you won't use the last 130rpm, you don't know that is the only problem - there may be other problems that aren't obvious. Those other issues could manifest themselves later when it is your problem again, particularly if they cause consequential damage.

As an example we had an "expert" recalibrate a machine for us and it was producing accurate components when he finished. However when we changed steel strength, the components were no longer accurate. Upon examination we found the method used only resulted in an accurate calibration for a particular thickness and grade of steel. In this case there were undetected issues that caused the calibration to be useless. We ended up having to reset the machine to factory base settings and then calibrate from there. My point is that something can look right but there can be errors in getting to the answer.

In your case, you know it's not right and you don't know the under rev is the only issue, you need to know they are working properly throughout the rev range including achieving the last 130rpm. As NormanB suggests you definitely want the calibration charts and the calibration certificates for the test machine at both dates. I suspect the answer lies there.

The issue I mentioned had just cost me a mid five figure sum in lost and defective production as well as customer problems. So I may be over.cautious but I wouldn't let them off! At the moment it's someone else's minor problem, it could
soon be your major problem.

well said logical

 

[NormanB]

If you assume the fuel pump phasing calibration and injector delivery is equal on both engines you should then consider engine variations such as swept volume, bumping clearances, valve timing and tappet clearances,cam and fuel pump shaft wear and timings. Despite living in a precise world of expectations, engines performance is the sum of all the minute adjustments we make to correct original design tollerances, friction, accumulated wear and tear and control adjustments. Suggest you keep working through and comparing the basics on each engine and their controls. Also check each prop shaft for restistsance to further is alignment, true or bent and glands.

But o/p reports low performance follows the pump.

 

[BartW]

we were advised to "open" the regulator screw a little at a time and whilst running at wot look for black smoke from the exhaust, and close a little if it is excessive, or open if no wisps of black appear.

that would be my approach aswell,
but The MAN guy strongly recomments against any DIY adjustments on the pump.

Or could it be the pump timing out a fraction? or the throw of the throttle lever....

we are fairly sure about the correct timing;
at the first start after that the second engine's rebuild was finished, that engine has suspiciously more smoke than the other,
they rechecked the complete alignment, and discovered a small mismatch of the timing (pump gearwheel was slightly misaligned, caused at Bosch, but re-adjusted with their assistance)
now both engines produce almost exactly the same small amount of smoke, over the total rpm range


during the swap of the 2 pumps, the timing was accurately checked,
and after priming, each engine started easy, and almost immediately...

boat bottom and props were cleaned a week before,
and we were sure that the engine pump throttle lever was at mechanical max

 

[BartW]

Is it possible the pumps were delivered to the test and calibration facility at different times? Or the facility was not aware these pumps were for the same installation. I would have thought that if they were aware then they could, within the permitted tolerances, provided a better outcome.

according the information that I have, both pumps were delivered to Bosch at the same time for simultanious calibration.
but I have no proove, nor any calibration charts about that,
I realise that this is the main issue to get sorted.

 

[BartW]

I dont pretend to be a specialist Bart but isn't the key factor whether this deficit in max rpm is stable or increasing. Has the 2170rpm been exactly the same since the engine rebuild or is this figure reducing year on year? If the former, I would be tempted not to do anything but if the latter you will be forced to do something

actually we didn't do many tests at max RPM,
due to several reasons, we were only ably / willing to do that at the end of last season,
I don't think the deficit is increasing,
and as others say, this 5% is not big, and I don't really need it,
BUT,
I've spend quite a lot of money on these rebuild's, and than you would expect this to be better.
before the rebuild I am sure that both engines hit 2300rpm (even slightly over)

wheneven I come to sell the boat, how would I explain to a future buyer;
that one engine doesn't hit 2300rpm, but apart from that the engines are like new ????

 

[BartW]

My view would be to get Bosch service to get it right if you aren't footing the bill. Whilst I note you won't use the last 130rpm, you don't know that is the only problem - there may be other problems that aren't obvious. Those other issues could manifest themselves later when it is your problem again, particularly if they cause consequential damage.

all agreed,



thank you all for your contributions and advice, much apreciated !

I'm going back to my service guy, (who has been good and helpfull so far)
and asc a lot more clarification about the Bosch intervention(s)
and insist a re-calibration or something along these lines.

cheers
Bart

 

[Deleted User YDKXO]

wheneven I come to sell the boat, how would I explain to a future buyer;
that one engine doesn't hit 2300rpm, but apart from that the engines are like new ????

Thats new? I thought you had married this boat for life, for richer or poorer, in sickness and in health?

 

[BartW]

I thought you had married this boat for life, for richer or poorer, in sickness and in health?

well that's true,
I'd probably better written: whenever my wife or kids come to sell the boat

 

[Deleted User YDKXO]

well that's true,
I'd probably better written: whenever my wife or kids come to sell the boat

Appropriately depressing thought for a Monday

 

[Bilgediver]

Is the max speed setting set too low. This sounds like a pump setting/governor problem.

 

[BartW]

!!! one more detail that might be important:

last summer during our return trip from Venice we had a oil leak from a broken O-ring,
from the oil cirquit junction, between the pump and engineblok housing.

my service guy made a apointment with a MAN service center in Trogir, (he knew them personally)
they took off the pump and repaired this leak. (all on one day with guests onboard)

only the next day on our way to our next destination we discovered that rpm of that engine did nog go above 1300 rpm anymore, we continued our holiday's at reduced speed (10kn), 1100 rpm on both engines

only 2 weeks later, after our arrival on our home berth in Tivat Montenegro,
our Man service guy discovered that the engineers in Trogir forgot to reconnect the turbo air pressure feedback hose to the injection pump !
(this connection is hidden under the intercooler)

the phenomen was exactly the same as it is now,
engine sound and smoke was / is normal
but :
then max rpm was reduced at 1200 rpm (because engine pump didn't have the turbo presure feedback)
now with turbo air pressure feedback max rpm is 2150

couldn't the fact that we ran a long time without that turbo pressure hose connected, (>150Miles, >15hours)
created a misalignment in that turbo air pressure feedback loop ?

 

[MapisM]

Interesting, B. Just a couple of Q to better understand (and the reason for asking is self-explanatory, I think):
1) was the inconvenience in the return trip from VE in the same engine that now is not reaching max rpm?
2) is the pressure sensor one of the parts that were swapped together with the pump, when your man did the test and the rpm reduction "followed" the pump, so to speak?

 

[NormanB]

That's interesting stuff. The turbo air tapping to the fuel pump is probably just a rate limiter on acceleration, to prevent overfuelling (black smoke).

More relevant I think is since all of that your team have transposed the fuel pumps and the low performance followed the pump.

 

[BartW]

Interesting, B. Just a couple of Q to better understand (and the reason for asking is self-explanatory, I think):
1) was the inconvenience in the return trip from VE in the same engine that now is not reaching max rpm?
2) is the pressure sensor one of the parts that were swapped together with the pump, when your man did the test and the rpm reduction "followed" the pump, so to speak?

Starboard engine had that inconvenience / the oil leak,
that engine had the repair in Trogir
that engine didn't get above 1300rpm after the repair because that hose was not connected
the hose was put in back to place after +150nm navigation, and then that engine got at max 2150rpm

boat had a lift out for cleaning, and SB engine still limited at 2150rpm max
Port engine was all the time performing correctly, could reach 2300rpm max.

last week, injection pumps were swapped,
and now its the Port engine that is limited at 2150rpm max.
(problem follows the pump)

there is no air pressure sensor component,
It is a only a 15mm Odiameter rubber hose, going from a connection point on the air supply tube (right behind the intercooler)
straight in to the injection pump.
(the turbo output air pressure is broaght straight in to the injection pump via that hose)