Volvo AD41 p-a help not getting over 3600rpm

[ianmacaulay]

Morning

For a while now my Ad41's have not been able to get over 3600rpm. both engines stat at very similar rpm but won't achieve any higher. They pull very well up to this

I have bought this up before on here but thought I start fresh now I have filtered out a few possible causes. The boat is equipped with A7 props rather than the A8 duos that it should of had from factory. I did have diesel bug but have also killed it of and filtered my tank with a 10 micron filter. Both engines pull well but one may pull slightly better but both achieve 3550-3600rpm. On A7 props she was in the past reaching 4100rpm what would be correct as it should have A8's.

Now this season I've put around 200-300l of fuel in her but she had 600 in for around a year. Would a fuel degrading cause my lack of rpm or is there anything I'm missing?


Thanks

Ian

 

[volvopaul]

Morning

For a while now my Ad41's have not been able to get over 3600rpm. both engines stat at very similar rpm but won't achieve any higher. They pull very well up to this

I have bought this up before on here but thought I start fresh now I have filtered out a few possible causes. The boat is equipped with A7 props rather than the A8 duos that it should of had from factory. I did have diesel bug but have also killed it of and filtered my tank with a 10 micron filter. Both engines pull well but one may pull slightly better but both achieve 3550-3600rpm. On A7 props she was in the past reaching 4100rpm what would be correct as it should have A8's.

Now this season I've put around 200-300l of fuel in her but she had 600 in for around a year. Would a fuel degrading cause my lack of rpm or is there anything I'm missing?


Thanks

Ian

You been making 4100 under load? I hope not , max under load is 3900 , anymore you risk damage if you leave the taps open. You should get 4250 a high idle in neutral, if it's less the Governor needs adjusting , check your getting full movement on the pump throttle arm to the stop.

 

[ianmacaulay]

Thanks Paul

Yes after a prop change by previous owner he incorrectly matched props and put A7 props on so revs were high. But time I put her back in to use I could only get 3550 rpm on the A7's. I know I need to be around 3900 and this should be achieved on bigger A8 props

I have looked at the movement on the throttles and when fully open they touch the limit screws with the wire seals on. I have even backed these off a turn to see if a difference is made.

thanks

Ian

 

[ianmacaulay]

Evening,

Any more ideas with this as I'm stuck.

If a turbo was to fail would there be a massive difference in engine rpm to show this?


Ian

 

[Momac]

If you change from A7 to A8 props you will probably pull lower revs , not higher.

 

[Ian MacAulay]

I agree ... But out the factory and the old removed props were a8's and runs at 3900rpm. Currently on the a7 I'm only getting 3500-3600 so there's a issue

So for me there's no point putting a set of a'8 props back on untill I get Revs back up

Ian

 

[gery w]

I had the same problem with my 41's checked all I could filters etc no change.
I made up a boost gauge to check charge pressure and found both turbos to be worn and not producing enough boost pressure.
You could also remove both exhaust elbows and have a look the clearance between the rotor blades and the exhaust housing.
Regards Gerry

 

[Ian MacAulay]

Thanks Gerry

It looks like its had one new turbo in the past on port side .

Ian

 

[gery w]

Mine looked OK aswell no play in shaft etc but it's the boost pressure that counts.
Have you stripped and checked the aftercoolers as the matrix can become blocked with oily deposits

 

[Ian MacAulay]

One turbo is clearly new and the other looks original with just a coat of paint on AND one engine does seam to pull better (the one with the new turbo). But both sit at same rpm at 3550rpm... Would one failed turbo make them both sit at identical Revs?

 

[Ian MacAulay]

She pulls real well when opened up but port engines Revs increased a lot quicker

Thanks

Ian

 

[gery w]

On mine one had more boost pressure than the other however at wot both engines pulled the same revs and would leave some black oily soot on the transom.
Do you have any smoke or soot?

 

[gery w]

The other thing you have to be sure tha both your tacho's are accurate I checked mine with a hand held tacho
Regards Gerry

 

[Ian MacAulay]

Thanks Gerry

I have just replaced the port side tacho with a brand new one both idle the same rpm. Down on top speed too...

Thanks

Ian

 

[Momac]

I have heard of low power being due to something simple like an air leak , not necessarily on ad41 but similar.
So might be worth getting Volvopaul or the like to check out the engines before forking out on expensive turbocharger.

I have certainly heard of a weak engine holding back the good engine but in that case a change of fuel filters sorted it out. Sounds like you have covered that one.

 

[gery w]

Yep it could well be something simple and cheap to repair make sure you check all that stuff first

 

[Ian MacAulay]

Morning.

have checked everything this weekend and also cleaned and inspected everything too. water tested and engines pull identical and rev to 4400rpm in N.

running on one engine at a time have both results on both engines to hit 2200rpm and both together 3600rpm at 33mph BUT buzzer and slight over heat.

its all indicating to over propped in my eyes but according to all other boat owners and cranchi it should be running A8 props not the A7 props so this seams odd.

But can one thing be cleared up...... have I put props on the correct way round and not put one on back to front causing this issue?


Ps...... Reason engines were in past pulling different was we found blockages in fuel lines but now repaired

 

[Ian MacAulay]

 

[Chris_d]

View attachment 55088

That is correct, it is impossible to fit them the wrong way round unless you a truly gifted numpty :encouragement:

 

[Ian MacAulay]

Is the rear (closest ) can that be put round wrong way ?? As it looks odd to me

I'm clutching at straws here as something not right