View Full Version : AD41D only reaching 2600rpm

05-19-2009, 05:57 PM
"hi every one
I have a 25ft alloy with a volvo ad41d driving a in tunnle shaft drive
It starts sweet and runs mean as soon as I get above 2500 rev the motor get louder and doesnt pick up much speed and with the hammer down will not go past about 2600 revs,it used to push 18 knots at 2800 and cruise at 21 at about 3200-3300 revs ,its had a new injector pump and new filters but this didnt change anything the boat has had very little use in the last yaer and not used in the last 6 months ,then I brought it the fuel tank was empty and there was a big build up in the water trap which I cleaned and put a diesel fuel cleaner in the tank,
any ideas would be much apreciated"

05-19-2009, 08:52 PM
That is the exact spot where the turbo normally kicks in and gives the injection pump 'free flow'. Check Your turbo pressure.

05-20-2009, 03:02 AM
can i just unbolt it and take it to a volvo mec or will the whole boat have to go in? and what do they do to pressure test it?

05-20-2009, 04:32 AM
"Hook up a turbo pressure gauge. Might be best to have a mechanic, preferably a Bosh diesel pump mech, on board if You are not familiar with it. It might be the turbo, it might be the injection pump. It all need to be run as a package to get it right."

05-23-2009, 02:48 AM
hi morten
heres a new twisit I got a mec to check it all out fuel lines are sweet and the recond injector pump was getting a good flow then he tested the turbo in neutral it will pull 3900 revs (went to 4500 accidently) easy but the turbos was not working bugger all then we tested it in gear turbo worked well but it struggled to get from 2000 rpm to 2500 rpm
so what do you reaken? what about the gear box or wrong prop?

05-23-2009, 03:07 AM
"Testing turbo in 'neutral' is not quite what I would recommend, but.
Bottom line is You need to get above 24-2600 IN GEAR to get turbo pressure high enough to 'free' the smoke limiter on the injection pump.
Gearbox problem - hardly! If seized bearings or similar it would probably have melted long ago or given rather heavy noise, unless You have a hydraulic box and not the MS3?
Propeller more likely. Might be fouled, might be damaged, or simply might be wrong (too heavy) all together.
If Your diesel mech knows what he is doing, have him TEMPORARILY adjust the spring load on the smoke limiter to make the pump free at a lower turbo pressure. This only for a short test purpose!!!"

05-23-2009, 04:21 AM
"I checked the prop its clean,undamaged and fairly new looking makes me wounder if the wrong prop has been put on
the one on there at the moment is 21p 17x18.5 with four blades I would be interested to hear your comments about it
what if doesnt know what hes doing I dont know if I want him to start adjusting stuff lol"

05-23-2009, 04:45 AM
"Well, anyone that tests turbo pressure on an un-loaded engine might make me wonder!
Your prop spec is a bit confusing.
What is it?
21" x 17" x 4?
21" x 18.5" x 4?
17" x 18,5" x 4?
What is Your gear ratio? (check the tab at the gear box, it should be stamped there)."

05-23-2009, 04:24 PM
lol thats what i was woundering to

now the prop has this stamped on it
LAMB 21p

on the gear box it has
MS4A 193 853398

on the round bit that goes into the motor has 853161

and there is the hour simbol with 8501
but I presume it just the first numbers that
you are talking about

05-23-2009, 11:08 PM
"We may have to 'reverse' a bit to get further.
What is the expected top speed of the boat?
That gearbox has a ratio of 1.93:1.
With a max rpm of 3800 and a pitch of 21" the nominal speed should be about 34 knots, or real closer to 28 knots?
How does this fit?"

05-24-2009, 12:38 AM
I think its max is about 23-24 knots and at 3200rpm should do about 20 knots does that sound abit better?

05-24-2009, 02:37 AM
Go back to prop manufacturer/boat builder and get the correct prop specs. Both what should be and what You have got.
Have You got a pic of the boat at land?

06-05-2009, 03:32 PM
"well it appears its got the wrong prop on there heres the specs I gave them ,waterline lenght 6.8m,weight 2700kgs,hp 200, gear ratio 1.93, max rpm 3800 and its a planing hull what would you recommend oh and its got a 4 blade prop at the moment"