Low engine revs

[muchy_]

I have a BMC 1500 diesel engine in a 30ft boat. The engine will only rev to 2500rpm. An engineer has told me that its because it has reached its maximum power and that it cant spin the prop any faster. I know that the prop pitch does have something to do with that but 2500rpm relates to 6-7knots. The thing that makes me wonder is that it reaches 2500rpm even when tied up, surely if it had reached its max power then the revs would be lower when tied up because theres more friction. It just seems to me that there is more power to be had there. Has anyone any expierence with this engine and what kind of revs could it safely be taken to?

 

[Guest]

Does it rev any more than that in neutral, if so then it is overloaded, eg prop too big, or you have a fuel starvation problem, not enough fuel to make the revs under load, an engine uses far more fuel when under load than just revving out of gear, also there could be other problems, check the governor setting on the inj pump, pump is upright, should be a alloy pencil type seal in the max rpm screw, if it is missing then it has been tampered with probably to slow down say a hire user, up it to about 3800 rpm and see what happens, also check the throttle cable for slackness, it may need adjusting.

Paul js.

 

[muchy_]

Where abouts on the pump would the max rpm screw be? I have adjusted the throttle stop and that increased revs slightly but I wondered if there was another screw to adjust the revs?

 

[Guest]

Have you adjusted the screw that sets the tickover speed ? that will only set the lows revs/ idle speed, the max screw is the other one same size nut about 8mm I think, the throttle arm moves up to it when you open the throttle, unscrew it to get more revs, that will be the one with the pencil type alloy seal, brake off the lockwire if it has one, the other thing is that the rev counter may not be correct, so dont blow up the engine if it is wrong.

Paul js.

 

[boatmad2]

When flat out under load does the exhaust smoke black smoke? this is the classic sign of an engine overloaded.
By the way in any 30ft boat this engine about 35hp is only going to give you hull speed which is about what you are getting. This boat and engine may have been set up for inland work ie 5-6 mph with slow engine revs for long life and good fuel compsumtion with quieter running.
I dont think you will get any useful speed increase with this engine.

 

[boomer]

Its amazing the things one hangs on to. Just found an original handbook for this engine in our archives. This gives maximum power output as 36 bhp @ 4000 rpm. Need to check you can at least achieve these revs in neutral. Good luck.

 

[muchy_]

Thanks for that piece of info, that will be a great help

 

[mtb]

I dunno about revving it that high
The cost of rebuilding aint worth it
Did you say what gearbox you have .
The main thing if not mechancle fault that governs engine speed is the propeller
Get the right size and pitch and things are great ,get it wrong then !!!

Example
A BMC through a PRM box to a 25"x16" prop was perfect for my old 40ft narrow boat .
I could on run at low revs but maintain correct speed with ease. On the tidal Thames it would realy go quite fast certainly above its design speed which meant no point because of wash .
Mick

http://homepage.ntlworld.com/boats
I want a big steel ex trawler / tug v / cheap or swap for tug

 

[boomer]

Munchy

If the documentation I have would be of any use to you, you are welcome to a photo-copy. I also have the Operators Handbook for the HyDrive hydraulic gearbox that was fitted to many of the BMC1.5s PM me.

 

[muchy_]

That would be a great help. If you have a diagram of the injector pump I would be very greatful. It's Muchy by the way(on account that I don't drink-----much!!!!). However, maybe it does go with the eating habits as well ;-)
Is there any chance you could e-mail it to me?

mike@mike-wright.co.uk

Many thanks..........