Volvo 19hp - max revs in neutral, but not while in gear

[vmattiola]

Hi all,

I'm having some trouble with achieving max revs on a Volvo 19hp diesel w/ saildrive.

In neutral, the motor happily revs up to 3200+ rpm, but while engaged in gear (forward or reverse), it only reaches around 2500 - 2600rpm.....? Any thoughts?

I'm thinking it has nothing to do with air intake, fuel supply, injectors, or cylinders, since it revs in neutral just fine. Something going on with the saildrive? Has fresh, clean, full transmission oil reservoir.

Throttle controls don't appear to have any stops which would prevent revving while gear is engaged.

I jumped in with a mask and looked for line around the prop (while in Greece now in the winter in 14C water....) and saw nothing. Some barnacles on drive and prop, but not enough that I'd think it could prevent achieving more than 2500rpm, right?

The biggest issue for us is that I'm only able to move our 31ft 7.5 ton monohull at about 3.2 knots on FLAT, CALM water. In these winds above 20 knots and choppy waters, I can barely maneuver, which is making entering ports and harbours very sketchy at times. I almost had to bail out of an approach because we were suddenly only making less than 0.5kts SOG in the channel....

Any suggestions are appreciated as we're making our way toward Israel and would love to be able to rely on this motor to get us in & out of ports.

[undercutter]

When did the problem start? It sounds like you have had this problem for a while???

There have been other threads on this same topic albeit with different engines and usually turns out to be a fuel problem. Usually if there is a unknown load such as fouled prop etc, there will be other indications such as black smoke from exhaust, vibration, etc.

When was the last time you did the filters?

Did anything happen just before this problem started?

There are so many possible explanations for a fuel supply problem that it would help to have some additional information.

[vmattiola]

Unfortunately I've only been aboard the vessel for about 8 days (delivery), and it's been a problem since our first day.

Records aboard show the filters replaced 3 or 4 months ago, and the racor bulb is very clear and clean.

[undercutter]

Well the first thing I would try would be to replace the primary filters on the engine. If the problem persists then disconnect the supply hose to the lift pump and place the hose in a 20 litre pail of fuel and run the engine this way. If this doesn't sole the problem I would look at the lift pump next.

There could be an obstruction in the return side but I doubt that is the problem.

After that, the next thing is the injection pump but again way on the outside.

Does the engine run smoothly at idle? What is the colour of the exhaust smoke under load?

[vmattiola]

Motor runs very smoothly at idle, doesn't seem abnormal there.

Essentially zero smoke under load either.

If it's a fuel supply problem, I'm confused how we'd be able to reach 3500 rpm in neutral?

[undercutter]

Because there is no load in neutral so the engine doesn't need the same amount of fuel to reach the higher RPM.

If the exhaust smoke is clean when in gear at the highest RPM that you can attain then it would indicate a fuel problem. If the smoke turns black then it could be an air intake or turbo problem. Not sure if that engine would have a turbo.

[sailormed]

[QUOTE=vmattiola;2324460]
In neutral, the motor happily revs up to 3200+ rpm, but while engaged in gear (forward or reverse), it only reaches around 2500 - 2600rpm.....? Any thoughts?
/QUOTE]

Doesn't seem abnormal to me. 3200 rpm unloaded 2600 rpm loaded, turning the screw, bearings, transmission, etc. Boat stationary in harbour, that is even more load then when navigating under engine.

[undercutter]

[QUOTE=sailormed;2324481]

Originally Posted by vmattiola

In neutral, the motor happily revs up to 3200+ rpm, but while engaged in gear (forward or reverse), it only reaches around 2500 - 2600rpm.....? Any thoughts?
/QUOTE]

Doesn't seem abnormal to me. 3200 rpm unloaded 2600 rpm loaded, turning the screw, bearings, transmission, etc. Boat stationary in harbour, that is even more load then when navigating under engine.

No, the volvo site recommends cruising at 300-500 rpm less than the maximum output of 3600 rpm. So I assume that the top rpm under load should be 3600 rpm. This would indicate that the engine cannot even attain full rpm while not loaded.

[undercutter]

[QUOTE=undercutter;2324488]

Originally Posted by sailormed

No, the volvo site recommends cruising at 300-500 rpm less than the maximum output of 3600 rpm. So I assume that the top rpm under load should be 3600 rpm. This would indicate that the engine cannot even attain full rpm while not loaded.

Therefore if there is no black smoke then the engine is not overloaded and thus it is a fuel problem.

[FSMike]

A couple of things things occur to me.
Do I assume correctly that you are making your reported maximum rpm under load while you are underway at your reported 3.2 knots?
You mentioned a few barnacles on the running gear, but didn't comment on the hull. Is the hull clean?
I hope you cleaned the prop while you were in the water?
Lastly, could it be that you are over propped?

[Wotname]

What FS Mike said ++
Dirty hull or over propped comes readily to mind.

19hp is way more than necessary to move a 31' at hull speed in flat calm conditions so therefore the only problems must be:
1. Dirty hull and/or prop (ie excessive drag)
2. Wrong (or faulty) prop (unlikely but possible, especially faulty prop)
3.Engine not developing full power (again unlikely but possible)

[undercutter]

Originally Posted by Wotname

What FS Mike said ++
Dirty hull or over propped comes readily to mind.

19hp is way more than necessary to move a 31' at hull speed in flat calm conditions so therefore the only problems must be:
1. Dirty hull and/or prop (ie excessive drag) = overloaded engine = unburned fuel = black smoke
2. Wrong (or faulty) prop (unlikely but possible, especially faulty prop) = overloaded engine = unburned fuel = black smoke
3.Engine not developing full power (again unlikely but possible) = overloaded engine = unburned fuel = black smoke

As I said the Volvo site indicates 3600 rpm at maximum operating speed. The OP cannot even attain this at WOT with the engine unloaded. There is no black smoke. The engine seems to run fine at idle and at top RPM unloaded. This is not an air intake problem as there is no black smoke.

Sometimes when you eliminate all the other potentials then it only leaves the obvious which is insufficient fuel. Now why is there insufficient fuel. fuel line obstruction, filters, lift pump, injector pump????

[undercutter]

One other thing that could be causing the problem is a partially closed shut down solenoid or manual linkage on the injection pump. Not sure whether this engine has an electric stop solenoid but I would assume so. If this solenoid was sticking partially closed then that would do the trick as well.

[vmattiola]

Of note, we're able to reach nearly 3600 rpm at dockside or at anchor in neutral.

Max rpm in gear = 2500 rpm while motoring (no sails) in flat water nearly no wind. In headwind of 18-20kts our SOG is essentially zero.

Hull is quite clean (although I was the one who cleaned it), and sail drive/ prop very barnacled. I was freezing tits cold and wimped out after a few mins of trying to scrape barnies off the prop. There are still some on the prop blades itself. Could this cause enough drag?

Prop is a double blade folding type which honestly looked quite small to me.

I will check out the stop solenoid today, maybe it's partially closed?

I'll also disconnect fuel supply from lift pump and try it 'filter-less', then disconnect outlet of lift pump and see if there's good pressure coming out?

[Wotname]

Originally Posted by undercutter

As I said the Volvo site indicates 3600 rpm at maximum operating speed. The OP cannot even attain this at WOT with the engine unloaded. There is no black smoke. The engine seems to run fine at idle and at top RPM unloaded. This is not an air intake problem as there is no black smoke.

Sometimes when you eliminate all the other potentials then it only leaves the obvious which is insufficient fuel. Now why is there insufficient fuel. fuel line obstruction, filters, lift pump, injector pump????

I don't disagree with you however, the OP reports 3200+ rpm at no load WOT. I am not sure how much the "+" really means so I take it the engine reaches close to max rpm at WOT unloaded.

The OP reports 3.2 kts max speed with flat clam conditions; without looking up the tables, I reckon you need maybe 8 hp max. to achieve hull speed for a 31' in a flat calm so 3.2 kts should only need say less than 6 hp. To have a fuel restriction to reduce engine output to 6 or so hp, it would have to be severe.

That said, I do agree the absence of black smoke does suggest a fuel restriction.

It would be great to know how the engine performed in the past at WOT in a flat calm.