Volvo penta 2002 low rpm at top end

[ollie1977]

Hi all

I've noticed that my maximum rev under full load is approximately 2,600 RPM on my etap 30 monohull. Though not certain, I'm reasonably confident that it was previously closer to 3,000. I have investigated and replaced the exhaust manifold whilst also flushing the tank recently to get rid of a diesel bug issue (full tank of new clean diesel) Neither action has had any impact on the rpm.

I should also say that the bottom is clean and when in neutral I can get close to 4000rpm.

I would be interested to hear any suggestion as to what I might investigate next to troubleshoot this issue.

Thanks

 

[Tranona]

You should be able to get well over 3000rpm (33-3600 is the normal maximum range) and at least 6.5 knots in flat water. At 2600 you should get about 5,5 knots. First check the propeller both for fouling, but also for size. If it is too "big" (diameter and/or pitch) the engine will be constrained and you probably won't reach the speed. No load rpm is irrelevant, and 4000rpm is over the maximum.

If the prop is the correct size then it suggests the engine is not producing full power which could be general wear, loss of compression of fuel delivery.

 

[ollie1977]

Thanks.

Reasonably confident that the prop width/pitch isnt the issue as i was achieving 3000rpm on the same prop until recently. One caveat to that is i have since replaced the shaft seals so removed the prop but i am struggling to see how reasssembly changed either variable.

I will checking for fouling this weekend. If it turns out to be loss of compression could this conceivably be due to a blockage caused by diesel bug which was present in the tank until recently?

Cheers

 

[paulbrown22]

Thanks.

Reasonably confident that the prop width/pitch isnt the issue as i was achieving 3000rpm on the same prop until recently. One caveat to that is i have since replaced the shaft seals so removed the prop but i am struggling to see how reasssembly changed either variable.

I will checking for fouling this weekend. If it turns out to be loss of compression could this conceivably be due to a blockage caused by diesel bug which was present in the tank until recently?

Cheers

It's a fixed prop as opposed to feathering? We had an interesting case a few years back with a Maxprop where we removed it for a cutlass bearing, gland replacement and prop service, it was put in a box with some random letters/numbers on it and the prop got reassembled to those numbers/letters which meant it was the wrong way round completely and the entirely the wrong pitch!

I stand to be corrected, but there wouldn't generally be any correlation between cylinder compression and diesel bug. Diesel bug could limit power, combustion, fuel flow, etc., the easy way to test to be to run directly from a small can of fresh fuel, bypassing as much of the existing plumbing as possible.

Depending on how badly fouled the hull/prop are, that can have a significant impact.

 

[PaulRainbow]

Thanks.

Reasonably confident that the prop width/pitch isnt the issue as i was achieving 3000rpm on the same prop until recently. One caveat to that is i have since replaced the shaft seals so removed the prop but i am struggling to see how reasssembly changed either variable.

I will checking for fouling this weekend. If it turns out to be loss of compression could this conceivably be due to a blockage caused by diesel bug which was present in the tank until recently?

Cheers

No.

 

[ollie1977]

It's a fixed prop as opposed to feathering? We had an interesting case a few years back with a Maxprop where we removed it for a cutlass bearing, gland replacement and prop service, it was put in a box with some random letters/numbers on it and the prop got reassembled to those numbers/letters which meant it was the wrong way round completely and the entirely the wrong pitch!

I stand to be corrected, but there wouldn't generally be any correlation between cylinder compression and diesel bug. Diesel bug could limit power, combustion, fuel flow, etc., the easy way to test to be to run directly from a small can of fresh fuel, bypassing as much of the existing plumbing as possible.

Depending on how badly fouled the hull/prop are, that can have a significant impact.

Btw it's a fixed prop

 

[Tranona]

3000rpm is still a bit on the low side, but agree it is the drop that is important to investigate. Changing the seal should not alter anything. Just check the shaft turns freely. While diesel bug and low compression are not connected, diesel bug and its consequences and constrained fuel supply at higher engine speed/load could be.

 

[Stemar]

The first thing I'd check is the state of the exhaust elbow. On my 2003, the water flow was slow, and power was down, and both symptoms came on relatively quickly. The elbow was almost completely blocked. A soak in brick cleaner restored everything to normal.

 

[ollie1977]

3000rpm is still a bit on the low side, but agree it is the drop that is important to investigate. Changing the seal should not alter anything. Just check the shaft turns freely. While diesel bug and low compression are not connected, diesel bug and its consequences and constrained fuel supply at higher engine speed/load could be.

Thanks...stupid question....is it possible to fix the propeller the wrong way round or does its design not permit this?

 

[Sandy]

flushing the tank recently to get rid of a diesel bug issue (full tank of new clean diesel

Did you clean/replace the pipework?

 

[ollie1977]

Do you mean fuel lines....my engineer did
.at least the section running from the pre filter which was completely clogged from diesel bug. I'm not sure he inspected beyond that.

 

[Tranona]

Thanks...stupid question....is it possible to fix the propeller the wrong way round or does its design not permit this?

No. It only goes on one way because of the taper and the other dimensions are by definition fixed. I suspect it was overpropped by about 1" pitch originally. Quite common in the belief that it improves fuel usage, which it does not. The loss of 400rpm is significant and if there is not fouling or obstruction suggests fuel supply the first place to look.

 

[Sandy]

Do you mean fuel lines....my engineer* did
.at least the section running from the pre filter which was completely clogged from diesel bug. I'm not sure he inspected beyond that.

Yes I mean the fuel lines.

I'd be looking at the whole system from tank to injector.

After a dose of the bug a few years back I replaced everything.

*you mean your mechanic, sadly the word engineer is not protected. It is a personal gripe of mine.

 

[ollie1977]

No. It only goes on one way because of the taper and the other dimensions are by definition fixed. I suspect it was overpropped by about 1" pitch originally. Quite common in the belief that it improves fuel usage, which it does not. The loss of 400rpm is significant and if there is not fouling or obstruction suggests fuel supply the first place to look.

Thank you....that's reassuring. I will check for fouling this weekend and report back

 

[Tranona]

If you have had fuel bug then the tank needs cleaning. You may have put in clean fuel but there could still be material lying in the bottom or in the pipe to the filter. Might be worth changing the filter and checking that it is clear or not.

 

[Sandy]

And don't forget the return lines.

 

[PabloPicasso]

No.

Are you sure you've got full fuel flow? Is a fuel pipe partially blocked, kinked, or perished inside (out of sight?).

Is the engine filter blocked (did you change it too) or an injector or fuel-Pump membrane gummed up? On those 2000 volvo engines many have a gauze filter in the fuel pump (don't ask how I know this!!)

 

[black mercury]

I'd be worried about it reaching 4000 rpm with no load. The max rpm of those older engines is 3200. Are you going by the rev counter on the panel? Also under load when it reaches 2600 and you keep moving the throttle lever to its max but the revs stay, do you notice black smoke coming from exhaust. Bear in mind you won't reach the max rpm under load when tied to pontoon.

 

[ollie1977]

I'd be worried about it reaching 4000 rpm with no load. The max rpm of those older engines is 3200. Are you going by the rev counter on the panel? Also under load when it reaches 2600 and you keep moving the throttle lever to its max but the revs stay, do you notice black smoke coming from exhaust. Bear in mind you won't reach the max rpm under load when tied to pontoon.

No black smoke...and 2600 is reached when throttle fully engaged.

 

[ollie1977]

Are you sure you've got full fuel flow? Is a fuel pipe partially blocked, kinked, or perished inside (out of sight?).

Is the engine filter blocked (did you change it too) or an injector or fuel-Pump membrane gummed up? On those 2000 volvo engines many have a gauze filter in the fuel pump (don't ask how I know this!!)

My has a gauze filter (or so I've been told) is this easy to access remove and inspect?