Knocking noise

[Tuscan]

Have a DM2 post service the oil filter was not secured properly by the mechanic and engine dan v low on oil briefly. 2 weeks later I've noticed an occasional metallic knocking followed by loss of power an bigger one off knocking noise then everything fine. So far I've been told it's the clutch then I've been told the injectors. Any ideas?

[frangar]

That sounds a bit of a worry!

 

Is it the same on and off load? Hot or cold etc? What's the oil pressure like compared to how it was before?

 

Stupid question but I assume the oil is the right grade and spec? Eg straight 30....something like Morris Golden film 30.

 

I won't ask who the engineer was.......

 

Cheers

 

Gareth

[Tony Dunkley]

Have a DM2 post service the oil filter was not secured properly by the mechanic and engine dan v low on oil briefly. 2 weeks later I've noticed an occasional metallic knocking followed by loss of power an bigger one off knocking noise then everything fine. So far I've been told it's the clutch then I've been told the injectors. Any ideas?

 

Is this an RN with a modern box, or a National or RN with a Bruntons box ?

[Tuscan]

That sounds a bit of a worry!

Is it the same on and off load? Hot or cold etc? What's the oil pressure like compared to how it was before?

Stupid question but I assume the oil is the right grade and spec? Eg straight 30....something like Morris Golden film 30.

I won't ask who the engineer was.......

Cheers

Gareth

Yes I'm thinking the worse, same hot or cold but intermittent then she runs fine. Will check the oil when I get back to boat.

Is this an RN with a modern box, or a National or RN with a Bruntons box ?

No PRM box it's a 1980 unit

[Tony Dunkley]

Yes I'm thinking the worse, same hot or cold but intermittent then she runs fine. Will check the oil when I get back to boat.

 

No PRM box it's a 1980 unit

 

Well that eliminates one expensive possibility. Is the momentary loss of power accompanied by puffs of blackish exhaust smoke?

[Tuscan]

Well that eliminates one expensive possibility. Is the momentary loss of power accompanied by puffs of blackish exhaust smoke?

 

Yes but not always black sometimes grey. The knocking sounds like flywheel hitting a coat hanger ( checked and it's free) then there's a bigger bang ( more like a spanner hitting the side) then it seems to set itself free. Just had a mate check recently topped engine oil after the recent loss with Morris SAE 20 not 30 . My error is this likely to cause the problem?

[Tony Dunkley]

Yes but not always black sometimes grey. The knocking sounds like flywheel hitting a coat hanger ( checked and it's free) then there's a bigger bang ( more like a spanner hitting the side) then it seems to set itself free. Just had a mate check recently topped engine oil after the recent loss with Morris SAE 20 not 30 . My error is this likely to cause the problem?

 

Obviously, without hearing it running it's not possible to be 100% sure, but it could well be a pintle in one injector nozzle sticking intermittently. Don't worry about the 20 grade oil, that's definitely not the cause.

When the service was done, did it include changing the fuel filter(s), and did it ever knock / smoke prior to the service?

Edited August 13, 2015 by Tony Dunkley

[Tuscan]

Obviously, without hearing it running it's not possible to be 100% sure, but it could well be a pintle in one injector nozzle sticking intermittently. Don't worry about the 20 grade oil, that's definitely not the cause.

When the service was done, did it include changing the fuel filter(s), and was the knocking / smoking present at all prior to the service?

Thanks Tony , smoking when under heavy load (dragging the bottom) my old boater mate ex plant mechanic whose been on boats for years reckons it's the injectors - mentioned it to the engineers at the yard they reckoned clutch.

[mattlad]

The valves sometimes stick on RN's.

[frangar]

I agree about the valves.....do you know when the head was last off for a decoke? I'm sure it's not that big a job on an RN to decoke the valves....might be worth getting the injectors serviced at the same time and just making sure the spill timing is ok.

 

Does the oil pressure stay fairly constant when the noise occurs? Just wondering if it may be a sticking oil pressure relief valve if ones fitted.

 

Odd noises are hard enough with the engine next to you let alone on the web!

 

By the clutches do they mean the ones inside the box or the drive plate? Does the noise happen when it's in neutral?

 

I think 20 might be a bit thin for an RN but that's only going to cause problems when the engine is hot.

 

One other thought....just check the filter is the right one...mind you this would show up with changing oil pressure.

 

Cheers

 

Gareth

[Tony Dunkley]

Thanks Tony , smoking when under heavy load (dragging the bottom) my old boater mate ex plant mechanic whose been on boats for years reckons it's the injectors - mentioned it to the engineers at the yard they reckoned clutch.

 

Hang about, we haven't finished yet !

As Mattlad says, the other most likely possibility is an intermittently sticking valve, but with the fault becoming noticeable so soon after a service when, presumably, the fuel filter was changed, it may be that a bit of disturbed muck from the filter body has found it's way to an injector.

If you've got a pump priming lever for your engine, then you can test the injector spray patterns and seat tightness whilst on the boat and either confirm or eliminate the injectors as the culprits.

With a PRM box, you can forget about the noise being anything to do with either of the clutches.

You can also stop worrying about it being anything major or very expensive, . . . . it isn't.

Edited August 13, 2015 by Tony Dunkley

[Tuscan]

Thank you all will research and come back

[twinpot]

Did you find the cause of the knocking noise, having a DM2 in my boat I would be interested to know.

 

Thanks.

[bassplayer]

I've just started a new thread about the oil level in a DM2 because I noticed mine started to make an intermittent faint metallic knocking noise recently. I didn't notice any loss in power or additional smoke though.

 

I found my oil was 30% above the low mark on the dipstick (I don't like to overfill the oil) . I then filled it to 80% (20% below high mark) and the sound disappeared!!