Volvo 2 Cylinder Noises

[GILow]

Hi cruisers,

I crewed on a boat last week with a 2 cylinder volvo diesel. Not sure of the model but i am guessing around 25 to 30 hp. I do know it has a sail drive and I think it is around 15 or so years old. Listening to it as we motored in after the race I could hear a noise that sounded like a bad big end rattle. I think I could hear this in addition to what I would consider a "typical" diesel rattle. If it was a big end rattle it was a very even on both pots.

Is this a normal sound for this sort of engine or an indication of potential problems?

Matt


Sent from my iPad using Cruisers Sailing Forum

[DougR]

Of course it's very difficult for someone who wasn't there to analyse what you think you heard..........

However many Volvo Penta engines of that era (and other engine brands as well) were equipped with "air filters" that looked like cylindrical canisters with tapering inlet pipes into the canister. These devices weren't so much air filters as they were inlet noise silencers. Running these one, two and three cylinder engines without the silencer in place makes one think that the connecting rods are about to depart the crankcase! The hammer noise from the air inlet pulse can be quite disconcerting.

Perhaps that is what you heard, or maybe the engine is on its last legs.

Rgds,
DougR

[GILow]

DougR,

Thank you for that description, it captures in words the sound I heard very well. I will surreptitiously check that out next time I am on board. Perhaps when he needs to change an oil filter again, I helped him do it last time.

I didn't want to be alarmist, but the last person who's boat I thought had cooling problems ended up siezing and destroying their engine about two weeks after I expressed my concerns. (She had the guts to confess this to me after the event. Particularly brave as one of her regular crew members told me I was an alarmist idiot and that the cooling was fine.)

Let's hope your diagnoses explains the noise.

I was not overly heartened when I asked a pair of boat mechanics I know over the weekend, and one of them replied... "What, strange noises from the Green Death?"

Matt

[a64pilot]

A dirty fuel injector will also make this noise


Sent from my iPhone using Tapatalk

[GILow]

Originally Posted by a64pilot

A dirty fuel injector will also make this noise


Sent from my iPhone using Tapatalk

Is that when it cracks open too early and pings?


Sent from my iPhone using Cruisers Sailing Forum

[a64pilot]

No what happens with a dirty injector is instead of a nice spay pattern that sprays a mist, you have more of a solid stream. It's simply varnish build up on the injector tip. A good cleaner like techron or sea foam will clean a dirty injector, but since they are so easy to remove, I'd just pull them and have them cleaned and tested at a Diesel injection shop. They will sort of dribble also and this does put fuel in the combustion chamber before it is supposed to be and does have the same effect of one cracking at too low a pressure in that fuel is present before it should which is pre-ignition and does knock.
If it's real similar to the cold Diesel knock but just doesn't go away when warm, I first suspect a dirty injector.

[GILow]

Hmmm... thinking back a bit, it was a very even sound, so unless both (all three) injectors were dirty it was probably not the cause. But then whatever makes one injector dirty would probably make all three dirty, so you might have it.

If DougR's suggested cause is eliminated by the presence of the air filters, I will ask if they've run any injector cleaner through the engine lately.

Thanks for the thoughts, I hate to be a doomsayer, but I also hate to think of a friend drifting around without an engine out on the Gulf with his family when I could have helped to prevent it by saying something.

Matt