petter mini-twin diesel engine

[garvellachs]

Our Cobra 750S has a Petter Mini-Twin diesel engine (765AC2W). It starts easily, following the handbook instructions, and runs well. Once warm it doesn't smoke significantly. But as it warms up it starts to "knock" irregularly and then regularly and quite loudly. There's no oil pressure gauge. Could it be a big end worn loose - would that only start to knock when the engine warms up? Or is it just part of the normal noise of an old diesel? Any thoughts from experienced diesel (or even Petter) owners?

 

[halcyon]

Could be old fashioned diesel knock, or we had a knock on our two cylinder Vetus due to engine mount failure. Another long story that rivals Volvo.
A lot depends on the definition of knock though.


Brian

 

[mtb]

Re: Could be many things

Try using a screw driver , put the metal end against the casing the other to your ear the noise should be easy to source .

(Most likely cause)
Excessive carbon build up causing pre detonation due to carbon getting hot.

Ignition pump timing to advanced .

Perhaps the oil is diluted this can happen due to the injector seals leaking

Re big end , you should consider that when the engine is off if the big ends were worn then its quite feesable the oil would drain out ,so that you would hear the knocking of the b/ ends at start up untill the oil pressure built up.

The knocking is it metalic sounding or from inside the engine .
Little end knocking due to small end bearing wear.
Last but not least it could be a broken piston ring .
It might be but I dought it , check the waterpump for a worn drive shaft and bearing.

Hows that lot !!
Cheers
Mick



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

 

[garvellachs]

Re: Could be many things

Thanks for the thoughts Mick.

I'll try the screwdriver thing - I've used it before on cars but I've been a bit reluctant to lean over the alternator belt etc. for safety's sake so far. I don't think the oil is diluted - seemed ok on changing recently - and I hear what you say about the big end being worse cold than warm. I think the water pump's ok.

I think it sounds mechanical (it's not like a petrol engine pinking for instance) but pre-detonation due to carbon is a possibility - I've not had the heads off yet. The sound seems bigger than a worn small end. I've no idea what a broken piston ring sounds like, but the good starting suggests to me the rings are ok maybe?

So I'll get some head gaskets and clean the carbon out I think.

I appreciate the help - Mike

 

[garvellachs]

Thanks for the reply Brian. What's good old fashioned diesel knock?

I've checked the engine mounts and they seem good. I've put a bit more info in a reply to Mick (mtb).

Cheers - Mike