Volvo Penta md2020 idle

[james pask]

Hi
I have a vp2020 3 cylinder diesel , fully reconditioned with Honed bores , new rings , polished crank ,Valves regroups , new injectors , etc etc - It runs really well and starts on the button , the oils still clear after 10 hours running - however it still clatters at idle , I’ve looked at many YouTube videos of 2020 running and they all seem to sound the same , I was wondering what makes the rattle / clacking sound ? .

[skipperpete]

Early timing can cause the sound you describe. If the injector pump was refitted without it’s original shim pack the timing is advanced. However, precombustion chamber engines are well known for noisy combustion, the earlier Caterpillar engines were notable in this respect but Kubota, some of the small Yanmar’s and the Shibaura (base engine of your MD2020) are also quite noisy at idle and while cold.

[a64pilot]

A cold Diesel or a low RPM Diesel which also has very low exhaust temps so it can be considered to be a cold motor will rattle because it’s a compression ignition engine, meaning the whole charge goes off nearly instantly as it all hits the ignition point almost instantly.
A spark plug engine doesn’t normally rattle because the spark plug initiates the burn, that propagates from one point and spreads throughout the combustion chamber.
If a spark ignition engine’s charge is initiated by compression, it too almost instantly combusts the whole charge, that’s called detonation and they will also rattle, and because they are not designed to tolerate it, the piston head often fails from it.

Diesels often quieten down at higher RPM as there is enough heat in the combustion chamber to initiate the fuel burn as soon as the fuel becomes present and it is a smoother flame propagation similar to a spark ignition engine.

Common rail motors can introduce a small injection event prior to the main event and make enough heat be available so that the fuel begins to burn as soon as it’s injected, sort of emulating a fully warmed up Diesel at higher RPM.
Old style injection systems at much lower pressure can’t do that, so they rattle.

It’s a normal operating condition of a mechanical injection Diesel.

[james pask]

That all makes sense thanks, the engine does quieten down at higher revs as you suggest - I'll check the pump timing shims too.
Cheers
James

[Fonseca]

Look if air is not entering the fuel feed line before the injection pump.

[Zoila DK]

Originally Posted by a64pilot

A cold Diesel or a low RPM Diesel which also has very low exhaust temps so it can be considered to be a cold motor will rattle because it’s a compression ignition engine, meaning the whole charge goes off nearly instantly as it all hits the ignition point almost instantly.
A spark plug engine doesn’t normally rattle because the spark plug initiates the burn, that propagates from one point and spreads throughout the combustion chamber.
If a spark ignition engine’s charge is initiated by compression, it too almost instantly combusts the whole charge, that’s called detonation and they will also rattle, and because they are not designed to tolerate it, the piston head often fails from it.

Diesels often quieten down at higher RPM as there is enough heat in the combustion chamber to initiate the fuel burn as soon as the fuel becomes present and it is a smoother flame propagation similar to a spark ignition engine.

Common rail motors can introduce a small injection event prior to the main event and make enough heat be available so that the fuel begins to burn as soon as it’s injected, sort of emulating a fully warmed up Diesel at higher RPM.
Old style injection systems at much lower pressure can’t do that, so they rattle.

It’s a normal operating condition of a mechanical injection Diesel.

What a great explanation to this. Learningful, - thanks a lot!