Engine whoosh - with audio

[matteo]

Hi all,

My CU 2.0L engine has recently acquired a slight whoosh/whistle when the revs drop following a tap on the accelerator (from idle). I've never heard this sound before - can anybody identify what might be going on please? I couldn't see a way to embed an audio file so here's a link: https://soundcloud.com/veedubber/cu-engine-whistle

At my last check, the cylinder compressions were good, but that was 6 months ago so I'm going to check compressions this week.

Cheers,
Matt

[matteo]

Hi,
I've checked compressions: 120 - 120 - 120 - 110 psi. So, some general wear as they used to be up around 130 (years ago) but I don't think this signals an obvious problem with a particular cylinder. It has been drinking more oil than usual though...
Matt

[Robsey]

That 110 may be just a little low.
It would definitely indicate a significant difference from the others.
And I am sure "they" used to quote all readings should be within 10% of each other. 110 is only just within 10% of 120.

I presume all rockers / tappets are adjusted up correctly.
My line of thinking is one of the valves on cylinder 4 not closing properly allowing leakage or blow-by.

Have you repeated the tests with a smidge of oil in the plug holes.

If there is no difference, it would indicate valve wear or mal-adjustment. Or worn valve stem seals.

If the 'wet test' provides a higher set of values, then the piston rings on cylinder 4 may be worn.

If you are using more oil... I assume it is being burnt off in the exhaust.

When warmed up, if it smokes briefly on each acceleration and over run (release accelerator pedal), then this points towards worn valve stem seals.
If it smokes all the time with a blue haze, then again possible piston-ring wear.

[matteo]

Hi Robsey,

Thanks for your reply. I have to confess in all my years of running this van I've not checked the valves. As they are of the self-adjusting hydraulic tappet type I'd always assummed I didn't need to check them. So now you've said that I'll have a look and see if they are at least free and moving OK.

 

[Robsey]

It may not be the tappets or valves themselves.
Valve seats can also wear,

but the symptoms that I described are with regard to the seals on the valve stems.

[ajsimmo]

No valve stem seals on these engines. Difference in compression not significant enough to worry about. It's just looking like an engine that's done some work in its time and is getting a bit tired, but hopefully plenty of life left yet. A bit like me.

Sent from my ONEPLUS A3003 using Tapatalk