Strange noise - engine on tickover

[oldporridge]

There's a strange noise coming from the engine compartment at tickover. It's at a much lower frequency than engine revs - a low regular soft 'thonk' about every second, ie 60 rpm, which is lower than the alternator pulley revs as well. It doesn't sound metallic or serious (I hope!) but quite puzzling.

If I rev the engine the noise disappears (or is disguised by general engine clatter and the exhaust?).

I first heard this beat a few months ago and have since done about 3,000 miles - it doesn't seem any louder. Everything else seems fine. Oil consumption remains negligible.

Any suggestions?

Thanks

1971 1600, alternator conversion, remote oil filter and cooler

 

[noddy]

Hi

Sounds like rod knock or piston slap on one cylinder. One way to identify which cylinder is making the noise is to get underneath with the engine running and use a T bar as a stethoscope. Put one end of the bar on a cylinder and the against the side of you head just in front of your ear, this way you should be able to here which is causing the noise.

Ian