PISTON BROKE

GLENN TORRENS SILENCES A SINISTER SOUND FROM HIS RESURRECTED 1981 HOLDEN COMMODORE'S SIX-CYLINDER ENGINE

- GLENN TORRENS

MANY OF US will know the thought: It’s the “hmmm ... what’s that noise?” question that sometimes crosses our minds when the cobwebs have been cleared and the dust has settled after starting a shed-, paddock- or backyard-find car engine.

It was the thought I had about my 1981 VC Holden Commodore I found in a wrecking yard in Cooma, NSW where it had sat for 25 years. Driven around the yard, then on to a trailer and towed home for a resurrection, it was in the quiet confines of my garage that I’d first noticed a mystery murmur from the 3.3 six-cylinder engine.

Hmmm. What’s that noise?

Any older engine – the odo of this showed 170,000km and of course it’s more than 40 years old - can produce a multitude of noises. Hydraulic lifters can make a tick-tick sound before the oil pressure pumps-up after a cold start, or if it fades as a hot engine idles. More ominously, worn crank bearings can create a deep rumble. A damaged conrod bearing has a distinct doonk-doonk noise as its gap is slammed shut when the piston above it takes the load of compression. A gudgeon pin, if worn or loose, can chatter, as can a piston, if it is badly worn or cracked.

Judging by the sound – and a few other clues – it wasn’t a dud lifter creating the sound in my Holden six. The annoying noise with the engine fast-idling disappeared as the engine warmed. But it could be heard again when the throttle was snapped open with the car in-gear … but only sometimes!