UK Car Repair: corsa 1.0 12valve 53plate tapet noise, hydraulic tappet, low oil pressure

Question
i have a 53 plate 1 liter 12 valve 3 cylinder corsa that after being sat 4 3 months drove fine 4 a couple of days but now has a loud tappety sound from number 1 cylinder and the oil light comes on and off any ideas?

Answer
Possibilities:

Low oil level.
Oil degraded due to being stood.
Mechanical failure of hydraulic tappet on #1 cylinder.
Oilway clogged.
Oil filter clogged.
Oil pump worn out.
Oil contaminated with fuel or water.


Check if there's any metal filings/chunks in the oil - easiest to do by pulling the dipstick and rubbing the oil between your fingers, any metal will be obvious.

Oil light coming on indicates low oil pressure, if there's loud tapping from #1 I expect the tapped has smashed.. probably due to sticking due to being stood, in that case instead of following the cam it gets hammered by the cam and smashes.