Hi Guys

I was driving along in my 1100 when suddenly it dropped to 2 cylinders. when i pulled over to check it out, it idles rough though when you rev it past 1500 it makes a metal on metal tapping sound. so it turns out i blew a head gasket between cylinders 3 & 4 which is why they are both down on compression by 100psi and why its running on 2 cylinders. though what would that metal on metal tapping/ratteling sound be??

you'll find out when you take the head off... could be all sorts of things, but maybe just a noise the combustion is making

the head has been taken off and it looks fine! no scores in the barrels or marks on the piston. its a mystery so far

Oftentimes escaping gases/noise from a blown headgasket can sound metallic or like loud ticking

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If the head gasket blows between cylinders 2 & 3 cylinders gases excape into the oposing cylinder and often out through the intake valve/into the carburettor. The noise you may of heard could of been this, it even can make the SU piston flutter.

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have you looked closely at the tappets? It sounds like an arm might be broken or cracked due to the other damage. Make sure you inspect them really closely, might not be as obvious as first thought. If not, then its most likely just the noise from the blown head gasket.

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Bluey-1973 Clubby - 1330, high lift, big cam, 7 port madness in progress..

Gumby-1978 Minivan, British Racing Green - 1310, high lift, mild cam, enlarged porting and chamber shape with big valve head, supercharged build in ever slow progress!