No compression on No3

[john.p.clegg]

Dear All

Can anyone help? Have just visited a 69/70 Plus2 and there is no compression on No3,the valve clearances are OK and looking down the plug hole all looks OK,without an endoscope I can go no further at the moment....I know it's a head off job....but ...any guesses?

Thanks
John

[MintSprint]

Have you tried the standard technique of pouring a little oil down the plug hole and re-testing, to see if it's the piston rings?

Any history from the current owner of how it lost compression? Burnt valves tend to go gradually; sudden and total loss of compression is more usually a holed piston.

Other possible causes, one would expect to show other obvious symptoms (dropped valve would make horrible noises; bent valve would increase valve clearance, etc.).

Having said which, I'd be interested in other opinions, 'cos I'm currently wrestling with a complete and sudden loss of compression on No. 4 cylinder on my car, with no obvious damage even with the head off! Piston and valves look perfect, yet absolutely zero reading on the compression gauge!

[memnon]

How about a broken compression ring?

[Wayne]

Use a differential compression tester. Put air into #3 and see where it is going. My vote is with a sticking valve. The air will go into the crankcase (piston or rings) the intake ( intake valve) or the exhaust ( exhaust valve)

Good luck
Wayne