1970 MGB Engine problem

[ormsky]

Recently bought a 1970 MGB GT (still running on leaded).
It was running fine, seemed to run best with super unleaded with Castrol valve-master.
With ordinary unleaded it seemed to have quite bad run-on when ignition switched off, but with the super unleaded it wasnt as bad (not sure why?)

Anyway, I thought I'd try Castrol Valve-master plus (with octane boost), with ordinary unleaded.
30 miles later the car seemed to develop an air leak from the manifold area but I couldnt feel anything around the inlet or exhaust manifold. Ran like sh*t and miss-fired, but managed to limp home from Anglesey.

Just done a compression test and number 3 pot has no compression at all!!!
With the tester in place on number 3 you can hear the air hissing through what I assume is a knacked valve or valve seat (haven't had the head off yet).

Don't know if it was related to using the valve-master plus, or just a tired engine?

Anyway, if you have what sounds like an air leak from the manifold area/through the carbs and engine runs like crap, recommend doing a compression test!!

Good time to upgrade to an unleaded me thinks!

[justinbaker]

May have run lean, and holed a piston. No compression at all though? Should get some I would have thought. I hope its just a stuck valve (open) so whip the rocker box of and use a tapping stick on the blighter.

[sheepy]

As Justin says, whip off the rocker-cover and see if it is something "simple" first. For example, broken valve spring.

[wildoliver]

I keep saying it but in all seriousness there is no need to use any of these valve protection products, in fact in my experience I tend to get most problems with head gaskets and burnt valves/pistons with cars that run webbers or use these potions, not saying either causes problems but it is a phenomenon I have noticed, the people running their cars for 12-15k a year on normal unleaded hard use on su's seem to get virtually no issues other than basic maintenance.

[ormsky]

Took the rocker cover off and couldn't see anything wrong, so today after work I took the head off.

No hole in the piston, but one of the valves has a small chip around the edge (could it have made contact with the piston?).

I'm tempted to look for a complete engine because:
- this engines already done nearly 80,000 miles since it was reconditioned
- if the valve did hit the piston then presumably there could be something else wrong?
- in my rush to get the head off, I loosened all the head bolts in sequence (except I didn't notice bolt number 11) what damage could that of caused?

Anyone got a good low mileage unleaded engine they're selling?

[wildoliver]

If the bores are in good condition with no wear ridge just get the head skimmed if it needs it and fit a new valve, don't waste money getting hardened seats put in till it starts to recess which it will probably never do, even if the head suffers recession you can still get seats put in then.