19 replies to this topic

[richw911]

1275 carb

Car lost power and was only running on three cylinders

I checked for spark which there was then changed the spark plug still the same.
I've just done a compression test and I've got 150 on the first three cylinders but the last one nearest the radiator has no compression at all.

From your experience is there any chance a head gasket can cause just one cylinder to go down or do you think it's the ring or valve?

The valves are moving freely.

They normally go between 3 and 4 dont they and you lose compression in both?

I know I won't know properly until omi remove the head just wanted to know if you can just lose one with a head gasket.

Any advice much appreciated :)

[carbon]

Are tappet clearances all OK?

 

Could also be burnt exhaust valve.

[Northernpower]

Is this a new rebuild or an established engine?

[richw911]

I've not checked clearances since the fault but it was done about a month ago

[richw911]

Established engine

[Northernpower]

If you're happy with the ignition side it's sounding like a burnt valve, it's unusual for the head gasket to go on number 1

[dyshipfakta]

Put a touch of oil in the bore and retry. If it still sucks it's the valves or the gasket and you will have to pull the head for both so that would be my next quick test.

[Magneto]

You're going to have to pull the head no matter which it is, but I'm betting a burned valve too.

Edited by Magneto, 03 August 2017 - 06:56 PM.

[richw911]

Ok thank's guys just had a thought It could possibly be a leaded head , I guess that could cause seat damage because I'm obviously using unleaded

[Rorf]

Or a hole in the piston   

[Homersimpson]

I've never known a burnt valve give no compression at all, i've always got at least 20PSI, if you take off the oil filler cap whilst its running do you get a load of back pressure which might suggest a holed piston?

[Homersimpson]

One other thing, do you have a compressor, if so you could remove the spark plug and stick an airline blow gun in the hole.  With the oil filler cap and an assistant you can check where the air is going, either out of the oil filler indicating piston and or ring problems, out of the exhaust or the carb indicating valves or to open air indicating head gasket or damaged to head or block sealing faces.

 

Once you have done this best to pull the head and assess the damage, hopefully just a really bad valve.

[richw911]

The head is off.... and it got a burnt exhaust valve on cylinder 1! Yay not too bad a job :)

Many thanks indeed for the help and pointers love this forum! :)

[carbon]

Couple of suggestions:

- first check the valve seat very carefully. Chances are it will be OK

- before putting back on the road check the fuelling, as running lean will burn out exhaust valves

 

Is the engine bog standard or modified?

[richw911]

Ok will do. It's fairly standard just a cooper free flow manifold and RC40 twin box exhaust.
The car was set up on a rolling road after I had the carburettor refurbished.

The engine is of unknown mileage and was purchased many years ago.