"leak" from spark plug

[MarkyB]

You can do a compression check with your thumb over the plug hole, you should be able to spot the difference between a good 'un and a bad 'un quite easily.
Just keep clear of the HT leads when turning the engine over!

[JOWETTJAVELIN]

Must you have the ignition on to turn the engine over? On early cars with pull-start the starter may be operated from the engine bay. Don't know if later cars have this feature.

[liammonty]

There should be a button (maybe with a red rubber cover) on the solenoid under the bonnet that you can press to turn over the starter- I think that will work without ignition on.

[MarkyB]

If you are lucky the solenoid will have a button underneath you can push.
Otherwise it's up to your beautiful, or otherwise assistant

[bmcecosse]

And take a lead off the coil if sparks worry you!

[oddbod]

You can do a compression check with your thumb over the plug hole, you should be able to spot the difference between a good 'un and a bad 'un quite easily.
Just keep clear of the HT leads when turning the engine over!

Do I need to remove 1 plug at a time, or all at once? I understand that if I use a compression tester I would remove ALL the plugs before I test, is that correct, getting shocked would put the tin hat on my week and I could do without it!

[bmcecosse]

Yes - all plugs out and throttle open. Normally would do it hot - bit I don't think you should run your engine. Cold result will tell all.....

[kennatt]

getting shocked would put the tin hat on my week and I could do without it! ............................................don't get too stressed about this it just gives you a jolt,can't hurt you,just makes you jump, the worst would be if your head hits the bonnet,or you bang your elbow.

[oddbod]

OK just done a compression test with a Gunson compression tester. Front to back while cold (and freezing overnight): 1 180psi; 2 170psi; 3 55psi;4 55psi. I think this means a new Head Gasket? I have a workshop Manual but any pit falls? The head is a 1275 940g (so I was told by its last owner) What type of gasket? Will I need to replace exhaust/inlet valves at the same time?
Sorry for so many questions at once!

[chesney]

Gasket gone between 3 and 4. Use a 1275 gasket (matches head).

[oddbod]

Thanks Chesney, would that be a mini 1275 head gasket, pardon my ignorance but I feel I need very clear instructions at this juncture as I am contemplating taking my engine apart ( easy bit ) fixing it, then putting it back together and it working properly,with no bits left over.

[chesney]

No bits left over
I'm sure a mini gasket would be fine, just make sure it has the right number of stud holes!

[MarkyB]

I think the thumb test would have shown up a 100psi or more difference.
A good cylinder will blow your thumb out of the way, a bad one will just make a more or less pathetic effort to do the same.

[oddbod]

If I removed the oil filler cap and put my hand over it I could feel the difference from when it was running properly, I just hope I havn't warped the head!!

[chesney]

Only one way to find out!

[MarkyB]

Tiny danger of that, it's cast iron, not ally!

[bmcecosse]

Oh yes - they do indeed warp, and more frequently they will easily BURN between the cylinders if run with a blown gasket - the 1275 head has a narrow land between. First check - IS IT a 940 head?? Look under the rocker cover for the casting number. Yes - 1275 Mini gasket (local autoparts place - get copper one if you can) everything spotless of course - smear of grease both sides and torque in steps to 44 ft lbf. But while the head is off -I urge you to grind in the valves (renew if burned) and fit new seals to the inlet guides. Then set gaps 12 thou inlet and 15 thou exhaust. Retorque the head after the first heat cycle - and reset the gaps of course. The compressions on 1 and 2 are very good (especially considering it was done cold) - so the engine must generally be in good order!

[oddbod]

Yep definately a 940 head.