2 black plugs

[horrace]

So heres where we are.... started horrace after a year off the road. Drove to his new home 1 mile away, it sounded like ut was firing on 3, so not a great start!
I had decided to upgrade to electronic accuspark so I got new dizzy, new coil (!) 4 super whizzo spark plugs with 3 prongs on the electrode and 4 new ht leads.
Fitted all the above and second time lucky (when I realised what I thought was no.1 cylinder was no.4!) it ran better than before but is a little rough. I have removed the spark plugs to check colour and no.1 and 4 are great colour but 2 and 3 are black as your hat.
Any clues as to the fault... other than the mechanic!

[simmitc]

What are the compression readings on all 4 cylinders?

[horrace]

no idea on that, id have to get a compression tester from somewhere for that.

[philthehill]

Before you rush out and buy, beg, steal or borrow a compression tester
When turning the engine over on the starting handle are the compressions similar, what do they feel like?

[horrace]

too late £25 seemed like a reasonable investment for a compression tester will check tomorrow, what should I be looking for in bar or psi?

[bigjim]

150 psi is about normal are you running twin carbs or do you have an air leak making 2 rich and 2 weak

[horrace]

no just 1 carb, wondering if the valves on 2 and 3 may have got some bits in them whilst they were open as it was stored and not run for a year?

[bmcecosse]

Check the valve gaps.... And swap the plugs over (1 &4 swap with 2 &3) - just to see if the colour moves with the plugs. There is always some mixture difference between the end and centre cylinders/plugs -but not as dramatic as you suggest!

[horrace]

Ill check the gaps tomorrow, but i just changed the plugs and the old plugs were sooty on 2 and 3 now the new plugs are sooty as well so cant be just those plugs.

[bmcecosse]

Fraid it sounds like a problem with the piston rings then - letting oil up to burn in these chambers......

[horrace]

thought oil was greasy black not sooty black? i figured it was too much fuel or not enough air?

[bmcecosse]

Indeed - but the engine doesn't separate the air fuel between the two cylinders fed by each port in the head........

[horrace]

compression test results
No.1 190 psi
No.2 150 psi
No.3 180 psi
N0.4 185 psi


its a 1275 head which is why i guess the compression is higher than big jim said?

[Tudge]

Seems like no2 is having a problem! Can try a wet test by putting a squirt of oil into the cylinder through the spark plug hole to see if it's the rings or valves.

[horrace]

So I squirt in the oil, then what? See if drains ?

[horrace]

just googled it! will try that next

[simmitc]

After adding the oil, repeat the compression test. The theory is that if the rings are leaking, then the oil will provide a seal and improve the reading. If the valves are at fault, then the oil will make very little difference. Ultimately, it might be off with the head; but the diagnostics can help pinpoint the problem. You're heading in the right direction, and learning about the car as you go.

[bmcecosse]

These results are very good -except for #2 of course - but even it isn't desperate... Did you check the gaps before doing the test? I would be tempted to run it and lean out the mixture little by little till you get a decent balance.

[horrace]

well, whaddya know..... turns out that no.2 and no.3 cylinders are leaking air from around the spark plug! I heard a hissing noise and squirted a bit of wd40 around the plugs and hey presto they bubbled away.
Now... Im not sure i should be chuffed as i found the problem or peeved as i dont know how to fix it (other than machining the head?)

[simmitc]

Well done for locating the root of the problem. As long as the mating surface is clean and new plugs (ie new sealing rings) are used, then they should seat and seal OK. Perhaps worth chasing the threads to make sure that the plugs are not stopping early before they seat properly. It is very unusual for for there to be a leak around the threads.