Voltage at Coil Terminals - Help Please

[AustinWood]

Have you tried moving the plug from No1 to a different cylinder?
Just because it fires when out of the engine doesn't necessarily mean it will fire under pressure.
It could still be a faulty plug.

["Slack Alice" Simon]

I took my engine to bits, replaced (amongst other things) the valves and guides, and so far have done about 50 miles.

OK, until I was coming home yesterday.   Then it goes on to three cylinders and makes a loud rattling noise.

Head off - No.1 valve stuck wide open, and it takes some effort to close it.

Manifold off, and valve out.   It looks like some slight foreign body had gone down the guide and jammed the valve.


Does the "thumb" compression test feel different from No. 1 to the others?


Bite the bullet - it doesn't take long.   Its getting the surfaces clean that takes the time.

And putting the collets back in.   I gave up after an hour and a half, and made a tool to hold the collets.

Sorted, five minutes later!

Simon

[Andy Bennett]

I had problem like this a while ago. On putting the plug on the head I had a big healthly looking (but yellowish) spark.
I swapped plugs and problem remained with same cylinder.
I remade the connection at the distributor end of the plug lead as the copper strands were looking tarnished and some had broken, so there were fewer strands left than in the cable.
Result was nice blue spark on the head and then healthy firing.
Just a thought as you don't mention anything about the plug leads.

Good luck
Andy B

[John P]

Curiously enough I have just re-made the connection at the plug end of the spark plug lead and replaced a more modern style plug cap which "screwed" into the lead with a traditional soldered on spade connector.

This seems to have solved the problem but unfortunately I've not been able to take it for a run as I've now found a water leak which I suspect is from the core plug at the back of the block.

Looks like either removing the engine or somehow moving it forward to get access to sort this out but at least the mis-fire and possibly also the poor starting have been resolved.   Annoying that I still can't drive it but I don't mind something like a core plug because at least I know what to do.

Many thanks for everybody's help,

John.

[Dennis Nicholas]

Bear in mind that the core plugs were there to let the sand out when casting complete so they are not really required.....i.e you can clean the area thoroughly using a mirror between bulkhead and block to see what you are doing, and then use JB weld to fill over the plug indentation.  I did this with a similarly placed plug on the back of my Scimitar V6 engine.  Since the JB weld (or similar) will sag or run off when it is a thick blob I used masking tape across the area to form a pocket into which the goo was placed.....first having primed the area with a thin smear of goo.  The remainder of the core plug can now rust away inside with no further leaks.
No the plugs are not there to stop cracked blocks if the water freezes in the winter............years ago I had a block and head crack in a 12/4 Riley with all plugs remaining intact. (water left in by me so the garage could move car but they thought I had drained it!!)

Dennis