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Sorry David but you have it back to front - the longer the points are closed the more time you have drawing current through the coil - closed points provide the chassis earth for one end of the coil thus taking current through the low tension winding - when the point open the change in current in the low tension coil induces a voltage and current in the high tension coil. there may be a problem with the condenser but I thought Frazer had changed it at some point.

Check the current that is being drawn through the coil with the points closed and see if it is as per spec on the new coil- the erratic behaviour will be caused by the overheating so cure that and you should be ok.

A thought - what voltage are you getting on the "12v" end of coil - is there a problem with alternator overcharging?

You're right Fred always get that mixed up and didn't check my notes last night when I posted, ..... Just proves that infallibility is not one of my many virtues....

This car is defying all logic, the timing appears to go in and out at will, last night the points closed completely then when regapped it started popping and banging. I switched it off and the next time it was like the battery was flat pointing to bad timing. We jump started it and eventually it ran very lumpy.

There are now five of us who are stumped including a good friend who builds racing engines for Austin Healeys!!

I changed the white wires a few years ago from D4 to D5 but still only get 12 volts at the coil as opposed to 13 or 14 as stated in a post on here. Is it possible that the ballast wire is still connected?

Seriously considering an engine change now........

Measure the voltage at the battery and then D5 - the source of the white wire to the coil - I think that comes from the ignition switch - if there is only 12v at D5 and 13 -14v at the battery ( may not be that high if the engine is not running) then you have some resistance in the circuit from the battery to D5. When you have volts at D5 and the points are closed measure the current passing through the white wire to the coil.
All this could just be a red herring but you perhaps need to understand what is happening to make the coil hot.

an obscure thought - is everything ok with the timing chain

D5 has a direct link to the battery via the ignition switch solenoid etc. It does not have the resistance wire in circuit. You should be getting battery voltage at D5, as Fred says.

I don't understand how your timing could change unless the drive slot on the pump has broken or the base plate on the distributor is loose or sticking.

It's best to set the points gap roughly with feeler gauges and then check and finally adjust with a dwell meter if you have access to one. I still use and old Gunson's one I bought almost 40 years ago.

Breaker gap is 0.020" and dwell is 36° +/-1° on distributor part number 79921929 and 50° +/-1° on distributor part number 7992820.

Back again, took the head back off today to find all four bores full of water, the three head bolts underneath the inlet manifold were not as tight as the others despite all being torqued to 55 as per the manual.

Could they have stretched and if so can you get new ones?

That's annoying...... if the OHC head is skimmed the bolts can bottom out in the holes in the block, they then torque down onto the bottom of the hole and not the head. Could this happen on the OHV heads too? The answer on OHC engines it to chop up to 3mm off the end of the bolts.

I also remember having to re-torque the head on an OHV engine a couple of times after fitting a new gasket. The manual doesn't mention re-torquing but I suppose it depends on the gasket if it compresses over time or not.

The manual also says that the gasket should be smeared with product called 'Wellseal' which is probably no longer available.

Wellseal is alive and well and will be used this time instead of Hylomar. I have been told to cover both sides of the gasket and the block and head then put it on. My friend who builds racing Healy engines has used Wellseal for 30 years and never had a leak from a gasket so hopefully it should work.