Bad earth somewhere, or something else?

[Bruins]

Hi All,

I have a 1967 tourer, completely rebuilt during covid (well got me out of the house much to my better half's relief). Had an issue with the lead not fully home between the coil and distributor cap a while back but easily solved. Only mod I did was fit electronic ignition (I know from reading strands on this and other websites this is a matter of heated discussion, like oil or grease in the steering rack!).

The engine developed an oil leak about 6 months ago, diagnosed as cylinder head gasket. Replaced this, de-coking and re-lapping valves at the same time and put back together, re-fitted carburettor etc. Now she just will not start; checked coil via resistance method, checked engine is earthed (she is positive earth). Fully charged battery turns engine over about half a dozen times and then loses power. Not the battery because only a year old and same happened with battery it replaced.

I also removed distributor cap and tested continuity pf all leads; OK. I have not tested again for spark to plugs (first time seemed weak and erratic. I suspect that under load something goes open circuit as the symptoms are the same as previous. Comments welcome; to sum up, drove car into garage, took head off and replaced gasket, re-assembled but now she won't start, very frustrating!

[myoldjalopy]

Did you re-set the valve clearances after replacing the head?

[geoberni]

Well quickly taking a read through of your post, one thing leaps out that me, and that is ...

Fully charged battery turns engine over about half a dozen times and then loses power. Not the battery because only a year old and same happened with battery it replaced.

A fully charged battery, especially a new one, should do a whole lot more than that; with the caveat that you have a sensible capacity battery and not brought something smaller than the original 40AHr rating that was the factory equipment.

So what is the battery?

I have electronic Ign too, and it's fine if the electrics are good.
Where it can cause problems is if the battery is struggling.
I'll use made up numbers just to illustrate the principle.

Electronic Ign requires 12v +/- 1v to work.
When turning the engine over, terminal voltage of the battery will drop, it's just how batteries work, pulling more current from them causes terminal voltage to drop. The effect is accentuated with an older tired battery.
So the fact that your battery is only managing to give you a handful of tries at starting the engine makes me thing that even at the first attempt, the terminal voltage could be dropping too low for the electronic Ign to operate, perhaps below 11v.

What I would do is charge the battery, stick a voltmeter across it and it will hopefully be showing 12.5v or more.
Crank the engine over and what is the terminal voltage dropping to?

Now the reason for this drop in voltage could be a stiff engine, depending how you put it together, or it could be a poor earth path back to the battery.

This comment about the spark also makes me wonder about the earth path....

first time seemed weak and erratic. I suspect that under load something goes open circuit as the symptoms are the same as previous.

[oliver90owner]

I expect it is a one or more poor connections.

The ignition system might checked without the engine turning (but not all).

Possibly check for spark by removing spark plugs, to reduce the load on the starter motor?

It could be a faulty starter motor, but not likely, given the information provided.

The use of a voltmeter to check voltage along the starting system would be my first move (along with checking for hot joints).

Whatever it is, it does not seem to be a difficult job to locate the fault.