No spark after rebuild

[qkingston]

So trying to get the 4a started after the complete rebuild. I have a newly rebuilt distributor from Martin Jay plus new Pertronix Flame Thrower coil supplied by him. New loom, new spark plugs (Champion L82C) and new leads. Engine turns over fine and all other electrical function are tested ok. I have 12V at the coil +ve but no spark from the King Lead (using a spark tester), other than a duff coil what else might be the fault?

Many thanks

David

[Lebro]

Check the points, & the thin earth wire inside the distributor, & the capacitor.

Is the firing order correct, Is the ignition timing right - how did you set it ?

Is the valve timing right ?

Bob

[boxofbits]

You should at some point get a spark, even if the ign/valve timing is out.

As Lebro comments the baseplate earth is important.

Sometimes the points have an oil residue on them from storage, so will need cleaning.

With the distributor cap off, do you get a spark when you carefully open and close the points with ign on with the tip of a screwdriver ( do not earth the screwdriver in any way.

When I got my distributor back from DD I didn’t need to touch or adjust anything other than timing, so coil is a possible but not probable.

Kevin

[qkingston]

Thanks Bob, I guess I was taking the distributor as a unit being correct as supplied and calibrated by Martin Jay. Firing order checked correct. I've rechecked TDC using a piston stop, checked the points, dwell angle and static timing using a Gunson Sparktune meter, followed RobH's fault finding guide, but still no sign of a spark...I'm scratching my head

David

 

[qkingston]

3 hours ago, boxofbits said:

You should at some point get a spark, even if the ign/valve timing is out.

As Lebro comments the baseplate earth is important.

Sometimes the points have an oil residue on them from storage, so will need cleaning.

With the distributor cap off, do you get a spark when you carefully open and close the points with ign on with the tip of a screwdriver ( do not earth the screwdriver in any way.

When I got my distributor back from DD I didn’t need to touch or adjust anything other than timing, so coil is a possible but not probable.

Kevin

Thanks Kevin, I've checked for spark at the points as suggested and that works...so distributor cap??

[roy53]

lead coil to distributor fault?  cap?

Rotor arm my bet

Roy

[qkingston]

Yes I suspect leads or cap potentially. Rotor arm as supplied by Distributor Doctor so I hope not...

[boxofbits]

Could be any of the above. You could check the points open ( about 0.015”) on the heel ofthe distributor cam. DD might just have screwed them in without gapping. Make sure your rotor is turning. Sounds okay electrically otherwise.

Kevin

[qkingston]

Thanks Kevin, is there a preference between the side entry and top entry caps? I have a Lucas side entry spare which looks well made, but went with the top entry to suit the push on silicon leads. What sort of resistance value would you expect from a lead? I measured between the coil +ve terminal and the HT connector :  10.24 KΩ, I then connected the king lead to the cap and measured 12.23KΩ from the terminal, sounds a bit high?

David

 

[Dic Doretti]

          If there is no spark at the king lead and the distributor has been rebuilt by the Distributor Doctor and there is a spark at the points then I would suspect the coil.

          Cheers

          Richard

[Lebro]

12 K for an HT lead sounds about right.

Bob

[Waldi]

Agree with Richard,

Can you try another coil?

And is the distributor turning when you crank the engine (is it engaged with the cam shaft drive).

Waldi

[ianc]

Coil is mounted on inner wing, but I cannot see evidence that its can is earthed - if no earth, no spark.

If no earth to the coil's can, then run an earth lead to one of its clamping bolts.

Ian Cornish

[RobH]

11 minutes ago, ianc said:

Coil is mounted on inner wing, but I cannot see evidence that its can is earthed - if no earth, no spark.

Sorry Ian but that is  incorrect. There is no electrical connection to the can of a coil and it does not need to be earthed. 

The only low-tension connections are to the two tags. 

[qkingston]

13 minutes ago, ianc said:

Coil is mounted on inner wing, but I cannot see evidence that its can is earthed - if no earth, no spark.

If no earth to the coil's can, then run an earth lead to one of its clamping bolts.

Ian Cornish

That's a good point Ian, I'll check that

David 

[qkingston]

1 minute ago, RobH said:

Sorry Ian but that is  incorrect. There is no electrical connection to the can of a coil and it does not need to be earthed. 

The only low-tension connections are to the two tags. 

Ah thanks Rob. Your fault finding guide is very helpful

[RobH]

post removed - this reply was not necessary as the previous one had been read.

 

Edited April 24, 2022 by RobH

[stuart]

You have checked that the distributor is actually turning I take it?

Stuart.

[boxofbits]

15 hours ago, qkingston said:

Thanks Kevin, is there a preference between the side entry and top entry caps? I have a Lucas side entry spare which looks well made, but went with the top entry to suit the push on silicon leads. What sort of resistance value would you expect from a lead? I measured between the coil +ve terminal and the HT connector :  10.24 KΩ, I then connected the king lead to the cap and measured 12.23KΩ from the terminal, sounds a bit high?

David

 

Hi David

You don’t really need to get into measuring resistance values of leads and all that. Put a plug lead into the coil (try 2 or 3) with a spark plug inserted, and flick the points open with the tip of a screwdriver as before with ign on. You should get a spark at the plug ( make sure the plug is earthed to the engine or the body). As advised above, make sure the rotor is turning when you turn the engine over on the starter. If it is, you should also try another cap and leads. Hope you trace it.

Kevin

[Michael Mckiernan]

Hi David , have you checked that you still have 12v at the coil when the engine is turning over ?

Possible that the feed drops out when you crank it over.

Mick

[Charlie D]

1 hour ago, Michael Mckiernan said:

have you checked that you still have 12v at the coil when the engine is turning over ?

That reminds me.
I’m not sure if the ignition switch is the same as it used to be when I had a Herald, but I had a similar problem after a rewire.

 I eventually discovered that I had wired the coil circuit to the “Radio” terminal on the ignition switch. This gave 12 volts to the coil when the ignition was turnrd “ON” but when I turned it to “Starter”, the feed was switched off. (The logic being that you don’t want the radio on when you spin the starter over in case the interference deafens you.)

Maybe a total red herring, but worth checking you have volts to the coil when the starter is spinning, not just when the ignition is on.

If not, and there is a connection for the radio on the ignition switch, maybe that is where the problem lies.

Charlie.

[qkingston]

Ok got it sorted and started first time since the restoration started 3yrs ago! Checked the condenser securing, changed the cap and the leads and hey presto! Now the ignition warning light doesn't go out, the carbs need setting up properly (won't idle on no choke), but sounds pretty smooth so I think the timing end is pretty close.

Thanks for all the really helpful advice, a major milestone!

David

[ianc]

Well done, David.  Onward and upward!

RobH is correct  and I was wrong - there is no earth required to the coil's can.

Ian Cornish

[MilesA]

14 hours ago, qkingston said:

Now the ignition warning light doesn't go out, 

Well done.

Also had this issue after a partial loom rebuild by me. I had failed to connect / connect properly the lead from the alternator. Problem solved. Worth checking if you have one.

Miles

[qkingston]

I'm on a roll, sorted the ignition warning light! I took the alternator plug off to do a continuity check on the Brown/Yellow wire to the warning light (OK) then when pushing the plug back on it went into the socket a little deeper and the warning light extinguished almost immediately on start up. On to the next one....