Cranks but won't fire...

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nrgserv said:
:D
not entirely correct johnny!
the coil works on a back emf, which is why you get a spark when the contact breaker opens. as the current in the primary dissapears, it induces a current in the secondary, and due to the number of windings, creates a high voltage. current is very low.
oh, an its ositive an negative, on dc, not live an neutral :D
not nit pickin, but the bad connections as you say wont help!

edit.
thinkin about it, you,ve pretty much just descibed an ignighter coil for the likes of jetwash burners or industrial fired boilers!
Click to expand...
im going off what i know bout the workings of a step up transformer wich only fires as you say when the primary voltage is released kinda like a big capacitor does unless yer cleffer like me and wire up an old relay to switch itself on and off giveing you bout 100htz alternating current then use that to check the fooker (but ffs put the marrigolds on when checking it ):D:D
 
Water247 said:
Your response was awesome mate and have it printed out. I started to work through it today but it was so cold I was struggling with the dexterity of me digits so gave in! I know you said to check the resistance from the coil body to battery -Ve which along with JohnyCurts point made me want to clarify that did earth through it's body/securing bracket, as previously JamesMartin said it doesn't earth through it's body but through the points (which made sense to me). So anyway, I tested the resistance from the coil body to battery -ve and couldn't get a reading (no path).I didn't yet check the resistance from the coil -ve terminal to the battery -ve terminal which logic says I should also do.

....So once this is done what's yer tipple??!!
Click to expand...
not sure where james got that bit from, he,s usually pretty accurate with his advise.
stick a jump lead on the coil body to battery neg and turn it over.
 
johnny curt 1 said:
im going off what i know bout the workings of a step up transformer wich only fires as you say when the primary voltage is released kinda like a big capacitor does unless yer cleffer like me and wire up an old relay to switch itself on and off giveing you bout 100htz alternating current then use that to check the fooker (but ffs put the marrigolds on when checking it ):D:D
Click to expand...

hmmmm......
step ups use a.c.
caps only store it. they dont increase it.
would like to see a relay switching at 100 hz!
an your 100 hz would be on/off/on/off etc. not alternating current.

bet your a laugh in the workshop tho:D
 
I am confused. If a high voltage is passed (is it passed by a physical connection or does it leap within the coil by the way?) to the HT out why does it also need to earth through its body? Does it not earth through the plugs in any way and therefore need the negative earth through its body for the current to allow to pass to it?
 
Very Simply points closed ignition on and primary coil winding has power.
As points open the condenser stops points burning.
Primary winding switched off causes voltage on secondary winding which then is transmitted to distributor and eventually to earth through plug.

Electronic distributors use trigger wheel and hall effect sensor.
As trigger passes sensor it creates a pulse which is not big enough to switch coil-so an ignition amplifier takes the pulse an switches coil (contactless ignition)
 
nrgserv said:
hmmmm......
step ups use a.c.
caps only store it. they dont increase it.
would like to see a relay switching at 100 hz!
an your 100 hz would be on/off/on/off etc. not alternating current.

bet your a laugh in the workshop tho:D
Click to expand...

lets just say not only do i think of doing things most wouldnt i fookin go there with it aswell :eek::eek::eek:

ive always understood hertz as a measurement scale for the rate of a change or fluctuation counted by actions per second such as if it goes on and off 50 times a second therefore its working at 50htz

old tv screens (cathode ray tubes ) operate at 50htz meaning the pixels are fired on and off at 50 times a second too fast for the naked eye to notice this unless yer put yer nose to the screen and youll see it going on and off that rapidly
 
Last edited:
Another thing people do on some points is incorrect fitting shorts permanently to earth
 
OK, a few simple facts about mechanical ignition systems.
The coil does body not need to be earthed.
The spark happens because.....
with the points closed current flows in the coil low tension (LT) circuit.
When the points open the coil sees a circuit through the condensor, through the chassis and back through the battery (which might as well be a piece of wire in these circumstances). This is a resonant circuit. The current bounces back and forward between the coil and the condensor at high frequency until the energy is dissipated in heat. It's the electrical equivalent of blowing across the top of a bottle. So, opening the points produces a burst of high frequency AC in the coil.
The High Tension (HT) and LT coils act as a transformer, stepping up the voltage of the AC burst in the HT coil. This then produces a burst of HT current which flows from the HT coil, through the spark plug to the block and back to the coil via the condensor. The HT and LT coils have a common connection in the coil.
oxides-albums-oxide-s-photos-picture5160-circ-ic.gif

You will only get a good spark if you test the coil by breaking the circuit at the points.
 
didnt know the coil ht was connected internally to the coil neg. thought it was the casing.
in that case, change the condensor.

i will research this when i am a bit more sober.

(but the essay still applies)
 
nrgserv said:
didnt know the coil ht was connected internally to the coil neg. thought it was the casing.
in that case, change the condensor.

i will research this when i am a bit more sober.

(but the essay still applies)
Click to expand...

Condensor changed already - no difference. Will still use essay :yawn: but just ignore the body/earth bit.

Thanks for all your pateince, this is slowly starting to make sense it's just taking a while for the picture to build in my head. Will hopefully be all the greater sense of achievment when it finally fires up for me :)

Right, I'm of for a run. Will report back with results soon.
 
have you checked the connection to the distributor and the connection lead to the points are not grounding also have you checked the high tension connection for corrosion( usually a brass or aluminium feral held in by a centre fixing screw and sealing washer to prevent dielectric's fluid escaping)corrosion can causing high resistance joint,have you checked the main h/t lead for continuity and for good connection's on both ends of the lead carbon type prone to breaking down with age
and finally is the coil the correct voltage some vehicles use a 6volt coil and a ballast resistor is wired in the run circuit and by passed when cranking engine to give better sparking when starter motor draws the voltage down(12v coil no ballast resistor) and try disconnecting condenser to confirm new condenser is ok
 
9 volt coil as this is usually whats voltage drops to during cranking ,resistor keeps coil input to 9 volts when running and not cranking ,you would get a good spark with 9 volt coil but not for too long,
 
jamesmartin said:
i was right after all ,but probably should have explained in more detail like oxides
Click to expand...
appears i have given misleading information.
not disbelieving anyone, i was under the impression the coil needed to be earthed, and while ****ing about in the workshop i took the time out to try it using an old coil, dizzy, plugs and battery.
i found you dont need the coil earthed!

sorry bout that!
:eek:
 
nrgserv said:
appears i have given misleading information.
not disbelieving anyone, i was under the impression the coil needed to be earthed, and while ****ing about in the workshop i took the time out to try it using an old coil, dizzy, plugs and battery.
i found you dont need the coil earthed!

sorry bout that!
:eek:
Click to expand...

Did it hurt?:D
 
...and a last thought before bed, do you have the flexible earth cable that goes from the dizzy body to the condensor mounting point?
 
Right... If you all form an orderly queue you can take a turn each at calling me a dick.

When I reassembled the dizzy with the new points and condensor I placed the nylon insulating collar BETWEEN the points and the braided earth cable/condensor so my LT coil circuit was never being completed. Thankfully with my new knoweldge of how ignition systems worked I was able to look at all the elements logically and follow them through until I saw the problem - so a big thank you to everyone for all the great info to help me understand what it was I was looking at.

So perhaps it was (at least) the points/condensor that were at fault after all as prior to changing them it was completely dead (and they would have been connected correctly as it was working with them up until recently).

I did the spark test again (with king lead) but still don't get a strong blue spark, though it was nice to finally see a consistent spark (even if it is a bit weak/orange). It's also a nice dry day today so interesting to see if the tempermental starting happens again in the damp. I may still need to sort some other bits out if so but for now he starts up so I am very happy and I can start using him again whilst I continue to check all the other bits.

SO, after all that who do I owe beer to? I think I am definitely 'in the chair'.
 
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