Changing Coils
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    mlb
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    Default Changing Coils

    I'm in the process of overhauling my igniton system and pretty much replacing everything. As ignition systems fall into the domain of white man's magic as far as I'm concerned, a bit of advice would be appreciated.

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    The car currently has an externally resisted ignition coil. I'm wanting to replace the coil with a 12v one just to tidy things up - and also I'm not too confident of the state of the resitor as I had to do a bit of a repair on it a while back. Is it possible to put a 12v coil in and get rid of the resistor. I'ts my understanding that the 12v coils are just resisted internally so to my way of thinking it's not going to make too much difference. However I'm thinking more of the other components that run off the coil - ie tacho. As they will now have around 12v fed to them will this cause an problems. Also will it increase the wear rate/damage the points?

    Cheers

    Matt
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    Moderator Alan S's Avatar
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    To my knowledge, if it has an external resister, then it has to stay an external resister. One guy recently reckoned he had replaced his with an internal one which didn't work out all that well.
    I once removed an external resister due to it blowing on me whilst I was out, so I could drive the car home only to find the new set of points I had in the car a few days earlier were totally shagged by the time I'd driven the car about10 klms home.
    Bosch I think you'll find sell a good style of coil with an inbuilt resister that is supposedly capable of delivering a good reliable spark. May be worthy of investigation, but logic says if the manufacturer reckons it needs a resister on the coil, then that's what it has to be for best results.
    The other option of course is to go for transistorised ignition.


    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

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    Contented Peugeot Driver addo's Avatar
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    Many tachos actually use the coil to supply the ground. Their positive voltage is fed to the gauge from your dash loom. In other words, the voltage at the coil is of no concern.

    Higher energy coils don't suck that energy out of the air. They draw more watts from your electrical system. In some instances this may exceed the current capacity of your present wiring. In other words, you could be digging a deeper hole. There's a nice little resistive block used on Chryslers and other cars which can be mounted to look neat/factory and be accessible.

    Problems with older dizzys: Shaft bushes flog out, allowing oil leaks and compromising advance mechanism. Advance springs stretch. Advance weight pivots wear and the weights cock and jam - unpredictably. Advance mechanisms run dry and get sticky. The net result of most of these problems is pinging - not nice to put up with. A rebuild is worth considering in conjunction with a recurve to suit your fuel/trans and driving habits.

    If you want more modern ignition a "bastard" distributor with a Bosch electronic module is the go, in conjunction with the HEC-716 coil. I love watching people get zapped by these; you can hear the spark! Performance Ignitions in Nunawading have done several of these distributors for me to suit different cars. They run a common cap (like, say, Toyota) so all parts are cheap.

    I know this sounds a digression but people often underestimate the effect of dizzy wear on their motor and the coil when working properly, plays a much lesser part whether it's a "hot" one or not.

    Regards, Adam.

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    In external resistor cars, the starting circuit usually bypasses the resistor so maximum voltage is delivered to the coil during cranking. When the key returns to the on position, the external resistor is then used. I'm not sure about 505's, but that's certainly how GM used to do it.

    '92 205 Mi16
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    mlb
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    Thanks for the guidance guys. So if I just change the coil for a 12v one with out any external resistance, chances are I could end up going through points like it's going out of fashion. I assume the condensors wouldn;t like it either then?

    Matt
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    More chrome aircleaners are sold than coils, but the market is similar in a way; it's something people can get their head around and like to justify swapping for a fancier one. You could use points/condensor off a 12V car and they'd be OK.

    A higher output coil will draw more current through the points and they will wear faster but it also draws more current through the coil feed - see my previous remarks.

    Honestly, just tidy it up and fit a nice resistor unit. More gains are usually had from a recurve.

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    Quote Originally Posted by addo
    More chrome aircleaners are sold than coils, but the market is similar in a way; it's something people can get their head around and like to justify swapping for a fancier one. You could use points/condensor off a 12V car and they'd be OK.

    A higher output coil will draw more current through the points and they will wear faster but it also draws more current through the coil feed - see my previous remarks.

    Honestly, just tidy it up and fit a nice resistor unit. More gains are usually had from a recurve.
    Thanks Addo,

    Just to clear things up, the intention of doing this is not for any power gains. There are far better ways of doing that than just changing the coil - and anyway my car doesn't need any more power the beast that it is - .

    The only reason I'm looking at doing this is to hopefully get rid of the resistor and tidy things up wiring wise. As I mentioned earlier I had to do a repair to the resistor and trim it a bit a few months back. My points have also worn out a bit quicker than expected, so I'm thinking maybe it's a faulty condensor - which I have already replaced yesterday - or a result of the shorter resistor. In a brainwave I thought why not just get rid of the resistor all together. Now it's looking like I can't.

    Matt
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    The resistor's only "wasting" a very few watts - far less than your radio. With the sourcing of modern condensors and points, a dodgy unit is always possible and that may well be what you've got. It's good to test your plaug leads for similar resistance to one another, too. and never trust plug gaps out the box.

    I'm emphatic about the other stuff because five years ago, found myself in a similar position; itching to spend on the ignition system of one car. Went chasing experts like Melbourne guru "jmac" among others. I was talked out of the fancy coils and MSD units etc and steered to the Bosch electronic with HEC coil. Could hardly be happier and it's low-key under the bonnet (I like that part). 50 thou plug gaps and three years life on a set with yearly regapping - I like it!

    Regards, Adam.

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    I've gone out today and bought a new resistor. Could anyone tell me what the proper resistance should be. The one that was there was 1.6 ohnm whereas the new one is around 2.3 ohms. I'm pretty sure that the guy gave me the right one as he knew what it was for and judging on the bits and pieces that have been fitted to my car by previous owners I wouldn't be surprised if the wrong one was fitted before.

    Thanks

    Matt
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    Contented Peugeot Driver addo's Avatar
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    Without the factory specs, you're guessing a little. The 1.5 or 1.6 certainly is the common Chrysler/Ford one. If you're not getting a nice fat spark off the coil lead when it's all said and done (and the coil meters up OK), you could try a lesser resistance. But it should be fine.

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