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drmini in aust
 Post subject: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 9:55 am 
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Joined: Fri Mar 19, 2004 6:19 pm
Posts: 39752
Location: near Baulkham Hills, NSW
I bought a new GT40 R coil over the counter a few years ago but never used it.
The other day I checked the primary resistance, expecting it to be around 1.5 ohms.
But it measures 3.1! Yes I checked my meter.
Unless these coils are made funny I guess Mr Bosch put the wrong label on it. Rumour has it they are made in China now.
It says GT40 R, use with resistor.... :-/

Worth checking resistance, when buying a coil. Not years later. :wink:

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:
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cooperess
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 10:30 am 
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1098cc
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Joined: Wed Sep 30, 2015 9:38 am
Posts: 1572
Location: Brandy Hill, NSW
Are you saying that a Mini won't run unless resistance is around 1.5 ohms?

I ask because I can't get my Mini to start using a new coil and resistance is 9 ohms.
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drmini in aust
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 11:16 am 
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Joined: Fri Mar 19, 2004 6:19 pm
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Location: near Baulkham Hills, NSW
No I'm not saying that. I bought it as a 1.5 ohms and it's not. Some electronic ignition performs better with a 1.5 ohm. Fatter spark.
3 ohm coils are for ignition points systems. Which I'm not building.

Re your 9 ohms resistance, if that's measuring across the coil only, it's buggered.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R. :mrgreen:
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cooperess
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 12:25 pm 
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1098cc
1098cc

Joined: Wed Sep 30, 2015 9:38 am
Posts: 1572
Location: Brandy Hill, NSW
It's a points system car and is 9 ohms across - to main and + to main and it's brand new.
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clip
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 1:40 pm 
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848cc
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Joined: Mon May 06, 2019 5:29 pm
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Location: Sunshine Coast QLD
cooperess wrote:
It's a points system car and is 9 ohms across - to main and + to main and it's brand new.

Just check the resistance of your meter leads and probes alone, whatever that comes out to will need to be deducted from the reading from the coil. Shouldn’t be much, maybe 0.2 or 0.3 but worth checking.
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68+86auto
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 3:32 pm 
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998cc
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Joined: Fri Oct 18, 2019 5:11 pm
Posts: 601
Location: Brisbane Northside
cooperess wrote:
Are you saying that a Mini won't run unless resistance is around 1.5 ohms?

I ask because I can't get my Mini to start using a new coil and resistance is 9 ohms.


Are you sure it isn't 0.9 ohms. 0.9 ohms is for a lot of electronic ignitions and will burn out points very quickly.

Minis with points ignitions should be about 3.0ohms. about 1.5ohms if a ballast resistor is fitted.

Electronic ignition varies depending on the manufacturer/model.

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Goldbrocade_62
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 8:16 pm 
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1098cc
1098cc

Joined: Mon Nov 06, 2006 8:54 pm
Posts: 1789
Location: Hunter NSW
Ac dodd spoke about tis on YouTube
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IndigoBlueCooperS
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 8:42 pm 
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998cc
998cc

Joined: Sun Nov 06, 2005 5:41 pm
Posts: 859
Location: Adelaide
The standard non ballast coil as used on the late UK Mini with factory electronic ignition for use with 65D distributor is 0.9ohms (from the UK Minispares site).
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timmy201
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 8:43 pm 
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1275cc
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Joined: Sun Apr 29, 2012 1:19 pm
Posts: 4494
Location: Wollongong, NSW
Goldbrocade_62 wrote:
Ac dodd spoke about tis on YouTube

He does lots of helpful videos on minis

Coils


Distributors

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cooperess
 Post subject: Re: Bosch GT40 R coil..
PostPosted: Wed Jan 25, 2023 10:07 pm 
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1098cc
1098cc

Joined: Wed Sep 30, 2015 9:38 am
Posts: 1572
Location: Brandy Hill, NSW
Thank you timmy - very helpful.

Think I may have solved this. I need to learn how to use my multimeter.
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