Pattern Ignition Coil Resistances?

[tzar250]

Hi

I've done a search through old posts about coils but can't find a definitive answer.

I have two new pattern coils - one from Yambits and one a "Whites" bought from Australia.

I've checked the primary and secondary resistances of both:


Yambits - 2.7ohm / 14.9Kohm
Whites  - 2.3ohm / 17.5Kohm

These are way higher than the Yamaha specifications (0.26 - 0.4ohm / 4.7 - 7Kohm) - expecially the primary resistance - which is near an order of 10 higher.  The secondary resistances were checked without the plug caps on - just to the HT leads.

I checked a standard OEM Yamaha coil with the same multimeter and I am reading in the correct range of resistances - 0.3ohm / 6.5Kohm.

Looking though old posts, it does seem that the pattern coil readings I am getting are similar to what others have measured.  So maybe that is the nature of these replacements?

However, in some of the posts, people have been stating they are using pattern coils with no problems at all and in some cases, improved running.

Before I fit one of these pattern coils I was hoping for some further reassurance that I'm not going to blow the CDI or other electrics.

Any input, thoughts, experiences appreciated.

[Sams Mum]

I would love to see any reply to this? Are they Ok as just fitted a new pattern one to mine and still no spark!

[enduras_wr200]

   Hi there guys, I am no expert whatsoever, especially on electrics, but my fiddling has shown me that unless you use a pretty good multimeter, readings can be way off. I have never had a problem fitting cheap alternative ignition coils on my TDR, whose  generator, pulser, ignition coils always read higher than the Yamaha values. Apart from that, have you checked the spark plug caps for correct resistance? That's a common problem that we easily overlook!


   Cheers, Fanis

[James P]

I have two new pattern coils - one from Yambits and one a "Whites" bought from Australia.

I've checked the primary and secondary resistances of both:


Yambits - 2.7ohm / 14.9Kohm
Whites  - 2.3ohm / 17.5Kohm

These are way higher than the Yamaha specifications (0.26 - 0.4ohm / 4.7 - 7Kohm) - expecially the primary resistance - which is near an order of 10 higher.  The secondary resistances were checked without the plug caps on - just to the HT leads.

I checked a standard OEM Yamaha coil with the same multimeter and I am reading in the correct range of resistances - 0.3ohm / 6.5Kohm.

Hmm, that is interesting. The standard Yamaha plug caps are 5kOhms each aren't they? If so, could measuring the secondary winding of a 'genuine' coil with plug caps fitted give something in the order of 15-17kOhms...?
The workshop manual is not clear on whether the measurement should be made with or without plug caps. It says "Connect pocket tester to spark plug leads" - it doesn't mention whether the plug caps should be removed or left in place and the pictures are a little blurred for me to discern whether the caps are still fitted or not. It is not outside the realms of possibility that Yamaha made a slight error in specifying the resistance without plug caps, but showing a picture with plug caps. I haven't got an ignition coil to hand to check for myself . I acknowledge that you made your own measurements without plug caps, which would suggest that Yamaha's specified resistance was measured in similar fashion.

If Yamaha's specified resistance applies without plug caps, could it be that the aftermarket ignition coil assemblies are made for use with non-resistor type plug caps??

I can't explain the large difference between primary winding resistances, other than to ask if your multimeter indicates 2 Ohms with the probes contacts held together?! That problem has caught me out once or twice .

Regards,
James

[tzar250]

Just an update to this old post.

I ended up buying and fitting a DynaTek Miniature series coil (DC11-1) with a primary resistance of 0.5 ohms - which is pretty close to the OEM Yamaha spec and a lot closer than the measurements I was reading off pattern coils. The DynaTek website suggests they tested it on a TZR and had good results.  I also have more confidence that this brand is going to be more reliable than a pattern part.

It fits pretty well in the standard location, although the lead outputs are not in the same place as the Yamaha coil - I have used champion non resistor plug caps to attach to the coil and NGK resistor caps at the sparkplug end.  Just using copper multicore HT lead rather than the optional Taylor silicon leads, as its just easier to fit the leads and caps together without having to have the correct crimping tool/skill.

I've done about 300 miles using the Dyna coil so far and - touch wood - it seems to function well.  Can't say I have noticed a measurable improvement in performance but it starts 1st or 2nd kick (which, to be fair, it did with the nearly NOS Yamaha coil previously fitted).  The only thing I have noticed is that the plugs seem to run with a lighter brown colour than on the OEM coil.  Maybe down to the higher output voltage?

Here are a couple of photos to show the arrangement.