Testing a Stator: More helpful info
Posted by Blaine
on Thursday, October 20, 2011 5:53 PM
Testing a stator…I was reminded of a piece of info that I was going to post at one time but forgot to. This pertains more to the 1990’s Cat stators and a little less to the newer style stators. Everyone knows when they look at their stator ohm specs that they give a range. For instance a stator that is supposed to measure 450 ohms the manual may give you a range of 380 to 500 or so depending on the temperature of the stator. When stators are warm after use they will give you a higher ohm measurement. The flip side of course is when a stator is cold it will give you a lower ohm reading henceforth the “range” a manual will give you which is perfectly fine. Here is an issue guys run into and don’t even know it sometimes. A stator’s ohms are based on the amount of wire on the coil..i.e. “X” amount of wire will give you “X” amount of ohms. This is pretty much based upon room temperature readings. When guys measure their stators when cold they may see something like 440 ohms or 435 ohms and think “It must be ok because it is in the range”. If at room temperature or cold if a stator ever measures MORE ohms than the recommended amount, in this instance 450, then it is bad. I posted that info last year but here is Pt.2 to this. I had a stator sent to me today off of a 1998 ZR600EFI sled. When I received it the stator had been in the mail box for a while at about 45 degrees or so outside. As soon as I brought it in I measured it. I measure all coils on all received stators before I work on them. All of the injector coils measured ok, fuel pump measured ok, lighting coils measured ok and the stator ignition coils measured 435 and 42 which according to the manual is ok plus neither coil was higher than the recommended 450 and 45 ohms. So, from experience I let it warm up to room temp in the basement…roughly 65 degrees or so and measured it again and it measured 45 ohms and 455 ohms. If you understand everything I wrote above then you understand that when the low speed coil measured 455 ohms that is more than the 450 ohms and the stator was at room temp so I know it was bad. Correlating it to what I said earlier, the ohms are based on the length/amount of wire on the coil so a coil doesn’t all of a sudden get more wire on it. Where I am going with this whole post is that guys ask us rewind guys all the time “How do I know it is bad?” and there are several answers that cover the spectrum from a coil being totally burned up and you can’t measure any ohms to a marginal stator that may even measure 440 ohms when at room temp. Other than measuring the AC voltage output from the ignition coils themselves sometimes it can be hard to pinpoint the stator as your problem. The number that it is hard to nail down as rewind guys in the minimum ohms you should see even when the coil is cold. I’ve seen coils measure 430ohms and are still good but in my example today I had a stator measure 435ohms when cold but when checked at room temp it ended up actually being bad. The same can be also said for the high ohm range..sometimes if the coil is shorting internally you can see very large/high ohm readings after the sled is run. The hardest stators to diagnose as bad are the marginal ones without checking actual AC voltage output from the stator which must be done using special measuring devices because a normal multimeter can’t measure it. I wrote everything above to basically say this: IF you have a no spark condition and the ohms aren’t real close even when the stator is cold, take the stator out and test it again at room temp and see if at room temp the stator actually shows its true ohm readings and reveals that one of the coils measures bad. If I wouldn’t have known to recheck the stator I received today after it was at room temp I would have thought that it was ok/in range or at least not showing any obvious signs of failure and sent it back to the guy….and I would have been wrong.
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