Re: Front mount coil

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Posted by Bruce (VA) on May 11, 2017 at 08:59:04 [URL] [DELETE] :

In Reply to: Front mount coil posted by Bob E on May 10, 2017 at 23:50:45:

Correlation does not imply causation.

The fact that the tractor wasn't running well with one coil and now it does w/ another coil does not mean the first coil was defective.

I have a coil on one of my N's that fits the description you gave; it came from a neighbor. He swore it was defective because his new coil got the tractor running. It's been on my tractor now for a few years.

I've got 3 frontmount 8Ns. In the past 17 years, I've had 2 coil failures; one was stripped threads on an otherwise good coil & the other really was a failure. No spark when hot.

Coil problems are difficult to diagnose. For starters, round coils are pretty robust & square coils arenít (because of the difference in insulation used), but neither one will hold up to a poorly done 12v conversion that allows too much current to the coil or leaving the key on (see tip # 38). Too much current creates heat which melts the insulation. Insufficient resistance in a 12v conversion will do the same thing. Rarely do coils just ďgo bad.Ē

There are a few ways to see if a coil is bad, but itís not possible to determine if a coil is good w/o some expensive testing equipment. If you detect a dead short or high resistance in the coil w/ an ohm meter, itís bad. If itís cracked, itís bad. If a sidemount coil w/ battery voltage to the primary will not jump a ľĒ gap from the secondary wire to the block, itís bad. But, here is the hard part: even if you do not detect a short, even if it will produce a spark, even if itís not cracked, that doesnít mean the coil will work when itís hot & under a load. So, itís a process of elimination. If the tractor starts & runs fine for 30 minutes or an hour then cuts off & refuses to re-start, and you checked for spark at the plugs & it had no spark at all, AND you have the correct voltage at the coil thatís a good sign that you have a bad coil. Let it cool off, restart it & if you have a good spark, odds are itís a bad coil. But, even then, you might end up w/ a spare coil on the shelf!

Bottom line.......coils do go bad, but I'll venture a guess that 75% of new N coils sold today are sold to folks who do not understand how to diagnose a poor spark problem or how a coil works. So, for those who donít know any better, in a no spark situation the first suspect is usually the coilÖÖand, more often than not, it isnít the problem.

Or as one regular around here humorously suggested: "Well, it is like this...I don't know or really understand what that black thing does & I am suspicious of the unknown, so I think the problem is the black thing."

" Problem was still lack of power on acceleration, some back firing, seemed to run better at full throttle then half."

That's not a symptom of a coil problem.

Put the "defective " coil back on the tractor & see if the problems reappear.

And, if you are in the habit of leaving the key on, you will have a lot of coil problems.


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