Effect of wrong coil installed

I have discovered that it appears that PO installed a coil which requires a ballast resisitor (coil says for use with external resisitor) when a resisitor was not installed - the PO said that after some work on the engine it ran well for a while then did not run.
I was able to get it to run but it ran bad with a bad misfire and eventually yesterday noted a weak spark and intermittent spark. I changed out the condensor but left the points alone as I thought they were ok - still ran bad so today (weather permitting) will change out points.
My question is: how quickly would this incorrect set up affect the new condensor (I probably ran it for about 5 mins)? Which would be better - to install an in line resisitor or install a different coil.
This is on a wisconsin TR10D engine - single cylinder - I believe it is magneto/coil set up.
Thank you,

Lee

Quite simply, the ballast resistor limits the
amount of * current * reaching the points,

Old cars had a ' drop out ' [ R terminal ]
which was wired into starter circut, this gave the points the full 12 volts during cranking, once engine started, the voltage from key went through a ballast resistor to limit current, prolonging point life. GM used a length of resistance wire on key to points wiring, Mopar used a ceramic resistor on firewall, Ford built a resistor into the coil. You can replace your coil with any combo, A Ford [ 68 Bronco ] coil requires no additional wiring, A GM or Mopar Coil requires an add on { Mopar Ceramic resistor ] resistor. I've got a GM coil, with a Mopar [ 66 Valiant ] Resistor, old GM horn pigtails plug into Mopar Resistor, beauty of this setup is, in severe weather, can shunt resistor with jumper, during hard to start conditions, remove jumper after fire up .

Leave the points & condenser alone for now,confirm WHAT TYPE ign system on eng,points/mag or points/12v coil(if 12v system,when you turn ign sw to on/run,you'll read 12v at one terminal of coil with a voltmeter/12v test light)IF it's a 12v ign system,then goto napa,local mower shop or ebay & get a coil designed for a kohler eng with 12v ign system,these coils have a built in resistor,reason existing coil failing is coil was used for point type auto ign system which used a ballast resistor/ballast wire,this limited voltage to coil to 10.5-11v when eng running & charging battery,anything over this voltage,coil will overheat & cause insulation break down in coil & also boil oil in coil,adding carbon to oil which will also short coil internally.When replacing coil MAKE SURE you put wire from ign sw on POS/+ terminal of coil or you'll have a mis-fire problem as you do now(resistor installed on pos/+ term internally in coil)if you had mentioned type of coil in orig post,you could have saved yourself a lot of trouble.

Here's the part number for Napa's coil. Cost about $18.00 unless they've went up. Hal
PS: It has the built in ballast resistor. Be sure to wire it as Joe suggested.
IC14SB

Using the coil meant for a resistor, without a resistor, just results in shorter points life. It's not somtthing that is going to cause sudden problems.

The smartest move is always the one whereby you put the tractor back to the way it was when it left the factory. In this case, that means installing a new coil that is designed to work on 12 volts. The one in your tractor at the moment is not a 12 volt coil, it is an 8 volt coil.

To make an 8 volt coil function in a vehicle with a 12 volt system, you have to put a ballast resister in series with the coil. The ballast resistor reduces the 12 volts to 8 volts so that the coil does not overheat and cook itself to death. That"s what"s happening to your coil right now.

The 8 volt coil was used in automobiles to help solve cold weather starting problems. When the temperatures drop, so does the ability of a car battery to supply 12 volts. When you engage a starter motor to crank a cold engine on a very cold day, the battery voltage can drop to 9 volts. This is not enough voltage to generate a fat spark across a cold spark plug when the coil is expecting a full 12 volts. And a fat spark is needed to ignite a rich mixture of cold gasoline in a cold cylinder.

To try and solve this low voltage issue, the 8 volt coil and ballast resistor was introduced in the mid-50"s. The solenoid that controlled the heavy current going to the starter motor had an extra terminal added to it. This extra terminal bypassed the ballast resistor and sent the full battery voltage directly to the coil. Since the full battery voltage could be as low as 9 volts, the 8 volt coil had no problem delivering a nice, fat spark to the plugs.

When the engine began to run, the operator stopped using the starter motor and the coil went back to being fed 8 volts from the ballast resistor. Bottom line.....your tractor never had a ballast resistor system because it was unnecessary.

My advice is this. Buy a new coil that is a true 12 volt model and buy a new set of points and condensor. Install all three and put this problem to rest once and for all.
Also, check the condition of the high tension wire going to the spark plug. Those do not last forever. The insulation breaks down and the power you need for the spark plug bleeds off and never makes it there. Use wire with a solid copper core, not the radio suppression type with the threads in it.

Thank you all for the very useful information - and, once again, I have learnt something I did not know.
A new set of points came with the tractor so will install those....to be honest I didnt change out the existing ones because it is a very fiddly job with the hydraulic pump system in the way - without that there it would not be a particularly difficult job....plus I am too lazy to take that off to change the points!
It was not until I removed the coil from its holder that I noticed the marking on it saying use with external resisitor (it is a blue streak coil - with original blue spark plug wire which I changed out to copper core wire).
Hopefully this will do the trick.
Lee

Putting in new points and not a new condensor is penny-wise, pound-foolish thinking. You can see when points are bad but you cannot see when a condensor is bad.....most of the time. The points rely on the condensor to give them long life. A bad condensor or a weak condensor will shorten the life of those "hard to get at" points and cause you problems with the way your tractor runs.

(quoted from post at 12:16:58 01/12/10) Putting in new points and not a new condensor is penny-wise, pound-foolish thinking. .

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I disagree. The quality of condensers lately can be pretty poor. What this means is, you might get one NEW that's borderline or even bad out of the box. IF the points show normal wear when you changed them, and it ran with a good spark, I'd keep the old one in. I'd certainly keep a new one handy for a spare.

In the period of about 67-7? when I "ran points" I only changed a condenser once or twice in any of my cars, and then sometimes it was to "throw parts" at a spark problem, and I often kept the old one until I was sure I'd condemmed it.

Todays parts---coils, points, etc, simply aren't what they were

You probably haven't been around long enough or worked on a lot of old 12v point/coil ign systems,if you bypass ext resistor/ballast lead to coil designed for same and maintain 12-14.5 to coil,if/when coil shorts out internally due to overheating & boils the oil in same you don't want to be in the area,as guts of coil & HOT oil can/will blow out of case,it's not a pretty sight,I've seen it happen twice,sooner/later your number may come up if you run without resistor/resistor lead.

(quoted from post at 15:03:09 01/12/10) You probably haven't been around long enough or worked on a lot of old 12v point/coil ign systems,if you bypass ext resistor/ballast lead to coil designed for same and maintain 12-14.5 to coil,if/when coil shorts out internally due to overheating & boils the oil in same you don't want to be in the area,as guts of coil & HOT oil can/will blow out of case,it's not a pretty sight,I've seen it happen twice,sooner/later your number may come up if you run without resistor/resistor lead.

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OK, I have located a napa coil for about $20 which has the internal resisitor - however, local tractor shop has a coil for a kohler engine for about $30 - which should I go for or does it not matter?

Lee

Neither coil requires an external resistor and that's the issue with your current coil. Therefore, either coil will run properly on your tractor's 12 volt system. Personally, I have a penchant for OEM parts over non-OEM. A genuine Kohler coil may not be made by Kohler but it is made to their specs.

If the other coil is in a box that says "Made in China", then I'd have to question the quality of the copper that was used in the windings. To me, the extra ten bucks spent to make sure I got a quality product is insignificant. Ignition parts come with no guarantee. Once you walk out the store, you own it. They will not take it back.

So if that less expensive coil fails on you, then where's the savings at that point?

Good point - also I will be supporting a small local business which has been very good in giving me advice over the years.

Lee

You misunderstood my reply,was not directed at you,but rather to reply posted by jdemaris.Do get a new coil either napa or kohler.

I've been a mechanic (auto, tractor, and diesel) for 40 years, so yeah, I've been around this stuff for a little while.

Modern coils when sold as "12 volts to be used with resistor" are usually just 6 volt coils. Run then on a 12 volt system (around 14 volts) they rarely, if ever fail. Points just have a shorter life.

Old 6 volt coils made in the 1930s, not as durable. But, that's not what we're talking about here.

I worked for a Wisconsin dealer back when those engines were current. We were never provided with exact winding specs on the battery coils used on the TR and TRA-10Ds. Just the YF-38A or YF-38B part #s. I do recall they had aprox. 3 ohms on the primarys and no external resistor was used.

You can use just about any coil as long as you wire it correctly. A single-cylinder engine does not have as high energy demands as a multi-cylinder engine. The main point is you want to have enough voltage available for cold-starting (over 20,000 volts), but don't want so much coil power that your points keep buring out.

A modern coil, regardless if it's being sold as a "6 volt" or 12 volt" is not going to burn up quickly. Nor will the points, regardless of how you hook it up. But, for a system that is going to last - you ought to have a coil with 3 ohms on the primarys, or a coil with an internal resistor.

If you don't want to do any rewiring, just buy yourself a single-cylinder coil at NAPA - # 41 519 21S. This has the correct primary resistance and does not need an external resistor. It is basically the same as what was originally used by Wisconsin.