Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

   I picked up a 1233.  The engine is a Tecumseh OHSK120 223618A with electronic ignition.  There was no spark. The prior owner said he had a trouble with spark and replaced the ignition module.  I tested for spark and there was no spark.  The engine has oodles of compression so I figured I'd just put in a new module so ordered one.

   After putting in the new module and setting the air gap to .012 I there is still no spark.  I disconnected the lead from the module per the Tecumseh manual in case of shorts but still no spark.

   On poking around the net descriptions of how modules trigger there is a mention the module passes a coil, an internal cap gets charged, the module continues past a trigger coil which switches a transistor to let the cap dischrge into the plug wire.  The magnets were a bit rusted so I filed them a little thinking the gap may be off or some of the rust spots too high.  They are pretty clean and the gap even. 

   I don't know if one of the two flywheel magnets is the trigger magnet or if some part is missing.  The flywheel has two part magnet and it does seem to have good strenth when pulling in a screwdriver.  The gap is set.  What else could be wrong other than a defective module?

david

Hey Trouts2,

The whole idea of a magneto tester is fine.  When I was working on Engines  back in the day we had one....but we never used it.

We only showed  the customers that they did not need a coil.  People came in all the time  "My coil is bad, do you have one?"

We aways had one,  for about  $45 bucks...  We were tired of selling them to people and then having to tell them there is no return on electrical parts when they brought them back.

The tester will show it has spark, but it won't  show failure due to heat , expansion or vibration (like a busted secondary winding wire that is comming open).

It is a neat display if you want to make a cut-away  with a working points/ magneto,  but to have a tester for all the diffrent sized flywheels (curve / size of the flywheel determines shape and mounting of magneto) would be too bulky for its worth..

Friiy

   The ohm reading between the kill terminal on the electronic module and ground is 0.  Since that’s the terminal that gets connected to ground through the on/off switch to ground the ignition I assume the module is bad.

 

   There are now three modules which the kill terminal tests 0 ohms to ground. ??

 

   I’m rebuilding an 8 with an electronic module so figured I could use that as a test bed. I first tested it’s module by putting the crank in, putting on the flywheel and rotating the flywheel by hand.  It got a spark.  I then put on the new module which would not get a spark.  Then I put on the old owners suspect module and also got no spark.  Just for confidence I put the original module on and no spark.  After flubbing around for a while I tested the spark tester on another engine that has good spark and got no spark.  I looked under the wire covering on the tester and a wire was open.  I resoldered the tester and tested it on the known good engine and got spark.

 

    On going back and testing all three modules on the test bed non got spark.  I retested the tester on the good engine and got spark. 

 

    I had cleaned up the rusted standoffs and connections and got good readings to ground so should not have been a problem.  I then checked the module kill terminal to ground and got 0 ohms.  I’m pretty sure that’s a bad module.  The other two now test 0 to ground – their all bad now. 

 

    My test setup was klugie.  The flywheel was not bolted on and setting the gap the magnets sometimes touched the coil iron.  My guess is that might have been enough to blow the modules.  So the questions are:

1. Is a 0 ohms reading from the module kill terminal to ground an indication of the module being defective?  I think so.

Is having the magnets touch the coil iron enough to blow the module?  It seems so.  When I say touch I had them touching and scrapped when turning the flywheel by hand and scraping the not properly set air gap.    

I don't know off the top of my head... depends on what kind a treansistor it has inside.   It could have zero resistance through the unit... or you meter could be reading Inifinite resistance....(my old fluke Says "LOW" when it reads unmeasurable high resistance)

Look at page 67 of the Tecumseh manuel for solid state igniton, Try swapping the leads ... you should show resistance , if I am looking at it right..

Should open one way ,   and closed the other if you swap the leads... Due to Diode D2..

Later...

Friiy

Friiy,

      That's the 3-11hp Tecumseh manual. 

   I got 0 ohms both ways with swapped leads with a battery powered analogue meter and zero with a digital meter.  If D2 is not biased I think I should have read the ohms of R1, the chrging coil or the output coil i.e. some value above zero.  Although the readings are bad I don't believe them and think all three coils are hosed.

   The test bed is very shaky.  The flywheel was scratching considerably across the bottom of the module metal legs against the magnets.  That should have been only going into the primary circuit but might have gotten a static charge over to the scr, transistor or diode – whatever is in there.  A direct connect to ground of the output circuit if accurate is not the best.

Trouts2

Hey Trouts2,

I am at work now , I don't have the manual with me...   I find it Very hard to believe that all three coils are bad....   Very hard to believe....  As far as the ignition magneto,  the design of the magneto should be the same internally regardless  of  overhead valve or l-head..

I have seen engines with magnetos Grinding on the flywheel as the engine runs at full speed.. They would grind because the top bearing went out or the the coil started to come loose and the magnets have draw the coil in... And they will run like this for days sometimes before they fail.  As far at the airgap... I have done experiments with the coil gat and had the engine running fine with a quarter inch gap on the coil..   I always set the gap by using a business card and let the magnets suck the coil down while I tighten it..

Anyway, what I am trying to say is,  the coils are not like your ipod,  They are simple and made for use and abuse..I still think something else is missing out the equation.

Friiy

   I also don’t think the modules are bad and bogus part of the equation is something I’m doing wrong and missing.  It should be, slap a module on, set the air gap, remove ground from the kill tab, spin the flywheel and get a spark.  ?? 

Friiy,

   After reading what you wrote and convinced that at least one of the modules must be good I gave testing another shot.  This time while messing around I got a tingle through my fingers while holding the tester with my finger between it and the block.  I could get consistant tingles and after a while of adjusting the setup finally got a few sparks.  I put in the new module and got tingles and a few sparks.   The original 12hp would not give tingles or spark. 

   I think the problem was a few things, broken spark tester for a while and a bogus test bed.  For a while I had the flywheel on the crank but the crank was not supported by the case cover.  After a while I put the cover on but not fully closed or attached.  For a while I also did not have the flywheel nut on so a few things were shakey with the test bed.  It will test modules but was inconsistant so the next step is to get a broken motor and set it up as a perminant test bed.  Actually two motors - one for points and one for SSI.

    Your last post was encouraging to not buy another module and give the test bed another shot.

UPDATE:

    Put the new coil on the 12hp and it fired up.  Fantastic.  1. That there spark and 2. The motor runs very well.  This motor had big kick back when turning the flywheel in reverse by hand so good compression but this is the first oppertunity to see if it would actually run. 

Thanks for the help,

David