Jump to content

Nominations for Tractor of the Month
Garden Tractors and Parts on eBay



Photo
- - - - -

New To Forum & St12 Tractor Question


  • Please log in to reply
34 replies to this topic

#1 smcelhe OFFLINE  

smcelhe
  • Member
  • Member No: 10537
  • 1 Thanks
  • 16 posts
  • Location: Pa

Posted July 16, 2012 - 08:53 AM

My son has a 1976 ST12 garden tractor that he rides around and sometimes pulls a cart to haul firewood.

Several months ago he shut it off and it would not start...I cleaned the carb, put a new plug in (not a CJ8)....tried spraying starting fluid in the cylinder....it would not start. I had spark...but I don't think it was good spark. Several days later I put a CJ8 plug in it and it fired up.

He used the mower for several months....ran fine....lately I noticed that it was getting hard to start, especially after he ran it awhile. Yesterday it wouldn't start at all.

I put a new CJ8 plug in it....put starting fluid and gas in the cylinder....it won't start. I have spark.

I was reading that the solid state ignition could be the issue....and that you can't buy new ones. I also saw where someone was making ignitions for these.

Is the problem with the external coil/ignition or with the piece behind the flywheel?


Any info would be appreciated.

Thanks Shawn

#2 HDWildBill OFFLINE  

HDWildBill

    Freedom is not Free. Thank those in uniform for your freedom.

  • Senior Member
  • -GTt Supporter-
  • Contributor
  • Member No: 6354
  • 8,697 Thanks
  • 8,555 posts
  • Location: Ga

Posted July 16, 2012 - 09:19 AM

First off Shawn let me welcome you to the GTTalk. We are glad you decided to join us.

I had a Murray not to long ago that was acting like what you describe. I took the cover off the flywheel and cleaned the area with compressed air then cleaned up the flywheel with a wire brush and re-gaped the coil pickup. It has been running fine ever since.

#3 JDBrian OFFLINE  

JDBrian

    Super Moderator

  • Super Moderator
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 2507
  • 9,574 Thanks
  • 14,136 posts
  • Location: Hubley, Nova Scotia - Canada

Posted July 16, 2012 - 09:25 AM

Welcome Shawn. Don't have any Sears tractors myself but it sounds like an intermittent electrical problem of some kind. On top of what Bill has said I would check all the wiring connections and clean the contacts. Check any safety switches that are in the starting circuit as well. Also you need a good connection from the engine chassis back to the battery - terminal. Good luck sorting it out.

#4 Bmerf ONLINE  

Bmerf

    Patina Farmer / Rust Collector

  • Senior Member
  • -GTt Supporter-
  • Contributor
  • Member No: 9846
  • 1,708 Thanks
  • 1,445 posts
  • Location: benton harbor, mi

Posted July 16, 2012 - 01:34 PM

I agree with what has been said. Clean flywheel and coil pickup. What type of motor does it have? I am not familiar with the external coil/ignition. All coils need some type of triggering device, could be a solid state ignition or points and a condenser. (for the year I would say points) The points could need cleaning or replacement. A condenser that is about to fail will suddenly die when it gets warm. Also the wire going under the flywheel could be making contact or about to break causing intermittent problems. Hopefully I am not too far off base. Good luck.

#5 smcelhe OFFLINE  

smcelhe
  • Member
  • Member No: 10537
  • 1 Thanks
  • 16 posts
  • Location: Pa

Posted July 16, 2012 - 02:02 PM

The engine is a Tecumseh.....it does NOT have points....I am pretty sure it has what's called a Solid State Ignition. The external coil is rather large and aluminum.

The outside of the flywheel has two post protruding from it...they are clean the the SSI is set at .010.

Please keep the info coming.....

Thanks Shawn

#6 MH81 ONLINE  

MH81

    Proud to be Deplorable

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 802
  • 27,243 Thanks
  • 28,599 posts
  • Location: N. W. PA

Posted July 16, 2012 - 05:43 PM

Shawn, first :welcome: to GTTalk

Second, you need to make sure of a couple of things before opening much up. There is a wire that runs up to the ignition switch, it is a ground out to kill the spark. If the switch passes much of anything thru it when it shouldn't be, the result is erratic at best spark. Disconnect the kill wire from the switch, make sure it isn't touching ground, & check for spark again.

If still no spark, phase two... Requires you not having a pacemaker or a weak ticker. ;) Take the wire you just disconnected from the ignition switch and pinch it with your thumb & finger. Then stick your pinkie From the same hand against something grounded. Have someone else crank the engine a couple of times. You should feel a very light tingle, kind of like checking a 9 volt battery on your tongue. If you do, the stuff under the flywheel is working, time to investigate further.

Please let us know what you find.
  • caseguy said thank you

#7 smcelhe OFFLINE  

smcelhe
  • Member
  • Member No: 10537
  • 1 Thanks
  • 16 posts
  • Location: Pa

Posted July 16, 2012 - 08:44 PM

MH81 Thanks for the response.

Here is what wiring I have on the tractor:

Three black wires coming from engine….two go to rectifier…one goes to the ignition switch.


From the ignition switch:

Black wire to to engine (one of the 3 mentioned above)
Red wire to Amp meter
Red wire to rectifier
Black wire to ground
Orange wire capped off
White wire to starter Solenoid

The black wire that comes from the engine to the ignition switch....is this the one I should disconnect????


It sounds like the problem could be with the ignition switch.....If so...I'll replace it. Can I still get them? Do you know where I can get one?


Please let me know.

Thanks Shawn

Edited by smcelhe, July 16, 2012 - 09:17 PM.


#8 MH81 ONLINE  

MH81

    Proud to be Deplorable

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 802
  • 27,243 Thanks
  • 28,599 posts
  • Location: N. W. PA

Posted July 16, 2012 - 11:20 PM

There should be only one wire coming from the engine to the ignition switch. Regardless of color, that's the one.

Follow the instructions above and don't replace the switch yet... We have to make sure you get the right kind, wrong one will fry the ignition in a heartbeat.

#9 smcelhe OFFLINE  

smcelhe
  • Member
  • Member No: 10537
  • 1 Thanks
  • 16 posts
  • Location: Pa

Posted July 17, 2012 - 05:03 AM

Yes....there is one wire coming from the engine to the switch.....I'll disconnect it later today and post the results.

Thanks alot for your help.

Shawn

#10 smcelhe OFFLINE  

smcelhe
  • Member
  • Member No: 10537
  • 1 Thanks
  • 16 posts
  • Location: Pa

Posted July 17, 2012 - 04:29 PM

Here are the test results.....

I disconnected the wire coming from the engine to the Key. The mower won't start....however....I can get spark. But it's difficult to get spark. The plug does not spark just laying on top of the engine cover....if I hold/ground the nut portion of the plug on one of the small bolts that hold the engine cover the plug still doesn't spark. To get spark....I need to hold/ground the end of the plug to the small bolt. Not the tip of the plug....but the end of the threaded portion close to the tip. When I get it just right....I have what appears to be good blue spark.


I held the wire coming from the engine and touched ground. I felt a small shock like you'd get when testing a 9 volt battery.

Again...thanks for the help.

Shawn

#11 MH81 ONLINE  

MH81

    Proud to be Deplorable

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 802
  • 27,243 Thanks
  • 28,599 posts
  • Location: N. W. PA

Posted July 17, 2012 - 04:49 PM

I would try another plug, if you haven't yet. Also, have you ever replaced the end of a spark plug wire before? I think I would try these things first, then we can try a couple of things under the tin.

#12 smcelhe OFFLINE  

smcelhe
  • Member
  • Member No: 10537
  • 1 Thanks
  • 16 posts
  • Location: Pa

Posted July 17, 2012 - 07:15 PM

Tried a new plug....have not put a new end on the plug wire.



Update:

I sprayed starting fluid in the clyinder and got it started. I have the side cover off and the throttle cable was un-hooked so all the tractor did was sit there and idle. I shut it off.... I had to connect the black wire from the key to the engine to get it to stop - the one I disconnected to test.


I was not able to get it started again.

One thing that I've noticed is....the starter gear and shaft is getting really really hot instantly. I had sprayed a little silicone on the gear and shaft yesterday and within 5 seconds of trying to start it today the smoke was rolling off the started gear and shaft. Every time we tried to start it the gear and shaft got really hot.

Could there be an issue with the starter taking too much power and not enough left for the plug?

Thanks Shawn

Edited by smcelhe, July 17, 2012 - 07:22 PM.


#13 MH81 ONLINE  

MH81

    Proud to be Deplorable

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 802
  • 27,243 Thanks
  • 28,599 posts
  • Location: N. W. PA

Posted July 17, 2012 - 08:01 PM

Well, the starter and the spark are separate circuits. The engine makes it's own juice for the spark and requires no battery.

If the starter is turning the engine slowly, it will not make a spark. Lots of physics here, but that's the short version.

I would pull the starter off the engine and check it out a little closer.

BTW, is it a starter with a gear or a separate unit and uses a belt?

#14 smcelhe OFFLINE  

smcelhe
  • Member
  • Member No: 10537
  • 1 Thanks
  • 16 posts
  • Location: Pa

Posted July 17, 2012 - 08:18 PM

The starter has a gear......

I'll pull the starter off tomorrow.

Are new/rebuilt starters available?

#15 MH81 ONLINE  

MH81

    Proud to be Deplorable

  • Staff Admin
  • Staff
  • -GTt Supporter-
  • Contributor
  • Member No: 802
  • 27,243 Thanks
  • 28,599 posts
  • Location: N. W. PA

Posted July 17, 2012 - 08:25 PM

Probably aftermarket ones available. Engine number would help with finding it.

If you have an old fashioned Rope Cup, you can take the screen off the flywheel, install the rope cup and pull start it to see if you have reliable spark.




Top