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Jason B

Tecumseh HT55c-3089 let the magic smoke out

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Greetings! My father and I picked up a little wheel horse this past weekend. Took a long time to figure out which one it was - we thought it was a 702 at first, but it looks like it is a 552. It has the Tecumseh HT55c-3089 engine. I hooked a battery to the tractor and hit the key. The engine would turn over, but had no spark. There are three fuses (I assume they are all fuses - one is a glass fuse like is found in 60's era cars. The other two are short, polarized, and ceramic) on the corner of the cylinder cooling fins just above the starter. I checked all three first when I got no spark since it was the easiest thing to do. I pulled the two ceramic fuses (?) because I had never seen them before. Checked them for resistance, and could only get a reading in one direction. I put them back in the tractor with the positive side facing down (where the positive cable hooks to the "circuit board" and commenced to cranking the engine. I noticed shortly after that the acrid smell of burning electronics and saw magic smoke pouring out the bottom of the pull start shroud. I assume I burned something up under the flywheel. I have not removed the flywheel yet - I will do that in the morning. Any idea what happened? I noticed the green and red wires running behind the flywheel are missing some insulation, but there are no burn marks and it appears they were not touching. Any help would be greatly appreciated. I will update once I get the flywheel pulled off and have a look-see at what's under there. 

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Welcome to the forum.

Click on the pictures

The two diodes rectify the AC current produced by the stator so DC current can charge the battery.

The ignition is self powered and the single ignition wire is grounded to the chassis to shut the engine off.

 

Garry

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Magic smoke near the flywheel?!     It could be that one or both of your diodes are installed the wrong way.    

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Posted (edited)

Welcome to the forum Jason. You will certainly will find all the help you need here.

What you have there with the Tecumseh/Lauson HT55 is a rather rare engine which is much misunderstood by most people. Its electrical workings are a bit unconventional compared to others and unfortunately many if not most found are discarded or destroyed due to the fact that it takes a bit of effort to understand their electrical workings. Many opt to just replace it with something else.  Parts for it are absolutely not easy to come by, but I encourage you to stick with it and save it. A few important things to keep in mind with that engine are, ignition switch and solenoid are unique to that engine. They are activated by grounding. Absolutely no voltage to be applied to magneto at anytime. These are the essential things to understanding that engine and not frying anything.

Smoke from under flywheel is never a good thing. Most likely coming from your magneto/coil.Probably happened by reversing the diodes although I have never come across that happening from that alone. Those diodes are directional therefor your resistance readings.Current flows through wires coming from under flywheel through diodes and into battery, therefor their directional ability. For the time being you can just remove them until you get engine going. Important specially if there is no battery in the system .They only have to do with the charging of the battery. I suggest that you start by reading  thoroughly the information supplied above by Garry our file moderator. You are going to find him a lightning fast and precise information provider.Just one of many invaluable members in here.Meanwhile I will look and supply links to many posts regarding that engine and similar issues that others have come across , some very recent, and I am sure many others will do the same.

Edited by formariz
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Take a good look at the wiring diagram for that tractor. Looking at your photos on the other thread, you have a 552 which does not use a solenoid. Rather it has an off switch which merely grounds magneto shutting off tractor, and a heavy duty push button starter. They should be located in the center of tower but yours has been modified. Be careful as to what switch is used. You may want to return everything to its original stock configuration.

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