I have a garden tool (roto tiller) with a 196cc engine. The engine is cooled using forced air, it is a 4 stroke engine. The engine has not been used for more than 2-3 hours so far.

I have tried to use the engine again today and I have faced some weird behavior. I am starting the engine, that works perfectly well. I start working with the engine and it does its job, however some 20-30 seconds later the engine just stops.

When the engine stops before that it can be clearly heard that something is grinding, i.e. is not OK. Same thing happened again today. The engine was running at moderate RPM for 20-30 seconds, then it seized up. I waited some 5 minutes, then I checked the engine oil. When I removed the oil probe a lot of smoke came out of the probe vent. The oil was almost boiling and I was glad I waited enough time to open it, even though the engine was only running for a very short time. The engine oil is filled up to a good level, the color is nice, the viscosity is good as well.

After that the engine was completely locked up. I could not even move it a single millimeter even though for "fun" I once was trying to use literally all my force to use the pull start. After letting the engine cool down for 20 or so minutes I could pull the piston again using the pull start. It took a lot of nursing with the carb to get it running again without producing tons of black smoke. The engine runs again for 20-30 seconds, then it slows down over a few seconds before it stops. After that the piston cannot be moved at all until I wait 20 minutes again for it to cool down.

Currently I know:

  • Oil is new and fine and not too much, not too little
  • Fuel is high quality, not contaminated
  • Air filter is perfectly nice

I am looking for a pointer where to start looking for problems.

  • Is this a new tiller or something you've had for a while? Nov 5, 2021 at 20:56
  • I am the first owner from a factory new tiller that I have not used more than 2 hours so far Nov 5, 2021 at 20:56
  • It sounds as though the rings may not have enough end gap, which when they get hot, they grow and stick the piston(s) in the bore. If you are sure there is a good oil supply and it's still under warranty, I'd take it back and get a replacement. Nov 5, 2021 at 20:59
  • I was assuming something growing out or proportion with heat as well. I am going to do another oil change tomorrow just to be sure but otherwise going to the seller would be my next step as well in spring :) Nov 5, 2021 at 21:01
  • Can you add a link to the exact one you own?
    – HandyHowie
    Nov 6, 2021 at 9:28

2 Answers 2


You have a bit of a start to the troubleshooting in your reference to boiling oil. You've noted that the oil level is not low, and low oil level would not necessarily cause excessive temperatures.

As the engine is air-cooled, the first place to check would be airflow. Ensure that the cooling fan is securely attached to the driving mechanism, often located at the flywheel which often contains the starter mechanism.

Check also the passages to which the air flows from the cooling fan. Any blockages will reduce the flow of air.

Having either a failed fan or blocked airflow will create higher temperatures. The boiling oil supports this problem, as does the slowing of the engine, followed by cooling allowing it to be restarted.

  • Thats a good idea, I was assuming that my current 5-7°C ambient temperature would make it alsmost impossible to have an engine overheat in a couple of seconds. Nov 5, 2021 at 21:05
  • If your ambient temperature was that low, it may have contributed to the unusually long running times!
    – fred_dot_u
    Nov 5, 2021 at 21:07
  • I am not entirely sure what unusually long runnig times you mean, but this might be just a language issue. In summer (35+°C) I sometimes could run the engine for 30 minutes wihtout issue, sometimes after a few seconds it seized up. It seems really random. Nov 5, 2021 at 21:14

So long story short I drained the old oil once more, disassembled the engine, thoroughly cleaned up the cylinder and piston, coated them in some 2-stroke oil, reassembled it, filled it up with pristine new 4 stroke oil, gave it a few dry strokes to get the 2-stroke oil everywhere. Then I started it again and it sounded great and was running in idle for quite some time without problems. The oil was also no longer getting hot enough to actually smoke.

However today I was trying to actually work with the engine again and after a couple of minutes it sounded like it "ran away" before going down with a loud rattle. Compression is gone and it wont start anymore, I assume the head or piston burst, not interested in disassembling it again to check what actually disintegrated...

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .