Has anyone had a dle 120 blow the spark plug out of the cylinder?
I have one that blew out after 8 flights. I have since replaced that same jug 2 more times. Each time it was replaced it blew out again on the first flight after they were replaced.
Engine ran fine each time until the blow outs.
Anyone have any ideas what would cause this problem?
Plugs were properly installed and tightened.

Did it take the cylinder plug threads with it?If so I would say the plug hole is over sized.

I could make some snarky comments, but will refrain. But, perhaps you could have stainless steel Heli-Coils installed?

Originally Posted by ghoffman

I could make some snarky comments, but will refrain. But, perhaps you could have stainless steel Heli-Coils installed?

^^^^^^^^

My guess is you over torqued the spark plug and damage the treads in the process but here on FG, a guy did had the problem on a 30 cc and it was the reverse - he did not tighten the spark plug with the same result as you.
There is a lot of DLE 111/120 out there..if it was a manufacturing defect..people will be all over it..

Yes it did take the threads out with it and also broke the plastic material in the plug cap. Replaced the entire ignition with new ones each time.
A flying buddy of mine had the exact same problem with the 120.
Every time it is the rearward cylinder —same cylinder side as my friend’s.
He ditched his and went DA as he thought it was a manufacturing defect.
Thanks guys for your thoughts and opinions.

How old is this engine? Has the engine ever been difficult to tune or have you experienced kick backs when starting? What airframe is it mounted in?

What brand plugs are you using

Engine is about 3 yrs. old. No kickbacks—always started and ran great. It is on a Hanger Nine extra 300. Flewfine first 8 flights and then blew out the plugs on that last flight ; and on the first flight the next two times. Last flight never got over half throttle for the most part.
Plugs or njk cm 6. Engine not flown much because I have 3 other 35% airframes and 7 other 50cc and 2 30cc planes.
All my planes have gas engines engines and have replaced plugs on them without this problem.
It is only one cylinder on the same side and it has ruined 3 cylinders.
Contacted Tom at VVRC after the second blowout and he said he had never really seen this problem.
Myself and my flying buddies think something else is causing this other than the tightness of the plug. We just cannot seem to come up with an answer.
I do not believe I am going to repair it again unless someone knows an answer and a “fix”.
Thanks guys— put your thinking caps on for me.

I would just heli-coil the cylinder would be the easiest and a good long lasting fix from my experience.

Use a 10x1 Timesert , problem solved ..Way better than a helicoil.
Did my 111 years ago

It is either oversized threaded hole in the jug or over tightening
An issue with the engine would blow the cylinder off of the crankcase or bend a rod before it could produce enough pressure to blow the plug out
Under tightening the plug will also cause the issue

Check the timing and intake for restrictions as well as cooling airflow. Something could be overheating that cylinder and weakening the metal or detonation may be showing which parts are weakest. Typically it would burn the piston and or seize first but cheaper china materials may be showing a weak point in the head when heat and detonation come into play. (I own and love 8 dles so not slamming) The next time the cylinder comes off check the piston real close for odd markings. Detonation can be hard to see if it's not too severe. Look at an old cylinder and see if there is any sign of detonation in the plug area. It could be signs of melting or pitting. A completely clean piston crown is suspicious as well.

I agree with Kmatch, if it's not defective parts or over-tightening then I would suspect detonation as the cause. Try backing the timing down a few degrees before trying it again and/or higher octane fuel.

I want to thank everyone for their time as well as brain power. You guys gave me some good info. And suggestions for me to ponder.
If I decide to try one more time to make a repair, I will be sure to update the results.
Thanks again,
Lamar