Jack Hyde

My Feedback: (1)

My friend lost 2 plugs while flying his TT120 powered plane today. He has been an avid rc flier for 30 yrs and has never had this happen before. The engine is new with 6 flights on it. Could the threads be sloppy? What is the cause of this and how can we fix it? Strangely yesterday another guy had a plug fly out of his engine while running on the ground. He put in a new one and had no more problems.

loughbd

Sounds like they weren't tightened enough.

Jack Hyde

My Feedback: (1)

Thanks. I am embarrassed that that didn't occur to us. If anyone else has had experience with an engine that spits out plugs I would like to hear about it.

loughbd

Never seen or heard of it happening

doubledee

My Feedback: (4)

It is always a good idea to check glow plugs for proper tightness periodically. Make sure the gasket is installed also as it also acts as a washer to ensure the glow plug stays in place. The glow plus should be tightened down good and snug but not so tight as to risk stripping the threads.

Regards,
doubledee

Hobbsy

My Feedback: (102)

20 to 24 inch/lbs of torque.

downunder

LOL...and you said that without even smiling, but given that your friend has only got about 30 years experience...

I've never had this happen either but I've heard of it so there must be a reason. I'm tempted to say bad threads in the head seeing it's a new engine that's suddenly sending plugs into orbit. But even bad threads should keep a plug in place if they don't strip when tightening. Although a
really loose thread mightn't keep it tight with all the vibration and pressure pulses. Just a thought

However I learned something myself today about plugs. I put a plug back into an engine I'd just finished stripping and cleaning. I turned the prop over and the compression just went blaaaahhh...down to nothing. It was leaking like a seive around the plug washer which turned out to be far too big (very loose fit on the plug) so it wasn't sitting central under the plug. I fitted a washer that was a close fit over the threads and now the engine will hold compression all day long. I double checked it with a bottle of Gas and Air leak detector I keep around for that kind of thing, it'll blow bubbles with the slightest of leaks.

Hobbsy

My Feedback: (102)

DU, there is a lot of variation in those gaskets, some of them aren't even round, some are thinner, some with loose fitting holes, as you said, and some egg shaped. The ones that come on Fox plugs are the most precise.