My Z80 keeps unscrewing the spark plug while flying. Even with the set screw that locks the shield in place intact. There does not seem to be any problem with the threads in the head.
Is this a sign that it is overheating? I don't have any baffleing but there is plenty of air openings in the cowl. Its fully cowled.
Has anyone had and fixed this problem? If so what did you do to fix it?

In about 60 flights I have never had a plug loosen in my 80. I'm still using the Brisk plug that came with my engine and I do have baffling. The engine never overheats. You can read the baffling article that I wrote for www.RCShowcase.com It's under their FAQ section. Over heating may be your problem

I've had the plug out several times to check for carbon build up and have found none.

Ken

The set screw on the shield has nothing to do with keeping the spark plug tight. You may not be tightening the spark plug enough when you install it, it takes a very thin wall socket to remove or install the spark plug if you don't have the socket that is supplied with the engine. My ZDZ 50 has never had the spark plug loosen while flying.

dirtybird, are you using the plug supplied with the tngine or one supplied by RCS ? If your using an Autolite replacement, the threads are cloce but not right. Found out the hard way. If you are usint the plugs supplied by RCS tighten that sucker down. I have three ZDZs 2-80s and a 100, never in 2 years hads a plug come loose. (except the Autolite I put in it.)

Are we talking about a ZDZ 80 or a Zenoah Z80 twin?

Zenoahs use Champion spark plugs, rubber caps, no shield, no interference, and they don't come out.....

This is a ZDZ 80 single. It was bought from Germany and came with the Brisk plug that I am still using. I put some anti seize compound on it and that may be part of the problem.
I thought I put it in plenty tight but it came out after it just one flight. I guess I will have to pull the cowl and check it after each flight.

Try pulling the plug and thoroughly remove the anti-seize. I've never had a problem with any of the plugs seizing on any of my gassers. My plugs always have oil on the threads so they can't seize. On the other hand the taper on the plug and seat is always dry. A little friction fit in this case is a good thing. You may have removed the friction with the anti-seize.

Ken

After about 100 plus flights with my zdz 80, the engine died while I was about 20 feet from the ground right after I pulled out from a torque roll. I managed to pancake airplane on the bushes, bent the gear. Upon inspection we found out that the plug came loose. Tightened it, bent back the gear and up I went. A few minutes later, dead stick again. Plug came loose again. A friend told me to really tighten it up good, both spark plug and set screw. Did what he said, and now have about 30 more flights without it coming loose.

dirtybird, after reading what Mike Dooley said in the ZDZ Support section I wonder if you believe what I said about removing the anti-seize. Whoever told you to always use anti-seize on aluminum heads was probably talking about automotive engines. These do not receive lubrication from the fuel like our two cycle engines do.

Ken

My problem seems to be that I didn't get the spark plug tight enough. They say to set it at 15 ft-lbs. Thats tight!
I don't understand why no-one else has had this problem.

The plug has to be tight because it's a tapered seat plug. Mine never got loose, but I think they could improve the engine simply by using the NGK CM6 plug and the same type of plug boot that is uses by DA. You don't hear about plugs falling out of 3W and DA motors because they use a crush washer.

dirtybird, be sure to give us a report on how it holds now that it's tight.

Good luck

Ken

I just came back from two 10 minute flights. No problem with the plug after setting it to 11 ft-lbs.

There you go. Good