Glow plug tightening torque

I can't offer any advice on torque specs... but I'm curious about approximately "how often" you remove and replace the plug? You mentioned applying after-run oil through the plug hole. Does OS recommend this be done frequently on their 4-strokes? If you're following their maintenance schedule.. then you probably haven't done anything wrong yourself. The head could have been tapped with a worn tap at the factory... perhaps it was a faulty casting.. or you may have been unlucky enough to have a plug with a bad thread.. who knows. Aluminum is not real forgiving when it comes to repeated threading into it.. with any force.

There "is" something you can do, to check your plug threads... and it's well worth doing with every plug you have. You can obtain a 1/4-32 "die" for the purpose of "chasing" the threads on your plug(s) before you screw them into an expensive and possibly irreplaceable cylinder head. Keep the plugs that have been chased/checked in a labeled segregated storage area, protecting their threads from contamination or being accidentally "dinged-up". Some guys screw them into holes drilled in a small rubber block-type "caddy" that's easy to store in your flight tote too.

Lastly... whenever I assemble any threaded parts; I "rotate" the part(s) as if to "loosen" them... while also applying light pressure, until I feel the leader-thread "drop-in". This results in a "click" that can be felt through your fingers when it happens. Tightening can then be commenced with the assurance that the threads are engaged properly.

I am guessing that the thread-repair you're having done, may be what's known around these parts as a "heli-coil"... although I'm not sure about the uncommon 1/4-32 thread application. That would be the easiest way to do it. Another alternative would be to TIG-weld the hole closed.. but this requires re-grinding/polishing in the combustion chamber.. and re-drilling/re-tapping the plug hole at the correct precise angle. I'll be very curious as to how the repair is made.

I hope I've given you some advice that you can apply Balogh. Best of luck with the engine when you get it back from the cook!

Balogh, even if you need a new cylinder head.. it will be worth the wait to have it. Many of our engines have parts that are no longer available. If this is an engine that you really enjoy and run often... you may want to research other common "wear-parts" while they're still available from OS... and order some "spares". I don't know much about 4-strokes.. but there must be valve-train components that incorporate multiple small precision parts; camshaft, valves, gaskets/seals etc., that will wear-out eventually from prolonged use. Does the case use bearings? If so; it may be worth having a replacement set of those too.