Forum

[Adrian]

My first attempt at drilling and tapping a 2nd spark plug thread in an Electra-x head for a decompressor was a bit of a mess (should have bought the pillar drill BEFORE attempting the job). Fortunately it all cleaned up nicely with an insert kit (not helicoil), the tap supplied picked up fine and left a good thread for the insert (whew...).



A.

[tedmunds]

Always screw in plugs by hand - not with a socket. Only use the socket once you have tightened the plug, that way you won't cross the threads.

[Revband]

It would appear that a simple job can be made quite complicated, some alloy heads come from the makers fitted with a Helicoil type thread, the cylinder head is subject to extremes of heat and the fitting of a threaded insert can cause more problems than it cures, once it is done and it comes loose due to dissimilar expansion rates the head is pretty much a door stop. Use a coil kit and fit the coil using a permanent thread lock.

[PeteF]

Two schools of thought about using threadlock on Helicoil type inserts:

Generally the manufacturers don't recommend it as it's difficult to keep the compound on the coil and not the fitting. If it gets on the fitting it could cause the coil to wind out.
I do know that almost every alloy thread on an aircraft body if fitted with a coil as standard and locking compound is never used. Lots of these fasteners will be subject to extremes of temperature change.

[Revband]

I see your point Pete, I should have said of course you must leave it to cure before fitting a plug, aircraft airframes I don't think have the fittings removed and replace as often as a Bullet spark plug.

[PeteF]

Trouble is that loctite and the like doesn't go off in the presence of air. You have to screw the thread in to exclude air to get to set. Yes, one would hope that aircraft wings aren't stripped down regularly :-0

[Nettshubby]

A couple of problems with locking fluids, one, they usually break down with heat, and a head gets hottest of all. Two, the fluids like Loctite set in the absence of air, which means the part between the insert and head sets, but any squeezed out in the plug part of the thread will set when the spark plug is inserted. Plug glued in!

[Revband]

2422 air cures 650deg.Good enough?.