This has happened twice now; first time about a year ago, the engine started making a missing sound at idle and I noticed one spark plug upper cap was dislodged. The plug itself was sitting in the threads but was only about finger tight. I tightened it back up and all was well till this week it happened again. I have retightened it but I want a permanent fix. The plugs are a long way down the narrow tube so I hesitate to try a helicoil re-thread job. Anyone tried the weaker versions of loctite for this? Ideally I want the plug to be removeable but not work loose again.
kazbanz,
Oct 3, 7:08am
The question to ask is WHY is it working loose? Did you tighten it enough so the crush washer is compressed? if the thread is damaged then glue isn't an option for a couple of reasons. -
franc123,
Oct 3, 8:27am
Have you pulled the plug out and looked st it? There has to be some reason it is happening, presumably the sealing ring is on it still?
aprilguy,
Oct 3, 9:27am
Yes the plug looks normal, washer still there, and it screws up normally. I might need to buy a little inspection camera to check the thread. I am guessing it must be the thread. I don't think it could vibrate loose, but it stayed in place a year after it worked loose the first time.
ml6989,
Oct 3, 10:17am
Is it tightening down on its seat or is there possibly an obstruction down the thread that gives you a false sense of it being seated? Perhaps a 14 X 1.25 tap, (with grease in the flutes to catch any swarf) run down the hole would eliminate this possibility.
marte,
Oct 12, 4:05pm
Double check that it's the correct sparkplug for it. I once found one shorter sparkplug in a 4 cylinder car.
framtech,
Oct 12, 4:18pm
New set of plugs which will have new washers on them, insert by hand until seated then use a plug torque wench set to plug manufacturers recommendations (usually 15 ib sq inch. for say a n9y . If the thread is buggered you won't be able to insert by hand (without the ratchet) and it won't torque down. If someone has cross threaded the hole in the past then it means taking off the head and having it fixed properly. I put a dab of coppercoat on the threads as i've seen plugs so tight that 200 ft lbs won't undo and have had to have them drilled out at the machine shop. standard plugs are as cheap as chips and the savings in better fuel economy will pay for them after a few tanks of gas.
aprilguy,
Oct 12, 4:22pm
They are the right plugs. I put a mini camera down the hole and the thread looks OK. As a test, I have swapped two plugs around and will check them for tightness from time to time, I think the crush washer might have suffered from too many tightenings as I had to loosen/retighten some of the plugs to retrieve the socket as the plugs were sticking in the rubber lining. If the plug loosens in its new hole, I will know for sure.
toyboy3,
Oct 13, 10:11am
Shouldn’t use copper cote on plug threads in aluminium cylinder heads as it eats the aluminium away. Use a aluminium based grease
gazzat22,
Oct 13, 12:57pm
+1 .Theres a Nickel based lube in a silver plastic container.
desmodave,
Oct 13, 1:45pm
Not a 100 but was it you that recommended use a length of garden hose to hold the plug while fitting by hand 1st . Bloody good idea i thought . You can't always see but you can feel without risking damage .
sr2,
Oct 13, 1:55pm
+2
Leave a copper coin in the bilge of an alloy tinny and see what happens.
theo35,
Oct 13, 2:55pm
What about nickel anti-seize? (i've been using it for years)
martin11,
Oct 14, 2:19am
Copper Coat has been used on Aircraft engines for years with no problems
franc123,
Oct 14, 2:36am
Yes that's right, you got a good memory!
gazzat22,
Oct 14, 7:50am
Loctite Nickel Anti Seize 771.
gazzat22,
Oct 14, 7:52am
Which Engines on which Aircraft?
framtech,
Oct 14, 5:47pm
good lord, I had a toyota car that had done 400,000k and the coppercoat hadn't corroded at all, in fact the plugs threads where as tight as they were when it was new, bit of a old wives tale me thinks, Ive been using coppercoat since 1982 and it hasn't eaten anything except the odd sandfly. but hold everything, I will amend my statement by changing the word coppercoat to anti seize, there you go - better than a happy pill. modern plugs have a shiney coating on the threads to stop seizing but cars that don't get a service much- i've seen rusty threads and very high touques to remove.
Lycoming Service Instruction No. 1042AF says:
"Use a copper-based anti-seize compound or engine oil on spark plug threads starting two full threads from the electrode, but DO NOT use a graphite-based compound
Continental and Lycoming on most 4 and 6 cylinder horizontally opposed engines . Cover most commercially made light aircraft .
kazbanz,
Nov 6, 2:15pm
ahh but to confuse matters--put said alloy tinny-completely freshly washed into Fresh rather than saline water and do the same thing :-)
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