Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Seized spark plug

Hi everyone!
Having a maintenance blitz on my 1984 +4 (Fiat engine) Mog. Decided to remove and check the spark plugs, only to discover that one has seized and won’t unscrew. I haven’t forced it as I don’t want it to break off, which could be an expensive top end removal!
Has anyone got any useful tips please?
Many thanks Smuggs.

Fill the plug recess with releasing fluid and leave overnight then try again. Once it's moving mop up any excess fluid before removal.

Try with engine hot, if not already attempted.

This, and make sure you use a correctly-sized 6-point socket. Also a nice long breaker bar if you can, it's a lot easier to apply gentle but increasing amounts of torque using a long bar gently tan it is heaving away on a short ratchet handle.

I know that opinions vary on this, but on spark plugs in older engines that are vulnerable to water ingress I use a tiny smear of Copaslip on the upper part of the threads to prevent seizing. Others will say you shouldn't do this as the copper grease will melt migrate down the threads and contaminate the combustion chamber but it's never happened to me because I don't splurge the stuff all over the place.

Also, try tightening it first. Sometimes that will break thing loose.

Not a nice experience, I had that happen on my 4/4 70th, fortunately I was at Life's and despite best of Matt's efforts, wide range of tools and experience with seized in plugs, the spark plug broke off in the head. So don't put too much pressure on it as the spark plug bodies will snap in half.as it did unfortunately with Matt. He managed to get broken section out without taking the head off with using a stud extractor etc. and a lot of penetrating oil and much needed patience. Best of luck

Keep the anti seize to the top half of the plug threads and only lightly applied. Depending on which type of plugs you have apply anti seize to the tapered shoulder or compression washer, slightly more generous here. Best not to use copper slip on an alloy head as the copper can erode the threads in the head. Rather use the alloy based slip. Don't forget lubrication will effect the torque setting in that it will take greater pressure on the threads and could damage them. I Just hand tighten and give them a small sneck actually holding the wrench like a T handle to do this. If you have the crush washer seat type you can actually feel the washer give and stop on a new plug.

If you can't shift the plug, try a hot engine especially if the head is alloy as it has a greater coefficient of expansion. No joy, then soak it in penetrating fluid overnight, deep welled plugs help here then back with a breaker bar. Keep trying to undo then tighten and it should give if not then sooner or later you will have to go for it. In the event that it shears you will need to drill out the centre of the remaining plug and use stud extractors to try and shift the b---er! Usually you can apply more rotational pressure on the steel remaining part and they generally give up the ghost then. If not it's a head off job!

I never really considered this, but I wouldn't think it would be a particularly quick process, would it? I've copaslipped the spark plugs in my garden machinery with no problems and my mower is over 25 years old.

But I'll switch to allyslip for the Morgan, it needs to last until I die!

Well yes I'll grant you that the corrosive element is fairly slow in regard to the spark plug area as generally there is no oxygen present but it will happen and its the aluminium that is the sacrificial anode. So slowly, slowly the integrity of the threads in the head will become compromised and one day as you tighten the plug the thread will fail. Interestingly the motor trade switched to ally slip some time ago as alloy wheels were corroding when copper was used on the hub mating surfaces. spark plug corrosion is noticeably less on the compression/crush washer type as this creates a far superior seal for the threads thus preventing water penetration. The motor trade still do not approve of plugs being applied with any product as this effects thread patency when torqued to the setting required. Again this is true but it doesn't take a genius to realise this and act appropriately. Now, lets consider the tapered shoulder type of plug, What a stupid design! Much like tapered shoulder wheel nuts in alloy wheels the steel plug seat when tightened into the socked will pick up alloy from the head. As the plug tightens and rotates it is in effect digging into the softer head and literally rips small particles out of the head surface and these attach to the surface of the taper on the plug, known as pick up. Every time the plug is reseated it occurs again and if the shoulder isn't polished between setting and returning to the head it will in fact be even more abrasive! Hamwich, You referenced garden machinery, Many times I have seen piston damage from the plug wearing the seat. As the wear lowers the plug deeper into the combustion chamber it eventually contacts the top of the piston. Just think how many times you end up taking the plug out on these rudimentary machines hence the wear ratio!
So the water sits in those deep well plug sockets in the ford Duratec style engines and bimetallic corrosion quickly starts. The steel on the plug shoulder is the first area to show this and the pressure that rusting steel can apply is quite a bit and it is the alloy head that cops the deformation even though it looks to be clean! Rust is very porous and allows deeper penetration of water to the threads and so it creeps down rusting the threads ever deeper. The rust swells in the threads and forces itself into the soft alloy threads of the head and just like you had used araldite you have a seized plug. Finally, just think how gently you tighten the plug in your garden machinery, Bet your not leaning on it like its the Jesus nut holding the helicopters rotor head on! Yet why do so many people have an 1/2" drive socket set on the job and tighten the plugs like it is! 16-20Lb foot is hand tight. Think of the old plug spanners with a simple T handle... yep! Hand tight!

Absolutely. My spark plug ratchet handle is a ⅜" drive Snap-On that is barely 4" long. Spark plugs are always snugged down with just wrist power.