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When driving my fuel injected 427 Fontana yesterday it felt a little rough to me like maybe not firing on all cylinders. I was going to spot check a few plugs to see what they looked like but then I googled about plugs and aluminum engine and saw a few sources saying plugs should always be torqued to various specific strengths depending on type of plugs (tapered or gasket), the type of threads and whether you have iron or aluminum engine. When I had my stock iron 351 I never thought twice about just pulling the plugs and replacing with ballpark "snug" strength. So I wonder does anyone really torque their plugs? The info I found shows minimal tightening strength numbers which would require a small torque setting and thus somewhat expensive wrench. Just wondering if torqueing is really necessary?

Original Post

Aluminum heads are the problem. AFR advises that with their heads DO NOT use a torque wrench on any bolt. Just tighten them "snuggly". That applies to the plugs too.

I have a long history with aluminum heads. Use anti-seize compound and triple check that the plugs are threaded in correctly and fully seated. All I can say in addition is, it's not unusual for spark plugs to come loose in aluminum heads.


My first car was a Corvair. It used the metal crush gaskets on the plugs. I remember starting the engine with a remote starter and the hood open. It blew out a plug at startup and the wire kept it from hitting my uncle in the head.

I think that car wound up have six inserts installed for the plugs?


It can really depend on if your head uses a compressible gasket or a tapered seat design. The gaskets seem to be the inferior design and whatever you do NEVER try to install or remove spark plugs on an aluminum head unless the engine is COMPLETELY COLD.

Aluminum threads expand to the point that a hot engine permits the threads to strip out completely when the assembly is hot. It's my opinion that all aluminum heads should have steel inserts for the spark plugs permanently installed by the manufacturers. Then you could torque the plugs in place. They disagree with me.


Look at that plug. Make sure the head threads aren't stripped out and make sure there are no aluminum remnants in the plug threads. Aluminum heads are not fool proof. They have a lot of issues iron heads don't.


Last edited by panteradoug

Thanks for the input. To complicate things more, someone mentioned that if I have a gasket type of plug that I am taking out and putting back in then the gasket may already have some compression to it and therefore could effect torque required or amount of wrench turn needed. Maybe in the end I will just pull a plug or two to take a look, apply a little anti seize & ballpark by feel maybe 1/4 turn in putting it back. I never knew plugs needed to be so accurate (one source attached).


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Last edited by does200

Thanks guys for all the input, I agree with the just snug idea (probably a good technique here is the old saying "less is more" rather than over tightening). Was able to get at one plug last night as shown, although it took some good force to unscrew it. Doesn't look too bad to me compared to other plugs I have seen images of, but hey I'm no plug expert. Only other thing I noticed was a small amount of oil coating the threads as shown. Cleaned everything with brake cleaner, wire brush and 220 sand paper & put back in snug with a bit of anti seize. Hopefully at 64 years old I still have enough contortionist left in me to get at the plugs further in.


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Last edited by does200
sjdennis posted:

Interesting topic!  The challenge is usually access.  Unless the engine is out of the car, it is a challenge just to get a socket and ratchet positioned to remove and replace spark plugs on an OHV  V8 like our cars.  Getting a torque wrenched positioned properly is impossible in most cases.  

Actually I am finding it very easy to get to the plugs, so at 64 it seems I haven't lost too much nimbleness. Almost all the plugs look pretty much like the one shown and just one more to go (the deepest on the passenger side). I know one person that just takes out the rear quarter windows to do the plugs then somehow shoehorns the windows back in. Before doing all this I probably should have started it up in the garage with the wife behind and have her look at the fuel injection gauge while I gave it a few revs. I changed the gas filter when I initially got the car a few years due to low power, but who knows what's up this time. At least I figure no harm in cleaning the plugs anyway.

Got it out today for a good run after cleaning all the plugs, and what a difference now runs smooth as butta. Plus checked my fuel PSI gauge out of curiosity and at idol was 40. So, it seems all is good. I am of course no engine guy but I am thinking when I started it a few weeks ago and let it idol in the driveway for a few minutes maybe that isn't good because the next time I took it out it was stumbling. Maybe it tends to fowl the plugs more if you don't get the engine hot and then let it sit.

This sounds like a first time/one time occurrence for you (fouling the plugs).

I can tell you that if it happens again, you might want to consider installing the Pantera Electronics Ignition Controller? It will fire fouled plugs and cleans them up within a matter of seconds so you will never need to clean them again if you use it.

MSD's will not and in fact have a nasty habit of failing completely after trying to start a engine with fouled plugs.

I run Webers so I am not a stranger to fouled plugs. The P-E positively eliminates the issue for ever.

tecnosound-jimcoyne posted:

Adequate torque wrenches in the proper range are available cheaply.


On an aside some guys like me love collecting tools ( 100% of them get used at some point on some vehicle ) I purchased an ' Inch / Pound torque wrench a few years back which sat unused until it was time to replace a Water Pump , pulleys and tensioner on a Mercedes Benz CLS 550 . 

Spring for the torque wrench...It will come in handy in the future.

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