Torquing spark plugs multiple times

[vavavroom]

I recently mentioned that I remove and inspect spark plugs every 20k miles or so to inspect them. Depending on their condition I may install the same spark plugs up to three times before replacing them. Someone said retorquing spark plugs was not recommended due to the crush washer being a one-time-use item. While I do not necessarily disagree with the sentiment in general, practically speaking I do not believe that torquing a spark plug repeatedly is more likely to cause any problems than is the gamble of letting fouling potential issues go unnoticed. If the washer was not sealing well there'd be visible signs of blowby making it past the threads and the washer.

The crush washer ensures a good seal between the seat of the spark plug and the spark plug. The washer is made from a soft alloy Depending on application, the seat is either flat or slightly tapered. Below are two pictures of an NGK crush washer that has been torqued three times over its life. Even after being torqued three times this hollow crusher still has some "give." and has not been completely compressed. I do however not torque to the high end of the specified torque range. I can't tell what alloy the washer is. Other than a more dull grey, the washer is light, soft, non-ferrous, and similar to aluminum.

Tapered seat


The cross-section of the reused crush washer shows it hasn't been compressed completely after having been torqued three times.

 

[GMBoy]

If they're easy to get to then looking at them is a good way to asses the motor' health. I'm sure the crush washers are fine.

 

[ecotourist]

I'd be less worried about the spark plugs than the head. I don't like torquing things too often in aluminum. With cast iron/steel sure.

 

[paulo57509]

I've often wondered with gasketed spark plugs, what is the design intent of the torque specification? Is it simply to ensure the gasket is crushed enough to ensure sealing? Or is it intended to ensure enough stress is induced in the threads to prevent the spark plug from loosening? I think it's the latter and the gasket seal is just along for the ride.

I remember the days where it was standard procedure to replace the gasket when ever removing and replacing the same plug. Boxes of gaskets used to be a standard thing on the shelves of most repair shops. Labor costs being what it is now, no one removes a spark plug to clean them and return them to service anymore.

From my two-smoke days of yore.....

Spark Plug Gaskets - Source?

I'm looking for a bulk quantity of 14mm spark plug gaskets/washers; the kind that crush during plug installation. All I can find are solid copper and steel aircraft-type washers. Anyone know of an online source for these washers? Used to be able to buy these by the box in the old days. Thanks.

bobistheoilguy.com

 

[Marcozi]

Why do you check them so often? I wouldn't suspect the plugs unless the engine was running poorly or the engine computer threw a code. What does the manufacturer recommend for plug life? If you're concerned, change the plugs 10k miles before the manufacturer's recommended mileage.

 

[Nesterenko]

That's OCD for sure. If the plugs are Denso or NGK iridium swap them out at around 80k miles.

 

[Snagglefoot]

Pulling plugs is definitely something from yesteryear, especially when you consider how difficult it is to change them on some V-6’s and V-8’s. Put in Iridiums and leave them in for 80 to 100,000 miles. With some Turbo motors they ask for a slightly earlier pull. The rest is just old man stuff.

 

[CarlB]

I recently mentioned that I remove and inspect spark plugs every 20k miles or so to inspect them. Depending on their condition I may install the same spark plugs up to three times before replacing them. Someone said retorquing spark plugs was not recommended due to the crush washer being a one-time-use item. While I do not necessarily disagree with the sentiment in general, practically speaking I do not believe that torquing a spark plug repeatedly is more likely to cause any problems than is the gamble of letting fouling potential issues go unnoticed. If the washer was not sealing well there'd be visible signs of blowby making it past the threads and the washer.

The crush washer ensures a good seal between the seat of the spark plug and the spark plug. The washer is made from a soft alloy Depending on application, the seat is either flat or slightly tapered. Below are two pictures of an NGK crush washer that has been torqued three times over its life. Even after being torqued three times this hollow crusher still has some "give." and has not been completely compressed. I do however not torque to the high end of the specified torque range. I can't tell what alloy the washer is. Other than a more dull grey, the washer is light, soft, non-ferrous, and similar to aluminum.

Tapered seat


The cross-section of the reused crush washer shows it hasn't been compressed completely after having been torqued three times.

Agreed. Don't worry, read your plugs as desired.

 

[Dave9]

What I usually do is wait till 75K+ to check (or replace if difficult to get to) factory plugs, then replace every 50K mi after that. This within the context that I don't put many miles on any one vehicle in a year, so we're talking closer to a decade.

 

[VersatileGuy]

The older the car, the more frequent an inspection interval. Sometimes, failing parts(i.e worn out fuel pumps and or fuel injectors) that still function will be put wear on the plugs such that their life will not be close to their rated service life.

20K is a bit excessive if running on iridium plugs and the engine feels fine.