Spark Plug Blow Outs

[JWA]

Thought I'd post a link to an article originally posted on FTE concerning the Modular Motor spark plugs, how much torque they'll really withstand before stripping out. Here's the link: https://www.ford-trucks.com/forums/1...ead-heads.html

Lots of thought went into conducting this casual testing. Its given me terrific confidence DIY'ing my own plugs and giving out advice for others.

Hope it's interesting and/or helps others!

[REDOVAL]

I've done mine a few times on my 02 PI heads and haven't had any issues. They certainly don't take as much torque as one would expect. As I recall most of the cases for damaging the threads and blow outs come from over-torquing them during installation. I always use anti-seize and I do them with the engine cold.

Thanks for the info either way! It's always interesting to find the mechanical limits of a dissimilar material threaded interface.

Scott

[carringb]

My pro tip.... Start the plugs by using a piece of transmission or fuel hose instead of a socket. If the hose starts slipping before you get a few turns in, it's cross thread. I cross-threaded one spark plug once, and it forever had a tendency to loosen up after that, needing to be re-tightened occasionally if it spent extended time (like more than 10 minutes) above 5,000 PRM. Fast forward 200,000 miles, and it eventually did blow out, when I thought it would make it the 115 miles home after I heard the telltale tick of it starting to back out.

[JWA]

Originally Posted by REDOVAL

I've done mine a few times on my 02 PI heads and haven't had any issues. They certainly don't take as much torque as one would expect. As I recall most of the cases for damaging the threads and blow outs come from over-torquing them during installation. I always use anti-seize and I do them with the engine cold.

Thanks for the info either way! It's always interesting to find the mechanical limits of a dissimilar material threaded interface.

Scott

Most of us with gasser motors have long debated what causes these blow outs---I don't know but original installation issues are certainly a high consideration. I wonder if this wasn't a defective head casting? Either way knowing these plugs will take upwards of 60 ft/lbs torque and comparing that against the factory spec of 7-13 ft/lbs I find it easy thinking my using 23-25 ft/lbs is far far from becoming a problem.

Originally Posted by carringb

My pro tip.... Start the plugs by using a piece of transmission or fuel hose instead of a socket. If the hose starts slipping before you get a few turns in, it's cross thread. I cross-threaded one spark plug once, and it forever had a tendency to loosen up after that, needing to be re-tightened occasionally if it spent extended time (like more than 10 minutes) above 5,000 PRM. Fast forward 200,000 miles, and it eventually did blow out, when I thought it would make it the 115 miles home after I heard the telltale tick of it starting to back out.

I did the hose on the plug trick my first few times as well---its a great trick and does in fact prevent any significant cross threading.

These days I use a Gear Wrench 80546 https://www.gearwrench.com/gearwrenc...-socket-6.html which works perfectly. With a bit of experience its an easy transition from the tubing to that tool. I do start the plug in the head simply by turning the socket with my fingers, any resistance immediately felt.

I did have a near miss on loose plug, vehicle less than 300 miles on it after I took delivery (165K at the time). Holding my breath I brought the torque up to 23 ft/lbs and it held. In fact to this day with over 290K miles and three-four plug changes using my method there have been no issues at all.

Oil leaks from the heads, coolant issues due clogged radiator and several sets of Bilstein shocks its been pretty much "trouble free" ever since.