@steve37 That's an interesting bulletin, Steve. I once went to a fastener manufacturer in SoCal — can't remember the name, but the initials were something like APD and it was somewhere like Oxnard — to upgrade some footpeg bolts on my Yamaha R1. The guy behind the counter said to always use a lubricant of some kind on bolts, but he noted that a lubricated bolt will tighten with less torque. With regard to spark plugs, the NGK bulletin sounds good, but I will add this: When I changed out my OEM spark plugs on my '13 Fit, one was in so tight that I had to use a pry bar. I got lucky, and it came out, but things could have gotten ugly.

Obviously, with spark plugs, you want them tight enough to stay put but not seize or break. I tend to cover-torque things in general, but I have never broken a spark plug. I don't know what causes seizing or if using anti-seize automatically means that the plugs are less likely to stay put.

 

^^^
Makes one wonder if maybe some of the spark plug problems are because of anti-seize.

 

Okay, but why now and why this engine? We've been using anti-seize on spark plugs for years.

 

I don't know...but I've heard many recommend anti-seize when installing plugs. Maybe the plug coatings have changed in the last few years?
I can understand (from the bulletin) how this could easily happen.

 

Since it's happening on the factory original plugs I'd say this has nothing to do with anti-seize and even less to do with over torqueing. I'd say it's the opposite...under torqued plugs. My understanding is that Honda even revised the torque suggestion from 13 to 18 ft lbs at some point.

90k Ish is the miles my buddies, bought new, Fit made it to on the original plus before it ejected #3.

 

Spark plug blow out is a known issue for 2009 - 2013 Honda Hit. See 2017 Manufacturer Communication posted to NHTSA website (https://static.nhtsa.gov/odi/tsbs/20...06924-9340.pdf).