Spark plug torque
Seasoned HDF Member
Joined: Jan 2011
Posts: 157,463
Likes: 57,019
From: Michigan 15 Minutes East Of Hell
I've been riding well over 50 years and I can't count the number of times I've seen loose plugs on a guys scooter ... Might be owner neglect, improper installation, worn threads, whatever ... but it happens and it can lead to major headaches ... A couple of times I've helped make "roadside" repairs with a helicoil kit and a whole lot of crossed fingers ... it sure doesn't hurt to check 'em from time to time if your replacement interval is less frequent
Update on my previous post re: NGK plugs. The torque I gave them apparently wasn't enough as the rear one lost it's torque and the bike was making a rattling sound. I was checking NGK's website and they say that all 14mm plugs in aluminum heads should be torqued 18-21.6 foot pounds, somewhat more than what Harley recommends. So they're now at 20 and the bike is quiet again. I'll check them again in a few weeks. I've never had a vehicle where spark plug torque was so critical.
Here's the link to NGK torque page http://www.ngksparkplugs.com/techinf...stallation.asp
Here's the link to NGK torque page http://www.ngksparkplugs.com/techinf...stallation.asp
Club Member
Joined: Sep 2010
Posts: 1,690
Likes: 457
I recently finished a 98" big bore build on the Ultra my wife rides. I put new spark plugs in to my normal hand feel torque. Just for the heck of it I got out a torque wrench and set it to 18 ft/lbs and put it to work on the plugs. I was surprised how much tighter that was than what I had them. I actually had to check and make sure I had the wrench set right. Lesson learned is to torque the plugs and check them from time to time.
Stage IV
Joined: Feb 2022
Posts: 4
Likes: 3
From: Florida
And if I'm not mistaken using that wrench in California causes cancer... or so I'm told. 
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Cruiser
Joined: May 2009
Posts: 219
Likes: 121
From: Central Maine
Old thread, but I wasn't the one to resurrect it, so may as well keep it going- I did plugs a couple days ago and were surprised that the old plugs were basically finger tight. 18 ft/lbs felt like a LOT more torque than I would have thought also!
