Snapped spark plug using torque wrench
Road Master
Joined: Sep 2014
Posts: 1,191
Likes: 233
From: North East, MD
I've never snapped off a spark plug, and I've used regular as well as torque wrenches over the years. How much force on the wrench would you have to apply to break off the plug?
Seems to me it'd be a lot- wouldn't the bigger risk be stripping out the threads in the head? Just wondering.
Once the wrench went past about a quarter turn, why didn't you back off?
Seems to me it'd be a lot- wouldn't the bigger risk be stripping out the threads in the head? Just wondering.
Once the wrench went past about a quarter turn, why didn't you back off?
Road Master
Joined: Jan 2016
Posts: 1,143
Likes: 433
From: Menifee, CA
Or use a beam or dial type torque wrench. The "click" type generally can't be trusted at the lower ends of the scale. Especially the cheaper wrenches...which is what I have.
A second on the lubed threads reply also. You need to reduce the torque significantly if you use anti-seize or oil on the threads.
The OP said the plug broke at the threads, level with the head, saying it looked like pot metal. I'm not surprised. I'd stay away from non-Harley plugs. The Harley plugs are only 5 bucks apiece and last up to 30k miles. HD sez to use anti-seize on the threads. Their torque spec is based on the use of a HD plug with anti-seize on the threads. I'd go with that. I know Harley doesn't manufacture spark plugs or motor oil, but they darned sure do specify how those things are to be made and used.
Thread Starter
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Cruiser
Joined: Apr 2009
Posts: 177
Likes: 15
From: Quincy, WA
I'm not an idiot
To some of you that have implied that I don't use common sense I would like to explain one more time. I have been doing all of my own work on four Harley's over the past 12 years. I have never snapped a plug before. As I said I normally wouldn't have used a torque wrench. This time I decided to try using the service manual. I torqued the plug in the front cylinder and moved to the rear cylinder. The plug was not tight when the plug broke at where the top of the threads meet the plug. I removed it with no trouble so the plug was obviously still loose. I was only trying to explain to be careful. I feel I may have run into a defective plug. I don't need anyone telling me I don't have common sense. I am only posting this to let people know I had a Champion plug snap on me.
Extreme HDF Member
Joined: Aug 2013
Posts: 16,271
Likes: 15,108
From: Somewhere SW
FYI, I have always tightened plugs without a torque wrench. I changed plugs in my 103HO Road Glide and decided to use a torque wrench set at 16ft lbs, in the middle of the specified range. Used a little anti-seize as the book says as well. Tightening and waiting for the torque wrench to activate on the second plug and snapped the plug flush with the head. Luckily I was able to back it out. From now on I will be going back to using a ratchet only. By the way, these were Champion plugs and the area that snapped looks like pot metal.
Road Master
Joined: Jan 2016
Posts: 1,143
Likes: 433
From: Menifee, CA
True that. But in this case, Harley has specified a torque value for the plugs WITH anti-seize on the threads. I think it would be a mistake to lower the torque by 25% since this spec is obviously based on lubricated threads.
The OP surely had a broken spark plug before he started. He wrote that the plug broke off before it was even tight. Therefore, he hadn't even gotten to an over-torque situation when the thing broke off. I always worry about a broken spark plug. They're small and easy to drop onto the floor when being handled. I inspect a new plug very carefully in bright light before installing. What surprises me most is that there are so few plug failures. I've never broken one, but once I had one stop sparking and cause me to spend a half hour of sweaty kick starting before I finally gave up and called for help. We never suspect a bad plug because it almost never happens.
Intermediate
Joined: Sep 2017
Posts: 42
Likes: 4
From: England
I have heard that there are some counterfeit plugs kicking around in the UK, a lot are sold on eBay, could also be the case in the US ,might have been the cause.
See this info on NGK , I would be suprided if they are not also counterfeiting Champion.
See this info on NGK , I would be suprided if they are not also counterfeiting Champion.
Last edited by Zeke 666; Oct 2, 2017 at 10:58 AM.
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