Snapped spark plug using torque wrench
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Cruiser
Joined: Apr 2009
Posts: 177
Likes: 15
From: Quincy, WA
Snapped spark plug using torque wrench
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.
I've watched many rookie mechanics make the mistake of using a torque wrench on plugs, either break the plug or strip the threads out!
All you need is hand tight, then 1/8 to 1/4 turn (45-90 degrees)
All you need is hand tight, then 1/8 to 1/4 turn (45-90 degrees)
Stellar HDF Member
Joined: Dec 2013
Posts: 2,198
Likes: 282
From: Long Island NY
I remember reading that you should reduce torque value when using anti-seize. I know it doesn't specifically say it in the article below but threads coated with anti-seize are considered "lubricated". This article recommends reducing by 25%...
https://www.antiseize.com/PDFs/torqu...ifications.pdf
https://www.antiseize.com/PDFs/torqu...ifications.pdf
Road Captain
Joined: Aug 2013
Posts: 519
Likes: 83
From: NC
I use a torque wrench on most things, but not spark plugs. Just gently snug them. Another thing to remember is if 16 ft lbs is at the lower end of your torque wrench's scale, it may not be all that accurate.
Seasoned HDF Member
Joined: Mar 2012
Posts: 100,455
Likes: 19,811
From: Centennial, CO
Glad you got it out with no trouble.
I do not use a torque wrench on spark plugs, never have.
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Road Master
Joined: Jan 2016
Posts: 1,143
Likes: 433
From: Menifee, CA
I guess I've been lucky. I've used torque wrenches on plugs ever since I could afford one. I still have a Western Auto wrench I bought in 1969.
I've never broken a plug. In fact I changed out my plugs yesterday.
I've tended to use anti seize on plugs in Japanese motors until I read that it isn't wise. I was surprised to see that Harley says to use it on theirs.
I've never broken a plug. In fact I changed out my plugs yesterday.
I've tended to use anti seize on plugs in Japanese motors until I read that it isn't wise. I was surprised to see that Harley says to use it on theirs.
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Elite HDF Member
Joined: Mar 2014
Posts: 4,214
Likes: 661
From: Prior Lake, MN
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: Sep 2014
Posts: 1,191
Likes: 233
From: North East, MD
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.