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  1. #1
    jmneill's Avatar
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    VXR/S Spark plug torque question

    Putting this out there for any of you guys that know how your way around a torque wrench..
    Bought the first torque wrench of my life to check and change out (with new) NGK plugs in my 2012 Yamaha VXS.
    These are 14mm plugs with a torque range of 19 to 21.5 ft-lbs.
    Here's the question:
    While I have made it forty years without a torque wrench and have changed out countless plugs, I decided to do this right.
    Here's my concern: I am certain I have NEVER torqued down a spark plug with the force I put into this 14" torque wrench.
    Wrench was an 10 - 80 ft ft-lb range tool, brand new and supposedly calibrated. I set it to 20 lbs and didn't stop till it FINALLY "clicked". (Probably one FULL revolution past the first sign of resistance.
    My question to you guys is, have I been under torquing spark plugs my entire life? Is one full revolution past hand tight too far?
    And, probably most importantly, have I likely damaged something, and if so, is it going to be the aluminum head, the plug, or both?
    I think I'm good to go if I never change plugs again. LOL But I'm really concerned that in one way or another I somehow went to far.

    Thanks in advance.

    jmneill
    Last edited by jmneill; 05-05-2015 at 04:15 PM.


  2. #2
    64physhy's Avatar
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    I don't think I've ever used a torque wrench. Usually, the spark plugs have directions on the box that say to go 1/2-1/3 of a turn past finger tight. 20 lb/ft is a lot of torque for a spark plug, are you sure that wasn't supposed to be in/lb? 1/2-1/3 past finger tight is right around 30-40 in/lb by my calibrated elbow.

  3. #3
    jmneill's Avatar
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    Quote Originally Posted by 64physhy View Post
    I don't think I've ever used a torque wrench. Usually, the spark plugs have directions on the box that say to go 1/2-1/3 of a turn past finger tight. 20 lb/ft is a lot of torque for a spark plug, are you sure that wasn't supposed to be in/lb?
    Yes, the box said 1/2 to 2/3 turn past finger tight, but NGK recommends using a torque wrench.. So, for better or worse I did..
    Below are their torque specs for various plugs and applications. I double checked with their tech, and he confirmed 18- 21.6 foot pounds.
    Spark plug type
    Thread Diameter Cast Iron Cylinder Head (lb-ft.) Aluminum Clyinder Head (lb-ft.)
    Flat seat type (with gasket) 18 ° mm 25.3~32.5 25.3~32.5
    " 14 ° mm 18.0~25.3 18.0~21.6
    " 12 ° mm 10.8~18.0 10.8~14.5
    " 10 ° mm 7.2~10.8 7.2~8.7
    " 8 ° mm -- 5.8~7.2
    Conical seat type (without gasket) 18 ° mm 14.5~21.6 14.5~21.6
    Conical seat type (without gasket) 14 ° mm 10.8~18.0 7.2~14.5

  4. #4

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    I checked my Yamaha VXR/VXS service manual and the torque is 18.4 ft/lbs. Were you installing new plugs or reinstalling ones that were already in the engine? Previously installed plugs will not turn that much to get the torque. New plugs will because these plugs have a metal gasket that needs to compress. These will feel much different than tapered seat plugs when installing. I had never torqued plugs in cast iron heads of cars and trucks in the many years of working in a garage even though I probably should have. You just get the feel for it. Aluminum heads are a different animal. To much torque and you can strip the threads in the head. To little and you can blow out a plug. I always use a torque wrench now. If your torque wrench is calibrated, you'll be fine at 20ft/lbs without any damage to the aluminum head threads.

    Sorry, just re-read and saw new plugs. Feel will be as described above.
    Last edited by Erierunner; 05-05-2015 at 06:27 PM. Reason: Read it all first

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  6. #5
    jmneill's Avatar
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    Quote Originally Posted by Erierunner View Post
    I checked my Yamaha VXR/VXS service manual and the torque is 18.4 ft/lbs. Were you installing new plugs or reinstalling ones that were already in the engine? Previously installed plugs will not turn that much to get the torque. New plugs will because these plugs have a metal gasket that needs to compress. These will feel much different than tapered seat plugs when installing. I had never torqued plugs in cast iron heads of cars and trucks in the many years of working in a garage even though I probably should have. You just get the feel for it. Aluminum heads are a different animal. To much torque and you can strip the threads in the head. To little and you can blow out a plug. I always use a torque wrench now. If your torque wrench is calibrated, you'll be fine at 20ft/lbs without any damage to the aluminum head threads.

    Sorry, just re-read and saw new plugs. Feel will be as described above.
    Thanks Erie. Maybe I'm used to tapered seat plugs, because these darn things felt like they were NEVER gonna tighten down. From finger tight, to the much anticipated "click" of the torque wrench was one LONG agonizing pull. Wish I'd began at 18 Lbs, but once I'd started, I just felt like I was "all in" and let it ride..

    I ordered four more plugs and was thinking about pulling all these out and checking for any signs of damage, but @ 20 lbs, hopefully I'm just a little over torqued, and haven't screwed to pooch. 78 hours of worrying to the 100 service.

    Thanks for taking the time to pull out the shop manual.

  7. #6

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    New plugs with the metal gasket will be as you described; long agonizing pull. If you want to check, pull them out and you can re-use. Just torque them with the wrench. The plugs will still seal properly. You'll see that you need less turning to get the torque. From 18.4 to 20ft/lbs isn't that much of a difference so, I wouldn't be worried.

  8. #7
    Chupacobra's Avatar
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    With torquing it that high I'd recomwnd the engine be COLD before you decide to pull one out. There's really absolutly no need to torque them.

  9. #8
    I'd be very dubious of using a torque wrench on plugs. You brain does a much better job of telling you whats right, and as others have mentioned, big difference between new and used plugs. My many years reading bike forums the number of people that have broken or stripped something using a torque wrench instead of common sense. I personally use a torque wrench on head bolts, nothing else. Also using a torque wrench that close to the bottom of it's range isn't something I'd be comfortable with, especially with a plug where the consequence of you getting is wrong is so bad

  10. #9
    jmneill's Avatar
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    Quote Originally Posted by Erierunner View Post
    If you want to check, pull them out and you can re-use. Just torque them with the wrench. The plugs will still seal properly. You'll see that you need less turning to get the torque. From 18.4 to 20ft/lbs isn't that much of a difference so, I wouldn't be worried.
    Well the suspense was killing me, so I went ahead and pulled them. You were correct, everything is copacetic. What a relief. Punched them all back down to 18.5 and all felt well. Thanks again for the exact number.

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