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Old 08-15-2009, 08:49 PM   #1
shemoves
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Default What would happen if spark plugs were not tight enough?

Spec is 15 ft. lbs. What would happen if someone were to only get them to around 10 ft. lbs.?

Reason I ask is that I am doing mine right now. I seem to be doing a pretty good job of feeling the 'stop' after the crush washer, I'm just wondering what would happen if I happened to not get them quite tight enough.
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Old 08-15-2009, 09:00 PM   #2
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1-They may loosen over time (leading to #2)
2-You may lose some compression pressure
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Old 08-15-2009, 09:02 PM   #3
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Hmm, well I guess that is better than stripping it. Would it be noticable over time or would the car just suddenly feel like it is misfiring?
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Old 08-16-2009, 01:34 AM   #4
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you will(should) be able to hear it...but if it spits the plug....THAT can strip out the head, too

harbor freight has a 1/4" drive 20-200in-lb torque wrench for $19.99

http://www.harborfreight.com/cpi/cta...temnumber=2696

perfect for spark plugs....Mine has served me well for years
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Old 08-16-2009, 02:45 AM   #5
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Old 08-16-2009, 03:30 AM   #6
shemoves
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I drove it around and it seemed fine. I managed to get them pretty tight...I'm just so paranoid about stripping them.

I have a torque wrench...but it is the bar-type that goes up to 75 ft. lbs. so I don't entirely trust it on something like this.
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Old 08-16-2009, 12:46 PM   #7
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If you have access to a vise and some dumbells, you can check your beam torque wrench. Clamp the square drive horizontally in the vise and hang a 15 lb dumbell from the handle, 12" from the pivot. Adjust the pointer to read 15 ft/lbs.

I did this with my clicker to check it's calibration. Of course it's not super accurate, but torque specs are just an approximate surrogate for measuring tension in the fastener anyway.
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Old 08-16-2009, 01:34 PM   #8
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Quote:
Originally Posted by gopsu View Post
the 1/4" drive one fits much better in the space available

as I have several torque wrenches and tried both the 3/8 drive ones I had....that lead me to buy the 1/4 inch drive one I listed, above
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Old 08-16-2009, 05:15 PM   #9
shemoves
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what is spec on the plugs in inch pounds?
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Old 08-17-2009, 09:36 AM   #10
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Quote:
Originally Posted by Uncle Scotty View Post
you will(should) be able to hear it...but if it spits the plug....THAT can strip out the head, too

harbor freight has a 1/4" drive 20-200in-lb torque wrench for $19.99

http://www.harborfreight.com/cpi/cta...temnumber=2696

perfect for spark plugs....Mine has served me well for years
Don't ask me how I know, BUT, should you "spit" a plug it will really, really get your attention. RP
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Old 08-17-2009, 11:16 AM   #11
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like scotty mentioned, 1/4" would be real handy. I did my plug changes couple month ago. i had no problem torqueing down three of plugs with 3/8" wrench but there was no room for the rear driver side one.
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Old 08-17-2009, 12:22 PM   #12
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Quote:
Originally Posted by shemoves View Post
what is spec on the plugs in inch pounds?
Multiply ftlbs by 12.

And it is common knowledge that bean torque wrenches are much more accurate. The accuracy lies in the fact that a stiff rod behaves like a spring in small angle bends. However, it's precision is the issue given you must rely on the graduations that are on the scale. Clicker torque wrenches aren't as accurate (in general) but are much more precise. With a beam wrench, unless it has been abused, the only recalibration you'll have to do is make sure the pointer is on 0 when it is unloaded. The obvious other disadvantage is having to be looking at the scale dead on (to avoid parallax) when setting the final torque. I'm sure this is the case on a Subaru flat four since you probably can't see the scale when when it is in position.

I milled out an aluminum arm and made a device like leecea mentioned for checking the accuracy of a torque wrench. I bolted a piece of cast iron that weighs 10lbs at the end of the arm and in the middle it has a nut on it that can slide in a milled slot with graduations on it for adjusting the distance away from the pivot. You must only take measurements when the weight is at 90 degrees from rest (arm is parallel to the ground). In the end it has proved that my 0-75ftlb Crastman bean torque wrench is 100% perfect throughout the range (within the precision of the scale)...I usually test it at 15lbft and 60lbft. My autozone 3/8" clicker is consistently 1-2 lbft too low in the early settings and gets more accurate above 30lbft (this is usually the case for clicker torque wrenches...more accurate in the higher range of the operating range). I haven't tried the HF 1/4" clicker I bought a few weeks ago because my device isn't good for measuring any less than 10 ftlb.
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Old 08-17-2009, 01:51 PM   #13
shemoves
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Quote:
Originally Posted by 09rexwagon View Post
Multiply ftlbs by 12.

And it is common knowledge that bean torque wrenches are much more accurate. The accuracy lies in the fact that a stiff rod behaves like a spring in small angle bends. However, it's precision is the issue given you must rely on the graduations that are on the scale. Clicker torque wrenches aren't as accurate (in general) but are much more precise. With a beam wrench, unless it has been abused, the only recalibration you'll have to do is make sure the pointer is on 0 when it is unloaded. The obvious other disadvantage is having to be looking at the scale dead on (to avoid parallax) when setting the final torque. I'm sure this is the case on a Subaru flat four since you probably can't see the scale when when it is in position.

I milled out an aluminum arm and made a device like leecea mentioned for checking the accuracy of a torque wrench. I bolted a piece of cast iron that weighs 10lbs at the end of the arm and in the middle it has a nut on it that can slide in a milled slot with graduations on it for adjusting the distance away from the pivot. You must only take measurements when the weight is at 90 degrees from rest (arm is parallel to the ground). In the end it has proved that my 0-75ftlb Crastman bean torque wrench is 100% perfect throughout the range (within the precision of the scale)...I usually test it at 15lbft and 60lbft. My autozone 3/8" clicker is consistently 1-2 lbft too low in the early settings and gets more accurate above 30lbft (this is usually the case for clicker torque wrenches...more accurate in the higher range of the operating range). I haven't tried the HF 1/4" clicker I bought a few weeks ago because my device isn't good for measuring any less than 10 ftlb.
good to know, thanks
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