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to torque or not to torque -oil and plugs

 
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Old 27 Jul 2003, 08:53 pm
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Default to torque or not to torque -oil and plugs

According to PTDIY it's recommended to use a torque wrench on the spark plugs and oil drain plug. I went to AutoZone to get a torque wrench and the guy there said it wasn't a good idea. That on newer cars they would 'back-off' if a torque wrench was used. He recommended getting them so they 'feel tight' and then check them again in about a week.

I have a 2003 GT. Suggestions?
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Old 27 Jul 2003, 10:23 pm
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I do my plugs at 13lbs like my service manual says.
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Old 27 Jul 2003, 10:27 pm
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Quote:
quote:Originally posted by Mean Green

I do my plugs at 13lbs like my service manual says.
Ditto on the plugs but never torqued the drain plug (always by hand).
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Old 28 Jul 2003, 12:43 am
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"The guy at Autozone" is your answer.
Do you think he has an automotive degree from an acredited school?
Do you think he's Master ASE certified?
Do you think he makes a living actualy fixing cars?

Therein lies the answer.

Misinformation spreads so rapidly from the misinformed.

If you plan to use a cheap torque wrench, you might as well not use one at all.
So... use a torque wrench, and use a good one. Any under $100 is a joke.
I've been a mechanic for a long time. I have the degree, I have the ASE papers, and I've yet to learn anything new or correct from "the parts dude" at a retail consumer oriented parts store.
Look for an ASE parts specialist at a professional warehouse distributer who supplies the local automotive shops.

Have you ever noticed that the pro repair shops DO NOT buy the parts they install and warranty from consumer grade parts stores?

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Old 28 Jul 2003, 03:07 pm
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Quote:
quote:Originally posted by MX-5

If you plan to use a cheap torque wrench, you might as well not use one at all.
So... use a torque wrench, and use a good one. Any under $100 is a joke.
I would like to put an engineers twist on your torque wrench comments.

My first job out of college was developing torquing specs for jet engines at Pratt & Whitney Aircraft. What I learned in that 6 month project is that torquing a threaded fastener is about the most inaccurate thing you will ever do with a measurement tool.

In simplest terms the purpose of torquing a fasterner to ensure that you are appling more force (in pounds) to hold the the parts together than will be applied in use which trys to seperate them. If you accomplish this the joint will not loosen. You can mathematically calculate what the clamping force will be for a given torque knowing the fasterner diameter and thread pitch. The error comes in because the calculation assumes no friction in the threads. For a given torque reading the actual clamping force can vary as much as 40% depending on the conditions of the threads, finish on the threads, plating, and/or lubrication used. The best you can hope for is about a 10% variation fastener to fastener. This is the reason for manufacturers going to torque to yeild head bolts. Once you yeild the bolt the clamping force now becomes a function of the fastener size and material.

The variation in accuracy from the least to most accurate torque wrench is about 1-2% and the cheap beam type tend to me more accurate than the expensive micrometer type. And even the least accurate is almost an order of magnitude more accurate than the other variations that will effect the loading in your threaded joint.

NOTE: I am not recomending a cheap torque wrench over a high quality one (you will never regret buying a good tool) but if you can't afford a good one and you are an occasional home mechanic a $25 wrench will serve you fine. A $25 dollar one just will not stand up to the day to day use from a professional mechanic.
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Old 28 Jul 2003, 03:27 pm
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Dave, there were enough spelling errors in that, to confirm your engineering background (LOL).
Hope you take that tongue in cheek as it was meant, from a BSME.
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Old 28 Jul 2003, 03:45 pm
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This Forum doesn't have spell check!

What's an engineer to do! [:I]
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Old 28 Jul 2003, 04:34 pm
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Quote:
quote:Originally posted by dgc333

This Forum doesn't have spell check!
What's an engineer to do! [:I]
Go to: www.iespell.com It's free and werks well
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Old 28 Jul 2003, 04:46 pm
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Join Date: Jul 2003
Location: ON, Canada.
Posts: 467
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House with garage = 200K
Full set of professional tools = 10K
Cost of learning by trial = 30 - 50K?

Oil change at dealer = 30 bucks

MMM... looks like that math degree is good for something after all...
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Old 28 Jul 2003, 11:56 pm
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Join Date: Jan 2003
Location: San Juan, Puerto Rico, USA.
Posts: 566
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Quote:
quote:Originally posted by dgc333

I would like to put an engineers twist on your torque wrench comments.

My first job out of college was developing torquing specs for jet engines at Pratt & Whitney Aircraft. What I learned in that 6 month project is that torquing a threaded fastener is about the most inaccurate thing you will ever do with a measurement tool.

In simplest terms the purpose of torquing a fasterner to ensure that you are appling more force (in pounds) to hold the the parts together than will be applied in use which trys to seperate them. If you accomplish this the joint will not loosen. You can mathematically calculate what the clamping force will be for a given torque knowing the fasterner diameter and thread pitch. The error comes in because the calculation assumes no friction in the threads. For a given torque reading the actual clamping force can vary as much as 40% depending on the conditions of the threads, finish on the threads, plating, and/or lubrication used. The best you can hope for is about a 10% variation fastener to fastener. This is the reason for manufacturers going to torque to yeild head bolts. Once you yeild the bolt the clamping force now becomes a function of the fastener size and material.

The variation in accuracy from the least to most accurate torque wrench is about 1-2% and the cheap beam type tend to me more accurate than the expensive micrometer type. And even the least accurate is almost an order of magnitude more accurate than the other variations that will effect the loading in your threaded joint.

NOTE: I am not recomending a cheap torque wrench over a high quality one (you will never regret buying a good tool) but if you can't afford a good one and you are an occasional home mechanic a $25 wrench will serve you fine. A $25 dollar one just will not stand up to the day to day use from a professional mechanic.
This reminded me of my old missile working days with the USAF.

I used to connect some parts to another (They are still secret) and the manual said:
Torque to 100 PSI +/-1, hit the coupler ring 6 times, retorque to 100 PSI +/-1 and repeat unti it retains the torque....
I loved it, hitting a real explosive missile with a hammer...[?]

Ian
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