OEM spark plug threads

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Oct 19, 2015 | 07:07 PM

#21

zeroptzero

Joined: Oct 2009

Posts: 29,848

Likes: 5,415

From: Ontario Canada

before reading some of Bill's posts I tended to use around 18 ft lbs torque on the my plugs, and I always found them really tight when it came to removal. I've since gone over 20 ft lbs for extra insurance, I just never find my plugs loose.

Oct 20, 2015 | 12:45 AM

#22

steven88

Joined: Mar 2005

Posts: 322

Likes: 3

So what is the recommended torque for spark plugs after Billman's findings?

Oct 20, 2015 | 03:11 AM

#23

Chuck S

Joined: Jul 2014

Posts: 13,826

Likes: 1,548

From: Chesterfield VA

I have a note penned in my shop manual that says the torque should be 24 lb-ft. This is up from the original 18 lb-ft. I think that came from one of Bill's earlier posts and/or Honda.

New OEM-spec NGK (7746) IFR7G-11KS plugs have anti-seize on the threads (plating?).

-- Chuck

Oct 20, 2015 | 03:23 AM

#24

starchland

Joined: Sep 2007

Posts: 7,336

Likes: 109

Can you try with head at operating temp? :0

Oct 20, 2015 | 03:52 AM

#25

zeroptzero

Joined: Oct 2009

Posts: 29,848

Likes: 5,415

From: Ontario Canada

^ I never install or remove plugs on a hot motor.

Oct 20, 2015 | 04:59 AM

#26

bitslop

Registered User

Joined: Sep 2015

Posts: 33

Likes: 0

Quote:

Originally Posted by zeroptzero

^ I never install or remove plugs on a hot motor.

How do you handle compression tests, then? I (as a non-mechanic) was wondering this just recently when I did my own compression test.

Oct 20, 2015 | 05:03 AM

#27

jkelley

Registered User

Joined: Apr 2012

Posts: 1,097

Likes: 1

Quote:

Originally Posted by starchland

Can you try with head at operating temp? :0

Yea that's a terrible idea lol... why would you want to apply any type of significant force to a metal that is hot? All metal will get "softer" with heat... ESPECIALLY aluminum

Oct 20, 2015 | 07:50 AM

#28

shind3

Registered User

Joined: May 2014

Posts: 594

Likes: 24

From: Pittsburgh

Quote:

Originally Posted by Billman250

Quote:

Originally Posted by cosmomiller' timestamp='1445273898' post='23779921

spark plug failed before the head threads stripped

Correct.

Was able to click off 75 ft-lbs.

When I stepped up to 80, the threads broke off the spark plug in the head.

Was able to spin the broken threaded piece out with pliers from the cylinder side.

Afterwards, I put a new plug in the hole. It went in with slight resistance as the threads were barely deformed.

Was able to torque to spec no problem. It could likely take another 70 ft-lbs.

Good insurance that 24-26 ft-lbs is super safe.

A lose plug will allow combustion gas to torch the threads resulting in stripping. Very safe to say if the threads are stripped, it was followed by torching.

Good info and test!

Oct 20, 2015 | 11:59 AM

#29

zeroptzero

Joined: Oct 2009

Posts: 29,848

Likes: 5,415

From: Ontario Canada

Quote:

Originally Posted by bitslop

Quote:

Originally Posted by zeroptzero' timestamp='1445341944' post='23780761

^ I never install or remove plugs on a hot motor.

How do you handle compression tests, then? I (as a non-mechanic) was wondering this just recently when I did my own compression test.

Good question, for a compression check:
I actually read that it is okay to remove plugs as soon as you turn off the engine, don't do it say 5 minutes after shutdown, either completely hot or completely cold. To reinstall plugs wait for the motor to cool down.

You know that a mechanic shop isn't going to do that though, they just want to the compression check done asap, so they will do it however they want.