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Spark plug torque?

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Brendan

Posts: 203

Joined: Sat Apr 04, 2009 7:59 pm

Location: Orlando

Post Sat Aug 29, 2015 3:51 pm

Spark plug torque?

I checked my spark plugs today after a 100 mile break in period and they are brown, leaning towards black and dry.

I put new plugs in to baseline change as i break in the engine.

I kicked a couple of times to prime the engine when i noticed one was hissing. LEAK.... OH KNOW.

What is the proper torque for the spark plug?

25 foot lbs sound right. 300 in.lbs ????
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Cobb

Posts: 21

Joined: Sat Aug 01, 2015 3:30 pm

Location: North East Ohio

Post Sat Aug 29, 2015 6:36 pm

Re: Spark plug torque?

Finger tight than 1/4 turn "max" is what I run. Just enough to compress the ring on the plug. Less with aluminum heads. Aluminum will take a set over time so over torquing will destroy the threads in an aluminum head eventually.
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Brendan

Posts: 203

Joined: Sat Apr 04, 2009 7:59 pm

Location: Orlando

Post Sat Aug 29, 2015 7:40 pm

Re: Spark plug torque?

It looks like i have a small divot in the insert. I put some soap bubbles around the plug and slowly kicked it and it bubbles formed .

I thought the threads would seal the head. Is there something I can put on the threads?
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Cobb

Posts: 21

Joined: Sat Aug 01, 2015 3:30 pm

Location: North East Ohio

Post Sat Aug 29, 2015 8:05 pm

Re: Spark plug torque?

Small divot on the insert ???
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Cobb

Posts: 21

Joined: Sat Aug 01, 2015 3:30 pm

Location: North East Ohio

Post Sat Aug 29, 2015 9:23 pm

Re: Spark plug torque?

The ring on the bottom of the plug should seal the head not he threads. Don't add any thing to the threads to seal it. Try a different plug if it still leaks the head may need re cut on the seat.
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knucklebolt

Posts: 434

Joined: Tue Feb 12, 2013 8:27 pm

Location: Six miles East of Cheney, Wa.

Post Sat Aug 29, 2015 10:06 pm

Re: Spark plug torque?

Inserts that let a 18mm head take 14mm plugs? If so...toss them inserts and get some 18mm plugs. !!! :)

ken.
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Samsup

Posts: 157

Joined: Wed Feb 25, 2015 2:35 pm

Post Sun Aug 30, 2015 6:36 am

Re: Spark plug torque?

Cobb wrote:Finger tight than 1/4 turn "max" is what I run. Just enough to compress the ring on the plug. Less with aluminum heads. Aluminum will take a set over time so over torquing will destroy the threads in an aluminum head eventually.


Proper Alu heads should have steel thread inserts.. At least originally they had, and our repros have it too, bare aluminum will wear down very fast!

But the general consensus of finger tight plus a quarter turn is about right.. They should be " just tight" not very tight, not loose either
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woody

Posts: 530

Joined: Mon Apr 15, 2002 12:01 am

Location: Wa, USA

Post Sun Aug 30, 2015 9:46 am

Re: Spark plug torque?

NGK plug installation instructions for 18mm plugs in aluminum call for 25 to 32 ft lbs torque.

Autolite calls for 28 to 34 ft lbs and their instructions for tightening without a torque wrench are finger tight plus 1/2 turn for 18mm plugs.
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Cotten

User avatar

Posts: 2939

Joined: Thu Sep 30, 1999 12:01 am

Location: Central Illinois, USA

Post Sun Aug 30, 2015 10:16 am

Re: Spark plug torque?

Brendan!

If you have a divot that prevents a seal washer from doing its job, its another vacuum leak.

The surface should be re-cut, which not impossible assembled, but not easy either.
You may need to pressure test it to be certain that there is not a leak around the insert.

Want to try a PEEK band-aid?

.....Cotten
PS: With today's fuels, a good mixture will make the plugs look quite lean.
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knucklebolt

Posts: 434

Joined: Tue Feb 12, 2013 8:27 pm

Location: Six miles East of Cheney, Wa.

Post Sun Aug 30, 2015 12:52 pm

Re: Spark plug torque?

As mentioned, I recently tried a pair of plugs that had a tapered seat, (Champion "45" I believe) instead of a washer, and they leaked bad...so I just took them out. Kicking over they gave no indication of leaking, but once the engine was running you could sure hear and feel the leak. Other than those, I don't think I've ever had a leaking plug on anything.

Brendan I think you said you are using D16's. ??

I always put a small "dab" of grease on the threads of the plug, and a little smear on the washer, so that there is nothing to "impede" the tightening, or give a false torque reading. (be it "feel" or an actual torque wrench) I've never used a torque wrench, have always gone by feel, and have always tried to use a minimum of tightness.

Any kind of sealer would probably wind up in the engine, which wouldn't be a good thing.

k.
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Brendan

Posts: 203

Joined: Sat Apr 04, 2009 7:59 pm

Location: Orlando

Post Sun Aug 30, 2015 2:15 pm

Re: Spark plug torque?

I inspected both inserts under a microscope, one insert looked like a wrench dented the I.D.
I put three different plugs in and pressure tested. They all leaked like a sieve.
I am so paranoid regarding air leaks that I have been testing every 20 miles.

This is the first time i found a leaky plug. I must have caused the divot in some way.

I plugged the hole, I got some grease and 800 grit sand paper then for two hours I slowly knocked down the small dent.

I hand tightened the plug and almost got a quarter turn with the wrench. No more leaks anywhere.
Went for a great ride.

I was never tightening the plugs enough the entire time.

AIR LEAKS ARE THE DEVIL. Nothing works correctly if there is an air leak.
Forget about adjusting anything if you haven't tested for an air leak.

I do have some air that bleeds slowly down the valve guides .


Thanks
Brendan

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