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Spark plug torque

carguy614

carguy614

Well Known Member
Getting different numbers when inquiring about plug torque values for Lycoming 0-320. Looks like 30 ft. lbs. Sounds tight to me...Is this correct??

Thanks...Chris
 
Correct torque for spark plugs on the O-320 is 420 in/lbs. or 35 ft/lbs. per Lycoming manual.
 
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carguy614 said:
Getting different numbers when inquiring about plug torque values for Lycoming 0-320. Looks like 30 ft. lbs. Sounds tight to me...Is this correct??

Thanks...Chris
Click to expand...

I've been using 25 ft lbs (with new gaskets) for 11 years and 2000 + hours. Never had a problem with lossening up or blow by. Your mileage may vary.
Tm
 
From the Champion Manual

I have written in my POH a spark plug torque of 30-35 ft lbs that I believe I got from the Champion's Aviation Spark plug manual. The guy in the hanger next to me is an IA and has all kinds of source material like that. I have been using 400 in-lb (right in the middle).
 
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Don't forget to use anti-seize on the threads. Torque is just a crude way of attempting to get proper tension in a joint by measuring friction. While most torque values are based on "dry" surfaces, I believe that the aviation plug suppliers base their numbers on a lubricated surface.
Terry
 
anyone have a smart idea to torque problem plugs?

I picked this thread just 'cause it has the best title.

I know the Lyc. spark plug torque is 420 in/lbs or 35 ft/lbs, but there's always those one or two plugs you can't get a torque wrench on.....using a U-joint ruins the torque transfer.

anyone have any bright ideas?
what about those colour coded torque stick/extensions from the auto parts store? I think they flex or 'give' when the correct torque is reached, so you could apply pressure with more dewices!? :)
 
Perry - our next door neighbor did a test on some of those colour-coded "torque sticks". He is a pretty sharp fella, with access to some lab-standard testing tools. His conclusion was these "torque sticks" are generally ok for rated value, +/- 25%, on a warm day. I seem to recall hearing him say something like "all bets are off" when it came to temperature changes vs torque.

What plugs do you have that are inaccessible? Lower plugs on your 9A / O-320? You might find a "wobble" socket extension (or two) would help get the torque applied.

BTW, spark plug torque is sort of like the primer wars and C/S vs FP prop wars. While we know the Lycoming recommendation stated earlier in this thread, Continental's recommendation is 25-30 lb-ft, for the exact same spark plug, in the same application. It's safe to assume the "safe" torque range is reasonably broad.
 
flyboy1963 said:
anyone have any bright ideas?
what about those colour coded torque stick/extensions from the auto parts store? I think they flex or 'give' when the correct torque is reached, so you could apply pressure with more dewices!? :)
Click to expand...

Those torque sticks are only for use with impact wrenches.

I have one of these ACDelco torque measurement adapters that I got primarily because I didn't 100% trust my torque wrench. It comes with a calibration card. Turns out my torque wrench matched it practically perfectly.

http://www.amazon.com/gp/product/B004VYUKTC?psc=1&redirect=true&ref_=oh_aui_search_detailpage

I mention it as an alternative to your torque stick idea. Unfortunately, it is bulky enough that if you can't use a normal torque wrench, you probably won't be able to use this either.
 
Tough access

flyboy1963 said:
I picked this thread just 'cause it has the best title.

I know the Lyc. spark plug torque is 420 in/lbs or 35 ft/lbs, but there's always those one or two plugs you can't get a torque wrench on.....using a U-joint ruins the torque transfer.

anyone have any bright ideas?
what about those colour coded torque stick/extensions from the auto parts store? I think they flex or 'give' when the correct torque is reached, so you could apply pressure with more dewices!? :)
Click to expand...


I'm guessing your having trouble getting a torque wrench on the upper rear spark plugs. Because of the baffles? I just put a small hole in the baffle in line with the spark plug, put the socket on the plug put an straight extension thru thru the hole in the baffle then on the socket. When done put aluminum tape over the hole (inside) until next time I need to pull/torque the plug.
 
flyboy1963 said:
but there's always those one or two plugs you can't get a torque wrench on.....using a U-joint ruins the torque transfer.
Click to expand...

The newer baffle kit designs utilize a hole in the side baffles for passing a socket extension through.
When not in use, a plug is inserted in the hole.
 
Plug torque

EMagair recommends 214 in/lb with bronE adaptor. Just FYI.
This raises a question why is 420 required with an 18mm steel plug ?
 
The spark plug is designed for a certain heat range or optimal combustion temperature range. The transfer of heat from the cylinder head to the plug can be affected if improperly torqued.
I have no idea what that tolerance for under torquing might be before heat transfer affects performance but I torque mine to spec 30-35 ftlbs.
 
Automotive Plugs

Don't forget, if you are using automotive plugs the torque values are different. I have a CDI Plasma III and torque my 14mm NGK plugs to 20 ft/lbs. I torque the adapters to 45 ft/lbs - the max, because I don't want the adapters coming loose along with the plugs when I remove the plugs.

This chart is from the NGK website:

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rvbuilder2002 said:
The newer baffle kit designs utilize a hole in the side baffles for passing a socket extension through.
When not in use, a plug is inserted in the hole.
Click to expand...

I'm using Van's FWF kit for my baffles and didn't get why there were two oblong holes in the rear cylinders' baffles that had to be plugged up with big rubber gaskets. Why are they called spark plug access holes--the wires come through the incredible expensive "figure 8" grommets on the rear baffles...:confused:

Penny dropped just this weekend, when I noticed how a socket wrench extension in my hand lined up with the still-installed dessicant plugs through those holes. Well duuuuuuuuuh...... :eek:
 
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