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Spark plug torques

Aviaman

Well Known Member
I have an eMag which uses smaller spark plugs than normally used by my O-360 cylinders. As a result, an adapter is threaded into the cylinder, and the Small plug screws into the adapter. What is the torquing technique? I would think the adapter would be torqued to the same value as Lycoming specifies for standard plugs. Then, since the smaller plug has a smaller radius of threads, a lesser value of torque would be used to seat the plug into the adapter. Does any one know how this is actually done, or can direct me to documentation ?
 
From the P-Mag installation manual:



Auto Spark Plug Adapters - Plug adapters permit the use
of 14mm automotive type plugs. Use short reach (SR)
adapters if your aviation plug callout is “M” type (for
example REMXXXX). Use long reach adapters (LR) if
your aviation plug callout is “B” type (REBXXXX). First,
install adapters with the supplied gasket on the spark plugs
finger tight. Then, insert the combined assembly (plug with adapter) in the engine and tighten to 18 ft/lb (standard auto plug torque) through the spark plug ONLY. Do not torque the adapter itself.
Note 1: If you install and torque the adapters separately, stresses will be focused at the adapter neck and can cause it to fail during installation.

Paul
 
Thank you.

After reading it, it seems the 18 ft-lbs is applied Only to the small plug, which in turn, torques the adapter into the cyl head. However the Lycoming specified torques for standard plugs seem to be in the 25-30 ft lbs range. So one might think the adapter needs to be torqued to that value.

But the eMag instructions caution specifically against that.
They say to torque ONLY the small plug to 18 ft-lbs AFTER the adapter is seated finger tight. I suspect what happens is that the small plug slightly expands the adapter, such that it is effectively seated, as if it was alone with 25-30 ft-lbs. torque.
 
I would follow the instructions from your manufacturer. Here's what I read from Lightspeed ignition on a plane that I worked on. .

http://lightspeed-aero.com/Products/Sparkplugs.htm


Gap spark plugs fired by Light Speed Engineering's PLASMA CDI systems to .032"-.045" for standard compression engines (7 - 8.5:1) and .026"-.034" for high compression engines (8.7 - 10:1).* Turbo and Supercharged engines should run a spark plug gap of .026" - .034".* Install the spark plugs and inserts using 15 and 25 lb/ft respectively, using anti-seize.

*
 
Also in Lightspeed's manual.... Adapter torqued to 35-45 ft. lbs. The plug gets torqued to 20 ft.lbs. short reach.

If you follow this, install the adapter on the plug using anti-seize on all of the threads, torque the plug and adapter to 20#, then with the plug in place, torque the adapter to 35-45 ft. lbs.

This process allows you to remove the plugs without removing the adapters.
 
I would follow the instructions from your manufacturer. Here's what I read from Lightspeed ignition on a plane that I worked on. .

http://lightspeed-aero.com/Products/Sparkplugs.htm


Gap spark plugs fired by Light Speed Engineering's PLASMA CDI systems to .032"-.045" for standard compression engines (7 - 8.5:1) and .026"-.034" for high compression engines (8.7 - 10:1).* Turbo and Supercharged engines should run a spark plug gap of .026" - .034".* Install the spark plugs and inserts using 15 and 25 lb/ft respectively, using anti-seize.

*

Also in Lightspeed's manual.... Adapter torqued to 35-45 ft. lbs. The plug gets torqued to 20 ft.lbs. short reach.

If you follow this, install the adapter on the plug using anti-seize on all of the threads, torque the plug and adapter to 20#, then with the plug in place, torque the adapter to 35-45 ft. lbs.

This process allows you to remove the plugs without removing the adapters.

Interesting - there is a conflict between these two torque sets, and both are from LSE's website. I've been using 15/25 for 13 years now. Adapters come out about half the time with the spark plug. I'm not sure I'd be comfortable torquing the adapters to 45...
 
Interesting - there is a conflict between these two torque sets, and both are from LSE's website. I've been using 15/25 for 13 years now. Adapters come out about half the time with the spark plug. I'm not sure I'd be comfortable torquing the adapters to 45...

Never install or remove the adapters without the plug installed in the adapter. To remove the adapter from the head, break the torque of the PLUG (less than 1/8th turn) then remove the adapter and the plug as an assembly.

If the adapters come out about half the time, does it mean that the adapters have lost their assigned torque values?

My adapters are torqued to 40 ft. lbs. and have never lost torque value..... They are checked at plug exchange.

My adapters are not made of brass...... They are from Lightspeed over 15 years ago.
 
Last edited:
Good idea!

Thanks! Every once in a while I surprise myself. :eek:

I also wrote the torques for the various brake caliper bolts on the wheel pant brackets.
Always found myself sitting under the plane thinking “what’s that supposed to be torqued too?”
 
Thanks! Every once in a while I surprise myself. :eek:

I also wrote the torques for the various brake caliper bolts on the wheel pant brackets.
Always found myself sitting under the plane thinking “what’s that supposed to be torqued too?”
We're required to placard tire pressure, fuel and oil type volume, so why not torques? I really like that idea and will get out my label maker today.
 
OK, can someone supply?

Aviation plugs:
Auto plugs w/ adapters:
Brake assembly:
Wheel assembly:

Magic marker at the ready.
 
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