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Spark Plug Adapter

Doug Eves

Well Known Member
I should know this but my memory is bad. I am changing my auto plugs for a new set for the first time. First plug I removed the adapter came along with it. When you reinstall the new plug are you supposed to put the adapter and plug back in as one unit or put them in separately. The first set have been in there since June 24 2017 which is 249 hrs ago. I seem to remember following some specific instructions when I did it but don not remember. Like to here from someone who knows how I could screw up something so seemingly simple.
 
From Lightspeed Plasma I Installation.......

LSI plug adapter info.PNG

I install the adapter on the plug. Install plug and adapter.
Torque the plug. THEN torque the adapter.

When I change the plugs, I remove and install only the plug.

If I need to remove the adapter, I do it with the plug backed off 1/4 turn
then remove the adapter with the plug.
 
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Recommend reading the manual. Pmag plugs are installed differently than lightspeeds. Many broken adapters from Pmag have been reported if torquing the adapter.
 
Recommend reading the manual. Pmag plugs are installed differently than lightspeeds. Many broken adapters from Pmag have been reported if torquing the adapter.

How is the adapter going to break if the plug is installed in it and torqued first to the plug torque spec.

P-Mag had problems at first with their instructions that said to torque the adapter first into the head. The walls of the adapter are thin and need to be supported.
Removing the adapter without the plug can cause the adapter (if brass) to split and fail.
 
As mentioned P-mags recommends a very difference approach. Also auto plugs use a much lower torque than aviation plugs. I would research your specific set up.
 
What my P-mag manual called for.

Just replaced all my plugs on my P-mag ignition durning condition inspection. Install adapter on the plug finger tight and then install both together on engine using a torque wrench on the spark plug only to 18 ft.lbs. When I removed the old plugs, some came out with the adapters still attached while other remained in the head.
A very economical experience.:)
 
How is the adapter going to break if the plug is installed in it and torqued first to the plug torque spec....
The walls of the adapter are thin and need to be supported....

Agree, the sensible method is "adapter on plug, screw assembly into head, torque plug, then torque adapter".
 
Latest Lightspeed and Pmag manuals

Here is the info from the current manuals.

As mentioned pmag and lightspeed recommend very different processes. The adapters aren’t the same. If you look at them side by side, you can see the pmag has a brighter brass look compared to the lightspeed. Lightspeed adapters take 35-45 ft-lbs of torque. Pmag recommends combining adapter and plug and only using 18 ft-lbs. You can break a pmag adapter at 18 ft-lbs by not installing it with a spark plug inserted.

LIGHTSPEED CURRENT MANUAL ENTRY

2.4 SPARK PLUG ADAPTORS AND SPARK PLUGS
• Aircraft engines using 18mm & 1⁄2” reach spark plugs use adaptors with the same outside thread and a 14mm & 3⁄4” reach inside thread.
Use LSE high performance HP plugs, Denso spark plugs starting with a W or NGK spark plugs starting with a B in their designation.
• Aircraft engines using 18mm & 7/8” reach spark plugs use one of the following:
o LSE long reach adaptors with 12mm inside thread for Denso X27GPR-U
or X24GPR-U or equivalent 12mm spark plugs.
OR
o Optionally, for high performance applications, use LSE HP-LR (long reach) adaptors with 14mm inside thread for high performance HP-LR or IKH 14mm spark plugs.
• Install adaptors in cylinder head using the supplied copper washer. Torque to 35 - 45 ft-lbs using anti-seize compound.
• Install automotive style spark plugs with their washer. Torque to 20 ft-lbs using anti-seize compound.


PMAG CURRENT MANUAL ENTRY

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.
 
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How is the adapter going to break if the plug is installed in it and torqued first to the plug torque spec.

P-Mag had problems at first with their instructions that said to torque the adapter first into the head. The walls of the adapter are thin and need to be supported.
Removing the adapter without the plug can cause the adapter (if brass) to split and fail.

Good question. Point was to follow the manual for his ignition. Look above at what Keith just posted for Lightspeed. You follow that method from their manual on Pmag adapters and well, history has shown what will happen.
 
Also, I can’t believe that the plugs look so perfect as I remove them. Clean as a whip and a light tan Color still functioning perfectly. I just thought it has been soooo long that I better change them. With mags and aviation plugs I would be constantly battling with fowling and difficulty with hot starting. (Injected motor) I told the emag folks that if all that their ignition ever did was to cure my hot starting that I would be happy. I definitely am so happy with this set up. Plus he gave me a free hat with headlights!!
 
Doug,

How many hours on those plugs? What percent power do you normally operate? LOP or ROP? Just looking for a data point of operation style and resulting good looking plugs.
 
There is 249 hrs on those plugs. I usually run around at 25 square and 9.8 to 10 gallons per hour. I use 2500 typically as that is the sweet spot for my engine/prop in terms of vibration. Even at higher altitudes (7000-10,000)where my manifold pressure is lower I maintain the same fuel flow. I don’t have my engine monitor connected in a way that will display % power so I am reluctant to deviate from the way I have been operating my engine for at least the last 1000hrs. Compression/leak down tests are still essentially the same as 150 hrs so I just continue onward. Lately I have been “slowing” down at lower altitude as I fly around going no where in particular. When I pull the manifold back to say 15/16” I will lean aggressively just to burn less fuel but l don’t do this a lot.
 
Here is the info from the current manuals.

As mentioned pmag and lightspeed recommend very different processes. The adapters aren’t the same. If you look at them side by side, you can see the pmag has a brighter brass look compared to the lightspeed. Lightspeed adapters take 35-45 ft-lbs of torque. Pmag recommends combining adapter and plug and only using 18 ft-lbs. You can break a pmag adapter at 18 ft-lbs by not installing it with a spark plug inserted.

I've been evaluating different plugs(14mm and 18mm) and adapters. I really wasn't thrilled with the idea of torquing the plug/adapter to 18fp (pursuant to pmag instructions), when standard aviation plugs are torqued to 35fp. I purchased a set of the adapters from Lightspeed and they appear to be a different material. Lightspeed lists their adapters as being high-strength aluminum bronze and as you pointed out, the torque ratings and procedures are also very different.

SDS shows a service bulletin on their website for "brass adapters" and updated their installation procedure similar to pmag procedure with a higher torque (22fp vs pmag 18fp).

April 26/19 Service Bulletin Regarding 18 to 14mm Spark Plug Adapter Installation

Due to a number of broken brass plug adapters, we've changed the procedure for installing these as follows: 1. Thread the spark plug into the adapter 2. Torque the assembly into the cylinder head using the PLUG hex to 19 ft./lbs. 3. Torque the ADAPTER further to 25 ft./lbs. Use only a thin stripe of anti-seize compound on the plug and adapter. Do not coat the threads. Although we've done multiple yield tests on the adapters torqued into a fixture and they fail at 32-35 ft./lbs., a number of people were snapping them at the originally recommended torque of 22 ft./lbs.


Lastly, FlyEFii also has a variant of adapters that are listed as the "strongest alloy of naval brass"
Their instructions for torquing are different.

CAUTION- Always install the brass spark plug adapters onto the spark plug first and then install the assembly
into the cylinder. Never torque the spark plug adapters into the cylinder without a spark plug installed – this
could damage the spark plug adapter. With spark plugs and adapters installed into the cylinders, torque the
spark plug only to 30 ft lbs. This will seat the washers on both the adapter and the spark plug with one step.


30fp seems like a lot for a 14mm spark plug, but that's their process.
 
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silly question...

Here is the info from the current manuals.

As mentioned pmag and lightspeed recommend very different processes. The adapters aren’t the same. If you look at them side by side, you can see the pmag has a brighter brass look compared to the lightspeed. Lightspeed adapters take 35-45 ft-lbs of torque. Pmag recommends combining adapter and plug and only using 18 ft-lbs. You can break a pmag adapter at 18 ft-lbs by not installing it with a spark plug inserted.

LIGHTSPEED CURRENT MANUAL ENTRY

2.4 SPARK PLUG ADAPTORS AND SPARK PLUGS
• Aircraft engines using 18mm & 1⁄2” reach spark plugs use adaptors with the same outside thread and a 14mm & 3⁄4” reach inside thread.
Use LSE high performance HP plugs, Denso spark plugs starting with a W or NGK spark plugs starting with a B in their designation.
• Aircraft engines using 18mm & 7/8” reach spark plugs use one of the following:
o LSE long reach adaptors with 12mm inside thread for Denso X27GPR-U
or X24GPR-U or equivalent 12mm spark plugs.
OR
o Optionally, for high performance applications, use LSE HP-LR (long reach) adaptors with 14mm inside thread for high performance HP-LR or IKH 14mm spark plugs.
• Install adaptors in cylinder head using the supplied copper washer. Torque to 35 - 45 ft-lbs using anti-seize compound.
• Install automotive style spark plugs with their washer. Torque to 20 ft-lbs using anti-seize compound.


PMAG CURRENT MANUAL ENTRY

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.

I'm doing mine (P-MAG) during conditional inspection today.
If you assemble, install, then torque to 18 ft/lbs, then won't the adapter be essentially 18 ft/lbs as well.
Why does it not need the 32 ft/lbs of standard plane plugs?

Daddyman
 
I'm doing mine (P-MAG) during conditional inspection today.
If you assemble, install, then torque to 18 ft/lbs, then won't the adapter be essentially 18 ft/lbs as well.
Why does it not need the 32 ft/lbs of standard plane plugs?

Daddyman

I have always thought about this too. But getting them plugs out every time sure is a bear so 18 ft/lbs must do the trick.
 
I have always thought about this too. But getting them plugs out every time sure is a bear so 18 ft/lbs must do the trick.

Indeed - I'm doing it like emagair recommends and so far the plugs are still in the engine, and the plug gasket and the adapter gasket are both sealing.

I'm not a mechanical engineer, so I can't say what the difference is with this application between the two mentioned torques, but that would be interesting to understand. How much of the suggested torque value is to "make sure it doesn't come off" and how much is "hold the thing on with a certain amount of pressure."
 
Why does it not need the 32 ft/lbs of standard plane plugs?

Daddyman

Who is to say it NEEDS 32 ft/lbs to stay in place? The fact that 32 is specified doesn't tell you how much margin there is. Remember, this is not a fastener carrying loads. The force on the plug from compression is pretty low.

Larry
 
I'm doing mine (P-MAG) during conditional inspection today.
If you assemble, install, then torque to 18 ft/lbs, then won't the adapter be essentially 18 ft/lbs as well.
Why does it not need the 32 ft/lbs of standard plane plugs?

Daddyman

I believe the torque call outs are based on the strength of the components and not necessarily the amount of torque required to hold the components in place.
 
I think what many people fail to realize is that these plug adapters are usually made from brass or bronze (lower tensile strength than steel) have stress risers on both sides and a wall thickness of only about .060.

By threading in the spark plug first, you take a lot of the strain off the adapter, making the whole assembly much stronger than the adapter alone.
 
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