18-14mm Spark Plug Adapters

I'm trying to figure out what is the difference/advantage between adapters marketed specifically for aircraft and other commercially produced products. The COTS (commercial off the shelf) items run anywhere from $3-10 each and are available in brass or steel. The ones sold through ACS are ~$20 each, the material is not specified. Is there a worthwhile difference between the products?

For what it's worth, I just had to replace a cracked adaptor--it came with the rebuilt engine so I do not know its pedigree. I plan to order a few from ACS to keep on hand.

EFII

The EFII adapters I recently bought are considerably nicer than those I previously had. $62 for four.

"Nicer" how, exactly? Just wondering. I bought eight from Brillman; they seem to be well made, but I don't know for sure whether I'll end up needing them or not. Apparently you can get new cylinders with 14mm plug bores.

Wasn't aware of any non-aircraft application of 18-14mm adapters. Where did you find a a COTS source? Seems like it would be worth checking out. I've found the tips of my adapters have eroded a bit. Would like to have a set of spares on hand.

The Brillman Co. has them for the antique tractor bunch. Apparently other than speed and altitude, they have a lot in common with Lycoming engines. 18mm plugs, magnetos, low RPM... lots of old guys using them.

I've been using the adapters from light speed klaus gets 15 apiece for them.

Bob burns
Rv-4 n82rb

Noah said:

Wasn't aware of any non-aircraft application of 18-14mm adapters. Where did you find a a COTS source? Seems like it would be worth checking out. I've found the tips of my adapters have eroded a bit. Would like to have a set of spares on hand.

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Old Harley motorcycles used 18mm plugs as well. I was suprized to see how many came up with a quick search. I just am not sure if those made for aircraft are any better. 4 for less than $25 is pretty appealing. I have spent considerable time trying to souce an acceptable 18mm auto plug with no luck. Everything i find is either non-resistor, wrong heat range, or wrong seat type. I cant find that perfect combo of 18mm, resistor, gasket seat, corrent heat range to match the lycommings needs. That leaves adapters as the only option.

I would think that the only 'gotcha' might be the reach of the adapters. As long as they are roughly the same length as the threads on the 18mm plug, I wouldn't hesitate to use them.

(Longer *might* interfere with a piston, and could carbon up on the exposed threads making them difficult to remove; shorter might mean cleaning the threads in the head with a thread chaser if you ever went back to 18mm plugs.)

FWIW...

Question about auto plugs?

I know that a lot of folks use the 14mm auto plugs when they switch over to electronic ignition or the G3I. Do any of you run auto plugs with your stock Slick mags? I don't know how, but I managed to buy Tempest URHM38E plugs (3/4") instead of the UREM38E (5/8") that fit my harnesses. I did not realize my mistake until I had them all opened up and on my work bench today so they are not returnable. The thought of comparatively inexpensive auto plugs I can obtain just about anywhere is pretty appealing to me as I sit grounded for days waiting for Monday to place an order from AS&S.

9GT said:

I know that a lot of folks use the 14mm auto plugs when they switch over to electronic ignition or the G3I. Do any of you run auto plugs with your stock Slick mags? I don't know how, but I managed to buy Tempest URHM38E plugs (3/4") instead of the UREM38E (5/8") that fit my harnesses. I did not realize my mistake until I had them all opened up and on my work bench today so they are not returnable. The thought of comparatively inexpensive auto plugs I can obtain just about anywhere is pretty appealing to me as I sit grounded for days waiting for Monday to place an order from AS&S.

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That is what i am planning to do for now with the intent to add EI when funds allow. I have bendix mags, but the install is similar. Well see how it works out.

EFII spark plug adapters

We make our spark plug adapters in house on our CNC lathe.
We hold the tolerances very tight for a proper fit to the cylinder and spark plug.
Spark plug threads are a slightly different size than bolt threads.
We are also very picky about overall fit and finish on all of our parts.
You can see this in the result.

I would imagine any of the available adapters will work.

Robert

rcpaisley said:

We make our spark plug adapters in house on our CNC lathe.
We hold the tolerances very tight for a proper fit to the cylinder and spark plug.
Spark plug threads are a slightly different size than bolt threads.
We are also very picky about overall fit and finish on all of our parts.
You can see this in the result.

I would imagine any of the available adapters will work.

Robert

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The units you produce look like a quality product. I have dug around on your website and ASC and cant figure out how to buy them.

EFII fittings

They are in the Additional Components section of the site:
http://www.flyefii.com/add_components/additional_comp.htm#Spark_Plug_Adapt
Robert

9GT;
I am running a Bendix S-200 mag with adapters, auto plugs and MSD 8.5mm Superconductor wire with MSD 90 degree boots. I set the plug gaps to .016", the value called out for aircraft plugs. The idea being so the mag could fire the plugs without stress. The left mag, with Retard Points & Shower of Sparks starts the engine via the auto plugs.
I'm running them on the top of my (X) IVO-360a1a, the adapters are from a Pmag I installed on my T-18. The T-18 has a 7:1 O-290, which runs fine with 18mm Autolite 386 plugs. So the adapters were spare.
I made the leads from a 50 foot roll of MSD super conductor wire and an 8 pack of 90 degree plug boots from an online hot rod supplier.
I adapted an old style magneto lead plate, which has threaded gland nuts for the lead wires, a good ePay find.
G3i has instructions for modifying a modern mag plate for 8.5mm wire, but I had the old style plate with the gland nuts and the 8.5mm wire is a near perfect fit without modifying the plate. I did have to make up some packing so the 8.5mm wire would be gripped when the gland nuts are tightened.
I consider this a successful repair, and have enough parts to do one more.
Probably less than half the price of a harness set, and it was fun to do.

9GT;
I re-read your post. You have Slick mags. I got so involved talking about my Bendix mag conversion...
G3i has instructions on converting Slick mags to 8.5mm wire also.
http://www.g3ignition.com/magmod.html
As I recall, it has detailed instructions & dimensions with tool & parts callout.
I'm happy with my Bendix conversion, the Slick conversion must surely perform the same?

Thanks for the info Scott. My buddy runs the G3i on his Cozy MKIV with IO-360 and really likes it. I am already nose heavy in my -10 and don't want to add the additional weight of the G3i so I am ordering up a set of new 18mm massive Tempest's.

9GT said:

Thanks for the info Scott. My buddy runs the G3i on his Cozy MKIV with IO-360 and really likes it. I am already nose heavy in my -10 and don't want to add the additional weight of the G3i so I am ordering up a set of new 18mm massive Tempest's.

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You can mod your mags for automotive plugs without adding the electric ignition. Of course the only benefit is the cost of the plugs and harness, no performance improvement.