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Use auto plugs? NGK? Check those ferrules are tight...

Paul Eastham

Well Known Member
You know, the ferrule, the little metal bit at the top of the plug where you plug the wire in.

I just checked my plane -- four out of four were loose and wobbly.
They are brand new NGK plugs replaced at annual only ~5 hours ago. I didn't notice them to be loose when I installed them, but didn't explicitly check them for this. And I've been using this brand/type for the past 10 years, never noticed this before.

I recently had some ignition trouble (old thread here) which I think was caused by this. First I thought it was caused by ignition wires (two of them were indeed flaky when bent just right so maybe I prevented a future failure there), then I thought it was the Lightspeed coil (one coil was indeed bad), but the root cause, according to Lightspeed, was probably the loose ferrule which causes heating in the coil and failure.

And of course who knows what kind of weak spark you get when that thing is loose...hopefully a gentle turn with a pair of pliers will keep them in place.
 
Yep, the ones with the removable tip are not recommend.

Get the ones with the fixed tip.

You have to ask for the specific 4 digit part number at the auto stores to get the right ones.

From the PMAG manual:

"NGK BR8ES 2.5mm Center Electrode (NGK stock #3961 has
solid/permanent terminal post, NGK stock #5422 has a screw on post)"
 
vice grips are your friend

Learned this ages ago when racing motocross - vice grips to pinch them a bit, then install them very tight. No idea why they still make the removable nipples - I guess some very old spark plug caps still need the threaded terminal.
 
Yep, the ones with the removable tip are not recommend.

Get the ones with the fixed tip.

You have to ask for the specific 4 digit part number at the auto stores to get the right ones.

From the PMAG manual:

"NGK BR8ES 2.5mm Center Electrode (NGK stock #3961 has
solid/permanent terminal post, NGK stock #5422 has a screw on post)"

Like Brantel said, order the specific 4 digit part number, but I don?t recommend ordering from Amazon. I did that and DID order the exact 4 digit part number only to receive the non-fixed tip.

Better off going to the Advanced Auto Part or Auto Zone.
 
Wow, I had no idea there was an alternate part. Been ordering the same part number from Rock Auto since forever, which was the recommendation at the time from a number of people on this forum. Just bought a 5 year supply, oops!
 
Wow, I had no idea there was an alternate part. Been ordering the same part number from Rock Auto since forever, which was the recommendation at the time from a number of people on this forum. Just bought a 5 year supply, oops!

Rock Auto also carries the fixed tip ones (#3961), and you can find them that way in their search function.
 
Plugged Up...

For auto plugs I like the Denso L-14U and Autolite 386, both available from NAPA or Amazon and selected WalMarts. They thread right in without adapters...

Additionally, I have used Accel plug wires for 25 years with no issues whatsoever.
V/R
Smokey
 
NGK plugs

Aircraft Spruce has the BR8ES with solid terminals. It's not listed specifically as such but that's where I buy mine and they're always solid tops.
 
Copper gasket

Smokey,

Do you use the copper aviation gasket with these, or the gasket that comes with the plug?

And do you torque to 32 ft-lbs or 18 ft-lbs?

Thanks,
Michael
 
I'm with Smokey on 18mm automotive plugs.
I use Autolite 386 thru a Pmag on my low compression O-290 powered T-18. (Bendix mag and Autolite aircraft plugs on the other side)
I've purchased Champion DR15Y 18mm resistor extended tip spark plugs, because they are a little cooler heat range, and intend trying them in my O-360 8.5:1 powered RV-8 when the BR8ES plugs wear out.
I like the idea of ditching the adapters. https://www.summitracing.com/parts/cpn-526/overview/ Non-Resistor: https://www.summitracing.com/parts/cpn-515/overview/ $2 cheaper each.
I seek 18mm Extended tip resistor plugs in cooler heat ranges, as the Autolite 386 runs completely clean with white porcelain. They show no heat distress, but according to literature spark plugs should run milk chocolate brown. Autolite 373 is a non resistor 18mm plug that is "cold" on their chart:
http://www.autolite.nl/bougies/pdf/pdf-heatrange.pdf
Extended tip plugs place the spark farther into the fuel-air charge for a (supposedly) better light-off and less fouling over time.
The Denso L-14U plugs are not resistor plugs, but if running resistor automotive wire, or maybe spiral core wire like MSD superconductor or Taylor or Pertronix, it might not matter. If you get no radio noise, it's OK?
NGK makes Resistor caps (to put on non-resistor plugs) but they are made for 7mm wire, and I use MSD 8.5mm wire so I have them 'on hand' but have not tried them yet. A good variety of 18mm .5" reach gasket type non-resistor plugs in cooler heat ranges and even extended tips are available.
Inductive reactance and resistance reduce spark plug current which increases spark duration, also the coil, wire and plug form an L-C tank circuit when properly set up. this causes an alternating current to flow thru the plug, for a discharge cycle that equals 'Multi-spark discharge' (rings like a bell until the voltage is too low to jump the plug gap)
This is a substantially unexplored topic. Too bad. Automotive spark plugs, wires and ignition systems have achieved an advanced state compared to certified aircraft parts.
Perhaps there should be a sticky so knowledge can be collected.
 
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Get the NGK plug typ that has a fix ferrule ... !

Why does people risk this again and again ... so many times disscussed here ... and from time to time people want to find the trouble they can get, by themself.
 
...The Denso L-14U plugs are not resistor plugs, but if running resistor automotive wire, or maybe spiral core wire like MSD superconductor or Taylor or Pertronix, it might not matter. If you get no radio noise, it's OK...

I ran a set of non resistor (BE8ES) plugs with my P-mag once and it caused all sorts of problems with the ignition itself. Several trips back to Brad trying to troubleshoot (including replacing a 113 board with a 114) - all to no avail. It was only after switching back to the resistor plugs that the misfiring, partial in flight shutdowns and other issues disappeared. P-mags will not tolerate non resistor plugs.
 
Toolbuilder: good contribution on problems with non-resistor plugs on electronic controlled ignition systems, I understand Lightspeed Ignition specifically sells DENSO spark plugs, for much the same reason. Possible coil damage can happen if non resistor plugs are used?
I'm sorry I didn't think of that while commenting last night. Auto Resistor plugs are often 5,000 ohms. (check the spec). I just checked my Unison UREM37BY Aircraft plugs at condition inspection, all four were 1,100 ohms give or take a few.
SwissEagle: I recall (not so long ago) that auto spark plugs of any kind were very unfavorably viewed by forum members. That barrier has finally been brought down. Now the same argument has slipped to 'allow' NGK BR8ES and BR9ES plugs and refuse all others? :rolleyes: Somebody tried them and the word spread.
BR8ES plugs are fine. The adapters have given trouble, and for good reason: they are very thin and sometimes fail.
Seeking an appropriate 18mm automotive spark plug shouldn't be met with the same 'resistance' that the NGK stock #3961 BR8ES plugs had to overcome to gain acceptance. Finding 18mm plugs in cooler heat ranges has been the issue. Old tractors that commonly use 18mm plugs like them hot. Champion D21 and Autolite 388 are examples.
Ford used taper seat 18mm spark plugs, so the good heat ranges these may offer would again require a special adapter: the gasket :(
Champion D series 18mm plugs are evolving, I just looked up the D9, a cooler plug with a new Stock Number of 509.
https://www.summitracing.com/parts/cpn-509
It is now a resistor plug. It is not an extended tip plug, but well worth looking into.
 
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Why not to go with what Emagair recommend ...

Hello Scott

This is what Emagair recommend, this is what is used on a few planes from my buddy's and also on mine:

NGK BR8ES 2.5mm Center Electrode (NGK stock #3961 has solid/permanent terminal post)

Installation:
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.

Warning:
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 do not clean them, I just replace them at 100h or annualy.

And it works :cool:

Better quality adapter you can get by Lightspeed or EFII.
 
Fixed ferrule Autolite 386?

Anyone know the part number from Rock Auto, Autozone, or Summit Racing for Fixed Ferrule Autolite 386 spark plugs?

Or other acceptable non-adaptor resistor spark plugs with fixed ferrules?
Thanks.

PS I hate crimping the ferrules o/w the 386 are running well with my pmags
 
Anyone know the part number from Rock Auto, Autozone, or Summit Racing for Fixed Ferrule Autolite 386 spark plugs?

Or other acceptable non-adaptor resistor spark plugs with fixed ferrules?
Thanks.

PS I hate crimping the ferrules o/w the 386 are running well with my pmags

A bit of red loctite will keep them in place very nicely. Just a little bit and avoid getting it on anything but the threads to have a low resistance connection at the base.
 
FWIW I use the solid tip NGK BR8ES PN:3961 on my dual P-Mag installation. There is no need to crimp or otherwise fixate the tip. Except for the solid tip, it is the same as the NGK BR8ES PN:5422.

:cool:
 
Anyone know the part number from Rock Auto, Autozone, or Summit Racing for Fixed Ferrule Autolite 386 spark plugs?

Or other acceptable non-adaptor resistor spark plugs with fixed ferrules?
Thanks.

PS I hate crimping the ferrules o/w the 386 are running well with my pmags

I have been using Autolite 386 18 mm plugs on my magneto (but not my electronic ignition) for over 20 yrs. I have never found a replacement 18mm resistor type plug with a non-threaded terminal end. I really hate using spark plug adapters.

They have generally worked well with the exception of the removable terminal nut, which I have never found a way to keep tight. Crimping has never worked. It seems the heat cycles causes them to loosen even after crimping.

Last year I replaced the spark plug caps with NGK 8381 LZFH non-resistor types (like used on lots of motorcycles) that allow me to use the 386 plug without the terminal nut since this cap attaches securely to the bare threaded end of the spark plug.

NGK LZFH Spark Plug Cap.png

They hold really tight, and I have had no further problems with loose plug caps.

Steve
 
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IK27

I’ve been using Denso IK27 plugs with the Lightspeed Plasma III on our O-320. They seem to work fine but they’re a bit hard to find. AutoZone just couldn’t get them and when I asked for them at the local O’Reilly’s they could not find them by the Denso part number. They insisted they needed the application... make, model, year. I have no idea of any of that. I finally found them at the local, independent family-run auto parts store. Kind of pricey for auto plugs, but still a lot cheaper than aero plugs. I like to buy local. It supports the local economy and it helps my economy because I don’t pay shipping.
 
...
Last year I replaced the spark plug caps with NGK 8381 LZFH non-resistor types (like used on lots of motorcycles) that allow me to use the 386 plug without the terminal nut since this cap attaches securely to the bare threaded end of the spark plug.

View attachment 10597

They hold really tight, and I have had no further problems with loose plug caps.

Steve
Hi Steve, this is a great idea. Obviously I can just buy some to check it out since they are very cheap, but how do they connect to the spark plug wire? I can't find any information on installation from the NGK website or other places that sell these. Thanks!
 
Hi Steve, this is a great idea. Obviously I can just buy some to check it out since they are very cheap, but how do they connect to the spark plug wire? I can't find any information on installation from the NGK website or other places that sell these. Thanks!

Mickey,

There is a threaded post inside the end that attaches the cap to the spark plug wire.

Just trim the spark plug wire flush, slip the wire seal over the end of the wire, screw the spark plug cap into the plug wire, and slide the seal over the end of the spark plug cap. It only takes a few seconds (and no tools) to install each one.

I would prefer the crimp on spark plug caps if they would work with these plugs, but since they don't, I have found this to be a good solution.

NGK has been selling these for recreational vehicles for many decades, and they seem to have stood the test of time.

I used to get ignition noise in the radio when one or more of the threaded Autolite 386 spark plug terminals would become loose, and I haven't had that problem for over a year now.

Steve
 
And on my Lycoming O-360-A4M.

FWIW in 8yrs and over 700hrs of flying I have never had a problem with the adapters. YMMV

:cool:

The only issue I have had with the adapters is changing plugs....sometimes the adapters stay in the engine and sometimes they come out with the plug. Despite using some anti-seize. My A&P advised torquing the adapters separately to a higher torque than the plugs. That seems to have addressed that issue.
 
Additionally, I have used Accel plug wires for 25 years with no issues whatsoever.
V/R
Smokey

With P-mags?

Looking at making my own wire harnesses for my dual P-mag setup...haven't done this before and looking for any gouge.

Thx!
 
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Checked my NGK with non-solid caps, one was loose so ordered the NGK spark plug connectors to solve the problem in the future.
 
Mickey,

There is a threaded post inside the end that attaches the cap to the spark plug wire.

Just trim the spark plug wire flush, slip the wire seal over the end of the wire, screw the spark plug cap into the plug wire, and slide the seal over the end of the spark plug cap. It only takes a few seconds (and no tools) to install each one.

...
Thanks Steve - I ordered 10 from these guys in the UK - it was a whopping 20 USD for 10 of them with shipping to me in Switzerland. :)

https://www.gsparkplug.com/1x-ngk-none-resistor-spark-plug-cap-lzfh-black-8710.html
 
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