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18mm auto plugs

rexbrewer

Member
Has anyone had long term good experience with 18mm auto plugs in an O-360? How many hours do they last. Which plug was used?
 
I use the 386's and they last 100's of hours. Also have used the Denso L14-U plugs with good success. THey are supposed to be non-resistor plugs, but surprisingly produced no noise on my 10 and still have them on the 6A. They are nickle coated, so the body doesn't rust like the 386's; Also a cooler plug. The 386 is a bit hot, but have never heard of an pre-ignition problems and I ran them on the 6A fo 600 hours.

Larry
 
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Auto

I use the 386's and they last 100's of hours. Also have used the Denso L14-U plugs with good success. THey are supposed to be non-resistor plugs, but surprisingly produced no noise on my 10 and still have them on the 6A. They are nickle coated, so the body doesn't rust like the 386's; Also a cooler plug. The 386 is a bit hot, but have never heard of an pre-ignition problems and I ran them on the 6A fo 600 hours.

Larry

Thanks Larry.

You say the Denso L14-U plugs run cooler I understand the plug running cooler, but wonder how you determine this. Do you use CHT, EGT, or plug condition to determine that they run cooler?

Thx, Rex

RV8 IO-360
 
Thanks! I understand hot/cold plug vs hot/cold engine. I'm asking how the plugs are, hot/excessive wear, or cold/fouled, and if any noticeable impact on how engine runs. Thanks.
 
Thanks! I understand hot/cold plug vs hot/cold engine. I'm asking how the plugs are, hot/excessive wear, or cold/fouled, and if any noticeable impact on how engine runs. Thanks.

IF a plug is too cold, deposits won't burn off. If too hot, they can create a source of pre-ignition. Out side of these two issues, heat range, generally, does not impact engine performance.

In my experience, both plugs were free of deposits and had no pre-ignition with either. However, as long as its hot enough to clear deposits, a cooler plug is preferred, as it will provide greater margins from pre-ignition, which are often seen only in extreme conditions.

I found a chart that compared heat ranges across manufacturers to determine that the Denso was a cooler plug than the 386. However, don't really know if that source can be fully trusted.

Larry
 
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I used the auto plugs with my P-mags. Cyl temps were HOT!!! Replaced with 14mm NGK BR9ES, temps normal!

DAR Gary
 
I helped pull 4 cylinders off to be repairs that was using 18mm autoplugs, as they didn't extend into the cylinder far enough, damaged the threads, etc. Luckily we caught it quick enough it was repairable.

Some Ignition companies warn about using them, instead of the adaptors. I would caution to be careful.
 
Has anyone had long term good experience with 18mm auto plugs in an O-360? How many hours do they last. Which plug was used?

Denso L14-U are excellent and are what I'm using. I know people who have run them for decades with 1000's of trouble free hours replacing them annually.

Honestly don't know why anyone would monkey around with the adapters.
 
14mm plugs with adapters

Denso L14-U are excellent and are what I'm using. I know people who have run them for decades with 1000's of trouble free hours replacing them annually.

Honestly don't know why anyone would monkey around with the adapters.
Hi Brian, emagair recommends plugs in this heat range:

  • NGK BR8ES
  • NGK BR8EIX Iridium Electrode
  • Denso IKH27 (for long-reach heads with LR adapters only.)

These are 14mm plugs that need the 14mm to 18mm adapter.

The L14-U would be in the heat range of an NGK 6, so somewhat hotter.

I know with my two-cycle motorcycle engines going from an 8 to a 6 would have given me a nice hole in the piston in about 3 minutes, but it seems aircraft engines are not quite as sensitive to spark plug heat range.

Reading various things on the Denso site, it seems that there are two extremes when choosing the right plug - is it hot enough to burn off deposits? is it cold enough to avoid detonation?

heatrange_img_05.png

It seems as long as the plug is between these two extremes, it's ok.

I just bought a batch of IK27 plugs and will run them for a while to see if I have any issues with deposits or fouling. The BR8ES plugs seem to be fine as well, but I like the fact that the IK27 are iridium, and they have solid terminals. They may be too cold, however. The IK27 plugs do look nice, and use a smaller socket, which is slightly helpful on the top of the cylinder where space is a bit limited due to the baffles.

These are 14mm plugs that need the 14mm to 18mm adapter.

Denso IK27 vs NGK BR8ES spark plugs.jpg
 
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RF Noise Electroair gone!

Recently removed my L14-U Nippondenso 18mm plugs and installed reducers and NGK BR8ES "SOLID" top, pn 3961, 14mm plugs.

I had RF noise, i.e. noise in the radios and intercom with REM37BY's and RF noise with the L14-U. I'm surprised to find, using NGK BR8ES plugs: All RF noise now is gone!
 
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