I tried some and had poor performance. I actually had a precautionary landing to replace them on a trip because of gaps closing on several.Why do we need adapters when using non-aviation plugs? Are there no 18mm plugs available in the proper heat range? Are the 18mm plugs simply more expensive?
Unfortunately, there is not a wide selection of reaches, resistor and heat ranges. Some are happy with the Autolights, some not.Why do we need adapters when using non-aviation plugs? Are there no 18mm plugs available in the proper heat range? Are the 18mm plugs simply more expensive?
I'm guessing these are the Autolite 386. These are a bit hotter than optimal for most, and "I think" the ONLY 18mm resistor plug available today.t’s a good question….I recently bought a set of AutoLite automotive plugs that were recommended here, for my NOS Electro Air electronic ignition system. They weren’t in stock at NAPA but arrived the next day and were cheap. 18mm
Yes. I figured they aren't very common. I think I saw some tractor motors use 18mm.I assume you are asking about 18mm non-aviation plugs?
Well...
a) you aren't going to find them in the local auto parts store when you need one on some cross-country
b) I can't think of the last time I saw an 18mm automotive plug. 1936 International pickup truck, maybe?
My x-340 was built with 14mm plug holes. When I recently had to replace a couple cylinders, the new cylinders I installed were 18mm. So, I have 4 spark plug adapters currently.When Mattituck was building my engine, they asked if I wanted 18mm or 14mm spark plug holes. I specified 18mm even though I knew I would be using an ignition that supported auto plugs. This was a mistake, but I didn't know at the time, obviously.
As others have said, the selection of 18mm plugs is very limited.
They are the 386s. There was a second plug that was suggested as well but I never checked availability because I wanted a hotter plug anyway.I'm guessing these are the Autolite 386. These are a bit hotter than optimal for most, and "I think" the ONLY 18mm resistor plug available today.
I’m considering running a test set in one side to see how they hold up in my application. Curious what configuration or use case you have that makes a hotter plug more desirable?They are the 386s. There was a second plug that was suggested as well but I never checked availability because I wanted a hotter plug anyway.
Curious what configuration or use case you have that makes a hotter plug more desirable?
That is probably the only benefit to hot plugs. All other use cases (sustained high power, Lean, ignition advance, leaded fuel, and a host of others) are made worse with hot plugs. Once your oiling clears up, keep a close eye on things!I have newly OH’d chrome cylinders and am still pushing oil past the rings and there is a slight tendency to foul the lower plugs.
While the instructions from the MFR should be given due consideration, there is a lot of things to question in this statement. For example, does the physical size of the hex wrenching surface define the operating characteristics of the plug? Probably not. If I had to guess, the fact that there is almost no selection of RESISTOR 18mm plugs drove someone to a NON resistor unit and that scrambled the brains of the Pmag (I’ve been there, done that). That OR a user used a Autolte 386, and had jumpers out in an edge case engine, hot day, and suffered pre ignition due to the hotter than optimal heat range of that particular plug., we have at least two reports from customers who tried 18mm thread plugs – with very poor (near disastrous) results
Here's quite a large selection of 18mm plugs. No idea if any are appropriate for our engines. There are lot more there than I would have guessed. Mostly for tractors and "classic" engines.Unfortunately, some of us are like children and don’t like to be told “no” without a good reason - often at our own peril (guilty as charged).
Same here. Autolite 386 plugs for couple hundred hours with no issues.I have been using the Autolite 386 plugs in two planes (RV4 and Glasair both with Lycoming 360s) for nearly two thousand hours. They have performed flawlessly. They are available from all four of the auto part store chains near me and all are under $3 each. The nice part of that is my "plug cleaner" doubles as my shop waste bin. To test longevity I ran one set until I got an intermittent miss which occurred at 317 hours. I change them at 100 hours since you can do all eight for less than $20. I have several friends running these plugs as well. I really like not having plug adapters. Just one testimonial but I am very pleased with these 18mm plugs.
Plenty of 18mm plugs. Once you narrow those down to "resistor" the list gets smaller. Narrow it down again to the compatible heat range and seat type, the list gets VERY small.Here's quite a large selection of 18mm plugs