Glow plug thread

[Jim Thomerson]

In Eric Henderson's engine column in the August 2012 Model Aviation, he makes a correction to his June 2012 column to say that modern glow plug threads are 1/4 x 28 rather than 1/4 x 32.  I have emailed him and asked which plugs and engines use the 1/4 x 28 thread.   I don't have either real modern engines or glow plugs, but all mine are 1/4 x 32.

[dennis lipsett]

That is news to me. Probably to everyone else in the hobby also. I Seriously doubt the truth of that statement.

Dennis

[RandySmith]

LOL

[Tim Wescott]

You mean I spent all that extra money on a 1/4-32 tap when a plain old 1/4-28 would have worked?

Wait a minute -- how come my glow plugs fit the 1/4-32 holes I've made?

[Brett Buck]

In Eric Henderson's engine column in the August 2012 Model Aviation, he makes a correction to his June 2012 column to say that modern glow plug threads are 1/4 x 28 rather than 1/4 x 32.  I have emailed him and asked which plugs and engines use the 1/4 x 28 thread.   I don't have either real modern engines or glow plugs, but all mine are 1/4 x 32.

   Saw that, but it's clearly not accurate. I have an Arden glow plug from about 1949 (not originally mine, of course!) and it meshes perfectly with a recent-issue Thunderbolt 4-cycle plug and fits any of my engines just fine. Take a glow plug and try to screw it into a 1/4-28 nut, it will to a little bit in and jam.

    Brett

[Jim Thomerson]

Got a reply from Eric apologizing for being confused.  1/4 x 32 it is for standard plugs. 

[L0U CRANE]

...And, 1/4-28 is our usual 1/4" shaft propnut thread... Metrics are their own thing, though...

[Steve Helmick]

While we're on the subject of glowplugs, I'd like to hear the explaination of why we now have medium reach glowplugs, instead of, or in addition to, shorts and longs. Not sure that the correct answer would come from an ARF/Park Flyer magazine, but I must admit that there is some fresh emphasis on actual building, which is an encouraging sign.  Steve

[dennis lipsett]

While we're on the subject of glowplugs, I'd like to hear the explanation of why we now have medium reach glowplugs, instead of, or in addition to, shorts and longs. Not sure that the correct answer would come from an ARF/Park Flyer magazine, but I must admit that there is some fresh emphasis on actual building, which is an encouraging sign.  Steve
[/quote


Steve,

I think it's because of the head design of some engines. The long actually extends about 1/2 thread into the combustion chamber and the medium ends at the end of the threads. That said there seems to be a distinct difference in running some of these engines with a long vs medium plug with the long seeming to advance the timing a little bit more then necessary. I keep a couple in the flight box and have on occasion used it to get the run that I wanted.

Dennis

[RandySmith]

While we're on the subject of glowplugs, I'd like to hear the explaination of why we now have medium reach glowplugs, instead of, or in addition to, shorts and longs. Not sure that the correct answer would come from an ARF/Park Flyer magazine, but I must admit that there is some fresh emphasis on actual building, which is an encouraging sign.  Steve

Hi Steve
The the ENYA plugs have always been a medium reach, longer than short, shorter than long.....

Randy

[Brian Hampton]

While we're on the subject of glowplugs, I'd like to hear the explaination of why we now have medium reach glowplugs, instead of, or in addition to, shorts and longs.

AFAIK the only medium length plugs are the Enya and OS but why both Japanese manufacturers went with this is open to question. What I do know though is that an OS plug in an OS 40VF (at least) isn't long enough to get the plug flush with the combustion chamber but an OS/Enya plug is perfect in my Enya 61CXLRS. I must admit I haven't checked my other OS or Enyas though to see how well their plugs fit.

The new OS BE (bio ethanol) engines use an 8mm glow plug thread because apparently a normal plug won't work properly with that fuel.