meowy84

Hello. Just a quick question I hope. Are all glow plug threads standardized and also of the same size? What I mean is that let's say I have a glow plug from an old Enya .09 2 cycle and want to put it in an O.S. .52 4 cycle, will the threads fit (let's not worry for a moment about heat ranges, etc.)? I tried this swap between the aforementioned Enya .09 and my old Veco .19 and the plugs were interchangeable. What about the others?

w8ye

My Feedback: (16)

1/4"-32 is standard size

Four stroke plugs are made different though the thread size is the same.

Enjoy,

Jim

Jim Thomerson

Most all glow plugs are 1/4 x 32 thread. Nelsons are different. Not sure if he makes a standard plug as well. There is an old 3/8 x ? that will fit some of the older ignition engines.

meowy84

Jim, it's interesting you mention spark ignition. Have a look at the other thread I just posted which directly relates to the plug issue. http://www.rcuniverse.com/forum/m_38...tm.htm#3885039

The engine in that thread has an odd glow plug thread. That engine however is something I'd like to convert back to spark ignition.

Flyboy Dave

My Feedback: (21)

Mecoa might be able to supply some new re-popped spark ignition parts
that you could adapt to that engine. It looks home-made to me too.

FBD.

William Robison

My Feedback: (3)

Meow:

As Jim said, 1/4-32 is the standard plug size now.

Back in the dark ages, when spark ignition was king, the standard thread was 3/8-24.

Arden's first glow plugs were also 3/8-24, because all the engines had that thread. Champion, as well as Arden and some others, made glow plugs in the 3/8 thread size.

When Arden started making his own engines the 3/8 thread was just too big, so he went to the 1/4-32 and everybody else followed.

As also stated, some now such as Nelson, use a different thnread. Why, I don't know, but they are the exception.

Just as a matter of interest - Arden's early plugs could have the element replaced without buying a complete plug.

Bill.

w8ye

My Feedback: (16)

The Nelson Gow Bee has a flat wound (stove) coil. It is two piece with the glow plug button and a retainer. The threads are 5/16" and the plug is used in speed circles.

The standard Nelson plugs are odd ball for all other brands of engines also.

Enjoy,

Jim

Jim Thomerson

Arden made an adapter for 1/4 x 32 plugs to fit a 3/8 x 24 hole. I think O&R made some 3/8 glow plugs.

iskandar taib

My Feedback: (5)

Nelsons are 11/32"x32, I think. Turbos are M8x0.75, if I'm not mistaken.

Iskandar

jaka

Hi!
But remember that all four strokes need the OS F plug!

mike109

G'day If your plug is an Enya #3, it will most probably be OK in a four stroke. The number is stamped into the side of the plug body on one of the flats. Enya recommend them for their own four strokes and I can't see why they would not work in an OS or Saito though I have not tried them. I am using one in my Enya 53 four stroke.

The thread will be 1/4 x 32 ie 1/4 diameter and 32 threads per inch.

It is more normal to use the OS F plug or Saito four stroke plug in four strokes. Other makers also make four stroke plugs. So far as I know, they all have the same thread arrangement though the OS and Saito F plugs do have that unthreaded end of the plug. Others may also.

Hope this helps a bit.

Mike in Oz

earlwb

Yeah they had a few different thread sizes for glow plugs in the early days, the 3/8 inch was the first early size, but there was a 5/16 size and of course the now standard 1/4x32 thread size glow plugs. In the early days they made a lot of somewhat proprietary sizes too.
I have a thread going showing glow plugs from the early days here: http://www.rcuniverse.com/forum/m_10545790/tm.htm

Now some four stroke engines do not have the glow plug hole drilled and tapped all the way through like normal. They have a tip on the 4 stroke plug that protrudes down through a hole that is not threaded. So you need to be careful and not try to use a RC Long glow plug as it will bottom on on the unthreaded hole at the bottom. In this case you can risk stripping out the threads trying to tighten up the glow plug on your engine. So you need to be careful as to which glow plug you use on these 4 stroke engines that use this design. The OS Type F glow plug and the Fox Miracle plug have the special tips on the glow plugs for these engines.

You can see how they drill and tap the glow plug hole partially through and use a short unthreaded part to go in towards the combustion chamber so that it is more smooth on the inside.
The overall length stays the same, they just don't drill and tap the glow plug hole all the way through. There is actually a slight performance improvement with the engines doing it this way too.

jaka

Hi!
Enya 3 plug will not work in an OS engine and I think all other four-strokes (except Enya ) if you intend to use 0-10% nitro.

iskandar taib

My Feedback: (5)

No one's mentioned "reach" yet.

Most engines use "long reach" plugs, some of the older small engines used "short reach". Then you have O.S. engines - which use "medium reach", for some reason. I've used long reach plugs in mine without any problems, though.

Iskandar

downunder

OS and Enya plugs both have the same "medium reach" but an OS plug is too short in my OS engines (long reach is slightly better in them) while an Enya plug is a perfect fit in my Enya 61. By perfect I mean the end of the plug is flush with the combustion chamber. With OS engines, their medium length plug is recessed by about a thread while a long reach protrudes by about half a thread.

iskandar taib

My Feedback: (5)

The raison d'être for Nelson plugs is that they seal at the bottom of the hole. The end of the plug is tapered, it sits against a matching tapered seat. The Turbo plug is based on the same idea, just smaller. The Nelson uses 11/32x32 UNEF threads, the Turbo M8x0.75. My guess is Nelson went for the larger size so that existing engines could easily be adapted to use Nelson plugs - you just need the appropriate bit with the appropriate bottom taper, and the appropriate taps. Drilling and tapping out the existing 1/4" hole wouldn't work unless the new plug was significantly bigger.

Iskandar

earlwb

One thing to watch out for is that on some of the four stroke engines (maybe all now), OS didn't drill nd tap the glow plug hole all the way through like one would expect. The OS F glow plug has a smaller tip to it, that fits into a hole at the bottom of the glow plug hole. If you try to use a "long" glow plug, it will butt up against that smaller hole or step at the bottom and not seat all the way down tight. A number of modellers have stripped out the glow plug hole trying to get the wrong glow plug to tighten up OK. The OS F glow plug as well and the Fox Miracle plug have that same tip on them so that either plug would work in a 4 stroke engine with that type of a glow plug hole in it.

If I remember correctly the Enya .09 used a short glow plug, but maybe it was a medium length though.
Usually for engines you can use a short or medium length glow plug in a engine that uses a long glow plug. But it does recess the glow plug a little and reduces the compression slightly too. But if you are at the flying field and want to get in another flight or two, it doesn't really hurt anything.
Some guys have used a couple of glow plug washer/gaskets to get a long plug to fit into a medium or short length glow plug hole in a engine before too. Do turn the engine over carefully to ensure the glow plug won't hit the piston on you though.

VampeD4

My Feedback: (80)

what tap do you use. the TPI or the UNEF ??

Jesse Open

TPI denotes the thread count per inch.
The UNEF defines the thread system. The thread count within that system varies as the diameter changes. 1/4-32 is the same as 1/4 UNEF.

706jim

Ok so we've pretty much agreed that 1/4-32 is the standard thread.

And that pretty much all glow engines have aluminum heads.

So when tightening the glow plug use moderate torque or you can easily strip those fine threads!

And I shudder when I read starting instructions that tell you to remove the glow plug to prime the engine.

The fewer times the plug is removed the better!

1200SportsterRider

Glow plug torque recommendation on the bottom.

This chart goes with the Tork-It torque wrench.

Jesse Open

Yes, with a few added points of clarification. That is how these forums play out. Such as explaining that 1/4-32 is only part of the thread nomenclature. The "UNEF" is also important as is more accurately describes the thread form.

The part where you say the less you remove the plug the better is also a good point.
We have way too many plug jerkers who seem driven to plug tinkering.

(The above comments pertain to sport flying.People who engage in racing toy planes are well known needle tweekers and plug jerkers. It is part of getting their edge over the other toy racers.)

Propworn

My Feedback: (3)

I have a little 1/4 32 UNEF Thread chasing die I make sure I run down each glo plug before installation. I remember in the old days sometimes the threads on the glo plugs were not so perfect and running the die down the plug helped save a lot of thread damage in the cylinder head. Not so much any more but old habits die hard.

Plug tinkerers LOL I guess I'm guilty of that as well. We used to pull the coil out just past the end of the plug. Seemed to get us a few more RPM.

GREG DOE

1/4" 20 is standard; 1/4" 28 is UNF (Unified national fine, this is the most common prop shaft); and 1/32 UNEF (Unified national extra fine). As a rule those of us who race check our plugs after every heat race, and often replace with a new plug, saving the used plugs for bench running, and test flights. Most races run at least 5 rounds, so if you go to 5 contests a year that's a minimum of 25 removal and replacements. At most contests I fly at least 2 glow events. In the past, sometimes it was 3 glow events. Multiply that by 60 years of racing, and add in building, and test running of engines, and I've cycled plugs in and out of racing engines over 4000 times, and we haven't even mentioned sport flying, which before electrics was almost all glow. I've probably stripped the threads in a couple of heads in all these years, and they were likely short plugs in .40 racing engines. Not the best application for using "shorts", but necessary after combustion chambers were modified. I use a 5/16" nut driver for a glow glug wrench because it keeps me from over torqueing the plugs. I too have a 1/4" 32 UNEF chasing die to clean up poor quality glow plug threads. Removing, and replacing plugs does not have to be feared as long as you are careful not to over tighten. I've seen people use small ratchet wrenches for the job, but I wouldn't recommend them, because it would be too easy to over tighten the plug. However, if they have a good "feel" for the torque, and it works for them, then by all means go for it. I've even seen a few people use a torque wrench when installing plugs.

1200SportsterRider

I like these Sonic Tronic 4c plugs, part number SOT-302, they take up all the threads in a Saito cylinder. The Sonic Tronics website has the wrong picture for the SOT-302 plug.


This is the correct picture for the SOT-302 4c Special for Saito and Enya.