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Old Feb 28, 2010, 10:45 PM
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Glow plug heat rating and reach

2 questions; please point me where these might have been answered already.

[1] What does the "heat rating" of glow plugs mean in physical terms, i.e. when they say this or that is a "hot" glow plug, and is there any system or uniformity between the manufacturers.

[2] What is the effect of glow plug whose threads are a turn or two shorter than the threaded socket in the cylinder head.

Context is that I am running 10 year old Irvine and MDS engines both of which hate nitro, and run happily on 80/20 home made fuel (good and cheap!) (or perhaps with a dash of nitro from old fuel cans I am using up), but I need some spare plugs. OS A3 which is rated a "hot" plug by local hobby shope seems to work fine, but is a bit shorter than stock plugs on both engines. (Both engines are easy hand starts and idle very well) with this plug.
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Old Feb 28, 2010, 11:13 PM
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Everett Wa.
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There is NO industry standard for heat ranges. I would keep a full range of glow plugs from one manufacture for testing purposes. I use the Rossi brand. Once I find the glow plug that runs best I then look for another cheeper brand that might fill the need just as adequately.

There are 3 three plug length. Two are industry standards. They are known as short reach, and long reach plugs. Now OS markets a range of plugs that don't adhere to ether standard. They split the difference.

Improper thread length will effect flame propagation across the combustion chamber. This is why engine builders and tuners will spend a lot of time and money to ensure that the glow plug fits the combustion chamber with as little discontinuity as possible. This is why many high performance engines use head buttons. These are found in many high performance 2.5cc engines such as the Rossi .15 and Cox .15 Conquest engines. Also most race engine use the cut down glow bee plug. This is often known as the Nelson plug.

Yes, most engine that are not built for the US market often run best on low or zero nitro fuel. These often run best with hot or very hot plugs if one is NOT using a tuned pipe. If you are having good luck with the A3 use it. I would look at a Rossi hot r/c 10cc glow plug. It will fit the head better and might actually give a few more RPM.

Friends don't let friends fly nickel,
Konrad
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Old Mar 01, 2010, 12:43 AM
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I agree pretty much with what Konrad said. Unlike car spark plugs, there's no industry standard for glow plugs but heat ratings for plugs are used in a different manner to spark plugs.

For a glow plug it's not so much the actual temperature of the coil but the ease with which it can initiate combustion. The easier it is, the hotter the heat range. Part of this ease of ignition though is the coil's ability to retain its heat after ignition which is especially necessary for idling where there's a comparatively long time for it to cool down somewhat.

Essentially though, the hotter a plug is then the easier it is to fire the mixture so heat ranges give the ability to tune the ignition point (advance or retard) for best power. Although there's no standard, a hot plug from any manufacturer is going to be fairly close to what another manufacturer has but if you were really finnicky you could try plugs from different manufacturers to find the ideal. Expensive though and not necessary for sport flying.

Both Enya and OS plugs are a medium length compared to the normal long and short reach plugs. No-one quite knows why . The ideal is to have the end of the plug flush with the combustion chamber surface but, once again for sport flying, it doesn't make all that much difference.
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Old Mar 01, 2010, 01:40 AM
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OS and all Japanese plug threads are 4.5 mm long. Always have been. Enya uses the same length in all their plugs from the #3 to the #6. OS does too. American plugs are 5.5mm for long reach and 3.5 for short reach. The Japanese don't complicate things. Why make two when one works perfectly well? The only "long" plug made by OS is the type F which is a four cycle plug but the thread length is 4.5mm.

Enya plugs are rated from hot to cold with the #3 the hottest and the #6 the coldest. The higher the nitro content, generally the colder the plug used. The Enya #3 and OS #8 are pretty much all around plugs for the 0 to 15%nitro user. OK up the about 25 %. OS A3 is a bit hotter I'm told.
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Old Mar 01, 2010, 01:05 PM
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Shorter plug, shorter element, less expense for valuable coil material = cheaper plug.
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Old Mar 01, 2010, 01:28 PM
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Not true. Enya has more platinum than most plugs and it shows in the cost. The higher platinum content the better the catalytic action and the better the plug works. Especially at idle. They also last considerably longer. Enya plugs are some of the most expensive. Especially the #6 cold plugs.
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Old Mar 01, 2010, 03:25 PM
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Quote:
Originally Posted by jeffie8696 View Post
Shorter plug, shorter element, less expense for valuable coil material = cheaper plug.
In my full race AMA Formula One full race Super Tiger 40X engines I made the head to fit the short reach plug. This was because the shorter element stayed in the glow plug better than the longer (less well supported) element of the long reach glow plug. This was using fuels with nitro content around 65% and at rpm over 22K. Again no cheap plug would last in that environment for a full race.

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Konrad
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Old Apr 02, 2010, 02:04 AM
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Quote:
Originally Posted by lawst-sole View Post
Not true. Enya has more platinum than most plugs and it shows in the cost. The higher platinum content the better the catalytic action and the better the plug works. Especially at idle. They also last considerably longer. Enya plugs are some of the most expensive. Especially the #6 cold plugs.
Hey Glowguy47, usna71 is back once again, how's it going Bruce?
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Old Apr 02, 2010, 09:39 AM
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Quote:
Originally Posted by Konrad View Post
In my full race AMA Formula One full race Super Tiger 40X engines I made the head to fit the short reach plug.
That's kind of interesting because, reading through the specs for the yet to be released new range of Rossi engines, they say the head is designed for their own short reach glow plug. Whether their plug is a similar length to the OS/Enya or a true short reach I guess we'll have to wait to find out.
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Old Apr 02, 2010, 09:53 AM
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I should mention that on some 4 cycle engines, one needs to be careful when selecting a glow plug. Look at the tip and if it is smaller than the threaded part make sure you get a glow plug that matches that. On some engines, they do not drill and thread the hole all the way through. They leave that last little bit of the tip unthreaded so that only the reduced size tip goes in towards the combustion chamber.

If you try to use a regular glow plug the threaded part butts up against the bottom and you run the risk of stripping out the glow plug threads.
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Old Jan 15, 2015, 09:34 PM
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Quote:
Originally Posted by Konrad View Post
In my full race AMA Formula One full race Super Tiger 40X engines I made the head to fit the short reach plug. This was because the shorter element stayed in the glow plug better than the longer (less well supported) element of the long reach glow plug. This was using fuels with nitro content around 65% and at rpm over 22K. Again no cheap plug would last in that environment for a full race.

Friends don't let friends fly nickel,
Konrad
Full Race?? Does that mean there is a half race and one third race too?
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Old Jan 15, 2015, 10:24 PM
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datsunguy, you resurrected a 5 year old thread. He wound up with his account suspended.
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Old Jan 16, 2015, 06:26 PM
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Just looking at past threads. The question came up at our field and I brought a micrometer and a bunch of plugs to prove a point. Japanese 4.5, American and most everyone else 3.5 and 5.5.
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Old Jan 17, 2015, 01:32 AM
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Bruce,


...Then the American Tower counts as Japanese...

Their Tower Power plug is practically a medium-reach, O.S. No.8 clone.

And they do offer their LC3 and LC4, which are true long-reach plugs (i.e. 5.5 mm), despite being Japanese...
And it is my experience that the LC4 makes medium/large O.S. aircraft engines run better then they do with the much-more-popular (and expensive...) No.8.
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Old Jan 17, 2015, 02:42 AM
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Who do you think makes Tower plugs?? Tower is the importer of OS products. Tower doesn't make things it just sells things. Ron Sheldon who owned Sheldon's Hobbies for years lost sales all Tower products because he went around Tower and imported OS products himself. Tower leaned on him and Sheldon couldn't sell ANY Tower stuff after that Couldn't sell what he had and that was a load of OS engines. He wasn't even allowed to give them away. I always wondered what happened to them.

Also Check out Enya plugs. They are ALL 4.5 mm in length. Never used or seen a LC# or LC4. The only plugs I use are Enya's. You ought to try one. I lived in Japan for 4 years and the most used plug in my club was the Enya#3. That's the plug that comes in Enya engines, including the 4 cycles.
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