Conference vmszoo::rc

    Just as an aside,

    Shorter plugs are cooler plugs.  This is the same rule as in full scale
    engines.  The part of the plug that extends out beyond the head is the
    part that stays hot,  A shorter plug dissapates more heat to the head,
    and runs cooler.

    John,
    
    I couldn't agree more with Randy's suggestion to get in the habit of
    discarding old, questionable glo plugs.  As he says, the fact that they
    light means almost nothing regarding dynamic performance and, if the
    three plugs you've tried in the O.S. .40 were all used plugs, then
    you've really not proven anything except, perhaps, that you've got
    three bad plugs that need to be sh*tcanned.
    
    By all means, get some new plugs and start over...you may find you have
    no problem at all and never did.
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				|      |        / |\	   	       
      	         \|/		|______|__(o/--/  | \	   	       
      | |        00	       <|  ~~~  ____ 04 ---- | --------------------
    |_|_|        (O>o		|\)____/___|\_____|_/	   Adios amigos, Al
      |     \__(O_\_	        |	  |___/	 o	   (The Desert Rat)

    	I have had some problems with Fox plugs in my OS40FSR.  They fail
    often if I'm trying to get full output out of the engine.   The failure
    is always either a blown element or a blown seal around the center
    post.  I switched to K&B plugs and the problem was eliminated
    completely.  
    	My original OS plug failed in my 91Surpass 4-stroke and all of the
    replacements I have tried have not run as well.  I first tried a FOX
    plug recommended for 4-strokes.  The idle was great but it ran rough at
    high RPM and sounded like it was starting to detonate when I leaned it
    out at all.  I think the plug was too hot.  I switched to a K&B (thanks
    to Dan Snow) and the conditions changed.  Now the idle is not very good
    but the high end seems fine.  I now think this plug might be too cold.
    I may have to pay the bucks for the recommended OS plug for this beast.
    It ran like a swiss watch with the original plug for over a hundred
    flights.
    
    Any comments??????
    
    Charlie
    

    Charlie,
    
    I'm the _last_ one to claim any knowledge (or desire for same) of
    4-strokes but I _CAN_ confirm that Fox plugs are absolute JUNK
    anymore.  If you bought a dozen of 'em on a card, you'd be lucky to get
    four that did _not_ have element or seal problems.  Fox _used_ to make
    a superior plug that was preferred by the entire R/C community but,
    about 5-years ago, that all went right down the ol' flusher!
    
    I still had about 10-plugs from a card I'd bought before the sudden
    demise in quality and, so, have continued to use Fox plugs up to the
    present.  However, I had a mail-order outfit fill out a credit I had
    with them with a half-dozen Fox plugs and only two of them were any
    good.  I still have 2 of the pre-problem plugs left but don't quite
    know what I'll try to run when they're gone.  Dan Parsons is quite high
    on running the Fox Miracle-plug in 2-strokes and I've bought a couple
    to try but haven't done so as yet.
    
    Frank Tiano has had some lengthy and rather blunt discussion of the
    problem with the Fox folks all the way up to ol' Duke his'self but 
    whether they'll acknowledge they have a problem and do anything to 
    resolve it remains to be seen.  I find it impossible to believe that 
    they haven't heard this plenty over the past 5-years or so and, to date, 
    nothing's apparently been done as the problem continues to exist and may 
    even have gotten worse.
    
    As to what plug you should run, since you already know they work and
    work well, if you can get 'em, go fer' the O.S.  I sure would and the
    peace of mind would more than offset some additional expense in _my_
    book.
						 __
    				|      |        / |\	   	       
      	         \|/		|______|__(o/--/  | \	   	       
      | |        00	       <|  ~~~  ____ 04 ---- | --------------------
    |_|_|        (O>o		|\)____/___|\_____|_/	   Adios amigos, Al
      |     \__(O_\_	        |	  |___/	 o	   (The Desert Rat)

Interesting...I use Fox plugs almost exclusively -- K&B has not
been high on my list of favorite brands!  Looks like I should
give them another try.  I have heard flyers split between what
they like/not like between the two; Phil carries only Fox, while
the other shop has both, plus the OS and Enya plugs (at big
bucks!).

It was on a recommendation from them that I tried the Fox Miracle
Plug, the one intended for 4-strokes, but alas, it went sour on
the first run -- because of my running it at full tilt, as I said
previously.

I mentioned the Miracle Plug to Phil this last weekend and he
said that he's had a number of customers ask for them and he was
considering stocking them, but he was happy with the regular Fox
plug and didn't see any real need to change.

Everything I've read in RCM from Clarence Lee, etc, says that
unless you run upwards of 30% nitro and/or radical timing the
heat range of a plug is irrelevant.  It could be that the
information (in '70s mags) is obsolete with ABC engines and the
modern 4-strokes, but I'm inclined to agree with it for now.

How do you say that now, "K&B"?  Don't they make engines or
something also?

We modellers are a miserly lot. We worry about the cost of good plugs and fuel
and go through a lot of hart ache to save a couple of dollars. Whats more we
bitch like hell when our cut price bargain of second grade material's don't
perform as well as the quality product that costs a little more. 

I am as guilty as all of you for doing just that, I suffered the consequences
of using inferior products for the lower price and learnt a lesson. You only
get what you pay for. 

I use a range of plugs depending on the motor and the type of performance
required. The most nitro I ever use today is 5%, most of my running is on
straight fuel. (Nitro in OZ is about US$25 a US Quart). I have a lot of success
using OS, Enya, and Rossi plugs in general sport engines. I have just started
using a Nelson plug in my racing engine which is a badge engineered GloBee
which is excellent. The price is high at $6 each. I can go through a dozen
plugs in a weekend so if anybody knows of a place selling them at bulk rates
please let me know. (see we all try to save a buck) 

I do have to disagree with Clarance Lee as I have said in previous notes plugs
do effect the performance of the engine. It is our way of adjusting the timing
of the burn. Hot plugs retard the timing; cold plugs advance the timing. On a
hot day (100�F+) the fuel burns more readily and you need a colder plug, cold
days or at altitude you go to a hotter plug. 

BTW. If any of you design engineers out there would like a little challenge how
about designing a devise that tests the temp of the engine by the resistance of
the plug. I "think" the change in temp during the cycle of the engine could
give some idea as to the suitability of a plug for a particular setup. I have
had the idea for some time but never really had the opportunity to test the
theory. Any ideas????. 

John 

    
    In a sport plane beater I'll run just about anything. Fox, Miracle
    K&B.
    For the choppers in the cool fall,winter and spring months I like
    to run an Idle bar less K&B. In the hotter summer months I switch
    to a cool rossi 7.
    For pattern I fly rossi or OPS. These plugs can be rather expensive
    but worth it.
    
    Tom

    This gives me the chance to ask a question I've been meaning to
    ask. How does one know which plug is a "hot" plug. Which is a
    "Cold" plug, and which is inbetween. "Is" there a way to tell, or
    is it strictly by manufacturer. If it's by manufacturer, can 
    somebody list here who makes a hot plug and who makes a cold plug.
    
    Steve

>>> Hot plugs retard the timing; cold plugs advance the timing. On a
>>> hot day (100�F+) the fuel burns more readily and you need a colder plug, 
>>> cold days or at altitude you go to a hotter plug. 
    
    I was keeping up just fine until I tripped over the first statement
    above.  Seems to me that the two statements are contradictory.
    
    Years ago, I remember that some (K&B?) manufacturers were producing
    plugs that were coded for various heat ranges.  I was using an early
    Fox Combat Special that would eat an ordinary plug in less than a
    tankfull.  If I couln't get a cold plug, I couln't fly.  My 
    understanding at the time, was that the higher compression of the 
    combat and racing engines dictated a cooler and sturdier plug. 
    My Stunt .35 wasn't fussy at all, but then neither engine was used 
    with a throttle so the overall plug design task was much simpler.
    
    

Tom T. mentioned that in certain cases he uses a non-idlebar plug in his 
choppers. Is there an advantage in an engine with a throttle in doing this??

What is the actual purpose of the idlebar anyway? Is it there to maintain heat 
in the plug area or is it there to provide cover so the element doesn't foul
and/or cool off too quickly in a low RPM situation?

I'm still running off a few cards of vintage Fox plugs that I bulk bought many 
years ago. I'll probably have to restock next season.

    Jim,
    	As a rule I always use an Idle bar less plug. 
    
    Why Idlebar's ?????
    
    	From what I know ... year ago in carb development the carbs
    were not that efficient in regulating the fuel/air mixture. This
    caused problems drowning the plug in fuel. The method of dealing
    with the issue was the addition of the idlebar to the bottom of
    the glow plug. This effectively reduced the tendency of the fuel
    splashing into the plug. As carb designs have been developed the
    need for this protection has lessened. With todays carbs there
    really isn't a need if one knows how to adjust the carb.
    
    
    Tom

Tom T is absolutely correct. Idle Bars are now virtually unnecessary.

The way to tell the temperature on a plug is to try it. The wire thickness, the 
required current to drive it are all guides but only guides. I tried once 
measuring the resistance but it was conclusive.

The number on the plug is only of limited value. OS for example use the numbers 
as I recall 1-4 for C/L and 4-8 for R/C. I have no idea why C/L and R/C should 
be different. The OS 7 and 8 are about the same plug but the 7 has the idle bar 
while the 8 does not. Tom said he generally has an idle bar I generally don't. It 
is personal preference you cannot say one of us is right and the other wrong.

The bottom line is use the plug that does the job you want the best, ignore the 
price as it is insignificant compared to the overall cost and value of the 
model. A bad run could loose you a model.

John.

    John, ???
    
    
    	I said I generally use an Idle bar less plug (one with no idlebar).
    
    
    	I suggest that people use a idlebar plug for the initial run
    in's of an engine when you're running it sickly rich. Once you have
    decided to lean out the engine then switch to the idlebarless plug.
    If your having problems setting up a carb then stay with the idlebar
    plug until you sort out the set-up.
    
    
    Tom

	How does a glow plug work ?

	I was under the impression that it was just used
only during starting and that the engine ran like a 
deisel after you disconnected the battery.

			Larry

    Larry,
    	A glow plug actually stays warm while the engine is running after
    the battery is removed.  It has a Rhodium SP?  Catylist in the wire
    that reacts with the methanol fuel and generates the necessary heat to
    keep the wire hot.  It is not like the glow plugs in a Deisel that heat
    things up just for starting.  A bad glow plug often will run the engine
    until the battery is removed.  The plug can become contaminated,
    preventing the Catylitic reaction from working.  
    	Model Deisel engines run on fuel containing Kerosine and Either.
    (and oil)  The Either acts as an igniter to get things burning.  There
    is no glow plug on one of these engines and they run on compression
    ignition just like full size.
    
    Charlie
    

	Thanks, that clears up a lot.  
Reading through this note The authors seem to think that 
glow plugs SHOULD be rated at HOT or COLD. I never
saw such a rating and If this rating was REALLY important
DOn't you think the Manufacturers would rate plugs ?

				Larry

Fox does rate their plugs hot or cold.


Other manufacturers feel that since they only have one temperature, why 
tell us and discourage half the purchasers 8^) This is why people swear 
BY certain plugs and AT certain others.

    Several manufacturers make heat ranges of glow plugs.  Rossi has
    several.  This is critical in piped engines.  The difference in heat
    range is similar to sparkplugs.  Hot plugs have less heat transfer area
    and therefor they stay hotter.  
    
    I have found that different plugs work best in different engines.  For
    example, I use Fox RC long plugs in my low performance OS25FP engine. 
    They last many flights and give good idle and good high end
    performance.  These same plugs will last one flight in an OS40FSR or in
    a YS45 with a pipe.  In those engines I use the K&B RC Long plugs and
    they last a long time unless I have a lean run.  The best thing to do
    is experiment and find what works then stick with it.
    
    4-Stroke engines are very sensitive to glow plugs.  Regular 2-stroke
    plugs do not work well in the OS 4-strokes.  I have found that the OS
    type F plugs work best in the OS 4-strokes.  (that's what OS
    recommends)  The FOX Miracle plugs work in 4-strokes but I have not had
    good luck with them in my OS91 or in my OS120.  By the way, the OS plug
    is twice the cost.
    
    Charlie
    

    
    What I learned about the different plags is that the diameter of the
    bore, where the catalyst sits, is an important factor of hot or cold.
    The bigger the diameter, the more gets the heat cooled by the fresh
    mix. The smaller the diameter the less heat gets lost.
    
    There is also a difference in the mounting position of the spiral :
    the deeper the position in the hole the hotter the plug. If the spiral
    is more in a outer position, it again gets more cool.
    
    A 4-stroke glow plug should have a small diameter and/or the spiral
    mounted deep inside the hole. A high rpm 2stroke on a pipe should use a
    plug with a wide bore and/or the spiral further towards the outside.
    
    A FP-series type of 2-strokes should work best with a plug in the
    middle.
    
    Hope I got this correct out of my memory....   Bernd