From: bill@c3177208.ssr.hp.com (Bill Chidester)
Subject: Re: FAQ? (questions about engines)
Date: Fri, 28 Aug 1992 22:00:48 GMT
Organization: Hewlett-Packard, Orlando Fl.
X-Newsreader: Tin 1.1scd1 PL4

: 
: Assuming that your needle valves are properly set:
: There are really only 3 possible things that can cause an engine to 
: stop or lose a lot of rpm when you pull off the glow battery.
: 1. Too cold a glow plug.

   Wrong direction -- a "hot" glowplug refers to peak temperature, it uses
   a smaller diameter wire element.  It's peak temperature is hotter than a
   "cold" plug (which has a larger diameter element), but a hot plug retains
   less heat.  It will cool faster and be more susceptible to quenching due 
   to a rich idle or rich run.  I have found that a cold plug will loose less
   RPM than a hot plug when you remove the battery.  The larger diameter wire 
   provides more surface area for the platinum plating needed to sustain the
   catalytic reaction, so they just "work better" than a hot plug. They idle
   better, have a more even speed range and higher top end than a hot idle-bar.

   Most sport fliers think "hot" means fast and good; "cold" means slow and 
   bad.  Cold plugs are much more rugged and last longer.  One of our club's
   best engine guys suggested going against conventional wisdom while I was
   trying to get a COX .074 running.  Everybody knows a small engine must have
   a hot plug!  He made me put in a dead-cold Enya, and the engine now runs
   flawlessly.

: 2. Too cold a fuel or bad fuel contaminated with water.  Cold fuel 
: is equivalent to low or no nitromethane.

    Actually, adding nitromethane to fuel will make an engine run cooler, not
    hotter (allowing lower temperature for a given RPM, or higher RPM for a
    given temperature).  From the engine's point of view, "cold" = "good", so
    it will run faster and more efficiently.  I agree with the water contami-
    nation, especially if you leave fuel sitting in an unsealed container in
    your flight box.

: 3. Low compression in the engine.
: 
: I would do the following to solve your problem.  First, change to a 
: new fresh fuel of at least 10% nitro of a reputable brand or one that 
: runs well in one of your friend's engines.  If that doesn't fix it, 
: then change to a hotter plug, e.g. a Fox R/C long idle bar plug or a 

     I really have to take exception to this advice.  Fox idle-bars are
     currently one of the worst plugs on the market.  Stu Richmond tells me
     that Duke Fox refused to use them in his own engines. Take a look at the
     elements of several samples -- some will look like overstretched springs.
     I don't like idle bar plugs in particular, and have taken to using Rossi
     or Enya cold plugs.  Bob Fiorenze and Don Muddiman both use the cold
     Rossi's in their jets and recommend them for their ruggedness.  They cost
     about $5.00 (as opposed to $9.00 for Enyas) and deliver good idle and 
     speed range (Something I never get with an idle bar).  There's another
     posting about "Crummy Glow Plugs" telling how they're made that is right
     on target.  We've found bad batches of Rossi's as well, so nobody's
     immune!  Try one of the cold Rossi's first, along with a fresh bottle of
     fuel.  Use your old fuel to clean your engines.

     My opinion is, for sport flying, the lubricant is much more important
     than the nitro content.  I use Morgan Mach 7, 5%, full synthetic.  I
     would rather ruin an engine and buy a new one than scrape caster residue,
     so I use synthetic.  Still, I've never lost an engine or a ring while
     using the Mach 7, but I'm very quick to richen a lean running engine.
     Mach 7 will form a scum inside the needle valve assembly every few 
     months.  Closing and loosening the needle valve several times prior
     to starting the engine will bring back an even engine run.  Every once
     in a while, the carb will need an actual cleaning.  The jet jockies use
     Byron's Synthetic/Castor blend.

:                    If that doesn't fix it, check to see if your 
: compression is good.  Maybe you need a new ring or piston and liner 
: if they are worn out or maybe you have a leaking head gasket.
: 
     Good advice, especially if you have leaned out a ringed engine.  A bad
     ring is hard to detect -- most of them will take a heat temper (or is
     is "de-temper?) and loose their spring.  An ABC engine is much more
     tolerant of a lean run, but easier to destroy with sand or metal 
     ingestion.  If you prang a plane, always, always, always, tear the engine
     down and clean it!  My advice is to use a cold, expensive, non idle-bar 
     plug, change to a high quality fuel and stick with the combination that
     finally works for you.  

     There are a lot of flyers doing very well with $40 engines running 
     $1.50 glow plugs -- all in all the value you get at the low end of the
     scale is quite good.  However, I go to the field to fly, not screw
     around with balky engines:  I think it's worth the extra money to save
     precious flying time.

----------------------------------
Bill Chidester
bill@c3177208.ssr.hp.com