Another quick question... and BTW appreciate all the help so far... Have a
.47 GMS aircraft engine. Should the glow plug be removed and cleaned after
every use? If so what should I clean it with? It seems to get mungy after
several uses... More questions: How often should the glow plug be replaced
with a new one? How do they typically last? Should I a have a stash of
extras? Thanks again ahead of time...
No. With the proper treatment and air/fuel mix, a plug should last a long time
with no maintenance.
It's ok for the plug to discolor. If it's getting "mungy"(?), the I'd suspect
the mixture is wrong. The element should be clean and not fouled with
deposits. Nor should it be whitish and "burned-looking". In the first
instance, your mix is too rich. In the second, it's too lean.
"There's a Hun in the sun!"
If the glow plug is getting dirty after a few flights, then you are using a
fuel with a lot of castor oil or running the engine very rich. The plug
should discolor a little and some hard carbon will settle in around the
face, but that is all. You do not need to clean it. This engine really
thrives on a fuel with 55 nitro, 15% synthetic oil and 2-3% castor oil. Run
that mix at the proper settings and you will be blesed with a very powerful,
reliable and durable engine.
K&B 1L and Fox standard long glow plugs work very well in this engine. If
those are not available, then Thunderbolt standard longs or OS A3 should be
| I think you meant 5% nitro. 55 nitro would probably blow up his
| neighborhood. Just a typo?
Considering that shift-5 is %, and 5% nitro is common and 55% nitro is
not, it seems almost certain to be a typo :)
However, 55% is not impossible. On-road racers regularly use 40%
nitro, and people occasionally will use even more. I believe you can
get up to about 65% nitro until there's not enough alcohol to make the
oil mix in properly.
And nitro isn't really explosive by itself anyways -- it needs to be
about 100 degrees before pure nitro even emits enough fumes to burn.
(Still, I wouldn't suggest testing this.)
More about nitro here --
I once asked a guy that drove full size Drag Racers what % of Nitro he used,
His answer was "The Whole Can"
I have used 50% in an Enya .53 that I used in Old Timer competition. I was
using castor only and it would not mix properly without some synthetic.
Made the engine run very well!!!.
If needed, the plug can be cleaned with 50% sulphuric acid. Degrease the
To make up the cleaner mixture: never add water to acid, but add acid to
water drop by drop. If you add water to acid, it may explode in your face.
Wear safety glasses all the time.
I never felt the need to clean a plug and put up with the assosiated mess.
When in doubt, fit a new one, and put the suspect plug in a plastic bag, so
you will not use it again in your engine.
For running in new engines, these old plugs often will be fine.
Depends what you mean by 'mungy'. If you mean you're getting
loads of dark crud all over the place, it's probably due to running too rich
and/or having castor oil in your fuel. Even with castor though, it
shouldn't 'gum up' after only a few flights......most likely, it's just too
rich. On the other hand, if the element is 'frosty' and white, you're
running way too lean. The element should stay clean and sort of shiny.
The best way to know if you need to replace the plug is to observe what
happens when you remove the glow clip after you start the engine. Taking
the plug out of the engine all the time is *not* a good idea......sooner or
later, you'll end up with stripped thread in the head, unless your engine
has a brass thread insert and not just plain alloy threads (don't ask me how
I know). If you remove the glow clip and the engine loses lots of revs
and/or stops, your plug is buggered. This is assuming the engine is tuned
correctly of course. The 'losing lots of revs' thing is also a symptom of a
too rich idle mixture. Commonly, the engine will 'load up', slow down and
splutter to a stop. However, if your engine is tuned ok and it stops when
you pull the glow clip off, the plug is finished. Basically, it means the
platinum in the element is no longer sufficient to keep the plug glowing
without the aid of external power.
How long a plug lasts is determined by how you treat it. Lean runs kill
plugs in short order......one lean run is often enough to ruin a plug (bad
idle behaviour etc). Running too rich is nowhere near as bad, but will
still eventually 'gum up' a plug, particularly if you use castor oil in your
fuel. I've got a couple of 4-strokes (YS .91FZ's) that have the original
plug still in them after more than 12 months of regular use. Still run
perfectly. If you look after them, the plugs should last ages.
It's always handy to have some spare plugs in your field kit. Nothing worse
than having a plug finally die (after endless months of fault free service)
and not having a spare! When I'm getting down to my last couple of spares,
I buy a whole card of new ones......keeps me going for a loooooong time and
means I've got some left in case some unfortunate soul doesn't have a spare
at the field :-)
Well I'd have to disagree here. I mainly fly CL stunt so all my engines
are run in a rich 4 stroke plus I use all castor. My ST G51 for instance
uses 25% castor and the only time I've ever changed a plug was when
trying to find the one that gave the best performance. I'd guess I've
put maybe 20 hours on that plug so far.
Adelaide, South Oz
MrB> Hi there,
On my GS.45ABC, if I ran it rich (using only castor oil in the fuel, as per
the racing regs here), it would gum the plugs up in short order. Lots of
dark crap around the face of the plug and in the recess where the element
is. I got a lot longer out of a plug if I ran it leaner, but not too lean
Mind you, do you idle your G51 at all? My .45 would run perfectly fine at
full noise (rich) with the gummed up plug, but wouldn't idle worth a damn.
Didn't even want to run below about 1/4 throttle, unless I changed the plug
for a new one. All would be well again, until the plug gummed up. After it
was fully run in, I didn't run it that rich anymore, so no more gummed
I too never had problems running an engine rich on castor in CL flight. The
engines stayed too cool to gum up.
Your problems seem to point in the direction of a tuned pipe that may be too
short, or a smallish mousse can, combined with a high compression ratio.
What exhaust did you run, how much nitro?
That is what I noticed when I started to use the engines for RC
flight, where demand on power was so much higher.
However, the very statement by mrBonk was, that too rich a mixture would
produce black crud and gummed up plugs.
In CL-stunt the engine is tuned very rich so it produces a whole lot less
power, and only spins up in verticals and overhead flight. According to my
experience, this does not cause the plug to foul. They last extremely long.
In RC flight I have not noticed the gumming tendency either.
My .21 MVVS RCcombat engine spewed black burnt oil (not alu particles),
until run in. Then the residue became a quite clear tan color. (20% castor,
standard two-chamber muffler, no nitro)
The statement above may however be comparing apples with pears, because most
RC flight times are so much longer. I one fortnight you may collect as many
flight hours as a CL application in a whole year. Also, after one too rich
flight, one tends to adjust the engine immediately.
I have never seen castor oil gum up a plug either, I fly about 98% RC
and the rest CL. The only times I have fouled a plug is when breaking
in the engine and running too lean. When running rich the raw fuel
actually seems to clean the plug, not foul it. Though the face does
turn darker, the important part, the wire, stays clean and bright.