Would arsenic have any effect on lead, I know it
dissolves some soft metals.
Hi
Jeff,
Oh, I don’t throw
them out – I have a bushel basket of used plugs. But, you are right they
are around $5.00 down here when purchased in
bulk/box.
The 3 electrode
ground shields the ceramic cone from the typical abrasive blasting pretty
well. Make it a pain to clean the stock plugs, but they certainly do not have
any noticeable wear after 25 hours so I save them.
I tried several
methods – but despite what the gun shops advertise there is no solvent for
lead short of foaming nitric acid (or something equally
hazardous).
I believe that if
someone had a powerful ultrasonic cleaning machine that placing them in a
solution of alcohol or something similar and using ultra sound to blast the
lead crystals off the ceramic might do the job. But, that is one device
I do not have.
But, you never know
when one may appear on ebay for $5.00 {:>)
Ed
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Jeff Whaley
Sent: Tuesday, July 07, 2009 12:44
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: SAG was:
[FlyRotary] Re: Muffler
Hey Ed, now
might be the time you cleaned a few SAG plugs and tested
them?
It seems hard to
believe that plugs need be thrown out after 25
hours.
BTW, up here in
Ottawa, I had to pay $17 each ($68 per set) for
stock Mazda plugs, on a trip south I picked up some in Ogdensburg NY around $5
each.
Jeff
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Tuesday, July 07, 2009 7:10
AM
To: Rotary motors in aircraft
Subject: [FlyRotary] SAG was: [FlyRotary]
Re: Muffler
There are undoubtedly
numerous possibilities as to what is happening/causing SAG. However, two
things are very clear:
- 100 LL does definitely reduce
the time spark plugs can be used before SAG occurs. The nominal time
period that I have found in my engine is 24-30 hours. You can take the
plug out and examine the ceramic cone and see the glint of what I
believe (but have not done a chemical analysis) of lead crystals.
Folks using MOGAS (such as Tracy) have reported going over 150 hours
without SAG. So I do believe there is a connection between 100LL and
the short interval of use before SAG.
I even
attempted to use TCP which is used in some aircraft engines and is reportedly
suppose to reduce lead deposits. It simply make the problem worst, but
upon further research I discovered that for this chemical to work the cylinder
head temperature has to be much higher than what our water cooled sparkplugs
typically see. In my case, the chemical caused further deposits (of some
sort) on the sparkplug and I barely got 5 hours out of the set I
used. This may in part explain why our sparkplugs seem to foul more with
100LL than aircraft sparkplugs – they don’t get hot enough?
- If you encounter SAG, then
replacing the sparkplugs immediately eliminates the SAG problem (for a
period of time).
So both of those
factors lead me to believe it is fouling of spark plugs rather than
pre-ignition. If pre-ignition then my dozens of times of SAG (like every
15 minutes on the 5 hour trip from Louisiana) would surely have resulted in
damage to the engine.
In any case, whatever
the cause, since I have been replacing my sparkplugs regularly at 25-30 hour
intervals I have encountered no SAG. YMMV
Ed
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of William Wilson
Sent: Tuesday, July 07, 2009 12:09
AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re:
Muffler
While the rotary design is a little more
resistant to the onset of preignition, once it happens, the rotary is damaged
just as easily as a piston engine or even more so. Drag racers suffering
preignition have dismantled their motors and found rotors dented in from
excess chamber pressure. It is possible that you have been having mild
preignition not enough to damage the engine, I suppose. Do you suppose
you have been running really excessively rich? That would also
contribute to plug fouling, low power and low EGT. If you have fuel
injection, a fuel map problem showing up only at high manifold pressures
(higher than you normally attain in your usual operating regime) maybe?
You should get WAY more than 10 hours on spark plugs even running
100LL.
If combustion were still taking place as you speculate then it
would ignite the incoming mixture during the intake cycle and cause a
backfire. So I think that is not it.
I assume you've seen this
but I found it interesting:
http://www.wankel.org/74_Ignition/74-22%20Spark%20plug%20life%20.htm
On Mon, Jul 6, 2009 at 7:17 PM, Steven Boese <sboese@uwyo.edu>
wrote:
I never found the
broken muffler part in the outlet of the muffler where it might have caused
increased back pressure even though it was possible for it to end up in that
location by standing the muffler on its end. The symptoms after
repairing the muffler were the same as before the repair was made so at this
point, I don’t think the broken part was a factor in the performance
issue. Looking back at the data log, the #2 rotor EGT dropped by about
250 degrees during the power deficit. Back pressure would probably
affect both rotors in a similar fashion so that would also point to SAG as the
culprit.
In response to your
and Bobby’s questions, at the onset of SAG, there were a total of 15 hours on
the plugs, 106 gal total of fuel burned, 53 gal of that was
100LL.
Ed is most likely
right that operating at the increased manifold pressure available at low
altitude made the SAG show up while it didn’t at lower manifold pressures that
I normally see.
The relatively small
amount of time and fuel that the plugs had seen when SAG occurred may also be
due to the low power levels and correspondingly lower combustion temperatures
permitting more rapid lead deposition on the plugs. It looks like I
should routinely change plugs every 10 hours or so. I did have extra
plugs along on the Texas trip and it would have been easy to
have installed them at the rotorfest.
The nature of SAG is
puzzling. The symptoms of decreased EGT, decreased power output, and
increased heat transfer to the oil and coolant are all consistent with
descriptions of pre-ignition more than that of spark plug misfire. In
piston engines, pre-ignition can rapidly lead to destruction, but the rotary
engine may be more tolerant of it. Maybe it isn’t a matter of no
ignition due to the spark plug not firing, but a matter of the fire not going
out between sparks. The lead in 100LL increases the octane rating by
slowing the combustion rate and thereby decreasing the tendency for
detonation. Maybe there is enough gas phase lead in the vicinity of the
spark plug with lead deposited on it that the combustion rate is slowed enough
to persist from one cycle to the next while the normal combustion rate occurs
in the rest of the chamber. This could result in a process similar to
pre-ignition. This theory probably has as much probability of being
right as the one I had concerning the apex seals
clicking.
Maybe I can
accumulate a pile of SAGGING spark plugs as big as Ed’s. That would be
verifiable at least.
Steve Boese
-----Original
Message-----
From:
Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On Behalf Of Todd Bartrim
Sent: Monday, July 06, 2009 6:23
PM
To: Rotary motors in
aircraft
Subject:
[FlyRotary] Re: Muffler
Hi
Steve;
So you now assume that your power loss is
directly attributable to SAG and not to the partially blocked muffler? Is this
correct?
I'm curious as I also use a homemade
muffler (SpinTech copy) and have wondered what the result would be if any of
the internal came loose. I wonder if your increased backpressure contributed
to the onset of SAG? And do you only burn 100LL, occasionally, or
never?
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