Today's Message Index:
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1. 04:53 AM - Re: #1 cylinder plugs are black (Thom Riddle)
2. 05:00 AM - Re: CHT J thermocouple replacement for Rotax 912ULS (Jim Butcher)
3. 05:09 AM - Re: CHT J thermocouple replacement for Rotax 912ULS (Martin Pohl)
4. 09:51 AM - Re: #1 cylinder plugs are black ()
5. 01:08 PM - Re: #1 cylinder plugs are black ()
Message 1
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| Subject: | Re: #1 cylinder plugs are black |
Ron,
Thanks for your response. My question should have been stated
differently. My question should have stated that I'm looking for any
peculiar characteristics of the 912 that might cause this problem
because I am relatively new to the Rotax 912 engine but not to engine
mechanics. I am an FAA Powerplant Mechanic and one of my airplane
partners is an A&P I/A but both of us are relatively new to Rotax 912
series engine. In any case, I appreciate your response and following
are my answers which might help others diagnose similar situations if
they arise in their engines.
****First off change the plugs. Unless you have access to a
pressure
tester to make sure they are not snuffing out under pressure
I will swap the nearly new plugs from this cylinder to another to see
if the same happens to the plugs from another cylinder or the same
plugs in the other cylinder.
****Make sure you have the proper heat range plugs! If the
porcelain is
shorter, it will run cooler and could run black.
I have the proper plugs in all the cylinders.
****You sure it is black from running rich, or could it be black
from oil
fouling?? Perhaps run a compression test, that will not tell you
if oil
ring leaks or valve stem seal, but if low hint to look further.
We did a compression test during annual inspection two weeks ago. Three
of the cylinders were 80 psi, including this one, and #4 was 78 psi.
We also removed the valve cover to see if there were a broken spring
and checked for too much valve lash. Negative on both counts.
****Are you using Whacker Silicone based thermal conductive
compound on
plug threads?
We are using standard anti-seize compound on plug threads but not on
the threads that extend into combustion chamber, which of course would
be a no-no.
****You have a CHT and EGT to help diagnose problems?
We have four EGTs. #2,3,4 were running between 1410F and 1480F during
cruise(normal). #1 was running around 1550F and the thermocouple probe
began falling apart and finally failed on last flight. We loosened the
intake manifold on this side to see if there were air obstructions but
there were not. However, there is a black streak along the bottom of
this intake manifold tube that runs right into the cylinder head port.
There is no such streak in the #3 cylinder intake manifold or on either
cylinder on the other side. I scratched and sniffed this black streak
and it smells like unburned fuel. I'm now convinced that there is raw
fuel being passed into this cylinder with the high velocity air during
cruise power, past the Y-junction in the intake manifold and thus not
showing up in the #3 cylinder intake manifold. This raw fuel is also
responsible for the high EGT reading on this cylinder as it burns in
the exhaust tube and the ultimate failure of the EGT probe. We will be
removing, disassembling, inspecting and cleaning this carb. I suspect
this will cure the problem but won't know for sure until we do it.
****If you look up mixture check procedures for 914 at take off
power,
they have you measure each cylinder for O2 content. They want a
minimum
amount to be certain that things are not running too lean.
Eastwood sells
such a tool, could be used to check for proper mixture at various
throttle
settings as well.
The EGT temps during all power settings tell us what we need to know
here but if all else fails, we may try this.
****Make sure float bowl shows no signs of overflowing, check
needle valve
and float look OK, clean carb while you are at it
This will be checked during carb inspection and cleaning.
****I am not certain on this one, but a restriction on exhaust is
not a
good thing, make sure clear on that cylinder
Checked and it is clear.
****If it is only happening on 1 of the plugs in that cylinder,
could be
besides a bad plug, faulty ignition pick up, coil, module or wires
As I said in the original post, it is happening to both plugs. Not
related to ignition system.
****You getting cooling problems on that cylinder, like too hot
or too
cool?
No cooling problems.
****MAKE SURE YOU HAVE PROPER HEAT RANGE OF PLUGS especial on
black
cylinder
You already said this. But thanks for the reminder.
****If you could somehow get hold of a EGT put it in suspect
cylinder. If
you turn off gas, you should not get a very severe rise, if you
do then
too rich.
See above.
Try it with a good cylinder to see what normal is. Remember
black could
be caused at many a throttle position. Choke motor when hot a
very low
throttle opening which you know is rich, and see what rise is.
Just be
very careful on purpose running lean like this above 50% power,
do it just
to get peak then retard throttle and turn on fuel.
Had enough yet?
If not, what motor you have?
912UL
How does it start? How does it start in cold?
Starts fine hot or cold.
How many hours?
385 hours and averaging about 150 hours per year.
MoGas or 100LL?
90% mogas 10% 100LL on cross-country trips
What is compression on 4 cylinders?
See Above
Did you install new length dipstick?
Came with engine.
What type of oil you running?
CPS AV-9
You checking oil properly where you do not have things overfilled?
Yes
Is there blue smoke coming out of exhaust, if 2 pipes, then the one
with #1 upon
cold start up? How bout black smoke on cold start up?
No smoke of any color.
Is your oil pressure excessive high,
No
has it changed since you did not have black plugs?
No
Let us know how you make out
Will do.
Thom in Buffalo
Message 2
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| Subject: | Re: CHT J thermocouple replacement for Rotax 912ULS |
--> RotaxEngines-List message posted by: "Jim Butcher" <europa@triton.net>
The VDO sensor is M10 x 1.5 thread.
Jim Butcher
Europa XS N241BW
Message 3
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| Subject: | Re: CHT J thermocouple replacement for Rotax 912ULS |
--> RotaxEngines-List message posted by: "Martin Pohl" <mpohl@pohltec.ch>
Jim:
Thank you for the information. I just got an email from Westach with specification
data for their J thermocouple sensor for the Rotax 912ULS. And - Spruce have
them in stock :D.
Rgds
Martin
--------
Martin Pohl
Zodiac XL QBK
8645 Jona, Switzerland
www.pohltec.ch/ZodiacXL
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=39775#39775
Message 4
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| Subject: | Re: #1 cylinder plugs are black |
--> RotaxEngines-List message posted by: <rparigor@suffolk.lib.ny.us>
Hello Thom
After reading your reply:
Chech exhaust for cracks/leaking
A retarded spark can cause high EGTs, did you check Rotax info and in fact
your ignition, the pick ups, and gaps are up to date?
I posted a site a while back that states it is easy to cross wires in
ignition wiring, did you check?
Give a try to go and fly on 1 mag, then the other at a high power setting,
do it for 5 minutes and see if there is a noticiable difference.
I don't like high EGTs, I know black is rich, but go looking for a intake
leak, a stumbling cylinder can cause unburned fuel to get into exhaust??
Look at cross tube, and other sources of air leak in.
When was last carb cleaning?? Did you look for ripped diaphram during
inspection? Look very close at the needle valve.
OK another, where do you have the float bowl vent terminating? If it is in
an area of lower pressure than ambient you will run lean, if in higher
pressure will run rich. Run to just downwind of air cleaner is often done,
look for kinks, restriction and leaks and route to ambient air.
Check you have latest recomondation for main jet, jet needle and position
of clip, O ring on jet needle, latest needle jet. Look for carb snot very
careful, check O-rings.
If you have a friend into BMW Boxers with carbs, have em give you a hand
with carb (they use type 64), or a Rotax guru.
After talking to the research guru at Rotax, Whacker is what should only
be used on plug threads. He did plenty of testing, and Whacker was hands
down winner. You want thermal conductivity.
When checking for exhaust cracks, be very careful looking for
obstruction/debris or whatever in the muffler. I hear a broken exhaust
pipe on the 914 shortly thereafter begins to play silent night.
Let us know what you find.
Ron Parigoris
Message 5
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| Subject: | Re: #1 cylinder plugs are black |
--> RotaxEngines-List message posted by: <rparigor@suffolk.lib.ny.us>
Hello Thom
Sorry, I posted miswiring info on Europa Group.
Anyway read on:
http://www.greenskyadventures.com/engineservice/TechTips/912Ignition/912IgnDiagrahm.htm
Good info at:
http://www.rotaxservice.com/rotax_tips/rotax_troubleshooting.htm
especial read causes of viabration
Ron Parigoris
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