TELEDYNMCS(at)aol.com
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 Posted: Mon Sep 25, 2006 4:49 am Post subject: JabiruEngine-List Digest: 2 Msgs - 09/24/06 |
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In a message dated 9/25/2006 2:58:20 AM Eastern Daylight Time, jabiruengine-list(at)matronics.com writes:
| Quote: | .....how important is
watching the EGT, especially of all six jugs? |
Hi Tim,
Nice to see some activity on this list for a change. I'm certainly not an expert, but I think I can answer your question. Monitoring all EGT's, as with CHT's MAP, Carb Temp, Oil Temp, Oil Pressure, etc, will help point to issues before they become problems. The issues I speak of in regard to EGT's are things like loose intake connections, improperly adjusted valves, a burnt or sticking valve, a loose spark plug, etc., anything that would lean out the engine and cause harm over time. If you had a problem where the engine was running too rich, this would also show up in EGT's.
I use a Grand Rapids EIS with a graphical display. Sometimes it is a borderline distraction with all the info in provides, but as I've been breaking in a 3300 on a Europa XS I've recently completed, I've found the monitoring of all EGT's a great help.
All 3300's shipped after s/n 722 were shipped with an "economy cruise" needle jet, along with a new Jabiru needle. The Jab needle is shaped with "steps' along its length so that it corresponds more closely to the performance curve of the engine. The stock Bing needle is a near constant taper and works, but isn't optimum. This factory combo leans out the mixture at the right places and the new needle allows the other portions of the carb to kick in when needed. The result is fuel burn numbers similar to the 912S in cruise. I'm seeing about 3.8 gph at 2900 rpm, resulting in a cruise speed of about 130 kts at 5000' on the Europa. I'm running a Sensenich hollow carbon ground adjustable at the moment, but I intend to switch to an electrically adjustable hub as soon as they are available for the Sensenich blades.
However, I found in the initial running of my 3300 that my EGT's were quite high, >1450 F. After some searching, conversations with Andy Silvester of Gulfcoast Sportplanes (where I got the 3300) and noodling out the problem I decided that the economy needle jet was probably too small for break in, resulting in a very lean mixture, as evidenced by the color of the plugs and the high EGT's. Taking Andy's advice, I switched to a 285 needle jet and the EGT's dropped 150F and the plugs are now a nice tan color. Interestingly, I noticed the other day while reading the most recent issue of "Jabba Chat" that the factory has switched to the 285 needle jet in favor of the 278 as of April of this year.
As the old saying goes, "An abnormally high EGT will tell you that you are about to french fry your engine. An abnormally high CHT will tell you that you just french fried your engine". This notion is probably more true for 2 strokes than 4 strokes, but the point remains the same.
In regard to preheating, I concur. I own a PA-25 Pawnee (0-540), a 7GCA Citabria (0-320) and the Europa with a 3300. I preheat all three year round, regardless of the ambient temperature. The Pawnee has both a Tanis block heater and EZ-Heat oil pan heater. The Citabria has just the EZ-Heat oil pan heater. My Europa has a heat pad similar to the EZ-Heat, but was obtained from JC Whitney. The heat pad on the Europa is automotive, but is nearly identical to the EZ-Heat, but about 1/3rd the price. I can usually get the oil temps to 140F before hitting the starter on any of the three , even on the coldest day. (and yes, we can get some mighty cold days here in January and February)
One thing I'd like to know is how many Jab owners out there are running carburettors other than the Bing? Aerocarbs, Ellisons? I'd really like to have mixture control and the Aerocarb looks like a nice unit for the price. Comments?
Anyway, good luck with your project. The best part is yet to come!
Regards,
John Lawton
Whitwell, TN - TN89
Europa N245E - Flying - 33.5 hours
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