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1. 11:44 PM - He assumed I knew what I was =?ISO-8859-1?Q?doing? (henry.voris)
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| Subject: | He assumed I knew what I was =?ISO-8859-1?Q?doing? |
13jan12
Gentlemen,
My pal Lance asked, So Do you wanna put the big piston in the front or the rear?
I assumed he was kidding He assumed I knew what I was doing A train-wreck of assumptions.
Deliberating shortly, we figured the larger piston would run hotter
and should live closest to the fan.
After a couple of hours of swearing, doing-it-again, and fumbling around we got
the thundering 447 back together Im sure we got most of those dang needle bearings
back in the wristpins
Back on the plane, the engine fired right up and ran strong But the cylinder closest
to the PTO (#2) was running a bit hotter than the cylinder closest to the
alternator (#1). At 5,000 RPM and above, the temperature difference (both CHT
and EGT) exceeded the difference allowed by the factory (36 CHT and 45 EGT).
I have attached a spreadsheet that reflects the temperatures at different RPMs.
I got back to Lance and he said that he had not been kidding about two sizes of
pistons I was sick.
Purchased a dandy little bore-scope from Aircraft Spruce and with more swearing
and fumbling about I could see what I have (done)
Cylinder #1, Closest to the alternator, 67.46, green dot
Cylinder #2, Closest to the PTO, 67.45, red dot
Cylinder #2 is hotter that shoots my theory about the bigger piston running hotter
Also the top of piston #2 has accumulated a coating of carbon in only 5 hours of
operation, while piston #1 is much cleaner. (Photos attached) I have run only
AV-2 two-stroke oil in an effort to minimize carbon build up Im somewhat disappointed.
In reviewing the spreadsheet It appears that each piston is operating within the
temperature limits set by the factory for operation. The problem is the temperature
difference between cylinder #1 and #2.
Before installing the digital engine monitor, I only knew the temperatures on one
cylinder I would have never have seen this problem and would probably be having
a great time out flying, right now.
When Rotax sets limits for the difference of temperature allowable between cylinders,
Im pretty sure they are figuring on both pistons being the same size (Krauts
are like that) A larger than normal temperature difference in an engine
with matching pistons could indicate a problem However, in an engine with different
sized pistons, perhaps this temperature difference should simply be expected.
Comments?
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Henry
Firefly Five-Charlie-Bravo
Do Not Archive
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=363708#363708
Attachments:
http://forums.matronics.com//files/piston_2_pto_6745_red_dot_116.jpg
http://forums.matronics.com//files/piston_1_alt_6746_green_dot_514.jpg
http://forums.matronics.com//files/cht_egt_run_13jan12_171.xls
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