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He assumed I knew what I was doing...

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henry.voris

Joined: 02 Mar 2007
Posts: 116
Location: Pueo Field, Kula, Maui

Posted: Fri Jan 13, 2012 11:34 pm Post subject: He assumed I knew what I was 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… I’m 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 (36º CHT and 45º 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… I’m 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, I’m 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?

piston #2, PTO, 67.45, Red Dot.jpg

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_________________
Henry
Firefly Five-Charlie-Bravo

Do Not Archive

John Hauck

Joined: 09 Jan 2006
Posts: 4639
Location: Titus, Alabama (hauck's holler)

Posted: Sat Jan 14, 2012 5:52 am Post subject: He assumed I knew what I was doing...

When Rotax sets limits for the difference of temperature allowable between cylinders, Iâ€™m pretty sure they are figuring on both pistons being the same sizeâ€¦ (Krauts are like thatâ€¦) A larger than normal temperature difference in an engine with matching pistons could indicate a problemâ€¦ However, in an engine with different sized pistons, perhaps this temperature difference should simply be expected.



Comments?



--------

Henry

 



Henry V/Kolbers:



This is the difference in size between your two pistons:  



0.0004 inch



I doubt 4/10,000 inch will make a whole lot of difference.  The 447 is not a watch.  Austrian standards are not that tight on 447 engines.  Most of the temp difference is probably difference in port size and shape, and other differences in air and fuel flow.  They don't do a good job of matching them with the cast iron sleeves.



What are the difference in size of bore of the cylinders?  Are they within 4/10,000 inch?



How accurate and repeatable is your instrumentation?  I've seen Kolbers ruin their flying experience because they couldn't get a couple of Westach gauges to agree.  Spent more time trying to get everything to match precisely than getting out there and having fun flying.



If it was mine, I'd take the warmer temps from the hotter cyl for operating limits, fly and enjoy.



I was told by an old time engine builder, that matched the ports and balanced my pistons, pins, and rings, on my 447's, "a little carbon is needed on the tops of the pistons to help lower operating temps of the piston."  Carbon acts as an insulator.



BTW:  I had good luck with my 447's.  I had two, one on the Firestar and one on the bench ready to go.  Balancing and matching ports made the 447 produce more power and reduced vibration.



john h

mkIII

Titus, Alabama - 20F at hauck's holler this morning.  Ain't going flying today.

_________________
John Hauck
MKIII/912ULS
hauck's holler
Titus, Alabama

Ducati SS

Joined: 15 Oct 2009
Posts: 93

Posted: Sat Jan 14, 2012 8:55 am Post subject: Re: He assumed I knew what I was doing...

Did you swap EGT probes? if so was the PTO reading still high? During reassembly did you align the cylinder intake manifold surfaces, check the intake manifold with a straight edge, do a post repair pressure test?   Remember unlike a 4 stroke a 2 stroke can leak unmetered air almost anywhere but the exhaust port. a small bit of old base gasket left behind can cause a lean condition.

beauford

Joined: 25 Apr 2007
Posts: 127
Location: Brandon, FL

Posted: Sat Jan 14, 2012 9:32 am Post subject: He assumed I knew what I was doing...

Brother Voris:



Your temps, as shown in your nifty spread sheet, show deltas on both EGT and CHT which closely resemble mine, but

the overall range of yours, is a little cooler.  My engine has had two green dot pistons installed about 130 hours ago and I just had it torn down and inspected last month out of suspicion that the crankcase seals were leaking.  Nothing significant was found, although one wrist pin was replaced as an "option" since it displayed minor wear.  Both con rod top ends and wrist pins showed some bluing which reflected the high temps for which the 447 is well known.



For what it's worth, the rear (PTO end) cylinder on mine has always run around 25 to 30 hotter on CHT and 40 to 60 degrees hotter on EGT.  I worried about that for a while... played games with minor adjustments of the angle of the Bing on the manifold, repeatedly checking fan belt/shroud, tinkered with jetting and needle, etc.  Finally decided

to hell with it and just flew it.  The CHT's were in the 380 to 405 range at WOT and the EGT's ran 1040 to 1100

at 5800 cruise.



Since the teardown inspection, head temps and EGTs have jumped up and I can't figure out why.  At WOT climb after about 45 seconds the rear cylinder is climbing through the red line at 425 and the front is right behind it at about 415... I have to throttle back and level off or they would continue to increase.  The EGT's are also higher and now show 1100 and 1150 at 5,800 cruise with the heads hanging around 400.  The plugs are both a nice brown color.  I have run it a total of about three hours since the teardown am about ready to re-torque the heads.



Other than the new wrist pin and all of the gaskets and seals, nothing was changed in the engine.  The work was done by an experienced, certified shop in which I have confidence.  The jets and needle in the Bing are stock sizes and show no wear. The IVO is loaded to the same 6000 RPM static as before.  I went so far as to replace all four of the EIS sensor probes to make sure they were giving accurate data...  They are.  I am baffled by the increased temps.



Overall, Henry, yours looks to be running cooler than mine.  Personally, I would settle for your temps and just go fly it, watching the plug color for anything strange.



My engine, on the other hand, definitely has a newly developed higher temp problem which requires attention...  In the absence of any better idea,  I am going to start with further searches for leaks in the manifolds and then move into the Bing jetting and setting business...



If anyone on the List has experienced similar high temp fun & games with a 447 and successfully whipped the problem, (or blew/burned it up, but executed a successful autopsy) I would appreciate hearing from you.



Baffled beauford in Brandon

FF-076

--

captainron1(at)cox.net
Guest

Posted: Sat Jan 14, 2012 10:04 am Post subject: He assumed I knew what I was doing...

The temps are directly related to air/fuel burn and its efficiency, How that mixture is being measured and ignited between the cylinders is what controls the temperature. One carb, two carbs, mixture ratios etc... . Too many variables and scenarios to have a canned answer to the question. Play with the mixtures see what happens if you have two carbs, if not I think what you got is what you got.



Ron Mason

=============================

---- "henry.voris" <henry_voris(at)yahoo.com> wrote: 



=============




13jan12



Gentlemen,



My pal Lance asked, âSoâ¦ Do you wanna put the big piston in the front or the rear?â

I assumed he was kiddingâ¦ He assumed I knew what I was doingâ¦ 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 togetherâ¦ Iâm sure we got most of those dang needle bearings back in the wristpinsâ¦



Back on the plane, the engine fired right up and ran strongâ¦ 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 (36Âº CHT and 45Âº 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 pistonsâ¦ 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)â¦

	Cylinder #1, Closest to the alternator, 67.46, green dot

	Cylinder #2, Closest to the PTO, 67.45, red dot



Cylinder #2 is hotterâ¦ that shoots my theory about the bigger piston running hotterâ¦ 



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 upâ¦ Iâm somewhat disappointed.



In reviewing the spreadsheetâ¦ 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 cylinderâ¦ 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, Iâm pretty sure they are figuring on both pistons being the same sizeâ¦ (Krauts are like thatâ¦) A larger than normal temperature difference in an engine with matching pistons could indicate a problemâ¦ However, in an engine with different sized pistons, perhaps this temperature difference should simply be expected.



Comments?



--------

Henry

Firefly Five-Charlie-Bravo



Do Not Archive





Read this topic online here:



http://forums.matronics.com/viewtopic.php?p=363707#363707





Attachments: 



http://forums.matronics.com//files/cht_egt_run_13jan12_269.xls

http://forums.matronics.com//files/piston_2_pto_6745_red_dot_188.jpg

http://forums.matronics.com//files/piston_1_alt_6746_green_dot_459.jpg

--

kugelair.com

Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Sat Jan 14, 2012 10:07 am Post subject: He assumed I knew what I was doing...

At 12:40 PM 1/14/2012, Richard Girard wrote:

  	  Quote: 	
		  Beauford, Do you have spark plug ring temp senders? If so, polish them up with Scotchbrite and do the surface of the head where the sender seats, making sure any debris doesn't go down the plug hole, of course. The senders work on resistance so any corrosion on them or the head will affect their readings. Just a thought. 	


 The typical self powered spark plug ring sensor is a thermocouple, not a resistance device.



 -Dana

 

 --

 Don't ever think you know what's right for the other person. He might start thinking he knows what's right for you.

    [quote][b]

byoungplumbing(at)gmail.c
Guest

Posted: Sat Jan 14, 2012 10:14 am Post subject: He assumed I knew what I was doing...

Since the teardown inspection, head temps and EGTs have jumped up and I 

can't figure out why.  At WOT climb after about 45 seconds the rear cylinder 

is climbing through the red line at 425 and the front is right behind it at 

about 415... I have to throttle back and level off or they would continue to 

increase.  The EGT's are also higher and now show 1100 and 1150 at 5,800 

cruise with the heads hanging around 400.  The plugs are both a nice brown 

color.  I have run it a total of about three hours since the teardown am 

about ready to re-torque the heads.



Other than the new wrist pin and all of the gaskets and seals, nothing was 

changed in the engine.  The work was done by an experienced, certified shop 

in which I have confidence.  The jets and needle in the Bing are stock sizes 

and show no wear. The IVO is loaded to the same 6000 RPM static as before. 

I went so far as to replace all four of the EIS sensor probes to make sure 

they were giving accurate data...  They are.  I am baffled by the increased 

temps.



Baffled beauford in Brandon

FF-076

 	  Quote: 	
		  >>>>>>>>>>>>>>>>>>>>


	


did you cross hatch the cylinder walls, and install new rings....  if so the 

higher temps may be there till things seat in.   if you did not change 

rings...  i am clueless.



boyd



do not archive.

Ducati SS

Joined: 15 Oct 2009
Posts: 93

Posted: Sat Jan 14, 2012 10:20 am Post subject: Re: He assumed I knew what I was doing...

I would strongly recommend a pressure/ vac. test during condition inspection, anytime you have unexplained variations in EGTs , and post repair. Even a good mechanic can make a mistake or install a defective part. A seal may become nicked on assembly, a bit of debris may be left on a mating surface or a small void in sealer may occur. Personally I do not even accept the allowed 1 psi per minute drop, the tighter they are the better they start and run. A pressure test will uncover  problems with seals, crankcase seal, gaskets and porous castings. A 4 stroke with a leaky crank seal or case makes a mess but a 2 stroke dies a horrible death.

byoungplumbing(at)gmail.c
Guest

Posted: Sat Jan 14, 2012 10:20 am Post subject: He assumed I knew what I was doing...

The senders work on resistance so any corrosion on them or the head will  affect their readings. Just a thought.



 -Dana

  

 >>>>>>>>>>>>>>>>.

  

 Dana

  guess i thought they were a  thermocouple.   depending on which metals are used thermocouples  create a small electrical voltage at different temps...   devices that  work on resistance  when the temps change,  i believe are  thermistors.

  

 boyd y

  

 do not archive

   [quote][b]

herbgh(at)nctc.com
Guest

Posted: Sat Jan 14, 2012 10:38 am Post subject: He assumed I knew what I was doing...

J type thermocouples....the egt sensors are K type... They generate a small current/voltage...and are very sensitive to resistive  connections...I generally make my own cht thermocouples...Herb 



  http://www.omega.com/thermocouples.html



 

 At 12:17 PM 1/14/2012, you wrote:

 [quote]The senders work on resistance so any corrosion on them or the head will affect their readings. Just a thought.

 -Dana

  

  >>>>>>>>>>>>>>>>.

  

 Dana

  guess i thought they were a thermocouple.   depending on which metals are used thermocouples create a small electrical voltage at different temps...   devices that work on resistance  when the temps change,  i believe are thermistors.

  

 boyd y

  

 do not archive

 

 [b]

henry.voris

Joined: 02 Mar 2007
Posts: 116
Location: Pueo Field, Kula, Maui

Posted: Sat Jan 14, 2012 10:48 pm Post subject: Re: He assumed I knew what I was doing...

14jan12



Thanks guys... FYI... I posted this same message on the Rotax List and have received zero responses so far. Kolb List rules...



John... Thanks... That's the type of information I was looking for. I have been inclined to just fly it, because both cylinders were running fine, just at different temps. 



You asked about my instrumentation... As part of this rebuild I installed the EIS 2000... When 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.



I plan to take the warmer temperatures from the hotter cylinder to set my operating limits.



I too like the 447. After having it all apart, I'm impressed with its simplicity and ruggedness. Even when it was tired, it would always start and run strong.



Ducati SS... No I have not (yet) swapped the EGT probes... During assembly I used an official Rotax tool to align the cylinders... But it bolted into the holes for the exhaust manifold, as I recall...



Thanks for the word on pressure testing. If I'm still unhappy after running this for awhile pressure testing will be next on my list.



Brother Beauford... Sorry to hear about your engine running hot again... I remember you were not happy when you first had the green dots installed... Hopefully Boyd is right and it'll cool down after the rings settle in. Good problem to have, because that means the fix is... you gotta fly it more.



You said you set your red line for CHT at 425... I noted with interest that the Rotax Operators Manual from Sept. 01, 2010 (page 37) increases the normal operating range for CHT... 374 to 446, with max at 500. 



Ron... as you said, "Too many variables..." That's why I like the 447... one ignition system, one carb. John and Brother Beauford have told me what I wanted to hear... The engine is running good... Go fly it. And the new EIS 2000 will give me the ability to keep a close eye on it. Thanks.



Boyd... Thanks for the great thermocouple site...



Aloha,

_________________
Henry
Firefly Five-Charlie-Bravo

Do Not Archive

Ducati SS

Joined: 15 Oct 2009
Posts: 93

Posted: Sun Jan 15, 2012 8:39 am Post subject: Re: He assumed I knew what I was doing...

The 447 on my firefly has a total of 13hrs. and the PTO EGT has read 60 to 75 degrees high from initial break in to present. Jetting changes helped but then I had to accept an over rich mixture on the mag side. I pulled the motor and it failed a pressure test. Leaking at the intake manifold. A straight across the cylinders showed them to be fine. The straight edge across the manifold was another story, way off. I reworked the mating surface and performed another pressure test, no leak. I will not know until spring if this solved the problem. One of the drawbacks to the 447 and 503 design is that it makes pressure testing the manifold difficult. To properly seal the exhaust ports requires removing the blower housing and installing block off plates, but this means disturbing the intake gaskets. Regardless the manifold was not straight.   A side note to this is that the intake assembly was probably the sloppiest i have ever encountered. The mag side gasket was the worst, sticking up from the floor of the port close to 1/8". The worst place to have an obstruction as flow initiates at the port floor. The manifold also had some quite severe casting flaws perpendicular to flow. Spent hours reworking interior of manifold and trimming gaskets. Wish I had time to rework the ports and cases but to many other mods on the list. Almost forgot, I am very suspicious of my EGT instrument,  I am going to swap it for one of the B Lite led units. The above initial pressure test was done with new gaskets.

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