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Generation 4 Engine

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Re: Generation 4 Engine

Postby PKnight » Wed Sep 18, 2019 8:31 am

The EGT range for the cruise is 600-720 deg C with a maximum of 700degC at greater than 70% power. For reference I get about 630 deg C in the cruise at 3500ft and 24ltrs per hour. See attached photo, the centre cylinders (3 and 4) are not monitored but are within 5 deg on CHT and 10 deg on EGT.
It is important to realise that EGT is NOT really measuring the exhaust gas temperature. The gas is much hotter. The thermocouple is measuring the average temperature over an ignition cycle in the cylinder where for about 25% of the time very hot gas is swirling around the thermocouple from the exhaust stoke and 75% of the time, nothing is going past the thermocouple as it cools down during the intake, compression and power stroke. I always think that the EGT is less of a measurement more of a ''hint' about what might be going on in the cylinder. Sorry for the lecture but it does lead to a possible explanation of the reading you are getting on one cylinder.
A couple of years ago I did replace a thermocouple on one cylinder that had been knocked about a bit during maintenance. (It happened to be Cyl 2). After installing the new thermocouple I was surprised to see reading that were 40 - 50 deg C higher than the other cylinders in the cruise. After much messing about I found that the position of the thermocouple in terms of how far the sensing head is inserted into the cylinder was critical in the impact on the readings. I got higher readings if the sensing head was closer to the cylinder wall and lower readings if the thermocouple was pushed well into the exhaust down pipe so it was closer to the centre of the pipe. I was surprised at the significant change in temperature that resulted from a small movement in the position of the sensor. I can only assume that the extreme swirling of the exhaust gas as it exited the cylinder caused very different heating of the probe.
Anyway ensuring that the probe was centred in the middle of the cross section of the exhaust pipe reduced the excess reading (Which did not appear to happen under full power as presumably the gas distribution was different.
Hope this helps. One cautionary note, I have no idea what effect, if any, the Hackman device might have.

I attach a photo showing readings currently obtained on a Gen 4 3300. 50hours of use, OAT 14 deg C, 3500ft with about 24 litres per hour.
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IMG_4445.JPG
PKnight
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Re: Generation 4 Engine

Postby skypics234 » Thu Sep 19, 2019 2:50 pm

RE: #2 EGT much higher than the rest in cruise Gen 4

I returned the carb from the 5-degree tilt toward the lean side to level.

Then, based on a response from another forum that said it is most likely the airflow turbulation into the carb, I tilted only the oval air filter to one side and that seemed to help somewhat.

Then, at 3500 MSL and at 2900 RPM I quickly leaned out the engine to lean of peak. This resulted in EGTs, including #2 which was still higher than the rest, to all come closer to each other. Of course, the RPM dropped from 2900 to 2750 RPM but ran smoothly burning 2.5 GPH.

Then I tried leaning to Rich of peak and EGTs were even lower and CHTs a bit higher. According to Mike Busch, this is the worse place to run so I won't do that.

The CHTs are just great with the from two running at 300 F and the back two running at 280 F. So with this cooling the valves should last much longer than I saw on earlier engines.

John M
Last edited by skypics234 on Sun Nov 03, 2019 2:34 pm, edited 1 time in total.
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Re: Generation 4 Engine

Postby skypics234 » Sun Sep 22, 2019 2:25 pm

Have resolved the issue of #2 EGT reading 100 F higher than the rest.

I returned the carb to level...meaning I took out the recommended tilt toward the lean side.

Someone on this or the Jab Camit forum mentioned he had put in a small 1cm diverter at the input of his carb.

So I thought I'd try tilting just my air filter to one side or the other. My filter is one designed for the two carb two-cycle Rotax 582. I have been using it on all three Jab 2200 I have owned.

I just plug off one of the carb attachment holes.

This carb measures 11" x 5" x 3". It fits into the recess in my firewall.

Results: The #2 is much closer to the next highest EGT and when I lean to LOP the EGTs are much closer at 2850 RPM.

John M
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Re: Generation 4 Engine

Postby skypics234 » Mon Sep 23, 2019 2:54 pm

PKnight:

Thanks for the response. I usually don't fret much about EGTs. I read Mike Busch's book on aircraft engines. Great info by the way.

I am familiar with tubulation in the pipes. However, you have made a good point about the insertion depth of the thermocouple.

My issue was pretty much resolved just by tilting the air filter and using the leaning to get the desired temps.

I find that the standard main jet shipped with the Jabs is typically a bit too fat for me, sometimes causing a bit of a stutter on WOT climb out. So I use a 240 in place of the 245. My field is 533 MSL.

When I take off from Big Bear Airport at 6700 MSL after liftoff I start leaning and can see the RPM increase as I lean. The Bing carb doesn't auto lean well enough at these altitudes so I use my Hackman.

I burn 100 LL with Decalin to try to keep the lead crud down to a minimum.

John M
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Re: Generation 4 Engine

Postby skypics234 » Fri Nov 01, 2019 2:57 pm

Hi Guys:

Here is an update on my Jab 2200.

My most recent Balackston Labs oil analysis has me concerned. They show high levels of copper, tin, and nickel. The oil had 45 hours on it. The engine has 69 hours.

Yet, I just got back from a 5-hour flight one way to Dead Cow Dry lake for the STOL DRAGS. I didn't participate.

The dipstick showed a drop from full to 1/2 after each leg which I consider great.

The engine easily took me over the Sierras at Lake Tahoe at 10,000 MSL with no problem climbing in my Avid MK4 with 20 gallons of fuel and a lot of camping equipment. So I can't understand why these readings.

I will do a borescope and leakdown and check the rocker boxes for telltale carbon trails from the exhaust valve guides which was typical on the earlier generation engines I've owned.

I'll let you know the results.

John M
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Re: Generation 4 Engine

Postby skypics234 » Sun Nov 03, 2019 2:45 pm

I had posted that my most recent oil analysis caused me concern. Here is what I have found out so far.

I opened the oil filter and found no metal particles.

I contacted jabiru and was told that at 69 hours the engine was still breaking in. Especially since I used Phillips 20-50 instead of straight mineral oil which caused a faster break-in. That said, I have read several articles that have recommended Phillips 20-50 for break-in as opposed to mineral oil.

My last oil sample had only 18 hours on it and this one had 46 hours so that was 250% of the first sample. Tin, Nickle, and copper were all up that same amount.

I will send in another sample to Blackston Labs at the 25-hour mark.

Engine compression, performance, and oil consumption are all well within spec.

John M
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Re: Generation 4 Engine

Postby skypics234 » Tue Nov 05, 2019 2:17 pm

After a nasty oil analysis from Blackstone I looked into the engine more closely and here is what I found.

The previous oil sample had only 18 hours on it and the latest one had 45 hours on it so, of course, there would be higher levels of metal.

Nick, from Jab supports says the engine is STILL breaking in so higher metal levels should be expected.

I believe I contributed to the longer break-in by adding Camgusrd at the 2nd oil change. Camguard has an inti scuff ingredient which is not recommended during break-in.

Borescope and compression are all good and a look into the rocker boxes found no carbon traces that are typical when exhaust guides are worn and leaking.

I will send in another sample at the 25-hour mark.

John M
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