jkarch

M20J GAMI spread issue (flow divider?)

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Hello,

 

I've had an issue spanning many years regarding fuel-flow and peak EGT.  I bought GAMI injectors about three years ago and installed them, hoping to get better fuel economy and lean of peak performance.  My M20J's IO-360 has always been reliable, but in general it tends to run a bit rich.  My GAMI spread has varied over time from 1.1 GPH to .7 GPH.  I worked with John Paul at GAMI to try to resolve the issue, which involves having cylinders 3 and 4 peaking early, followed by 1&2 peaking much later around .7 to 1.1 GPH depending on throttle settings and altitude.  Given the fact that 1&2 and 3&4 share common Cam lobes respectively, John Paul was concerned about Cam Lobe wear.  But this issue has happened over hundreds of hours and hasn't worsened, and Cam Lobe wear would have resulted in a required overhaul by now.  Oil analysis shows no such evidence of cam lobe wear, and the oil filter is fairly clean with normal wear for its age at about 1200 hours. Compressions are all in the high 70s. I could do the valve lift test as he proposed, but I decided to attack fuel flow first.  Yesterday I decided to do the bottle test with my mechanic where you disconnect the flow tubes from the injectors, apply full throttle and turn on the boost pump to check flow, and discovered some strange findings.  When full throttle is applied and mixture is pulled back about 65% of the way I received the following results in this photo:  #1 is clearly the richest cylinder, and it takes a long time for it to peak, whereas #4 peaks much sooner, followed by #3.  #2 is an anomaly, as it appears to peak around the same time as #1.  Looking at the results here, I'm thinking I need to have my fuel spider changed/overhauled.   This test was done without the fuel injectors installed.  I also ran this test at full rich, which shows similar results except #2  isn't as lean is it is in this photo proportionately to the other flows, but still follows the same patterns.   A few months ago my mechanic and I fixed an induction leak by replacing all induction gaskets, and yesterday, my mechanic set the mixture leaner as the engine's been running too rich, so he doesn't suspect an induction system leak.    Is the fuel spider the smoking gun in this problem?  If it is, why does #2 appear to peak later than #4, unless I'm looking at a secondary EGT peak in #2 and have been missing the first peak all along?

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The fuel injectors set the flow not the divider. The test is meaningless without the injectors attached. Without the backpressure of the injectors the diaphragm in the divider will not raise properly and you will be seeing the divider acting like you are at idle not off idle flow. There is not much in the divider that can affect flow off idle. If it makes you sleep better at night you might soak the injector lines in Hopps #9, they never get cleaned and can build up deposits just like injector nozzles. They would be the major flow restrictions with the injectors removed.

Did you do this test with the injectors installed too? what were the results? 

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What are your cylinder head temps and exhaust gas temp look like when you're running about a hundred Rich of peak? A partially plugged fuel injector or line will make the rest of them run rich. In this case, I would expect to see #2 CHT abnormally low and egt high.

From your bottle test, number 2 is clearly restricted somehow. I doubt seriously it's your fuel spider. more than likely you have a restriction in the #2 line or the injector itself. it really doesn't take much of a restriction to cause some strange numbers.

As MK indicated, do the bottle test with and without the injectors.

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1 hour ago, Guitarmaster said:

A partially plugged fuel injector or line will make the rest of them run rich.
 

That isn’t the case. The RSA-5 regulates the fuel pressure delivered to the injectors, not the volume. Even if one injector was compleatly blocked the other injectors would see the same pressure as when it was flowing. 

In any case the servo doesn’t set the mixture, you do with the red knob. It just tries to make a pressure that maintains the same fuel air ratio with changes in throttle (air flow through the servo).

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4 hours ago, jkarch said:

Hello,

 

I've had an issue spanning many years regarding fuel-flow and peak EGT.  I bought GAMI injectors about three years ago and installed them, hoping to get better fuel economy and lean of peak performance.  My M20J's IO-360 has always been reliable, but in general it tends to run a bit rich.  My GAMI spread has varied over time from 1.1 GPH to .7 GPH.  I worked with John Paul at GAMI to try to resolve the issue, which involves having cylinders 3 and 4 peaking early, followed by 1&2 peaking much later around .7 to 1.1 GPH depending on throttle settings and altitude.  Given the fact that 1&2 and 3&4 share common Cam lobes respectively, John Paul was concerned about Cam Lobe wear.  But this issue has happened over hundreds of hours and hasn't worsened, and Cam Lobe wear would have resulted in a required overhaul by now.  Oil analysis shows no such evidence of cam lobe wear, and the oil filter is fairly clean with normal wear for its age at about 1200 hours. Compressions are all in the high 70s. I could do the valve lift test as he proposed, but I decided to attack fuel flow first.  Yesterday I decided to do the bottle test with my mechanic where you disconnect the flow tubes from the injectors, apply full throttle and turn on the boost pump to check flow, and discovered some strange findings.  When full throttle is applied and mixture is pulled back about 65% of the way I received the following results in this photo:  #1 is clearly the richest cylinder, and it takes a long time for it to peak, whereas #4 peaks much sooner, followed by #3.  #2 is an anomaly, as it appears to peak around the same time as #1.  Looking at the results here, I'm thinking I need to have my fuel spider changed/overhauled.   This test was done without the fuel injectors installed.  I also ran this test at full rich, which shows similar results except #2  isn't as lean is it is in this photo proportionately to the other flows, but still follows the same patterns.   A few months ago my mechanic and I fixed an induction leak by replacing all induction gaskets, and yesterday, my mechanic set the mixture leaner as the engine's been running too rich, so he doesn't suspect an induction system leak.    Is the fuel spider the smoking gun in this problem?  If it is, why does #2 appear to peak later than #4, unless I'm looking at a secondary EGT peak in #2 and have been missing the first peak all along?

  I’ve never met a four-cylinder, injected, angle valve Lycoming with the spread that high..GAMI rightly focuses on Continental engine because most normally aspirated Lycomings have excellent fue/airl distribution. I agree with Rich’s post above. Running a flow test sans injectors tells you nothing. John Paul may have been on to something. You have an engine that is performing unusually. It seems you’re trying to correct the symptoms. Even if you run this test with the injectors, you’re likely going to get different amounts of fuel because GAMI has adjusted the flow to correct for the imbalance. 

I would have a jug pulled to verify cam condition.  You’re chasing your tail until you verify that all four cylinders are pulling the same volume.

Edited by Shadrach
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If 3&4 are peaking early, my theory is your cam is bad, particularly the lobe that’s shared between 1&2 intake valves, they don’t open as wide, less air gets in, richer mixture.

 Edit:

 BTW, I had the opposite problem (1&2 peaking together, followed by 3&4 1.1 gph later), talk to my engine guys today, I have a bad cam.

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You can have your GAMI Injectors fine tuned by GAMI.  Call them and speak to one of their tech support people. They will have you send them data from your engine analyzer.  From that information they will have you remove some, or maybe all, injectors and send them back for calibration. I think they charged me $100 including return shipping and gave me a 2 year guarantee on all the injectors.

I had a problem running LOP on my TSIO-360 and they identified the problem to 2 injectors. They calibrated it based on my data and I have never had a problem since. My GAMI Spread is less than 0.1 GPH.  All the cylinders go LOP almost at the same time. 

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12 hours ago, CaptRJM said:

You can have your GAMI Injectors fine tuned by GAMI.  Call them and speak to one of their tech support people. They will have you send them data from your engine analyzer.  From that information they will have you remove some, or maybe all, injectors and send them back for calibration. I think they charged me $100 including return shipping and gave me a 2 year guarantee on all the injectors.

I had a problem running LOP on my TSIO-360 and they identified the problem to 2 injectors. They calibrated it based on my data and I have never had a problem since. My GAMI Spread is less than 0.1 GPH.  All the cylinders go LOP almost at the same time. 

John Paul who was referred to in the first post is GAMI’s go to guy during the tuning process. He was the first person to speculate that the cam could be a problem.

Edited by Shadrach

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Welcome back, JK. It’s been a long while...

1) The test you shared a picture of is interesting... the Mooney engine gurus have a name for that...

2) It is often referred to as the baby bottle test for fuel injector flow testing... often, they use four baby bottles.... the weight of fuel is measured on a decent scale...and compared to the time that the test took to execute...

3) The fuel injectors are the final resistance to flow of fuel.  So doing a flow test without the fuel injectors, unfortunately leaves you repeating the test...

4) There is an actual procedure for this, that makes sense to follow... keeps you from getting misguided or only partially testing what you are looking to do...

5) the reason GAMI sells balanced fuel injectors is because they can get the GAMI spread pretty close to zero and within .5gph easily... I believe. See their site for their promise.

6) Any resistance to starting over with the fuel injectors this time?

7) As for measuring valve movement with the cam lobe driving the valve stem... There is a procedure for that too... if a cam lobe is missing, it can be found by making a measurement.  Your mechanic can look this up as well... 

8) Measuring cam lift and fuel flow of each cylinder can get you reliably close to finding out what your engine is capable of.

9) What is your current GAMI spread in flight?  Check Savvy If you need a procedure for that too.... 1.0 isn’t a normal GAMI spread after GAMI has properly supplied fuel injectors...

10) Also check where the GAMI injectors are in the engine, they are numbered, and often get misplaced over time by unknowing mechanics... or owners... or somebody....  check the logs to see what FI number belongs in which cylinder...

11) three things to look for....

  • Baby food jar test with fuel injectors in place...
  • cam and valve looking to see evidence of a missing cam lobe...
  • GAMI injectors in the right place as evidenced by the logs and matching number on the FI...

That’s some good news, not everything is a cam problem... especially when you have no evidence of bits of metal in the oil... once cams start going away, the hardness to resist wear is already missing...

At MS there are many knowledgable people.  Many are really helpful too...

I’m just a PP, not a mechanic... I have read a bunch of stuff from other people on MS...

Best regards,

-a-

 

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Thank you all for the responses so far. A couple more details.  The issue has gone on for at least 300 hours. In fact I don’t think my engine has ever been tuned. It’s not like there has been any gradual worsening in the spread.  I took the advice of many of you and reran the test with the injectors attached. The photos show the bottle test with the injectors. There are two examples here. The one photo with a more even distribution shows mixture full rich and full throttle with boost pump on, while the one that is less balanced has the mixture pulled out from 5.8 gph to 3.8-4 gph.  Leaning definitely worsened the fuel distribution. It’s odd to see  1&3 and 2&4 matched even though 3&4 peaks before 1&2.  However I did have my mechanic clean the fuel lines with Hoppes #9 today and found that the distribution with rich mixture improved significantly.  In flight I found the EGTs to be more even when rich and the engine ran more smoothly overall across the band, including aggressive leaning above 8000 feet. I did not have time to run a full GAMI lean test. Incidentally GAMI recommends running the test full rich without injectors installed but I now have all 4 quadrants including rich and lean and with and without injectors installed. Injectors balance flow somewhat but they are not fully even. Pulling out the mixture worsens the spread however.  Pulling a Jug is likely a last resort for a smooth running engine. I’m more likely to pull the engine monitor which is old than a jug. My only issue is the fact that the cylinders don’t peak simultaneously however the engine runs reasonably smoothly even when lean. One thing I did notice is #1 doesn’t have a sharp EGT peak like the others. I will test fly again and rerun flow test in flight and post more details but I find the uneven flow to still be disconcerting.

Thanks again to everyone who responded- Josh

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6A7ECCC3-3AF0-4B61-906D-2C19258FF9AC.jpeg

Edited by jkarch
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Josh, you need to account for the fact that you have Gami injectors and that John Paul has made adjustments to balance your cylinder peaks as closely as possible. That is not the same thing as making sure all of the injectors flow at the same rate. Stock Lycoming injectors do a pretty good job of evenly distributing fuel to each cylinder.  Fortunately for us, Lycoming’s tuned induction system does a pretty good job of evenly distributing air to each cylinder. For this reason almost any injected, angle valve, four-cylinder Lycoming will run pretty well across the mixture spectrum. As an example my IO 360 A1A will run smooth to ~100° LOP down low with ample MP available. I actually start to get a second EGT rise on #2 (leanest cylinder) as the engine goes rough. I can’t go quite that far higher at higher altitudes, but wouldn’t want to. My engine is not unique among angle valve, four-cylinder Lycomings, in fact it’s pretty typical. Tuning these engines is not part of GAMI’s core bussiness. GAMI would be the first to tell you that in most cases they have little to offer over the stock Lycoming injectors. GAMI’s are designed to match the fuel flow to the airflow at each cylinder. They are not designed to match the injectors to one another. My earlier recommendation to have one of the jugs pulled is a bit aggressive. Measuring cam lift is less invasive and can be done in a matter of hours with just the rocker boxes removed.

 

Edited by Shadrach
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Shadrach, what altitude should I be doing the lean test at? I typically have been doing it at full power and 8500 feet. I’m thinking of cleaning up my stock injectors and reinstalling them to test again. Had I known GAMIs weren’t useful for IO-360s I would have considered not getting them though they definitely made the engine run smoother even with the stock settings 400 hours ago.  I will have to look at the valve lift test.  Everyone including my mechanic has told me that cam lobe wear would have resulted in a useless engine by now because it’s gone on since I’ve owned the plane (300-400 with GAMIs) and I have put 7-800 hours in 7 years since buying it. The oil filter and analysis is clean and the idle is very smooth and power seems good but that’s subjective. One thing I don’t understand is why fuel flows become more uneven when the mixture is pulled out.

Edited by jkarch

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jk,

you are getting closer...

But you seem to be focused on a wide range of things....

1) As in FF balance under full throttle, while full rich, with the pump on... when balance is the least important part of FF in this leg of the flight... mixture full rich is intended to be spraying excess fuel, for cooling EGTs under this condition.

2) Stick with Ross... he is pretty clear at explaining the ability to match air flow to fuel flow in each cylinder...

3) Expect to only be able to balance things in a very narrow range of operating conditions... typically this is cruise settings over a range of altitudes...  you get what you get when operating in the other regimes...

4) Nothing explains how your fuel distribution is working like sharing a Savvy graph of your EGTs and CHTs for an entire flight including start-up, run-up, climb, cruise, descent and landing....  FF, airflow, for each cylinder, under various conditions in a picture!

5) what engine monitor do you have, can you download your data to a PC, can you take a screenshot???

6) You seem to be putting in a lot of effort but not aiming for a well defined solution...

7) When you cleaned with hoppe’s, did you collect anything coming out of the fuel injectors?

8) did you use an ultrasonic cleaner?

9) Any aha! Moments of finding anything?  (You have to look closely to see things)

10) got a pic of your FF gauge and engine monitor?  It is OK not to have these devices... but I get the feeling we are trying to solve a problem without instruments to solve the problem with... :)

Pp thoughts only, all stuff I read on MS....

Best regards,

-a-

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4 hours ago, jkarch said:

Shadrach, what altitude should I be doing the lean test at? I typically have been doing it at full power and 8500 feet. I’m thinking of cleaning up my stock injectors and reinstalling them to test again. Had I known GAMIs weren’t useful for IO-360s I would have considered not getting them though they definitely made the engine run smoother even with the stock settings 400 hours ago.  I will have to look at the valve lift test.  Everyone including my mechanic has told me that cam lobe wear would have resulted in a useless engine by now because it’s gone on since I’ve owned the plane (300-400 with GAMIs) and I have put 7-800 hours in 7 years since buying it. The oil filter and analysis is clean and the idle is very smooth and power seems good but that’s subjective. One thing I don’t understand is why fuel flows become more uneven when the mixture is pulled out.

Do you mean your fuel flows are more even or your EGT numbers are more even? It’s not the same thing? It’s indeed possible that your distributor as an issue but it certainly wouldn’t be common.

I don’t want to get into a huge discussion regarding intake design but you should understand that GAMI built it’s business on the Continental “log runner” intake. Those types of intakes look like a tube with an intake splitting off for each cylinder. Air enters at the front or the back (depending on applicantion) of the cylinder bank’s manifold and terminates at the last cylinder in the bank. Air for each individual cylinder on a bank is taken from that bank’s that common manifold.  Every time in intake valve closes fuel from the injector migrates back into the manifold.  The next cylinder in line gets air from the manifold plus a little fuel from the cylinder(s) preceding it.  This means the first cylinder in line as the leanest and the last is the richest. GAMI solved this problem by decreasing injector flow from the first to the last cylinder in a bank. This means that each cylinder gets a similar fuel air mixture even though the injectors are flowing at different rates. Why do I mention all of this? Because Lycomings don’t have a log runner intakes and therefore don’t suffer from fuel migrating from one cylinder to the next. Your engine has tuned intakes designed to deliver a balanced volume of air to all four cylinders. In theory, and typically in practice Lycomings don’t need tuned injectors, they just need to flow at the same rate. A GAMI tuned continental will yield a baby jar test that looks much like the one you’ve shown us.  Flows will be uneven but the cylinders will be getting even air/fuel ratio and therefore peek at the same time.

Barring some strange and unusual malfunction, A Lycoming engine should have ~equal air flow and  ~fuel flow to each cylinder in stock configuration. Given that yours doesn’t, I’d be more interested in finding out why then trying to “tune” the problem away with different volume injectors.

You should be able to run a Gami spread test at almost any altitude. 8500 should be fine. You just need to be able to get lean enough for the richest cylinder to peak. You are conducting this test at full throttle correct?

Edited by Shadrach
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5 hours ago, jkarch said:

Shadrach, what altitude should I be doing the lean test at? I typically have been doing it at full power and 8500 feet. I’m thinking of cleaning up my stock injectors and reinstalling them to test again. Had I known GAMIs weren’t useful for IO-360s I would have considered not getting them though they definitely made the engine run smoother even with the stock settings 400 hours ago.  I will have to look at the valve lift test.  Everyone including my mechanic has told me that cam lobe wear would have resulted in a useless engine by now because it’s gone on since I’ve owned the plane (300-400 with GAMIs) and I have put 7-800 hours in 7 years since buying it. The oil filter and analysis is clean and the idle is very smooth and power seems good but that’s subjective. One thing I don’t understand is why fuel flows become more uneven when the mixture is pulled out.

Follow the instructions for obtaining the Savvy Test flight profile data here: http://content.savvyanalysis.com/static/pdf/SavvyAnalysisFlightTestProfiles.pdf It should be done at WOT at a power level no more than 65%. 

Pulling off the rocker covers and measuring valve lift or depression height in comparison to an adjacent cylinder will give you a quick idea if you have a cyl that isn't getting enough air. This needs to be done with a warm engine though so the lifters are still fully pumped up with oil. Its important to realize that a worn cam lobe is not the only way to cause an excessively rich outlier cylinder. You could also have a leaky lifter that's not fully pumping up with oil or a bent push rod from a sticky valve or even dry valve lash clearance out of tolerance. An even less invasive method that I've had some clients us is to compare valve lift is with a borescope, a little more subjective; but it should tell you if you need to look any closer. 

Yes, you should have measured your gami spread before ordering them, since few io-360's need them, but that's not to say gami's can't improve your mixture and few io-360's really do need them - just not many.

You're getting good advice above.

Edited by kortopates
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Kortopates,Shadrach,  Carousam, CaptRJM, and TeeJayEvans, Thank you all for that information.  I will rerun the GAMI test per the Savvy Test Profile, and will also find a way to get the valve lift test done.  It does seem I have a hard time getting #3 and #4 to peak without roughness, unless I'm looking at the secondary peak, but it's also possible I'm not moving as slowly as the Savvy Test Profile suggests.  Regarding the cleaning in an ultrasonic bath, that would be worth doing especially for the fuel lines.  I think the injectors themselves are pretty clean but I might as well do that.  As for the uneven flow, that may only be part of the story, and there may be a combination of fuel issues and air issues, including valves.  It's strange,because the engine is extremely smooth and runs very well while rich, and it's also strange that the flows are not even.  I did call a company that deals with fuel metering today and found out that I should check the fuel servo as well to make sure the air intake part doesn't have any fuel staining in it, so I guess I have my work cut out for me.  I'll post as I get through these hurtles.  In the meantime, the engine does run smoothly, I just don't know what the story is with the actual GAMI spread.

 

-J

Edited by jkarch

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Running smoothly while rich is easy to accomplish.... the more rich the less noticeable fuel flow and airflow differences will become... when you get near peak, the wheels fall off this method... one cylinder will peak first, and go lean first, and will keep going lean until it stops burning...

Have you seen pictures of your exhaust valves?  Want a few?  :)

Often, people are are reviewing what went wrong in their monitor’s graphs...

Valves are supposed to rotate around their stems... when they don’t problems begin...

Somebody invented the dental camera for taking pictures of valves...

use the search... the pizza is good, other uneven discoloration is bad...

There is a ton of work to do that might not be necessary...

posting graphs from the engine monitor would help get to the point...

Any chance of making headway with the monitor?

Best regards,

-a-

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The problem with my monitor is it unfortunately is the UBG-16, which does not include fuel flow, so acquiring good data out of it is tough.  My method of finding peak is rolling back the mixture and finding peak for each individual EGT, then marking the value of fuel flow for which that happens.  However, I am wondering if perhaps I am not advancing the vernier slowly enough, and missing the main peak and then the only time I see a peak is the secondary peak on 1&2 when the engine runs rough.  3&4 have well defined peaks and troughs, but 1&2 is hard to find.  They are not quite so sharp but more a burble up then down just a few degrees, followed by a rise again that takes the engine to roughness around 1500F.  I need to actually rerun this test and photograph each peak as I find it.  Trouble is, I have to flip through each EGT to get the actual number then compare it to a separate fuel flow instrument.  If I had something like the new CGR30P, I could data log it and send it to SavvyAnalysis.  I'm strongly thinking about getting this new monitor.  It's possible there may be issues with some of the EGT channels too.

 

-J

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Can you see the state of the valves if you remove the valve covers, or do you need to borescope the cylinder through the spark plug hole?

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Ahhh....

Leaning using the Theory of relativity...

Just thought about this for somebody else...

 

One thing you could use in lieu of having FF meter... is a theory of relativity... not THE theory of relativity, but similar...

Imagine if you would...

 1) Let’s say you are in cruise...

2) You know how far out to pull the mixture knob to get in the neighborhood of the peak... so you go there...

3) You begin twisting the knob, somewhat slowly to see the first cylinder to peak... put a chalk /grease pencil mark on the mixture knob at the top... count the degrees of rotation of the knob to see all four cylinders peak...

4) If the first to peak and last to peak is in the same 360° of rotation of the mixture knob, that is pretty close... if one is far from peaking with the other three... you have relatively found the outlier, without a FF meter...!

5) from experience around here, something gums up the works... a deposit forms in the fuel injector and inhibits flow... the slowed flow causes an early peak... the extra fuel shows up in the other three injectors...

6) Ask your friends with a similar engine and a FF gauge...how many GPH do you see @20”MP before and after one rotation of the mixture knob...?

7) Relatively speaking, how many mixture knob rotations does it take to go from first peak to last?

I would rather have a FF gauge...

PP dream, not an actual procedure. Not from a CFI or mechanic...

We have one MSer that really liked his UBG16...

Best regards,

-a-

 

 

 

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Carusoam,  I don't even think I get a fraction of a GPH on a revolution on my vernier mixture!  I did notice something that was somewhat disconcerting, however.  Depending on mixture settings,  I see example #7 in the SavvyAnalysis page: https://www.avweb.com/news/maint/egt_and_cht_interpretation_198791-1.html

However, even though my gauge *occasionally* looks like #7 when partially leaned out where it seems 3&4 are at their peak but 1&2 are not, my temperatures are all inline, so there is no evidence of decreased CHT.  I think I've had this behavior for years too.  Example #7 does show an example cam lobe wear, but also says CHTs are reduced along with EGTs.  That's something I don't see. My CHTs stay all around the same, except for #3 which is a secondary CHT and runs 25-50F lower.  I will run some more tests then post some photos--

 

Best,

 

J

Edited by jkarch

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J,

I just grabbed this from another plane thread...

Check the remarks section in this ad.... last couple of lines...

This is somebody describing how he knows he needs a cam... (similar engine, O360, not an IO360...)

https://www.trade-a-plane.com/search?category_level1=Single+Engine+Piston&make=MOONEY&model=M20C+MARK+21&listing_id=2331685&s-type=aircraft

PP thoughts only, not a mechanic...

-a-
 

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21 minutes ago, jkarch said:

Carusoam,  I don't even think I get a fraction of a GPH on a revolution on my vernier mixture!  I did notice something that was somewhat disconcerting, however.  Depending on mixture settings,  I see example #7 in the SavvyAnalysis page: https://www.avweb.com/news/maint/egt_and_cht_interpretation_198791-1.html

However, even though my gauge *occasionally* looks like #7 when partially leaned out where it seems 3&4 are at their peak but 1&2 are not, my temperatures are all inline, so there is no evidence of decreased CHT.  I think I've had this behavior for years too.  Example #7 does show an example cam lobe wear, but also says CHTs are reduced along with EGTs.  That's something I don't see. My CHTs stay all around the same, except for #3 which is a secondary CHT and runs 25-50F lower.  I will run some more tests then post some photos--

 

Best,

 

J

A few things to consider. Normally secondary EGT readings run hotter not colder if they use a spark plug washer type thermocouple. A secondary EGT peak requires going very lean of peak EGT. It’s the result of a slow burning combustion event entering the exhaust down tube and directly heating the EGT thermocouple.

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I wonder if I’m focused on the wrong peak, those peaks are at high 1400F (1498F) with the fast probe. There’s a region where the egt initially climbs out of the 1300F range to 1400.  The fuel flow where I see what might be a secondary peak that I may be confusing as primary is around 8.8 GPH at 8500 feet (0C). In addition I think my fuel flow is off by a bit so that number may be 8.5 GPH. ROP tends to be around 10GPH as I recall.  I’ll have to double check... Makes me wonder if this is a combination of leaning techniques, uneven fuel flow or distribution and possibly valve or valve related.. I’ll keep digging.

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Jk...

Something is missing....

each cylinder peaks exactly one time.   

Mixture goes from ROP, to peak, to LOP until the engine quits.

How are you seeing a ‘second’ peak?

You should be seeing one peak per cylinder.

When leaning ROP, the first cylinder to peak is important...

When leaning LOP, the last cylinder to peak is important...

Does this make sense for you?  What is missing?

Best regards,

-a-

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