engine roughness, leaning

Guest Discussion
1

I have a recent experience to report that I believe will be of interest.

I own 952DS (the 100th SR20). During its first sixteen hours of operation the engine ran flawlessly. Between hours sixteen and twenty, I experienced periodic vibration. I surmised that this was a fouled plug (after all, a lot of oil blew through the engine before the rings seated) so was not overly concerned.

When the periodic vibration became more frequent, I started to trouble shoot. I eliminated airframe causes, as with the engine at flight idle and a high airspeed (in a dive) the vibration was not there. Likewise, my instincts told me it was not the prop.

By twenty hours the vibration was constant in flight, but absent on the ground. I had the plugs and injectors checked, as well as a compression test. Two plugs were somewhat fouled, but compression was excellent. The aircraft ran great on the ground, but at altitude the vibration persisted. I grounded the airplane, and waited for a visit from the Continental rep.

Here’s what it was: the fuel pump lost some of its initial efficiency as it broke in. Although this loss of pressure was very slight, when combined with the altitude-compensating aneroid there was inadequate fuel flow in flight. The vibration was pre-detonation. Yikes! Even with the engine peaked, and then enriched, not enough fuel was getting to the engine. The fix took about thirty minutes, and consisted of checking metered and non-metered flows, and increasing fuel pressures slightly. Incidentally, the pressure readings prior to adjustment were within the tolerances specified by Continental–Cirrus had set the engine up correctly, this is simply a combination of post-delivery fine tuning, and a finicky system. Wish that damn aneroid didn’t exist.

One final comment–I’ve owned a bunch of airplanes in the past twenty years, and the suggestion that the SR20 should be flown lean of peak just plain bugs me. It is counterintuitive to everything I thought I knew about engines. While it makes for impressive economy numbers, and enhances the range statistics, I’m not doing it.

While I’m sure it works, I personally don’t think this type of operation is consistent with making TBO. Every mechanic I’ve talked to, including those with intimate knowledge about Continental engines, shares this opinion. So as for me, I’m going to run the engine 50-75 degree rich of peak.

2

I have a recent experience to report that I believe will be of interest.

… (report omitted)

David,

Nice report. Thanks for posting it.

One final comment–I’ve owned a bunch of airplanes in the past twenty years, and the suggestion that the SR20 should be flown lean of peak just plain bugs me. It is counterintuitive to everything I thought I knew about engines. While it makes for impressive economy numbers, and enhances the range statistics, I’m not doing it.

While I’m sure it works, I personally don’t think this type of operation is consistent with making TBO. Every mechanic I’ve talked to, including those with intimate knowledge about Continental engines, shares this opinion. So as for me, I’m going to run the engine 50-75 degree rich of peak.

You might want to read http://www.avweb.com/articles/pelperch/pelp0018.html>this and check out the [GAMI web site.

They make convincing cases for running lean of peak. I understand that since SR20’s have a tuned induction system, they get some of the same benefit (e.g., running smoothly lean of peak) as GAMI-jector equipped engines.

-Mike](http://www.gami.com)

3

One final comment–I’ve owned a bunch of airplanes in the past twenty years, and the suggestion that the SR20 should be flown lean of peak just plain bugs me. It is counterintuitive to everything I thought I knew about engines. While it makes for impressive economy numbers, and enhances the range statistics, I’m not doing it.

While I’m sure it works, I personally don’t think this type of operation is consistent with making TBO. Every mechanic I’ve talked to, including those with intimate knowledge about Continental engines, shares this opinion. So as for me, I’m going to run the engine 50-75 degree rich of peak.

I bet if you run ROP your cylinder head temps are going to be close to 380 to 400 degrees (very high and very bad). Running LOP or even peak EGT at 65% power will bring them down to less than 350 or 360 (or lower) and your engine will last a lot longer. For more info, check out the AVweb articles (www.avweb.com) re: Pelicans Perch and Big Bore Continentals. There is also information on the gami injectors site (ok, the SR20 continental does not have gami’s but it does have a well crafted and reasonably balanced induction system).

Continental recomends running peak EGT at 65% power or less. You flat out can not hurt a continental engine by running peak EGT or LOP at 65% power or less (cruising only…NOT during the climb out!).

And most of the mechanics are flat out wrong and misinformed about leaning procedures. Ours told us to run our big bore continental at 75 degrees ROP. The cylinder head temps were way to high (390…enough to ruin a big jug in heartbeat) we backed off to 65% power and 50 degrees LOP. Everything is much much cooler (cyl head temps of 320 degrees) and the engine runs smoother and quieter. We lose about 7 knots but the ride is quieter and the engine loves it.

I urge you to make your own decision based on the facts. And don’t take my word for it. You should take the time to really learn what’s going on in your engine with regards to leaning and what really causes pre-detonation. You will be a safer pilot with a fatter checkbook.

Mark

4

While waiting for my Cirrus, I have been flying a Cessna 182 with a Continental 470. The Cessna Pilots Accociation (CPA)puts out a lot of good information from a full time staff of very experienced and knowledgable folks. Contrary to what I had heard from mechanics and CFIs in the past, CPA strongly recommends agressive leaning below 65% for Continentals. They have a whole technical bulletin devoted to this and it is a frequently asked and answered question in their magazine and weekly electronic newsletter.

Lou

I have a recent experience to report that I believe will be of interest.

I own 952DS (the 100th SR20). During its first sixteen hours of operation the engine ran flawlessly. Between hours sixteen and twenty, I experienced periodic vibration. I surmised that this was a fouled plug (after all, a lot of oil blew through the engine before the rings seated) so was not overly concerned.

When the periodic vibration became more frequent, I started to trouble shoot. I eliminated airframe causes, as with the engine at flight idle and a high airspeed (in a dive) the vibration was not there. Likewise, my instincts told me it was not the prop.

By twenty hours the vibration was constant in flight, but absent on the ground. I had the plugs and injectors checked, as well as a compression test. Two plugs were somewhat fouled, but compression was excellent. The aircraft ran great on the ground, but at altitude the vibration persisted. I grounded the airplane, and waited for a visit from the Continental rep.

Here’s what it was: the fuel pump lost some of its initial efficiency as it broke in. Although this loss of pressure was very slight, when combined with the altitude-compensating aneroid there was inadequate fuel flow in flight. The vibration was pre-detonation. Yikes! Even with the engine peaked, and then enriched, not enough fuel was getting to the engine. The fix took about thirty minutes, and consisted of checking metered and non-metered flows, and increasing fuel pressures slightly. Incidentally, the pressure readings prior to adjustment were within the tolerances specified by Continental–Cirrus had set the engine up correctly, this is simply a combination of post-delivery fine tuning, and a finicky system. Wish that damn aneroid didn’t exist.

One final comment–I’ve owned a bunch of airplanes in the past twenty years, and the suggestion that the SR20 should be flown lean of peak just plain bugs me. It is counterintuitive to everything I thought I knew about engines. While it makes for impressive economy numbers, and enhances the range statistics, I’m not doing it.

While I’m sure it works, I personally don’t think this type of operation is consistent with making TBO. Every mechanic I’ve talked to, including those with intimate knowledge about Continental engines, shares this opinion. So as for me, I’m going to run the engine 50-75 degree rich of peak.

5

One final comment–I’ve owned a bunch of airplanes in the past twenty years, and the suggestion that the SR20 should be flown lean of peak just plain bugs me. It is counterintuitive to everything I thought I knew about engines. While it makes for impressive economy numbers, and enhances the range statistics, I’m not doing it.

While I’m sure it works, I personally don’t think this type of operation is consistent with making TBO. Every mechanic I’ve talked to, including those with intimate knowledge about Continental engines, shares this opinion. So as for me, I’m going to run the engine 50-75 degree rich of peak.

I bet if you run ROP your cylinder head temps are going to be close to 380 to 400 degrees (very high and very bad). Running LOP or even peak EGT at 65% power will bring them down to less than 350 or 360 (or lower) and your engine will last a lot longer. For more info, check out the AVweb articles (www.avweb.com) re: Pelicans Perch and Big Bore Continentals. There is also information on the gami injectors site (ok, the SR20 continental does not have gami’s but it does have a well crafted and reasonably balanced induction system).

Continental recomends running peak EGT at 65% power or less. You flat out can not hurt a continental engine by running peak EGT or LOP at 65% power or less (cruising only…NOT during the climb out!).

And most of the mechanics are flat out wrong and misinformed about leaning procedures. Ours told us to run our big bore continental at 75 degrees ROP. The cylinder head temps were way to high (390…enough to ruin a big jug in heartbeat) we backed off to 65% power and 50 degrees LOP. Everything is much much cooler (cyl head temps of 320 degrees) and the engine runs smoother and quieter. We lose about 7 knots but the ride is quieter and the engine loves it.

I urge you to make your own decision based on the facts. And don’t take my word for it. You should take the time to really learn what’s going on in your engine with regards to leaning and what really causes pre-detonation. You will be a safer pilot with a fatter checkbook.

Mark

Thank you for your response Mark. You’ve got me thinking, but also confused. During the post-adjustment flight with the Continental factory rep he also opined that ROP would be preferable to LOP operation, despite the training material from Wings Aloft, etc. In fact, his opinion was that ROP would in this application make achieving TBO without a top more likely. What’ya think?

6

I also enjoyed and agree with Mark’s comments. It’s worthwile looking at the Avweb material and reading the articles on the GAMI website.

Heat is the destructive force in engines. Specifically, and a good deal of research has gone into this, CHT’s in excess of 400-415 degrees will begin IMMEDIATE deformation of the heads. All it takes is ONE overtemp event and you may be on your way to an early top overhaul.

Further, the single probes installed in most engines typically are at the coolest spot. The infomation that you want is the hottest. So, you may lean to 50 ROP but you actually may have one EGT above peak! But, as Mark points out, the engine killer is the CHTs. If you run at 65-70% and keep the CHTs down (hopefully 350-380) and use the aircraft on a regular basis, you should expect long life from your engine.

My two cents…

Thank you for your response Mark. You’ve got me thinking, but also confused. During the post-adjustment flight with the Continental factory rep he also opined that ROP would be preferable to LOP operation, despite the training material from Wings Aloft, etc. In fact, his opinion was that ROP would in this application make achieving TBO without a top more likely. What’ya think?

7

All I can say is JPI or GEM or ARNAV (someday)…

Any engine monitor worth it’s salt would have told you what was going on. No guess work at all. No potentially damaging extension of a flight. And most importantly to me, EARLY WARNING of any developing problem, including, heaven forbid, ones that are going to cost you an engine.

Consider if you KNEW five minutes before your engine was going to fail, how much greater your chances for a safe ending would be.

8

All I can say is JPI or GEM or ARNAV (someday)…

Any engine monitor worth it’s salt would have told you what was going on. No guess work at all. No potentially damaging extension of a flight. And most importantly to me, EARLY WARNING of any developing problem, including, heaven forbid, ones that are going to cost you an engine.

Consider if you KNEW five minutes before your engine was going to fail, how much greater your chances for a safe ending would be.

AMEN! You don’t have an engine monitor, GET ONE! I am a believer. Don’t wait for ARNAV to display it. GEM or JPI … check 'em out!