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IO360-A1A Needs Help

drone_pilot

Well Known Member
Hello All,

I?m sorry that this post is so long but trying to provide plenty of detail...

Airport Elevation is 3600 feet.

I installed a used IO360-A1A engine on my 7A after having it rebuilt. It has always been hard to get the mixture lean enough at idle. Likewise, after flying and getting the engine hot it idled horribly after landing. I?ve read a lot of articles that made me feel this is normal but a few weeks ago the engine quit on final after pulling it back to idle and I landed about 100 feet short of the runway threshold. The only damage was a totaled threshold light, scuffed paint on the side of my nose wheel fairing, and my ego. :)

I immediately pulled the entire injection system off of the airplane and sent it to Airflow Performance. They overhauled the whole thing.....servo, flow divider, reduced the size of the restrictors, new injector lines. After installing it wasn?t as tough to get the idle leaned although I have a hard time getting a definite 50 rpm rise pulling lean to shutoff. I have a very light 3 blade Catto Prop if that makes a difference. I know the inertia is not as great with a metal prop.

I flew touch and go?s to stay in the vicinity of the airport and test the system at all power settings. The first two touch and gos went great. The the third touch and go, I got engine roughness after pulling the throttle to about the 1200 rpm range. I increased the the throttle up a tad to smoothness and forced the plane down. Once I had the runway made, I pulled throttle back to idle. As I was flaring, I could see the prop getting too slow. I slightly increased the throttle and saved the engine from dying. I taxied to the ramp and noticed the hot idle was much better than it had ever been. Some local pilots also commented on how much better it was running.

I taxied to the ramp discouraged by the roughness that I feel would have killed the engine at low rpm. I set the mixture to full rich. I slowly increased the throttle until about 1/2 inch before full throttle where the engine would completely lose power. Just like it was flooding out entirely. This repeated over and over again. Before takeoff, I always have leaned the engine so I didn?t know this was an issue. The lean was usually pulled out 1-1/2? before takeoff. Engine runs all the way up to full throttle with that setting although the static rpm is only about 2000 rpm on the Catto 3 bladed prop.

When the engine was rebuilt, the mechanic timed the engine. I purchased the piston stop, timing indicator, and mag timing light so I could verify the timing. My engine has a placard calling for 25 degrees before top dead center but I have read where Lycoming moved the spec to 20 degrees. When I checked the actual timing, I am seeing about 18.5 degrees before top dead center.

Would this timing cause the engine to drop out at full power? I am seeing 360-390 degree CHTs. Peak lean shows about 1425 degrees on the EGT.

Please help me to troubleshoot.
 
your timing shouldn't be an issue. What is the fuel pressure while all this is happening?. Merry Christmas, Mahlon
 
check plugs

I would pull all the plugs and try and get a reading on whats going on.
Maybe post the pics to see if anyone can help.
Will probably tell you if you are over lean or too rich.
Next I'd check for induction leaks, intake tubes seated correctly against the clys
rubber boots no holes. I would set timing correctly to 25.
If you an impulse mags, make sure the mag has "snapped" or impulse has fired before timing.
Let us know what you find.
 
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AFP idle

I've got the same engine and AFP system on my -6. Went thru the same scenario in setting my idle mixture - my first flight landing was dead stick when the engine died on short final. Make sure you're adjusting the idle setting when the engine is hot, a cold idle setting may not be ideal.
 
I am at 4,000 elevation (same as you for all purposes). I had heck trying to get the idle mixture to give me any rise at all when pulling idle cutt-off with my parallel valve engine. It sounded like a radial at idle but ran good at higher rpm. Taxiing in hot it would fart and backfire and I had to go full rich to help. Unlike yours mine has a stock Bendix RSA-5AD1 fuel servo. That didn't matter in my case. We tried to adjust idle mixture to no end and the number of turns on the idle mixture link was way out of spec. We even went as far as replacing the fuel servo with an exchange. Replacement didn't make any difference.

Shout out to BobRV4 for his post above. Amongst his checklist is one item we found. The one-piece induction tubes on the parallel valve engines use a large o-ring seal where they stab into the intake sump during assembly. Apparently the fellow who installed the induction tube for cylinder #2 "rolled" the seal when pressing in the tube or subsequently fitting it and didn't notice it. Thus I had a big honkin' induction leak there. Removal of the induction tube and rolling the seal straight and applying DC-4 prior to re-assembly made things fine and the engine ran normal. I encourage that to the o-ring type seals used at the sump end of the induction tubes be lubed prior to assembly and a subsequent inspection prior to first start as the seals can shift when aligning the flanges on the cylinder head end.

Jim
 
Thanks for all of the great advice! I'll begin troubleshooting and let you all know what I find out.

Mahlon - Fuel pressure runs pretty steady at 28 with the boost pump on and drops to 26-27 with boost pump off.

I also ran across a post early this morning (search XP-400 Still Coughing) where the timing between the cam and crank was off by one tooth and created almost an identical problem at full rich and high power as what I have. I also read that I can set the #1 cylinder to top dead center, pull the rocker cover to the #2 cylinder and check for both valves to be closed. Moving the prop left or right a little should open either the exhaust or intake valve depending on direction. At top dead center both should be closed. If one valve is open, then there is misalignment in timing between the cam and crank. While there tonight, I'll try this since it's not too big of a job to accomplish and may save a lot of tail chasing in the grand scheme of things if there is a timing error assembled in. I had a local mechanic rebuild the engine who is pretty good but after getting to know him better, I have seen him make mistakes. I feel it could be possible that he missed the timing on the gear teeth. I hope not but I'm going to check just to make sure.
 
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As I was reading the original post I was thinking the symptoms were exactly what I experienced in the past with a recently overhauled engine. The internal timing was off by one tooth. After going through the previously enumerated procedure as provided to me by a lycoming technical representative it was determined that the engine was mistimed. Upon further examination it was determined that the idler gear was mismarked. Once we reset the idler correctly the engine performed as it should. That was one expensive lesson as we chased a fuel problem for a long time without a cure.

The timing is pretty easy to check and I would do so since the engine was recently overhauled and the timing could have been set wrong. You might save a bunch of work and money.
 
I also read that I can set the #1 cylinder to top dead center, pull the rocker cover to the #2 cylinder and check for both valves to be closed. Moving the prop left or right a little should open either the exhaust or intake valve depending on direction. At top dead center both should be closed. If one valve is open, then there is misalignment in timing between the cam and crank.

Both valves are slightly open at TDC during the EX/IN stroke transition, though they may appear closed. You are not looking to verify that both are closed, only that a turn in one direction will equally close one and open the other. The behavior will be opposite in the other direction. If only one valve is moving, that is a clue that cam timing could be off.

Larry
 
Since the fuel pressure is good( I am am assuming that your instrumentation is accurate) I would vote for the valve timing as well. Valve overlap on number two should be happening when number one is at TDC. Valve overlap is as one is closing and the other is just opening. The procedure is listed on page 11 or 12 of the Lycoming troubleshooting guide.
https://www.lycoming.com/sites/default/files/SSP-475.pdf

If the valve timing is off the overlap will occur several teeth of the flywheel away from TDC not just one or two. If it is occurring within one or two teeth of tdc on the flywheel then it is OK and your feel of the valve movement is a little off.
Merry Christmas,
Mahlon
 
Update

So last night I went out and set the timing dead on at 25 degrees before top dead center. I also pulled rocker cover on #2 while #1 was still at TDC, both valves appeared closed. Moving the prop in one direction, I could see one valve moving, moving the prop in the other direction, I could get the other valve to move. I still don't feel confident in what I was looking for along with the proportion of prop movement to where I see valve movement. If anyone could send me a link to Lycomings document, I'd certainly appreciate it.

I took the airplane outside and heated the engine up to about 130 degrees oil temp and cylinders around 320. It was cold outside (at least for the Southwest about 50 degrees tops today). The engine idle fluctuates 710-780 rpm and MAP shows 9.9-10.1". It was very windy out of the North today so that probably had some effect on idle bouncing around. I am using the magnetos in conjunction with Dynon Skyview to get my tachometer reading.

With mixture full rich, I advance the throttle fully and smoothly. Things go great until 26" MAP and 2100RPM then advancing the throttle past that the engine loads up quickly like throwing 5 gallons of gas at it suddenly. RPMs drop off several hundred and I hear slight backfiring. When I lean the engine, I can get 2220 static rpm and 26.1 MAP. Keep in mind that I have a 3 bladed Catto cruise prop which digs into the wind at a steep angle so 2200 rpm static is what I'd expect. Also, field elevation is 3600' so not sure where MAP would sit closer to sea level.

Once again, if anyone can lead me to the Lycoming bulletin on how to check the cam to crank timing, I'd appreciate it. The local mechanic looked at it last night and said their is nothing wrong. Then again, he didn't know you could check the timing that way until I had mentioned it to him. I just want to make certain that is not the issue since I have already put a lot of time and money into this issue..
 
Since the fuel pressure is good( I am am assuming that your instrumentation is accurate) I would vote for the valve timing as well. Valve overlap on number two should be happening when number one is at TDC. Valve overlap is as one is closing and the other is just opening. The procedure is listed on page 11 or 12 of the Lycoming troubleshooting guide.
https://www.lycoming.com/sites/default/files/SSP-475.pdf

If the valve timing is off the overlap will occur several teeth of the flywheel away from TDC not just one or two. If it is occurring within one or two teeth of tdc on the flywheel then it is OK and your feel of the valve movement is a little off.
Merry Christmas,
Mahlon

Thanks Mahlon!

I did not see your post until after I had posted my update. The Lycoming procedure gives me better detail of what I need to look for. I am thinking this has to be the problem because it is too repeatable no matter what else I do. Once. The engine is pulled and the accessory cover is opened, is it a very easy job to align the gear teeth? I've seen how the marks need to align, I'm just wondering more what else has to come apart to fix the issue?
 
So last night I went out and set the timing dead on at 25 degrees before top dead center. I also pulled rocker cover on #2 while #1 was still at TDC, both valves appeared closed.

I noticed you put it to 25 degrees before TDC to set the timing, did you move it to TDC for the test?.....it should be right at TDC for this test.
Just in case you missed that.
 
Idler gear mismarked

As I was reading the original post I was thinking the symptoms were exactly what I experienced in the past with a recently overhauled engine. The internal timing was off by one tooth. After going through the previously enumerated procedure as provided to me by a lycoming technical representative it was determined that the engine was mistimed. Upon further examination it was determined that the idler gear was mismarked. Once we reset the idler correctly the engine performed as it should. That was one expensive lesson as we chased a fuel problem for a long time without a cure.

The timing is pretty easy to check and I would do so since the engine was recently overhauled and the timing could have been set wrong. You might save a bunch of work and money.
That's kind of scary. Another thing to check.
 
Thanks Mahlon!

I did not see your post until after I had posted my update. The Lycoming procedure gives me better detail of what I need to look for. I am thinking this has to be the problem because it is too repeatable no matter what else I do. Once. The engine is pulled and the accessory cover is opened, is it a very easy job to align the gear teeth? I've seen how the marks need to align, I'm just wondering more what else has to come apart to fix the issue?

Once the accessory case is off, it is easy to correctly align the timing marks on the gears. The Idler gear between the crank gear and the cam gear can easily be removed (slides in and out of engagement) and then you can turn the crank gear only until the marks on it get to the right place to match the marks on all three gears.
Merry Christmas,
Mahlon
 
Today I went to the airport armed with the Lycoming instructions ( Thanks Mahlon! ) to check cam to crank timing. Pulled the top plugs, put cylinder #1 on the compression stroke, and found top dead center. Pulled rocker cover from the #2 cylinder. As soon as I move the prop in the direction of rotation, the intake valve began opening according to the procedure. Unless, I just don't get it, I am pretty sure this engine is timed correctly.

Test #1
I put the engine back together and performed another test run just to see if I wasn't holding my mouth just right the first time. I got the same results. With engine set to full rich and advancing the throttle the engine begins to flood out about 3/8" before WOT. RPMs drop dramatically and just before that I can see the EGTs dropping rapidly. Reducing throttle recovers the engine.

Test #2
Don at alrflow performance mentioned that I could have turbulence at the air intake, so I removed the snorkel and ran the engine with the throat wide open. It looked like I could get the mixture to about 1/4" from full rich before things fell apart but overall, the result was the same. EGTs start dropping off, then the engine loads up and sounds absolutely sick.

I'm stuck at this point. If the engine is timed correctly, what else could it be? The entire injection system was just overhauled at Airflow Performance. Could the servo be pumping too much fuel at high rpm? When the engine is leaned, it develops power to full throttle.
 
From your description of the timing test I’m not sure you have checked it yet as you only mentioned the intake valve.
With #1 at TDC #2 valves (companion cylinder) are in the overlap position, ie BOTH valves should be moving as the crank passes through TDC. The exhaust is closing and the intake opening. A few degrees before TDC the intake is still closed, a few after TDC the exhaust is closed.
BTW, with the crank at TDC, you can rock the crank 2-3 degrees back and forth either side of TDC very easy as the pistons do not move. You can detect TDC very easy this way and confirm the marks on the ring gear support you are using are at least close.
Hope this is helpful.
Tim Andres
 
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what is the fuel flow when running bad full rich at full power and what is it after you lean out and get to 2200rpm? egt at the same data points?
Mahlon
 
what is the fuel flow when running bad full rich at full power and what is it after you lean out and get to 2200rpm? egt at the same data points?
Mahlon

I can't answer that one. I temporarily removed the red cube when reinstalling the overhauled injection system as I wanted to relocate it in order to keep some tight bends out of my fuel lines. I didn't realize that I would have these issues before removing it.
 
Let me ask the question this way. My airport is at 3650' MSL (5100' density altitude at time of test). I have the idle set to give about a 50rpm rise while leaning to shutdown. If I leave the mixture at full rich at this altitude and give full throttle, should my engine run wide open there without any leaning? Right now I can get 26.1 MAP and 2200 static rpm (fixed pitch Catto 3 blade) as long as I lean the engine. It begins flooding around 2000-2100 rpm if I Leave the mixture in full rich.
 
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I can't say specifically for YOUR engine but in general, with a carb. or FI on any Lycoming at 3650 ASL, you would expect to lean it some for best power. At 4300 ASL I am normally about 25% mix lever throw arc lean of full forward, for take off power, but still safely rich of peak. The EGTs are still below my 2400 ft full rich /full power take off values.
 
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Isn't there an enrichment circuit on the servo that will give additional fuel at the last little bit of throttle travel, to keep the engine fat and happy at full power? Could that be set incorrectly and delivering too much additional fuel for those last few manifold pressure inches?
 
Isn't there an enrichment circuit on the servo that will give additional fuel at the last little bit of throttle travel, to keep the engine fat and happy at full power? Could that be set incorrectly and delivering too much additional fuel for those last few manifold pressure inches?

Hi Greg,

I am not aware of that. The RSA servo is kinda built like an Apple Mac. They give you an idle mixture setting and an idle speed setting. Other than that, there isn't anything else for a regular guy like me to set. Leaning, it seems to run fine. I'm just wondering if I should expect to leave it full rich and go full throttle without the thing flooding out on the last quarter inch of throttle at my altitude up here on top of the Caprock.
 
RSA

Hi Greg,

I am not aware of that. The RSA servo is kinda built like an Apple Mac. They give you an idle mixture setting and an idle speed setting. Other than that, there isn't anything else for a regular guy like me to set. Leaning, it seems to run fine. I'm just wondering if I should expect to leave it full rich and go full throttle without the thing flooding out on the last quarter inch of throttle at my altitude up here on top of the Caprock.

The RSA Servo should run just fine at your elevation when set to full rich. The RSA servo will actually flow less fuel at altitude then at sea level,when set to full rich mixture.

Is it possible that you have something going on that is fooling you into thinking the engine is going too rich, when the problem is something else? Perhaps your fuel flow is actually falling off when it exceeds a certain flow due to a piece of debris or a leak somwhere on the ?suction? side of the fuel system?

Skylor
RV-8
 
The RSA Servo should run just fine at your elevation when set to full rich. The RSA servo will actually flow less fuel at altitude then at sea level,when set to full rich mixture.

Is it possible that you have something going on that is fooling you into thinking the engine is going too rich, when the problem is something else? Perhaps your fuel flow is actually falling off when it exceeds a certain flow due to a piece of debris or a leak somwhere on the ?suction? side of the fuel system?

Skylor
RV-8

I took my Red Cube off in order to relocate it for better fuel line routing. A mechanic was watching it while I was running it up at full rich. As soon as my RPMs started dropping off at full throttle, he said it was putting out a lot of black smoke. That's why I would say that I am going too rich. Even though my RSA is freshly overhauled, is this a possible failure mode of an RSA servo?
 
When you can answer Mahlon's questions, you'll likely find the solution.

IMO, at that DA, you will need to lean the mixture to get full power. I typically start leaning at around 2000' to maintain takeoff EGTs of 1200-1250 near sea level.
 
When you can answer Mahlon's questions, you'll likely find the solution.

IMO, at that DA, you will need to lean the mixture to get full power. I typically start leaning at around 2000' to maintain takeoff EGTs of 1200-1250 near sea level.

I ordered new fuel lines from TS Flightlines today so hopefully I can answer those fuel flow questions shortly. And what you are saying leads to the basis of my question. Right now I cannot leave my mixture full in and get the throttle to full in before the engine goes to crud on the high end. Leaning, I can get there just fine. I just want to know that my engine is running as should be expected for a fuel injected engine. It's a bit of a different animal than the carbureted engines that I have used in the past.
 
what is the fuel flow when running bad full rich at full power and what is it after you lean out and get to 2200rpm? egt at the same data points?
Mahlon

Hi Mahlon,

I finally have some data for you.

My airport elevation 3650 MSL
Density Altitude at time of test 5110

Leaning the engine I could turn 2210 rpm static, 9.5 gph, 25.8 MAP at full throttle.

Leaving engine full rich I can only get to 2100 rpm static, 25.4 MAP, and advancing throttle past that goes to 15.2gph and floods the engine and drops the RPMs dramatically with maybe 3/8" of travel left in the throttle. It showed about 14.2gph before advancing the throttle.

Would this be numbers to be expected? The prop is fixed pitch Catto 3 blade cruise prop. It takes a pretty big bite of air.
 
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