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  #11  
Old 12-08-2017, 07:46 PM
drone_pilot drone_pilot is offline
 
Join Date: Jan 2014
Location: Hobbs, NM
Posts: 194
Default 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..
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  #12  
Old 12-08-2017, 07:56 PM
drone_pilot drone_pilot is offline
 
Join Date: Jan 2014
Location: Hobbs, NM
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Quote:
Originally Posted by mahlon_r View Post
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/defau...es/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?
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  #13  
Old 12-09-2017, 12:09 AM
sstocker31 sstocker31 is offline
 
Join Date: Sep 2011
Location: Sherwood Park, Alberta, Canada
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Quote:
Originally Posted by drone_pilot View Post
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.
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  #14  
Old 12-09-2017, 04:28 AM
rv8ch rv8ch is offline
 
Join Date: Feb 2005
Location: LSGG
Posts: 2,131
Default Idler gear mismarked

Quote:
Originally Posted by Jrskygod View Post
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.
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  #15  
Old 12-09-2017, 07:53 AM
mahlon_r mahlon_r is offline
 
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Quote:
Originally Posted by drone_pilot View Post
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
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  #16  
Old 12-09-2017, 09:20 PM
drone_pilot drone_pilot is offline
 
Join Date: Jan 2014
Location: Hobbs, NM
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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.
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  #17  
Old 12-09-2017, 09:46 PM
tim2542 tim2542 is offline
 
Join Date: Aug 2009
Location: Redding,Ca
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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

Last edited by tim2542 : 12-09-2017 at 09:49 PM.
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  #18  
Old Yesterday, 03:55 AM
mahlon_r mahlon_r is offline
 
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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
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  #19  
Old Yesterday, 06:40 PM
drone_pilot drone_pilot is offline
 
Join Date: Jan 2014
Location: Hobbs, NM
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Quote:
Originally Posted by mahlon_r View Post
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.
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