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  #41  
Old 09-01-2015, 06:47 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by BillL View Post
Here is the Shell answer man explanation - it sounds just like the wording of the Lycoming SB.
Thanks Bill! It is an interesting explanation.

I note that leaning for taxi would not by itself raise temperatures as noted.

Mighty tough to taxi an RV at 1200 RPM. If the explanation is true, there should be a correlation between long taxi times and sticking. Any field reports along that line?
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  #42  
Old 09-01-2015, 09:56 AM
jchang10 jchang10 is offline
 
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I usually bring RPMs only up to 1200. Not sure higher rpms are needed. I can get EGTs up to 1200 to 1300F by leaning slowly. Then pull mixture when it gets rough.
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  #43  
Old 09-01-2015, 10:58 AM
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az_gila az_gila is offline
 
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Location: 57AZ - NW Tucson area
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[quote=boomer;1010397]
Quote:
Originally Posted by Bill.Peyton View Post
[font="Arial"][size="2"]I thought I would post this in the RV10 list since it applies to the IO540 D4A5 typically installed in the RV10, although feel free to move it.


Lycoming Service Letter No. L197A (Supersedes Service Letter No. L197) January 19, 1988 (http://www.lycoming.com/Portals/0/te...Avoid%20Valve%) details a few techniques to minimize valve sticking, including not taxiing at idle and running up the engine to 1800 rpm before shut down.

-John
Not sure of the publication dates, but the Lycoming Flyer Key Reprints also talks about operation to reduce valve sticking, yet does not mention the 1800 rpm bit...

It is always best to reduce power in increments so that engine
temperature changes will occur gradually. It is also
beneficial to continue the engine cooling process after
landing by insuring that several minutes of engine operation
at 800 to 1200 RPM are allowed before shut down. At large
airports this is usually accomplished by the time taxi to the
parking area is completed. At airports where clearing the
runway puts the aircraft in the parking area, a short period of
additional operation in the 800 to 1200 RPM range prior to
engine shut down will allow temperatures to stabilize.


http://11hc.44rf.com/manuals/engine-...y_reprints.pdf

Around page 54
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  #44  
Old 09-01-2015, 11:59 AM
BillL BillL is offline
 
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Quote:
Originally Posted by DanH View Post
Thanks Bill! It is an interesting explanation.

I note that leaning for taxi would not by itself raise temperatures as noted.

Mighty tough to taxi an RV at 1200 RPM. If the explanation is true, there should be a correlation between long taxi times and sticking. Any field reports along that line?
I don't think we are just talking about leaning for temp, although that would greatly help. The actual peak combustion chamber temperatures are quite low at low manifold pressures (relative to 27"). Once, I was checking a 1967 Alfa Romeo Spider with 45 DOCE Weber carbs. It would not idle smooth enough for me. I had the bright idea of testing compression with the engine running. At a dead idle condition, the compression pressure was only 40 PSI. I would discharge the gage, and watch 6-8 counts as the pressure came up and peaked. Compare that to 170psi with the throttles open (not running) for 10: Cr. . Now think about the peak pressure of combustion and temps produced. I don't know what 1800 rpm manifold pressure is, but way higher than 900 rpm idle. I wish they had talked about the actual temperature needed for the lead bromide reaction, that would help.

The rest of the story: The DOCE's (one butterfly, one venturi, and one float per cylinder)have air volume and mixture adjustment at idle, in addition to throttle plate adjustments. By getting the air balanced, then the mixture tuned that throat in. Purred like a kitten.
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  #45  
Old 10-30-2018, 01:31 PM
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I found this thread because the current owner of my RV-8A (with parallel valve O-360) recently had a rough running engine and noticed it wasn't making full power during a formation takeoff. Local mechanic pulled the valve covers and the #1 valve is in bad shape, discolored and wobbly indicating significant guide wear. A couple other exhaust valves also indicate signs of wear. The airplane has been well maintained and flown regularly. Engine has 850 hrs on an Aerosport Power overhaul (new exhaust valves and guides installed at overhaul in 2002). It has dual Lightspeed ignition so CHTs run a bit hotter than they would with mags (typical of any elec ignition system), but not out of line with other RVs using stock engine/cowl arrangement. Using Exxon Elite 20W50 oil.

Quote:
Originally Posted by DanH View Post
Group...does field experience suggest angle valve engines exhibit less valve sticking?
Poking around on the internet I found this article which is over 20 years old but a good overview of Lycoming valve issues:

https://www.aopa.org/news-and-media/...and-powerplant

The article notes (related to DanH's question above) that parallel valve engines are more likely to have issues than angle valve engines. This is of interest to me as I'm building a -14A that will get an angle valve engine...but I'm still scratching my head as to why some folks with parallel valve engines have no issues running to TBO, and other (like my -8A) develop problems. The local A&P suggests not only doing the 400 hr 'wobble test' (Lycoming SB 333C) but actually reaming the exhaust valve guides every 400 hrs just as preventative maintenance on the O-360 (even if it passes the wobble test). Is anybody out there doing this?
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  #46  
Old 10-30-2018, 02:10 PM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Quote:
Originally Posted by czechsix View Post
I found this thread because the current owner of my RV-8A (with parallel valve O-360) recently had a rough running engine and noticed it wasn't making full power during a formation takeoff. Local mechanic pulled the valve covers and the #1 valve is in bad shape, discolored and wobbly indicating significant guide wear. A couple other exhaust valves also indicate signs of wear. The airplane has been well maintained and flown regularly. Engine has 850 hrs on an Aerosport Power overhaul (new exhaust valves and guides installed at overhaul in 2002). It has dual Lightspeed ignition so CHTs run a bit hotter than they would with mags (typical of any elec ignition system), but not out of line with other RVs using stock engine/cowl arrangement. Using Exxon Elite 20W50 oil.

Poking around on the internet I found this article which is over 20 years old but a good overview of Lycoming valve issues:

https://www.aopa.org/news-and-media/...and-powerplant

The article notes (related to DanH's question above) that parallel valve engines are more likely to have issues than angle valve engines. This is of interest to me as I'm building a -14A that will get an angle valve engine...but I'm still scratching my head as to why some folks with parallel valve engines have no issues running to TBO, and other (like my -8A) develop problems. The local A&P suggests not only doing the 400 hr 'wobble test' (Lycoming SB 333C) but actually reaming the exhaust valve guides every 400 hrs just as preventative maintenance on the O-360 (even if it passes the wobble test). Is anybody out there doing this?
We should note that there are different problems here. With sticking valves, it is caused by oil coking and sticking to the valve guide, reducing clearance. It is usually from excess heat on the valve, though one could argue that reduced oil flow can accelerate the issue as increased flow takes heat out of the valve.

Your problem outlined above, excessive valve guide wear/clearance, is different and typically caused by different conditions. Oil starvation is one reason, though there are several others, including bad geometry.

Larry
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