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  #11  
Old 08-24-2015, 09:08 PM
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Bill.Peyton Bill.Peyton is offline
 
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I will check it out tomorrow and see .....
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  #12  
Old 08-25-2015, 01:09 AM
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az_gila az_gila is offline
 
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Quote:
Originally Posted by Ivan Kristensen View Post
Bill,
Check and see if you if your cylinders are marked with the number 3 with a circle around it. You can find this mark on the top of each cylinder on the bottom left hand corner next to the valve cover near the drain tube.

If a circle with the number 3 is stamped in this location then the SB referred to above does not apply. Now if you do have this symbol and still have a valve sticking problem then obviously something else is going on.

I now have 685 hours on my engine and it continues to run great. I run mine exactly the same way you do yours with mostly long cross country flights and always LOP. The only difference is that I use Aeroshell W100 Plus with no other additives.
Don't do the above, read the Lycoming documents carefully instead.

SI 1485A calls for a letter "C" in a circle stamped on the cylinder boss for the drain back fitting.

http://www.caa.si/fileadmin/user_upl...sb_SI1485A.pdf

And in answer to a previous question I had, ECI cylinders have the same markings

http://eci.aero/pdf/03-11.pdf

Superior says to follow the Lycoming instructions and also provide Hi-Chrome guides

http://www.superiorairparts.com/down...ers/L00-21.pdf

The dates look like 1998 for Lycoming, 1999 for Superior and 2003 for ECI for the new hi-chrome guides, but the presence of the stamped marking is the key.

As always, RTM
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Last edited by az_gila : 08-25-2015 at 01:18 AM.
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  #13  
Old 08-25-2015, 01:10 AM
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Quote:
Originally Posted by Bill.Peyton View Post
Ivan,
Do you know what the significance of the "3" is?
Absolutely none... but the "C" might stand for "Hi-Chrome"...
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Half completed RV-10 QB purchased
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Grumman Tiger N12GA - flying
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  #14  
Old 08-25-2015, 07:57 AM
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Bill.Peyton Bill.Peyton is offline
 
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According to the SB, all cylinders manufactured after 1998 use the newer "C" guide. This was a factory new engine in 2011. I would conclude that it must have the newer guide. I will check next time the cowling is off to be sure.
I suspect that the excessive amount of oil usage, 1 qt every 5 hours, during break-in and for at least 50 hours after that, could have caused this premature accumulation around the guides.

The fact that the hesitation is no longer is further evidence that the guide was the issue. With all compressions being greater than 76/80, I don't believe that I have a burned valve or seat. I will give it a few more hours before I pronounce this totally resolved.
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  #15  
Old 08-25-2015, 09:26 AM
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i had my mechanic do the 388 SB on the exhaust valves. it took him an hour to do it. i had everything ready for him. $80 well spent. all measurements were wiithin tolerences.
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  #16  
Old 08-25-2015, 09:32 AM
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Ivan Kristensen Ivan Kristensen is offline
 
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Default Cylinder identification

I stand corrected! It is the "C" stamped in the location mentioned above that indicates the "Hi-Chrome" content in the valve guides. I got my information from an "engine man" at a well known engine re-builder, which proves once again that event "Experts" get it wrong once in a while. I suspect that he just misspoke but I will try to find out what the circled "3" stands for.

In any event, Bill's original post as well as subsequent posts brought an issue to the fore which we all can benefit from and also links to the correct information.
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  #17  
Old 08-25-2015, 10:46 AM
jchang10 jchang10 is offline
 
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Can someone do a "nice" detailed writeup with big pretty pictures like the other thread, too? My head is spinning with the Lycoming instructions.
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  #18  
Old 08-25-2015, 11:40 AM
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Quote:
Originally Posted by Ivan Kristensen View Post
I stand corrected! It is the "C" stamped in the location mentioned above that indicates the "Hi-Chrome" content in the valve guides. I got my information from an "engine man" at a well known engine re-builder, which proves once again that event "Experts" get it wrong once in a while. I suspect that he just misspoke but I will try to find out what the circled "3" stands for.

.....
"3" and "C" sounds like an accent problem, eh....

Anyway, it really says that it is best to confirm important data by going back to the manufacturer's data, it was really easy to find with Google - don't do a Tim Allen.
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  #19  
Old 08-25-2015, 08:38 PM
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Bill.Peyton Bill.Peyton is offline
 
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Someone asked, so I thought I would create a summary of the Lycoming Sticky Valve Issue.

Lycoming has several Service Instructions dealing with this topic. It has been around a long time. It affects all Lycoming Engines. This issue manifests itself as a miss or hesitation and is the result of a sticking exhaust valve. This does not affect the intake valve. This is due to the Intake Valve being continually flushed with cool fuel and some amount of oil which leaks around the guide. On the intake stroke this material is sucked in around the guide and also through the intake port when the valve is open. This keeps the intake guide relatively immune to build up on the guide. On the other hand, the Exhaust Valve guide gets blasted with hot gasses as it opens to allow the combustion products to exit. These hot gasses help form lead and oil deposits on the guide and on the valve stem external to the guide in the exhaust port. A better explanation of this is contained in Lycoming Service Letter 1425 A. You can read and download it here.... http://www.lycoming.com/Portals/0/te...20Sticking.pdf

Lycoming Service Bulletin 388C describes a procedure whereby the exhaust valve guide-to-stem clearance can be determined using a fixture clamped on the cylinder head. This procedure is non-invasive and designed to identify if you have or may be close to having an issue with a sticking exhaust valve. You can read the procedure and download it here http://www.lycoming.com/Portals/0/te...0Condition.pdf

Sometime in the late nineties, Lycoming redesigned the exhaust guide to address this issue. Lycoming Service Bulletin 485A describes the nature of the redesign and how to identify if you have the newer design. The service bulletin can be read and downloaded here.... http://www.lycoming.com/Portals/0/te...0Procedure.pdf

In summary, Lycoming recommends that you should either have your exhaust guides tested or reamed out at either 400 hours of service for the older guides, or 1000 hours of service if you have the newer designed guides. But.... this does not guarantee that you won't have the issue prior to the aforementioned time in service. If you fail to recognize the slight hesitation or burble and continue to fly without inspection, you run the risk of the valve severely sticking and coming into contact with the piston. This will undoubtedly ruin your day. The key is to recognize the symptom and maintain your engine.

I hope the summary is useful. If anyone finds any errors or omissions please let me know.
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Last edited by Bill.Peyton : 08-25-2015 at 08:40 PM.
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  #20  
Old 08-25-2015, 09:47 PM
BillL BillL is offline
 
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Thanks for the summary Bill. A little different story, but not to affect the end, and that is the heat transfer process of the exhaust valve. The exhaust valve is indeed heated by the exhaust gas, and it is cooled by the time on the seat, and through the stem. Neither are good, cool, heat sinks. The guide must have some lubrication, and does pick up oil from the top. It will migrate down the stem, but in most engines that path is cool enough not to coke the oil. In our Lycs/Clones it is not cool enough. While some of the combustion products are deposited on the valve and stem, it is very unlikely that it is the source of these deposits. Most guides have a relief cut in the lower part to shroud the stem and prevent combustion deposits from traveling back up the stem. I have not done measurements on this engine design. The likely cause of the issue is the oil coming down the guide coking and reducing the stem/guide due to the high temperatures in the stem/guide area.

Edit: This is a fundamental engine design issue. The temps caused coking that caused the guides to wear, so they improved the wear resistance of the guides, now they stick because the root cause remains. The root cause is the guide wall temperature is too high. Running LOP, cooler EGTs, and CHT's will certainly help, if not eliminate, the sticking. The challenge will be the break-in conditions. Cool ambients and leaning will help to the point that CHT and cooling is not compromised.

None of this changes the SB and our vigilance to recognize the onset of an issue.
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Last edited by BillL : 08-25-2015 at 09:57 PM.
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