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  #1  
Old 06-10-2022, 10:01 PM
UrbanM UrbanM is offline
 
Join Date: May 2019
Location: Salt Lake
Posts: 59
Default Compression Ratio

Dear list.
Had an issue come up during engine runup that is going to cause me to have to replace a cylinder. I have an experimental version of a 0-320 E2D wide deck with 9.2 C/R. Due to prior history I am considering a top overhaul on the other 3 and while I am at it I may consider changing the compression ratio back to a more stock 8.5. The engine data plate shows 9.2 so would I need to change this? Would it be considered a major change or alteration? If anyone has been through this tell me what you think.
Thanks,
Kirk

Last edited by UrbanM : 06-11-2022 at 07:29 AM. Reason: add dialogue.
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  #2  
Old 06-11-2022, 07:03 PM
Nashpdman Nashpdman is offline
 
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Location: Nashville
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Quote:
Originally Posted by UrbanM View Post
Dear list.
Had an issue come up during engine runup that is going to cause me to have to replace a cylinder. I have an experimental version of a 0-320 E2D wide deck with 9.2 C/R. Due to prior history I am considering a top overhaul on the other 3 and while I am at it I may consider changing the compression ratio back to a more stock 8.5. The engine data plate shows 9.2 so would I need to change this? Would it be considered a major change or alteration? If anyone has been through this tell me what you think.
Thanks,
Kirk
NOT an expert! But here's my thoughts. Do you hold the repairman's certificate? If so, it's my understanding you can do whatever you want. What's the valve issue? There are methods to lap valves in place and maybe save the cylinder?
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  #3  
Old 06-12-2022, 12:55 AM
BobTurner BobTurner is online now
 
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Originally Posted by Nashpdman View Post
NOT an expert! But here's my thoughts. Do you hold the repairman's certificate? If so, it's my understanding you can do whatever you want. What's the valve issue? There are methods to lap valves in place and maybe save the cylinder?
The Repairman certificate lets the holder sign off the annual condition inspection. Period. Nothing else. Anyone may legally work on an EAB aircraft. Experimental engine, data plate means nothing. The only legal question is whether or not this is a major change, requiring a return to phase 1 OpLimits. Best not to guess: ask a DAR or call your FSDO.
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  #4  
Old 06-12-2022, 06:33 AM
UrbanM UrbanM is offline
 
Join Date: May 2019
Location: Salt Lake
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Thanks for the responses, guys! Bob, you nailed it, its the legal question. Local FSDO has not been helpful with amateur built stuff and EAA had a very knowledgeable informative staff but many of them were layed off during COVID. To top this off my local and highly regarded DAR retired recently and left a huge void.
So here is the back story; I purchased the plane from from the builder who had an experimental 320 E2D built from parts (And with a Data Plate) by a repudiable shop (Whose name I won't mention). At around a hundred hours an intake valve stuck open which bent the pushrod and resulted in a landing at the nearest airport. Cylinder assembly replaced and then at the next condition inspection low compression on another cylinder caused by the ring gaps being all lined up. That cylinder was replaced. I bought the plane about 200 hours later and figured the engine issues were behind me. Compressions were excellent, oil usage was 1 qt per 25 hours and the oil analysis and filter inspection were well within limits at every change. At 385 hours an intake valve on another cylinder broke near the top of the stem and decided to exit the engine by busting a hole in the top of the cylinder. I can post pictures but some viewers may find them disturbing.
The paperwork shows all new Lycoming valves were used and I have stacks of yellow tags for all the parts that were not new. I am at a loss to understand how a clean well built engine can have these issues. I spoke with the shop in Alamosa Co and they said they have never heard of a stuck intake valve (Plenty of exhaust valves of course). So my options are replace the cylinder assembly with the big viewing port in the top, or top all 4 cylinders to make sure I have fresh quality stuff, or lastly, the local engine shop can do an IRAN for 6250. plus parts. In the interest of protecting my sanity I may just have the shop tear the whole thing down so I can be assured it is all within spec and serviceable. I am not blaming my issues on the C/R but I am contemplating returning to stock to see if this might help.
Sorry for the long winded post. Not doing any of this to be a Karen or throw a shop under the bus. If anyone else has had problems with a low time engine you are not alone.
Thanks!i

Last edited by UrbanM : 06-12-2022 at 07:12 AM. Reason: spelling
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  #5  
Old 06-12-2022, 07:12 AM
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jcarne jcarne is online now
 
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Originally Posted by UrbanM View Post
I can post pictures but some viewers may find them disturbing.
I'm betting most of us would not find them disturbing.
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  #6  
Old 06-12-2022, 09:38 AM
UrbanM UrbanM is offline
 
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I'm betting most of us would not find them disturbing.
This is the exterior obviously. The borescope pics are the usual hammered piston and cylinder stuff. I am grateful this happened on the ground and that it went out of the top of the cylinder and not through the top of the piston where it would have done more damage. The exhaust valve looks untouched.
Kinda new to piston engine aircraft ownership. I've had gliders for the past 20 years and only about 2300 hours of piston time and except for a stuck exhaust valve on an 0-360 power Scout I've never had any issues. I figured I would buy a plane with a well documented engine and stay within Lycoming limitations and careful maintenance I would be OK. So far during disassembly there is nothing to indicate any corners were cut.
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Last edited by UrbanM : 06-12-2022 at 09:41 AM.
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  #7  
Old 06-12-2022, 11:11 AM
lr172 lr172 is offline
 
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Stuck intake valves are pretty uncommon. The fact that you had one, as well as another broken one, I suspect someone left the valve guides too tight. They are installed undersized and reamed to proper size by the installer. Possibly a bad batch of valves. I would wash my hands of those cylinders and start fresh with new or have them overhauled by a good shop with all new valves and guides.

FYI, you don't get poor compression from having the ring gaps lined up. Highly pressurized air will turn a sharp corner almost as easily as going straight through two gaps. Rings are always moving and it is not uncommon for the gaps to be aligned at various points in there service life. If that were a real issue. the manufacturers would have installed something to keep them from rotating. Yes, we install them offset and hope they rotate at the same rate, but often they don't.

Larry
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Last edited by lr172 : 06-12-2022 at 11:18 AM.
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  #8  
Old 06-12-2022, 02:06 PM
BobTurner BobTurner is online now
 
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Originally Posted by lr172 View Post

FYI, you don't get poor compression from having the ring gaps lined up. Highly pressurized air will turn a sharp corner almost as easily as going straight through two gaps. Rings are always moving and it is not uncommon for the gaps to be aligned at various points in there service life. If that were a real issue. the manufacturers would have installed something to keep them from rotating. Yes, we install them offset and hope they rotate at the same rate, but often they don't.

Larry
+1. While having the gaps line up might result in a small dip in compressions, the usual recommendation is to fly and re-test. Doing a top overhaul because the ring gaps lined up was very poor advice.

PS. There are several DARs on this forum. If you change the title to “Back to phase 1?’ Or something like that, one of the DARs might offer his opinion.

Last edited by BobTurner : 06-12-2022 at 02:08 PM.
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  #9  
Old 06-12-2022, 06:04 PM
Nashpdman Nashpdman is offline
 
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Originally Posted by BobTurner View Post
The Repairman certificate lets the holder sign off the annual condition inspection. Period. Nothing else. Anyone may legally work on an EAB aircraft. Experimental engine, data plate means nothing. The only legal question is whether or not this is a major change, requiring a return to phase 1 OpLimits. Best not to guess: ask a DAR or call your FSDO.
Thanks for the clarification on the "repairmans" certificate. Learning everyday!
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  #10  
Old 06-12-2022, 06:20 PM
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jcarne jcarne is online now
 
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Quote:
Originally Posted by UrbanM View Post
This is the exterior obviously. The borescope pics are the usual hammered piston and cylinder stuff. I am grateful this happened on the ground and that it went out of the top of the cylinder and not through the top of the piston where it would have done more damage. The exhaust valve looks untouched.
Kinda new to piston engine aircraft ownership. I've had gliders for the past 20 years and only about 2300 hours of piston time and except for a stuck exhaust valve on an 0-360 power Scout I've never had any issues. I figured I would buy a plane with a well documented engine and stay within Lycoming limitations and careful maintenance I would be OK. So far during disassembly there is nothing to indicate any corners were cut.
Gruesome indeed. Like you said though, good thing it came out the cylinder limiting the damage.
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