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Lycoming 390 valve issue HELP

L

larrys

Well Known Member
We have an RV14A with about 65 hours. It is time for the annual and while doing the compression test it came out to 78 80 80 50. 50 was on cylinder 1. After asking a few people they say "just run it an hour and retest". We will do that but we also brought in an RV builder on the field with lots of experience and he said the same but did not know what it was. It seems to be on the intake side which is odd. So we scoped the cylinder and found something weird. When the valve first touches the seat it seems to go sideways a bit to seat. Like the stem and valve head are not lined up. So we scoped another cylinder and it looks exactly as it should, great fit, no movement. I was told they are meant to "spin" but this is sideways. And over time it should oblong the valve seat.

The motor is the recommended motor for the RV14A 390 Lycoming and we paid extra for the balanced Lighting bolt in red.

Bottom view of video is the valve moving sideways to seat
https://youtube.com/shorts/lJ26jvCYXfw

Has anyone heard of such an issue? We have not notified Lycoming yet. We will do the test as recommend in there paperwork. But it does not seem right.

Hopefully the you all will know.
thanks, Larry
 
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Yes, it is very common for that to happen when the valve guide gets real loose. If it is not loose (more likely), then the machinist did not properly index either when reaming the guide or when cutting the valve seat. It could also be poor indexing when shaping the stone for cutting. Unfortunately a pro will need to get into the cylinder and address the issue. It is also possible that the machinist hogged out the guide (i.e. it is loose), but that will still require work. Recommend a compression test to confirm that the leak source is the intake valve (will hear the air rushing out of the servo or carb). If it is the intake valve that has the odd movement AND the compression test air is coming from the intake, then the cyl has to come off and sent to a shop to address. Lyc should replace that cyl under warranty as it is a manufacturing defect. ABSOLUTELY not normal for this to happen at 65 hours and likely doing it since day 1.

FYI, if compression goes from 78 to 50 in a 65 hour old engine, the answer is never to run it some more and see what happens. Bad advice even though it may be appropriate for an engine with 1000 hours. After investigation, then yes, that may be a valid approach if a logical cause cannot be found or seen, like a ring issue. But it should not be ignored. I had the same thing on my overhauled 540. 50/80 on #1 at first annual. Pulled the cyl and found a cracked compression ring. Fortunately superior sent me a brand new cyl assy.
 
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intake

Yes, we did the compression test and the intake blew air that could be heard when closed.
 
larrys said:
Yes, we did the compression test and the intake blew air that could be heard when closed.
Click to expand...

assuming the same intake is the one that moves funny. If so, the geometry if off and preventing the valve from closing completely. It needs to be re-worked (probably will need a new guide and seat) and suggest you start with a warranty claim. Hopefully Lyc will honor that. if the valve is getting a lot of side load pressure when it closes, I would want a new valve as well.
 
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thank you!

lr172 said:
assuming the same intake is the one that moves funny. If so, the geometry if off and preventing the valve from closing completely. It needs to be re-worked (probably will need a new guide and seat) and suggest you start with a warranty claim. Hopefully Lyc will honor that. if the valve is getting a lot of side load pressure when it closes, I would want a new valve as well.
Click to expand...

Yes we will! Really thank you for your help to confirm what I know is going on.
Hope Lycoming follows through, they should?
 
larrys said:
Yes we will! Really thank you for your help to confirm what I know is going on.
Hope Lycoming follows through, they should?
Click to expand...

My son lives in Denver. Need to take care of his fellow Rockie Mtn. neighbors. good luck
 
lr172 said:
My son lives in Denver. Need to take care of his fellow Rockie Mtn. neighbors. good luck
Click to expand...

I've been around other parts of the world, yet I'm excited to come home! We fly out of Meadowlake KFLY if you are in the neighborhood.
Thanks Larry
 
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