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  #1  
Old 11-09-2019, 04:11 AM
flysrv10 flysrv10 is offline
 
Join Date: Jan 2010
Location: Florida
Posts: 380
Default Valve wobble test out of spec.

Just did a Valve Wobble test and all 6 ECI cylinders are out of spec. Max wobble per lycoming Service Bulletin 388C for my valve is .035. Cylinders 2,4 and 6 were between .045 and .050. All other cylinders were near or at .035 limit.

I do not have any issues but decided to do the test due to the hours on the engine. The IO540 engine has 1400 hours from brand new ECI cylinders and has been running well. Oil consumption has been 1 qt per 10 hours and borescope shows good symmetrical pattern on all valves.

So my question for the engine experts is what to do next? Rework or replace the cylinders that are out of limit? I hate to do major surgery on a perfectly good running engine but want to the right thing. The SB, although it indicates upper limits for valve wobble was issued to check for tight clearances and sticky valve issue.

Thank you.
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  #2  
Old 11-09-2019, 05:37 AM
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Great post. Glad you were pro active on looking into the health of your engine. I would not call it a good running engine. You are wearing out valve guides like crazy. Why? I am no expert but something should be done. New valve guides seems like a good idea. Good luck Florida neighbor.
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  #3  
Old 11-09-2019, 05:49 AM
flysrv10 flysrv10 is offline
 
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Hey Turbo, You have recommendation in SE FL to replace valve guides?
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  #4  
Old 11-09-2019, 06:24 AM
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I'd keep flying it if it were mine, plan on a top in a few hundred hours.
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  #5  
Old 11-09-2019, 06:26 AM
flysrv10 flysrv10 is offline
 
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Quote:
Originally Posted by Walt View Post
I'd keep flying it if it were mine, plan on a top in a few hundred hours.
This is music to my ears. What is your recommendation based on? Thanks.
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  #6  
Old 11-09-2019, 08:51 AM
pa38112 pa38112 is offline
 
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How comfortable are you that your jig or your technique is not the source of the high readings? Just a little looseness of the jig on the valve stem, or a little too much force when applying the side load can make a big difference. It seems a little odd to me that 3 cylinders would go bad at the same time. (The ones are limit are not bad. They could have left the factory that way).
If it were me I would fly another 20 hours and then re-test them. At the same time I would remove the intake and exhaust and do a visual inspection on the valve stems. If the first test is correct I would fly another 50 hours and see if the wear continues.
The test is meant to find tight valves due to carbon/lead build-up. A stuck valve is the real enemy. You have good oil consumption. Worn valve guides should show an increase in oil consumption.
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  #7  
Old 11-09-2019, 09:08 AM
lr172 lr172 is online now
 
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Quote:
Originally Posted by pa38112 View Post
. Worn valve guides should show an increase in oil consumption.
While I have no first hand experience, given the horizontal orientation of the valve and the anemic oil flow to the rocker box, I doubt that worn guides would show noticable increased oil consumption like they would on most auto engines.

Larry
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  #8  
Old 11-09-2019, 09:28 AM
flysrv10 flysrv10 is offline
 
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Quote:
Originally Posted by pa38112 View Post
How comfortable are you that your jig or your technique is not the source of the high readings? Just a little looseness of the jig on the valve stem, or a little too much force when applying the side load can make a big difference. It seems a little odd to me that 3 cylinders would go bad at the same time. (The ones are limit are not bad. They could have left the factory that way).
If it were me I would fly another 20 hours and then re-test them. At the same time I would remove the intake and exhaust and do a visual inspection on the valve stems. If the first test is correct I would fly another 50 hours and see if the wear continues.
The test is meant to find tight valves due to carbon/lead build-up. A stuck valve is the real enemy. You have good oil consumption. Worn valve guides should show an increase in oil consumption.
The test was done by a shop. They disclosed that they had only done the test once before but they did get second opinion from other techs in the shop before concluding that the test was valid. Hence, I am here asking for advice.

The stems felt loose to me but I have nothing to compare them with.

If I remove the valves, I might as well do the guides since it requires removing the cylinders?
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  #9  
Old 11-09-2019, 11:41 AM
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hgerhardt hgerhardt is offline
 
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I'd leave it alone. The main purpose of the Wobble Test is to identify insufficient clearance, which leads to stuck valves. Your oil consumption is great and the valves don't show signs of distress.
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  #10  
Old 11-09-2019, 01:34 PM
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DanBaier DanBaier is offline
 
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From what I recall in the Lycoming engine school, when the valve opens / closes, it doesn't move in a straight line; rather there is a little side action to it and if you were to watch it close you'd see it kind of snap into position as it closes. As the engine ages, excessive valve guide wear could cause the valve to seat incorrectly leading to the valve failing.

In this case, I'd suggest a look at the valves with a borescope to see if there are any telltale heat issues. AOPA has a good chart with illustrations at https://www.aopa.org/-/media/files/a...inal.pdf?la=en . If you see any evidence of green tint to the valve or if the heat signature is obviously uneven, then the risk of a valve failure is very high, and I wouldn't fly the airplane in that condition as I expect the valve would probably fail sometime in the next 8 - 10 hours.

Dan
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