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  #21  
Old 08-15-2022, 10:34 AM
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rocketbob rocketbob is offline
 
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I've lapped more valves than I can count. At least 10 in the past year. Never have had any issue as I usually have owners do full power runs down the runway before rechecking compressions and borescope. No problems with paste or scratching of the cylinders as I do check before and after to see if this may be an issue.

Lapping fixes non-rotating valves.

Typically I clean the stem off via the spark plug hole, and clean off carboned up springs and seats also. Usually clean the guides as well.

Pulling a jug on a Bonanza for example is a huge effort so lapping makes a lot of sense. The key is to lap valves before there's low compression issues.

One Bonanza I annual is well past TBO running very strong thats had all of the valves lapped about 3 years ago. The owner was considering an overhaul at the time, and now there's no discussion of it.
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  #22  
Old 08-15-2022, 12:32 PM
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https://www.youtube.com/watch?v=71cMqxZtgAs

mike bushes explanation about this subject.
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  #23  
Old 08-17-2022, 03:10 PM
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Mike's video makes it look so easy! I watched it at least 4 times to try and absorb as much as i could. I also read some articles on the topic.

I had a go today - I've never messed with aircraft engines before so good I had some help from some experienced mechanics!

the rope i purchased was too compressible, good job maintenance had some thicker stuff. Getting the rocker arm off was the next challenge - I would have given up at that point had i not had some help. The shaft that goes through the rocker arms was in tight and needed some persuasion to come out.

The valve guide felt good according to the mechanics with the valve sliding smoothly within it.

Trying to get the valve paste in the right place was a challenge. Cleaning up was a challenge. Fiddly but achievable with some patience.

Getting the rockers back on was hard because the hydraulic tappets on the intake valve had filled with oil and didn't want to move.

Pressures before lapping were 58 and after it dropped to 20! I was thinking of ordering a replacement engine at this point.

The engineers said dont panic, may be a speck of paste has been left in site. Go do a full power ground run to see if that moves anything and then recheck. I managed the ground run and then rain and time stopped play. Ill recheck in the next day or 2.

Im not convinced i lapped long enough (i did just a couple of mins with coarse then fine compound using a slow drill speed)) and only changed direction once and did not move the valve in and out whilst lapping. I've only realised all this after doing more research on how to lap valves - I should have done that before.

Can lapping make the valve worse? If not, i'll give it one more go as now i know how to get the valve springs off and back on, it should be a bit easier.

Thanks for any critique of my technique and how it can be improved.
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Last edited by david.perl : 08-17-2022 at 03:19 PM.
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  #24  
Old 08-17-2022, 03:17 PM
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Quote:
Originally Posted by david.perl View Post
...
Can lapping make the valve worse? If not, i'll give it one more go as now i know how to get the valve springs off and back on, it should be a bit easier.

Thanks for any critique of my technique and how it can be improved.
Great to hear, David! I've only watched the videos and listened to podcasts and am very interested to hear your results after the next engine run, and perhaps after a bit more lapping. I have never heard that it can make things worse, so I agree with your mech's assessment - don't panic!
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  #25  
Old 08-18-2022, 07:53 AM
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Pressure came backup to 78/80 on retesting
phew, no need for new engine
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  #26  
Old 08-18-2022, 09:28 AM
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So, at least $3000 saved (probably an under estimate of changing a cylinder).
For a cost of what... $20 in materials and some time? Not counting what you needed to pay your helpful mechanic.
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  #27  
Old 08-18-2022, 11:31 AM
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Quote:
Originally Posted by blaplante View Post
So, at least $3000 saved (probably an under estimate of changing a cylinder).
For a cost of what... $20 in materials and some time? Not counting what you needed to pay your helpful mechanic.
Yes well pleased, we pay pounds to your dollars so likely saved even more. I was quoted GB£5,000 for cylinder replacement. The engineer said they used to lap in place all the time but now its not worth their time and they just remove the jug.

It cost £20 in materials plus purchasing the Ablescope 400 which for its price is a great bit of kit and will be useful at future inspections. Plus a few hours of time, £70 in thank yous and also my membership to Savvy QA who interpreted the borescope images within 1 hour over a weekend- im also gleaning some useful data from their flight data analysis tool.

I also learned a lot about valves and the importance of borescoping them at regular intervals.

I think if i was doing a lot of these, I would invest in a valve wizard as getting the springs compressed and the collets out and then back in was a fiddle. I did email about postage to the UK but never heard back.
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  #28  
Old 08-18-2022, 01:05 PM
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My inspector does not appear impressed i did this. He said at the least ground run and change oil and filter. How would any grinding paste that may have been left get thought the oil filter?
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  #29  
Old 08-18-2022, 01:53 PM
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Quote:
Originally Posted by david.perl View Post
My inspector does not appear impressed i did this. He said at the least ground run and change oil and filter. How would any grinding paste that may have been left get thought the oil filter?
So you’ve got guys over on your side of the pond that are like that too?!

Bottom line, I think, is that if you have to satisfy him before you can fly, then an early oil and filter change are cheap (compared to the amount you’ve saved over doing a cylinder change already….), and if it gets you back in the air, well - it might be stupid, but you can be “right” and grounded, or say “yes sir” and go fly…..

And no - you shouldn’t have any remnants of grinding compound survive to show up in the oil….

Paul
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  #30  
Old 08-18-2022, 02:06 PM
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David, good the hear of the success - yea you have to lift and go back and forth. I experimented 40 yrs ago and that works best.

High confidence that you will get good readings after a flight hour or two, oil change and filter. Engine will still be happy, can not hurt and will make a happy (or less grumpy) inspector.

Good for you stepping this through. You will find easy/proper ways of getting past the reinstallation difficulty of the rockers.
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