Lycoming Wobble Test
- Thread starter Skymac
- Start date
I believe the Lycoming bulletin gives instructions on fabricating DIY tool versions to check the wobble.
Dan Thomas
Touchdown! Greaser!
- Joined
- Jun 16, 2008
- Messages
- 12,389
- Display Name
- Dan Thomas
That bulletin was issued when Lycoming was having valve guide wear issues. In 1998 they went to a high-chromium-content bronze that pretty much solved the problem.
From SI-1485:
1000-hour checks are "recommended." We never had any such problems with any of our Lycs in the flight school in engines built or O/H after 1998. But maybe some aftermarket cylinders still have the old guide material?
From SI-1485:
1000-hour checks are "recommended." We never had any such problems with any of our Lycs in the flight school in engines built or O/H after 1998. But maybe some aftermarket cylinders still have the old guide material?
FYI: On a number of the Lycoming model variants certified under Part 33 after 2015(?), the exh valve guide test became mandatory under an airworthiness limitation section in the manual. Examples below. Has caught a few people off-guard having an ALS now vs previous models.
I was thinking about making something a little more robust.
All of my engines are within 6 years old of being factory new and it’s very much a thing to check still. I’ve not seen one wear out but they sure need to be reamed and the valve stem cleaned to prevent one from sticking. It seems to be in the 800-1200 hour range when I’m seeing issues on fixed wing engines.
Had one slightly stick open the other day for a few seconds and that’s what’s made me wonder what others were using to test the tolerances per the SB, I must have missed the fabrication part. Again, not really worried too much about it, but they certainly do benefit from a pass on the reamer.
All of my engines are within 6 years old of being factory new and it’s very much a thing to check still. I’ve not seen one wear out but they sure need to be reamed and the valve stem cleaned to prevent one from sticking. It seems to be in the 800-1200 hour range when I’m seeing issues on fixed wing engines.
Had one slightly stick open the other day for a few seconds and that’s what’s made me wonder what others were using to test the tolerances per the SB, I must have missed the fabrication part. Again, not really worried too much about it, but they certainly do benefit from a pass on the reamer.
I wonder how much this depends on how the engine is operated. Too rich and the valve stems gunk up. Too lean and the valves burn. Optimal operation strikes a balance between these.
It is likely a factor. Even the Robinsons I service which are operated rich and are continuously at high altitude (5,000+) don’t seem to have serious problems with this.
pfarber
Pattern Altitude
- Joined
- Jun 20, 2021
- Messages
- 1,653
- Display Name
- pfarber
There are way cheaper (approved) alternatives. A simple clamp on dial gauge or readily available precision ground rods to make go-no/no-go gauges.
$8000+ for a tool to measure stem wobble/vavle guide wear? yeah, only in aviation.
$8000+ for a tool to measure stem wobble/vavle guide wear? yeah, only in aviation.
Spruce also wants $8902 for the reamer.
