Lycoming 0-360 Pushrod gap inspection interval

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Baron62

Pre-takeoff checklist
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Baron62
Hello, I'm bringing in my first plane for its first annual next month and the local IA suggested that he can inpect the clearance/gap of the push rods as part of the annual inspection. Engine is 0-360 A4M with 600 hrs SMOH and it seems to run fine with good compression measurements from the pre-buy. He said that he has been doing this check and finding many engines needing adjustment/new pushrods. He also said same customers have been happy and reporting increased power after the adjustment. Is there a recommended interval for checking the gap? Does anybody else recommend this check/adjustment?

I tend to be old school in regards to not taking something apart unless it is needed for some reason. I read a Mike Busch article stating that more issues occur from over-inspecting. Let me know your thoughts. Thanks
 
Not a mechanic but I thought that hydraulic lifters maintained push rod gap/position/spacing
 
IA stated that hydraulic lifters had limited range of adjustment.
 
it is called dry tappet clearance,, google it. read.

when the hydraulic unit in the lifter body reaches the point it can no longer take up the wear that has occurred it will be time for an overhaul.

you might ask your A&P to do the wobble check on the valves, rather than the dry tappet clearance.
 
600 hours since major? I wouldn't mess with it.

If dry tapet clearance was bad, some bloke put the wrong length pushrod in it at overhaul.
 
bnt83 said:
600 hours since major? I wouldn't mess with it.

If dry tapet clearance was bad, some bloke put the wrong length pushrod in it at overhaul.
Click to expand...
If they did, it wouldn't have lasted this long.
 
IIRC the dry tappet clearance is .028" to .080". It's set using various pushrod lengths when the engine is assembled. It should never need resetting unless the cylinder is changed or some valve work is done on it. The hyraulic lifters look after it otherwise. The only Lycoming I'm aware of that needs periodic valve clearance checks (100 hours) is the O-235, whch has solid lifters.

In 1998 Lycoming went to a high-chromium-content valve guide and the wear problems mostly went away. From http://www.caa.si/fileadmin/user_upload/pageuploads/AD-NOTE/AD-2006/093_sb_SI1485A.pdf we read:

Improved exhaust valve guides were initially incorporated into some cylinder assemblies beginning in April 1996. Since March 1, 1998,
all engines, cylinder kits and spare exhaust valve guides shipped from Lycoming contain the improved material. Cylinder assemblies which in
corporated the improved “Hi-Chrome” exhaust valve guides when the engine was shipped from Lycoming are identifiable by the letter “C”
stamped inside a circle on the boss for the drain back fitting. The individual guides made with the improved material can be identified by a 5°
chamfer at the top of the guide (See Figure 1). Once guides made from the improved material are installed in all cylinders on the engine, it is no longer
necessary to complete the mandatory 400 hour inspections specified in the latest revision of Service Bulletin No. 388. It is recommended that the
inspection procedure from the latest revision of Service Bulletin No. 388 be completed at 1000 hours of operation or half way to the recommended TBO, whichever occurs first.
 
19 years later? Probably a third of them, anyway. Maybe more.
 
Thanks for all the feedback and info. This engine was built in 2007. I am going to tell the IA to not inspect the push rods.
 
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