B737-800
Maintenance Airframe; Maintenance Powerplant
Maintenance Lead Technician 3; Maintenance Technician 25
Communication Breakdown; Confusion; Troubleshooting
Aircraft Equipment Problem Critical
General Maintenance Action
Aircraft; Manuals; MEL; Human Factors; Chart Or Publication
Non-Routine [write-up]; #1 Engine Accessory Gearbox (AGB) lower clevis mount has excessive play. I let Supervisor know about the problem; and then we both started to look into the limits. I could not find any limits for the lower clevis mount rod [link] in the Aircraft Maintenance Manual (AMM). The Supervisor then told me he had found an Engineering Repair Order (ERO) for another airplane with the same problem as this one. After measuring the looseness; we had 1/8 of an inch play. Then I was told that Engineering and the Engine desk both said I didn't need an ERO for the aircraft and that I could make a deferral per AMM 72-63-00-200. I called the Engine desk and he said to defer it under AGB Housing for damage. I did not feel this was the right way to go; but I was unable to find any other limits for the clevis rod; so [with] the assurance of both Engineering and the Engine desk knowing what we had; I went ahead and placed it on a deferral per AMM 72-63-00-200.
Reporter stated the Accessory Gearbox (AGB) on NextGen B737 CFM-56-7 engines are bigger; beefier; than the older series CFM's used on the B737 Classics. There are two Main attach clevis points; an Upper and Lower position; on the Engine Fan Case; that use a figure-eight shaped link; not a rod; but a link to connect the AGB to the Fan case. Each figure-eight shaped Link has two titanium steel alloy balls inside; one end connected by bolt to the Upper or Lower clevis on the AGB and the other link end connected by bolt to the Upper or Lower clevis fitting on the Fan case. There are also four or five rod-end side links with adjustable turnbarrels that also secure the lateral load of the AGB to the fan case. His concern is with the Upper and Lower AGB Main attach points.Reporter stated they check for lateral play by forcefully pushing and pulling against the AGB at the Main links and measuring the radial play (wear) at each location. The bolts were not loose in the mounts. He could not see the inside surface of the bushings that are installed at each clevis ear; unless they remove the mount bolts. But their mechanics are not allowed to remove any Main Upper or Lower bolt; per the CFM Manufacturer's Manuals. The Manufacturer has a Jig that is used for removal and replacement of the Fan case/AGB Main mount bolts.Reporter stated the Aircraft Maintenance Manual (AMM) states that if any displacement is noted in the AGB bushings; the bushing must be replaced or remove the engine. The displacement he noted appeared to be in the lower clevis mount on the AGB. There were not; and still are not; any wear limits for lateral play; unless the play has been determined to be from worn bushings. So he deferred the item per their Engineering and Engine Support desk.Reporter stated the very next night; the engine was replaced at one of their Maintenance Stations for excessive bushing wear at the same Lower Main attach mount he previously wrote-up and deferred. But; since the bushing wear can only be determine by removing the mount bolts; which is only approved for the Manufacturer to do; who made the decision to remove the engine; or how was that decision reached. Since he deferred the item as a Lead Mechanic; he would like to know. He is concerned the same condition also exists across the industry for other Operators of NexGen CFM-56 engines.
A Lead Mechanic working a B737-800 aircraft noticed 1/8 inch radial play at the Accessory Gearbox (AGB) Lower clevis mount on a NexGen CFM-56-7 engine. Although no wear limits could be found; he was told by company Engineering and their Engine Support desk he could defer the wear. The engine was replaced the following night for excessive bushing wear.