Returning a pickled engine to service after long storage
A four-cylinder Lycoming O-320 in a privately owned aircraft has been in an unheated coastal hangar for 22 months. The engine was preserved with an oil-based preservative, desiccant spark plug adapters and a sealed intake and exhaust; the logbook shows the propeller was rotated by hand every 30 days for the first 12 months but not thereafter. The desiccant plugs are now pink. The oil filter was not changed at preservation. The aircraft is being returned to service for a 100-hour inspection. The owner wants to install fresh oil, charge the battery and fly. The engine has 1,900 hours since new and 300 since top overhaul. There is surface corrosion on the crankcase and a small oil stain at the No. 2 cylinder base. The hangar is 2 km from the sea.
1. What do the desiccant color and the 10 months without rotation tell you about corrosion risk?
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Pink desiccant means it has absorbed moisture and is no longer protecting the engine. The engine has been in an unheated coastal hangar for 22 months, with no recorded rotation for the last 10 months. Without rotation, the preservative oil film can drain from camshaft lobes, lifters, cylinder walls and crank journals, and moist air can reach those surfaces. The small oil stain at the No. 2 cylinder base and the crankcase surface corrosion are further signs that moisture has been active.
The corrosion risk is therefore high, not merely cosmetic. The camshaft and lifters are especially vulnerable because they are splash-lubricated and can pit while stationary. The engine should not be started on the owner's plan until the internal condition has been assessed.
2. List the inspections and servicing you would perform before first run, and what findings would stop you.
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Before any run, I would remove the desiccant plugs, borescope all cylinders and rocker boxes, cut and inspect the oil filter, drain and inspect the oil for water or sludge, and check the oil suction screen. I would inspect the crankcase for corrosion, check the magnetos and ignition leads, and verify that the intake and exhaust seals are intact. I would pre-oil the engine with the correct preservative or lubricating oil until pressure is indicated at the gauge, then change to service oil.
Findings that would stop me include pitting or rust on cylinder walls, camshaft lobes or lifters, corrosion on crank journals, water in the oil, a contaminated filter or screen, or a corroded valve train. Surface corrosion on the crankcase alone may be treatable, but internal pitting is not something to run and hope. If internal corrosion is found, the engine needs disassembly, not a fresh oil change.
3. If the engine cannot be run for another 6 months, what preservation steps would you require?
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I would re-preserve the engine rather than leave it in its current condition. That means draining the service oil, adding the approved preservative oil, pre-oiling or fogging the cylinders as specified, installing fresh desiccant plugs, sealing the intake and exhaust, and protecting the exterior with an approved preservative. I would record the date and the products used.
The owner must follow a written preservation schedule, including periodic propeller rotation and desiccant inspection, and the engine should not be rotated without a preservative oil film. If the desiccant becomes saturated again or the schedule is not followed, the engine should be inspected before return to service. The deferred 100-hour inspection and the corrosion findings should be documented so the next AME knows the storage history.