CENTRILUBE SELF-OILING CAMSHAFTS
For the Lycoming 320 / 360 / 540 / 541* series engines
IDENTIFYING THE PROBLEM
In 1995, Firewall Forward noticed an increasing number of warranty claims related to camshaft and lifter wear on Lycoming engines. In an attempt to resolve the problem, the company tried using only new camshafts in its overhauls, but the failures continued. Cam and lifter wear problems as indicated by metal in the oil filter occurred in as little as 100 hours after the overhaul on some engines models.
INVESTIGATING THE CAUSE
The New Firewall Forward in association with Centri-lube technologies initiated an all-out effort to determine the true cause and cure it. Initially, the problem was attributed to corrosion, types of oil, lack of additives, engine inactivity, improper warm-up or cool-down, problems with metal alloys, oil filtration, etc. An in-depth study of ”Tribology” (the science of lubrication and wear of sliding surfaces) was instrumental in understanding this premature wear issue.
First, a thermal mapping of the camshaft lobe and lifter face was performed during live engine operation. A thermal imaging camera and data acquisition system determined the actual temperatures of these surfaces at various engine speeds. The mapping and analysis revealed that the surfaces were operating at temperatures that exceeded the ability of the oil film to adequately lubricate the sliding metal surfaces.
The initial factors evaluated that contributed to premature wear were:
- Surface finish of the sliding surfaces,
- Pressure upon the sliding surfaces (valve springs),
- Velocity of the sliding surfaces (RPM),
- Lubrication oxidation point (max temperature), and
- Lubricant viscosity
ENGINEERING THE SOLUTION
The solution was elegant in its simplicity: provide direct lubrication via oil holes in the camshaft lobes. This innovation is used today by a majority of engine manufacturers in the automotive and marine industries and has effectively eliminated premature camshaft/lifter wear.
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Firewall Forward tested the feasibility of this solution on the Lycoming engines. Because all Lycoming camshafts are hollow, oil could be introduced into the interior of the camshaft. With both ends of the camshaft blocked, the oil enters through the precisely drilled holes at critical points on the camshaft lobes and directly onto the lobe ramp area. Thermal imaging once more provided the necessary data for the exact size and location of the oiling holes.
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The perfected solution achieved a substantial decrease in operating surface temperatures with a corresponding increase in hydrodynamic planing between the sliding surfaces. The initial 200 engines operating with modified camshafts in a four year period have confirmed the success of the modification. The effectiveness of the modification allows The New Firewall Forward to offer this exceptional warranty to our modified camshaft customers: four years/100% warranty with unlimited flight hours.
* Lycoming 541 Series requires enlarged oil filter & baffling modification to comply with Supplemental Type Certificate