Along with magneto failure and fuel contamination, the major problem with the OX 5 is valve function and lubrication.   This, of course, includes the rockers and rollers. (Young people think they started "Rock-N-Roll"... Curtiss built them first). Valve function depends on condition and timing. The original valves were adequate in design and composition. They are scarce and most OX 5 overhauls use modern replacement valves. The OX 5 requires the same care in grinding and lapping as any other engine. A narrow contact is required between the valve face and the seat. This is obtained by grinding the seat at two different angles and "hand-lapping" to a good fit. This can only be done properly if the valve stem and guide are in good condition.

Valve timing begins with a good cam-shaft! Good OX 5 cam-shafts are rare. Even if they look good and measure good on the bench, they may be unusable in the OX 5 engine! OX-5 camshafts may be twisted. This would give unusual valve timing on number eight cylinder. A number of such cam-shafts are in existence. (Foster Lane found two of these prior to a good one). The twist may have occurred by twisting the propeller while the cam-shaft bearing is frozen at one end, or a frozen rocker assembly. Beware of twisted cams!

Worn lobes can be determined on the bench, as well as irregular or rough surfaces. It is, however, difficult to measure unusual or irregular contour of the cam surface on each side of the cam lobe. This determines the initial opening and closing of the valves relative to top center of the piston position.

Most camshafts are found to have considerable variation in lobe contour. This may be a characteristic of the original manufacture, or due to wear. This can cause as much as 13 or 14 degrees of difference between the valve function of cylinders on the same engine. Do not be alarmed! The OX 5 is very tolerant of such irregularities and will perform just fine. (Curtiss suggested the difference between valve timing should not exceed 6 degrees).

Both intake and exhaust valves should be set at 0.010 inches with a cold engine. (This too could be altered to compensate for cam irregularities). Any greater clearance will cause a retarding in the opening of the exhaust valve and an advance in the exhaust closure. Any greater clearance of the intake rocker will cause the valve opening to be retarded and the closing to be advanced. Some recent OX 5 operators suggest that rocker clearance to be 0.012 inches for a cold engine. The following is a set of data for typical OX 5 that is performing quite well.

Note:         ATC means after top center

                BTC means before top center