1 - The 61" Panheads (EL designation) were only made during these years.
2 - All 61" and 74" parts are interchangeable, during these years.
3 - The 61" flywheels can be used in the 74" cases, but the 61" wheels are 1/8" smaller in diameter than the 74" wheels. If you use 61" wheels in a 74" case, you will have to build up
the oil scraper, to prevent the rear cylinder from getting too much oil. Also, you will have to relieve the oil scraper clearance, if you use 74" flywheels in the 61" cases.
1 - The pinion shaft was changed for this year, to what would be used up through 1957. To use the later in this year, you must change the bearing race in the case, the pinion shaft,
bearing rollers and cages, all pinion gears, and timing cover bushing.
2 - The 1954 and earlier panheads return top end oil by draining it through a passage in the cylinder. This, in turn, is channeled through a passage in the crankcase, sandwiched between
the cylinders and left case, and down into the oil trap under the flywheel oil scraper.
3 - 1948 to 1954 lifters are solid, with a hydraulic pushrod. Did not work very well.
1 - The left case and sprocket shaft was changed to accept Timken tapered roller bearings. The sprocket shaft was splined to accept a spring-loaded compensating sprocket. Now this being
said, the early 1955 year models used the older tapered shaft and standard sprocket, while the later 1955 models used the later splined shaft and compensating sprocket.
2 - 1955 and up engines drain the top end oil down through a passage in the cylinders, opening into the inside wall, just above the crankcase. This oil hits the piston skirt, and falls
down into the crankcase, to be picked up by the flywheels. If you use early cylinders on late cases, be sure to drill a hole on the inside of the cylinders, to allow the oil to have a means to
get into the cases. If you don't have an old cylinder to pattern by, drill the hole 1-5/32" from the bottom of the cylinder to the hole center. The hole should at least be 1/4". Also, put a
plug of some kind in the outside hole. Usually, the hole is threaded and an allen screw is inserted with high temperature sealer. Chamfer the inside hole to round the edges.
3 - 1955 and up engines use the 'O' ring intake manifold, replacing the threaded plumbers intake.
4 - The left hand case and the left hand flywheel are the same from 1955 to 1964, as a matched set. However, the left hand flywheel is the same from 1955 to 1980 (74" engines). It is
better to interchange only 1955 to early 1973 left hand wheels, as the balance factor is 50%. Whereas, the balance factor is 60% for late 1973 to 1980 left hand wheels.
5 - In 1955, the solid lifter/hydraulic pushrod was switch to a solid pushrod and a hydraulic lifter/tappet. Worked much better.
1 - The 1958 pinion shaft change to use a larger main bearing. The bearing is used up through the 1984 Shovelheads. The pinion shaft was used up through 1973.
1 - In 1963, the top end oil feed became external lines, from the lower part of the head, to an oil pressure tap in the right case.
1 - The panhead became an electric start model (and last model year for the panhead). The left case was changed to accommodate the new electric start solid primary covers. This left case
and primaries were used up through 1969 (1966 to 1969 shovelheads). The 1965 to 1969 left sprocket shaft is longer.
2 - The 1965 engine came with an auto-advance distributor, which will work on any 61" and 74" OHV models from 1936 to 1969.