THE PINION gear is the small gear on the right-hand end of the crankshaft which drives the camshaft. It has exactly half the number of teeth as the camshaft drive gear so that the camshaft turns at half crankshaft speed.
As the pinion gear drives the camshaft, it needs to be indexed to the crankshaft so that the cam timing can be accurately set. Earlier pinion gears were fitted to splines on the pinion shaft with a master spline used to determine correct location. Later gears were fitted to a taper and indexing was achieved with a woodruff key.
Although it is not common knowledge, pinion gears are available in different diameters so that engine builders can fine tune the lash between the gears. This is not generally necessary with engines that are rebuilt using all the original timing gears as these parts were well matched at the factory.
The most common time to check for the precise meshing of the timing gears is when a new camshaft is installed. Most high performance cams come with a cam drive gear already installed which may vary slightly in diameter from the original H-D gear. If there is excessive gear lash with the new cam installed, it may require a slightly larger pinion gear to take up the clearance. In the unlikely event that the new cam is too tight, and there is no detectable lash, it may require a smaller pinion gear.
Alternatively, reputable cam grinders such as Andrews Products offer both oversize and undersize cam drive gears for all their camshafts to overcome various fitting problems.
Andrews Products also sell gauge pins for accurately comparing diameters of gears. These pins sit in-between the teeth of the gear and can be held in place with a rubber band, the diameter can then be determined with a measurement taken across these pins. This measurement is used to select either a larger or smaller pinion gear by comparison. In other words, it isn’t the actual diameter of the gear that matters but rather whether it is larger or smaller than the troublesome gear.
Measuring the pinion gear diameter.
Removing a pinion gear.
The three different styles of pinion gears offered by S&S for the Big Twin single cam engines. Most of these gears are now obsolete from Harley. Fortunately, all these gears in their colour coded sizes are available through Redgrave Motorcycles for engine builders setting perfect gear lash, or restorers of older engines looking to replace a badly damaged gear or one that might be missing altogether. The pinion gear on the left is to suit engines from late 1977 through to 1989; the gear in the centre covers 1954 through to early 1977; and the splined gear on the right will fit all Knuckleheads and pre 1954 Panheads. Note, some very early Knuckleheads may require a pinion shaft upgrade to accommodate the separate pinion shaft.
Pinion Gear on 1916 Harley-Davidson. The pinion gear setup in its most basic form, driving the camshaft on this early single cylinder engine.
Pinion gear installed in an early generator Shovelhead. In this case a Brown 33-4127 1954-1977 gear was required to give correct meshing.
Unfortunately, good pinion gears for early engines are scarce, but occasionally some little gem comes to the surface such as this brand new (still in the original wrapping) pinion gear to suit 1937 and up WL series engines.
The replacement pinion gears featured in this article are produced by S&S Cycle and are available in all the oversizes and undersizes that were offered by Harley. They also carry the same colour coding used by Harley-Davidson. Engines covered by this range of gears include Knuckleheads, Panheads, Shovelheads and the early Evolutions.
Redgrave Motorcycles stocks the full lineup of these gears and are happy to help with any related problems. Call for more info: 02-9484-9955.
Article compiled by Richard Nicholls at Redgrave Motorcycles.