Fitting Pinion Shaft Bearing

The fitting of pinion shaft bearing is done in much the same way as fitting lower rod bearings (see "Fitting Rod Bearings"). A plug fit is first determined using an inside micrometer or telescoping gauge or, preferably, by trial and error using sets of various size rollers. Determine plug fit using pinion shaft that will be used on engine being overhauled, or spare shaft of exactly same size. When a plug fit has been found, pinion shaft will enter bearing slowly under its own weight, will turn with only a very light drag and will have no perceptible shake.

A running fit is determined from a plug fit by subtracting one-half the desired running fit clearance from the size of the plug fit rollers.


Running fit clearance is .0008 to .001 in. loose. See "Engine Specifications," Section 3A. If a plug fit was achieved with .0006 in. oversize rollers, subtract one-ha If running fit. clearance from plug fit roller oversize. Use figure representing minimum of tolerance span, .0008 in. One-ha If the minimum tolerance allowed (.0004 in.) subtracted from roller over

Figure 3E-29. Lapping Pinion Shaft Bearing Race size (.0006 in.) indicates that .0002 in. oversize rollers should be used to produce a suitable running fit.

Oversize rollers are available in .0002, .0004, .0006, .0008 and .001 in. sizes. All calculations should therefore be made to nearest available even-numbered size. In the example above, it would be possible to arbitrarily decide upon .0006 in. as a running fit rather than the .0008 in. if desired. Final decision would rest largely upon intended use of motorcycle. For high speed work, the more free fit would be better, while the closer tolerance is suited to road use at average speeds. This consideration may be made in fitting all tolerances.

All fitting must be done with bearings that are clean and dry. Oiled surfaces will take up some clearance and give a false reading.

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