Johnson Service Bulletin 957 - New Motors with .020" Oversize Cylinder Bores

Issued June 8, 1963, this bulletin explains the occasional shipment of new factory engines with .020-inch oversize cylinder bores, the OS identification code, and service replacement requirements.

Johnson Motors gray Service Bulletin letterhead

June 8, 1963

SUBJECT: NEW MOTORS with .020" OVERSIZE CYLINDER BORES.

A new procedure is now in effect under which NEW MOTORS will occasionally be shipped from the factory with .020" OVERSIZE CYLINDER BORES. This is similar to the practice currently being followed by many automobile manufacturers. At present, only the 75 h.p. model is so affected, however, this may apply to other models in the future.

In establishing this procedure, we will in all cases allow for an additional rebore in the field. For example, a new engine would be bored .020" oversize at the factory only if .040" oversize pistons and ring sets were available for the engine in the field. Conversely, engines such as the 40 h.p. for which only one oversize piston is available, would be shipped from the factory with standard bore sizes only. This new procedure will apply to only a very limited number of engines each year.

Factory photograph showing location of engine serial number plug and inset with OS identification code

Figure 1

IDENTIFICATION:

The serial number plug in the cylinder will provide a means of identifying an engine shipped from the factory with oversize cylinder bores. Code letters "OS" will be stamped on the plug immediately below the serial number - see insert, figure 1.

Page 2
SB #957

Dealers are requested to check the serial plug when ordering replacement pistons or ring sets for engines having the "OS" code. When the code appears, merely order .020" oversize pistons and ring sets for service. Refer to oversize piston and ring set listings on page 84 of the 1963 Master Price List for part numbers.

Warranty replacement cylinders or powerheads shipped from OMC Parts Depot, and, service replacement cylinders shipped from your Parts Distributor will be supplied in standard bore sizes only. Therefore, when replacing a cylinder or powerhead on one of these factory oversize bore engines, remove the code "OS" when transferring the serial number plug, so that the new cylinder or powerhead is properly identified for future service requirements.

Sincerely,
JOHNSON MOTORS
Robert Compton
Administrative Assistant

RC:eb

Note: Post on 3, 5½, 10, 18, 28 and 75 h.p. indexes.

Historical service reference

Engines marked OS below the serial number were supplied with factory .020-inch oversize cylinder bores. The bulletin directs dealers to the 1963 Master Price List, page 84, for the corresponding piston and ring set part numbers.