July 1, 1960
SB-#791
SUBJECT: REDESIGNED PISTONS AND PISTON RINGS - 35 H.P. MODELS
Figs. 1 and 2 show the new (A) and old (B) piston ring and piston
dowel pin assembly. In order to eliminate any possibility of
dowel pin failures, the 35 H.P. piston assembly was redesigned to
incorporate a larger dowel pin (Fig. 2A) similar to that used in
the 40 H.P. engines. This dowel pin change requires a new piston
ring having greater relief at the gap so as to fit properly.
In order to reduce service problems to a minimum, the new ring (Fig.
1A) was designed to be compatible with the old piston and dowel pin
assembly as well as the new style piston and dowel pin assembly.
Consequently, all the old 35 H.P. piston rings (Fig. 1B), both
standard and oversize, have been obsoleted and superseded. (See list
below.)
The new-style piston and dowel pin assembly, still carrying the same
number, is now being shipped from the parts distributors. Exercise
extreme caution when using the new piston assembly and be sure the
new-style piston ring is used. It is suggested you scrap your old
style rings or tag them for use only with the old piston assembly.
The larger dowel pin is easily identified and no problem should be
encountered if reasonable care is exercised.
The piston rings that have been changed are as follows:
Obsolete 304712 Piston Ring Std. Superseded by 308003
Obsolete 304595 Piston Ring .020 oversize - 308005
Obsolete 304597 Piston Ring .040 oversize - 308006
The following piston and dowel pin assemblies have been changed using
a larger dowel pin, but the part numbers remain the same.
377409 Standard
377073 .020 oversize
377074 .040 oversize
JOHNSON MOTORS
W. W. DeWees
Service Department
NOTE: Post on your RD series index.
WWD:eb
W. W. DeWees