IH: Engine Mechanicals

Rocker Modifications

  • A certain number of 1974 and 1975 XL & XLCH models were produced with modified rocker arms and rocker covers. These were machined to prevent interference between the rocker arm and the inside of the rocker cover due to a thickness variation in the covers. 1)
    • The only suspect rocker arm covers were the ones stamped with the letter “M” in the casting surface (which contains the pushrod entry holes). When replacing a rocker arm with the “M” stamped in the casting, you must grind 0.050“ off the top of the rocker prior to installation to provide enough clearance between it and the cover (when the valve opens).

Rocker Box


* . . . Splitting Rocker Boxes

Rocker covers are all the same technically from 1957 to 1985. 2)
Different part numbers are a different finish or style.
The should be no concerns about mixing ones from different years respectively per side.

There is, however, a front and a rear.
It has to do with the location of the oil feed lines. 3)
The front box has the hole to the rear. The rear box has the hole to the front.

Year Model Part Number
57-70 XL/XLH/XLCH 4) 5) 17514-5717515-57
(polished) 6)
83 XLX 7)17524-8317525-83



Rocker boxes from a 68 XLCH. 9)

71-85 (except XLX)

The 71 up have a thicker rib across the pushrod side and most people feel they're more rigid. 10)
They do look better under a strobe light than the early ones.

71-85 rocker boxes (F: 17514-71 and R: 17515-71). 12)

Rocker Arms

Rocker arms on a 69 XLH 13)

HD Service Bulletin #678 dated December 17, 1974
1952-1957 HD Parts Catalog for al Sportster and K Models pg 4
1954-1976 HD Parts Catalog pg 5
6) , 7)
1979-1985 HD Parts Catalog pg 7
8) , 11)
photo by The Doctor71 of the XLFORUM http://xlforum.net/forums/showthread.php?t=1946888
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