Determining piston ring gaps 12 11 070 Removing ignition magneto • Install piston ring in cylinder and measure 60 mm (2.36 in) from top edge of cylinder with feeler gauge to determine gap. • Unfasten retainer on right engine housing cover. 12 5 500 Wear dimension: Ring gap (all piston rings) ............ 1.0 mm (0.039 in) Determining piston pin clearance • Measure diameter of piston pin bores in piston stroke direction using an internal micrometer. • Measure both ends of piston pin with microme- ter. Wear limits: Bore in piston, vertical...max. 22.030 mm (0.867 in) Piston pin dia. ..............min. 21.980 mm (0.8654 in) Radial clearance in piston .........................max.
0.050 mm (0.002 in) E110180 11 25 671 Assembling pistons • Remove the central locking screw and install handle, BMW No. 12 5 500 . • If necessary, remove ignition trigger (4). 11.35 L Note: The side marked “Top” must face toward the piston crown. Install the piston rings with their gaps offset by 120°. 1 2 3 E110190 • Remove the cover, noting the thrust washer (arrow). E110170 1. Groove for rectangular-section ring 2. Stepped micro-taper ring 3. Groove for spring-steel oil control ring • Use feeler gauge to measure float of piston rings 4 in groove. Wear limit, ring float in groove . 0.150 mm (0.006 in) E110200 E110190 E110190 4 E110200 E110200