Removing piston
Remove piston pin circlips.
Press out piston pin with drift, BMWNo. 116581.
Note: Mark exhaust-valve side on piston crown.
Disassembling piston
Remove piston rings with piston ring pliers.
Carefully clean piston.
Check piston for signs of damage.
Determining clearance of piston in cylinder
Measure cylinder bore at 55...65 mm (2.17...2.56 in) from the upper edge with an internal micrometer at three points (1, 2, 3).
Make a note of the largest value as dimension "A".
Measure piston diameter "B" at distance H=16 mm (0.63 in) from the lower edge at a right angle to the piston pin axis.
Note: Determine piston clearance: Dimension "A" minus dimension "B" = piston clearance.
Piston clearance:
- When new: 0.024...0.040 mm (0.0009...0.0016 in)
- Wear limit : max. 0.100 mm (0.0039 in)
Determining piston ring gaps
Slip piston ring 60 mm (2.36 in) into cylinder from top and use a feeler gauge to measure ring gap.
Wear dimension:
- Ring gap (all piston rings): 1.0 mm (0.04 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 micrometer.
Wear limits:
- Bore dia. in piston, vertical: max. 22.030 mm (0.8673 in)
- Piston pin dia: min. 21.980 mm (0.8654 in)
- Radial clearance in piston: max. 0.050 mm (0.0019 in)
Assembling pistons
Note: The "Top" must face towards the piston crown. Install the piston rings with their gaps offset by 120°.
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 in groove.
Wear limit, ring float in groove: 0.150 mm (0.006 in).