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
![](https://motoinstruction.ru/img/bmw/10/116799.jpg)
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".
![](https://motoinstruction.ru/img/bmw/10/116800.jpg)
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°.
![](https://motoinstruction.ru/img/bmw/10/116801.jpg)
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).