Disassembling and Assembling Pistons
Disassembling and assembling pistonsTools
Preliminary work
Removing pistons, preliminary work
1. Remove piston.
Tools and materials
Piston disassembly
Information
Piston disassembly - component overview
Identification of pistons
Markings on piston crown: Replacement pistons from Porsche Parts Service are only obtainable in one dimensional group 'X' and in two weight tolerances '+' and '-'. The weight tolerances are listed in the table.
^ Marking X appears as a large colored stamp in the center of the piston crown and as a small engraved feature -1-.
^ Marking + or - appears as a large colored stamp in the center of the piston crown and as a small engraved feature -2-.
Note: Pistons are installed as standard in three dimensional groups: I, X and II.
Pistons are installed as standard in two weight tolerances: + and -.
These data are all engraved on the piston crown. To uniquely identify a piston, it must be carefully cleaned (brass brush, ultrasonic bath). If, in spite of very thorough cleaning, the data are unreadable, the piston must be weighed together with piston rings, piston pin and the two circlips. Thorough cleaning (ultrasonic bath) is also absolutely essential to the weighing operation as otherwise the measurement result will be false.
1. A piston removed for repair is cleaned and identified. If it needs to be replaced, an X - piston with the identified weight tolerance + or - is ordered as a replacement part and installed.
Disassembling pistons
Note: If reusing a piston, do not remove combustion residues on the piston crown are mechanically!
Note: When disassembling the piston/connecting rod unit, note or mark the position, relationship to cylinder and installation position using a waterproof felt tip pen.
1. Fix piston on retaining device.
2. Remove both piston-pin circlips using a small screwdriver. To do this, guide the screwdriver through the small cutout and carefully lever out the piston-pin circlip.
3. Insert piston in retaining device 9597 (leave space below for the piston pin) and drive out piston pin using plunger 9500/8.
4. Remove connecting rods from the pistons and place to one side.
ATTENTION Engine damage if piston rings overstretched!
^ Do not overstretch piston rings with piston ring pliers. Spread the piston ring until it just fits over the piston.
5. Remove piston rings. Place the piston on a clean surface and look for the gaps in the piston rings.
Note: Compression rings and oil scraper rings are installed and removed differently.
6. Remove the piston rings starting from the piston crown. To do this, move the middle point of piston ring pliers Gr. 1 NR.58 into the gap in the relevant ring. The holding arms of the piston ring pliers should clasp the piston ring from above. Do not overstretch it!
7. Relieve the piston ring pliers and remove the piston ring from the pliers.
8. Remove the three-piece oil scraper ring as follows: First, remove the upper and lower rings by hand by carefully forcing them away from the piston. Then remove the oil scraper spring carefully in the same way.
Assembling pistons
1. First assemble the three-piece oil scraper ring. To do this, carefully stretch the oil scraper spring by hand at its gap to a point where this can be positioned over the piston in ring groove 3. Carefully force apart a ring in the oil scraper ring by hand and fit it into the third piston ring groove below the oil scraper spring. Fit the second ring in the same way over the oil scraper spring.
2. When fitted, the gap in the oil scraper ring must be offset by exactly 180° with respect to the gap in the oil scraper spring. Make sure that the oil scraper spring is in the middle of the oil scraper ring.
Note:
^ The two compression rings have different strengths and can only be installed in the appropriate groove.
^ If the piston ring has the inscription TOP, this must point to the piston crown.
3. Insert piston ring into the piston ring pliers. Make sure that, when installed, the designation of the piston rings is pointing in the direction of the piston crown -A-. Spread the piston ring until it just fits over the piston.
4. Fit piston rings. Using the piston ring pliers, insert the middle piston ring into the second ring groove in such a way that the inscription TOP is facing the piston crown. Insert the top piston ring into ring groove 1 in such a way that the inscription TOP is facing the piston crown.
5. Check that the piston rings are correctly seated and positioned. Make sure that the oil scraper spring is inside the oil scraper ring. In the case of the piston ring in ring groove 2, the inscription TOP must point to the piston crown. The top piston ring must be installed in such a way that the inscription TOP is facing the piston crown. The gaps in the individual piston rings must always be offset by 120°.
6. Pre-fit piston-pin circlip in assembly sleeve. To do this, insert the ring in assembly sleeve 9500/9 so that the ring gap is at 6 o'clock or alternatively 11 o'clock (piston crown on top), the assembly groove of the assembly sleeve pointing towards the piston crown.
7. Position the assembly sleeve on an even surface with the groove facing downwards and use the assembly aid 9500/3 to drive down the circlip into the installation position so that the circlip is under tension and sitting in the correct position -arrow-.
8. Check installation position of piston-pin circlip in the assembly sleeve.
9. Position the assembly sleeve on the piston so that the assembly groove of the assembly sleeve points to the piston crown.
10. Insert plunger 9500/8 through the assembly sleeve and fit the piston-pin circlip by tapping it with a hammer into the groove of the piston pin eye.
11. Fix piston on retaining device 9597 with fitted piston-pin circlip facing downwards.
12. Gap of circlip must point downwards away from the piston crown (analogous to 6 o'clock, alternatively 11 o'clock). Place piston pin and connecting rod in installation position. Align connecting rod with matching number so that the matching numbers point to the exhaust side -A-. Illustration shows direction of travel in this case and connecting rod code on one side.
13. Fit oiled piston pin through the piston and connecting-rod eye as far as the circlip. Using a plastic hammer, tap gently on plunger 9500/8, driving the piston pin into the pre-fitted piston-pin circlip -arrow-.
14. Fit the second piston-pin circlip using the same procedure. Align gap of circlip so that it points downwards away from the piston crown (analogous to 6 o'clock, alternatively 11 o'clock) -arrow-.
15. Check connecting rod and piston for smooth operation.
Note:
^ The connecting rods are cracked and together with the matching numbers cannot be mixed up!
^ Connecting rod bolts and bearing shells must always be replaced.
^ The identification of the connecting-rod bearings is located on the connecting-rod journal of the crankshaft.
16. Fit connecting-rod bearing shells in connecting-rod big end and connecting-rod bearing cap. The retaining lugs must be positioned in the appropriate grooves and on the same side -B and C-. The matching numbers -A- must be the same and on the same side (when installed they point to the exhaust side). Tighten the connecting rod bolts by hand and position the complete connecting rod ready for assembly.
Subsequent work for installing pistons
1. Install piston.