Removing and Installing Pistons
Removing and installing pistonsTools
Information
Component overview of piston
Component Overview:
Identification of pistons
Piston Marking:
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 centre of the piston crown and as a small engraved feature -1-.
^ Marking + or - appears as a large colored stamp in the centre 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.
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.
Preliminary work
Preliminary work for removing pistons
1. Remove engine.
2. Remove cylinder head.
3. Remove chain case cover.
4. Remove oil pan.
5. Remove crankcase lower part.
Removing pistons
Removing pistons
Holding Bridges At Bearings 3 And 5:
1. Secure crankshaft with holding bridges 9677 at bearings 3 and 5 to prevent it from falling out.
Note:
^ Connecting rod bolts and bearing shells must always be replaced.
^ Turn the crankshaft so that the crank pin of the piston to be removed stands vertically upwards.
2. Remove one piston after another, mark them and place them on a clean tray. The arrow on the bottom of the piston points in the direction of travel.
3. Remove the piston of cylinder 1 by unscrewing the connecting-rod bolts.
4. Remove the connecting-rod bearing cap and place it on a clean surface.
5. Press the piston downwards out of the cylinder, for example with the handle of a hammer, and receive it with the other hand.
Matching Numbers And Installation Arrow A:
6. Fit the connecting-rod bearing cap again immediately on the big end of the connecting-rod bearing with the bearing shells and place the entire piston on a clean surface.
7. Mark piston with No. 1 (with a felt-tip, not with a prick punch or other sharp-edged tool).
8. Remove the remaining pistons using the same procedure.
Note:
^ Note the association between the connecting-rod big end and the connecting-rod bearing cap as the cracked connecting rods only fit in one position.
^ The retaining lugs of the connecting-rod bearing shells are always located on the same side in order to prevent the bearing shells from turning.
Retaining Lugs Of Connecting-Rod Bearings -B And C-:
^ The connecting-rod bearing cap and the big end of the connecting-rod bearing have the same connecting-rod numbers.
Note:
^ Note the association between the connecting-rod big end and the connecting-rod bearing cap as the cracked connecting rods only fit in one position.
^ The retaining lugs of the connecting-rod bearing shells are always located on the same side in order to prevent the bearing shells from turning.
View Of Connecting Rod Numbers:
^ The connecting-rod bearing cap and the big end of the connecting-rod bearing have the same connecting-rod numbers.
Installing pistons
Installing pistons
Note:
^ 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.
Note:
^ The pistons must already be pre-fitted (pistons, piston rings, connecting rods and fastening material) before performing the next step.
^ Install with the number on the connecting rod -A- to the exhaust side.
^ When installing the piston in the crankcase, the direction of travel arrow on the piston crown must point in the direction of travel.
Surface With Cylinder Number Marking:
^ The code on the connecting-rod big end and connecting-rod bearing cap must be on the same side -A-.
Allocation:
^ The direction of travel arrow is on the same side as the connecting rod code -A- as is evident on the piston shown. This can be installed as standard on one cylinder bank side as shown, and on the other cylinder bank side, the connecting rod code is on the opposite side. However, when the pistons are fitted at a later time, it is absolutely necessary that they be aligned in the direction of travel (see the following point). Install with the number on the connecting rod -A- to the exhaust side.
Installing Pistons:
^ The direction of travel arrow must be pointing forwards when installed (in direction of travel).
1. Turn the engine in the engine support so that the crankshaft lies at the bottom.
Turning Crankshaft:
2. Install piston. To do this, turn the crankshaft with a wrench (a/f 27) until the corresponding crank pin is pointing vertically downwards.
3. Cylinder, piston and Piston ring restraining strap for 944 - S2 and Boxster and 911 Carrera (996) NR.57 leicht einolen.
Compressing Piston Rings:
4. Align piston-ring set (staggered by 120°) and compress piston rings using piston ring restraining strap for 944 - S2 and Boxster and 911 Carrera (996) NR.57. Ensure all piston rings are correctly pre-loaded by the special tool -see figure-.
Installing Pistons:
5. Position piston on the cylinder from above and push it into the cylinder, using the handle of a hammer if necessary. When doing so, make sure that the direction of travel arrow is pointing forwards-see arrow (illustration shows cylinder 1)-.
Pressing In Piston:
6. Push piston downwards until the connecting-rod bearing sits on the crank pin. If necessary, use the handle of a hammer to push it -see figure-.
7. Oil connecting-rod bearing shells and crank pins.
Note:
^ The piston connecting rods are cracked and only fit in one position (in conjunction with the matching numbers).
Surface With Cylinder Number Marking:
^ Install con-rod code towards exhaust side -A-.
Retaining Lugs For Connecting-Rod Bearings -B And C-:
View Of Matching Numbers -A-:
8. Then fit connecting-rod bearing cap with bearing shell (twist locks facing each other) --> Retaining lugs for connecting-rod bearings -B and C-. The connecting rod numbers must face each other --> View of matching numbers -A-. Screw in con-rod bolts by hand.
9. Fit the opposite piston (cylinders 1 and 4).
10. Fit other pistons using the procedure described above.
11. Turn crankcase on the assembly support until the crankshaft is on top.
12. Tighten con-rod bolts that have been replaced. Turn the crankshaft until the corresponding crank pin is pointing vertically upwards. Tighten bolts with a multiple-tooth socket Initial tightening 1 6 ft. lbs. Initial tightening 2 15 ft. lbs.. Initial tightening 3 30 ft. lbs.. Torque angle (final tightening) 90°.
Turning The Crankshaft:
13. Once all pistons have been correctly fitted and secured, turn the crankshaft in a clockwise direction to check it, using a ring wrench (a/f 27). When doing so, watch out for stiffness and irregularities. If the crankshaft cannot be turned or if it is very stiff, check whether the installation direction (arrow) of the pistons, the pistons and the cylinders (markings) and the connecting-rod cap and connecting-rod big end all match.
14. Remove holding bridges 9677.
Subsequent work
Subsequent work for installing pistons
1. Install crankcase lower part.
2. Install chain case cover.
3. Install oil pan.
4. Install cylinder head.
5. Install engine.