Fitting the pistons

Fitting the pistons

KS | Kolbenschmidt | Motorservice

What do I need to watch out for when fitting pistons? When installing pistons, there are many things to watch out for — from ensuring the pistons and connecting rods are assembled flawlessly and making sure that the pistons are inserted into the cylinder correctly to performing a proper test run on the engine. Our step-by-step guide demonstrates how to perform some of these steps and provides valuable tips and advice on working with pistons.

Assembly of pistons and connecting rods

Fitting the pistons
Before installing the connecting rods they need to be checked for distortion and twisting with a suitable testing instrument. Position the piston and the connecting rod according to the installation direction. The oiled pin is carefully inserted into the pin bores of the piston and into the connecting rod eye of the connecting rod. For pistons with tightly toleranced pin bore, insertion of the pin is easier if the piston is heated to approx. 40 °C.

For swimming pins
Retainer rings are supplied for fixation of the pin. Used retainer rings must no longer be used. To prevent lasting deformations, the retainer rings must not be pressed together too hard.


Assembly of connecting rod with fixed pin
The bore in the connecting rod eye must have a pressfit to the pin. For assembly the connecting rod is to be heated to 280 - 320 °C (no open flame!). Afterwards quickly insert the well oiled and cold pin into the connecting rod eye. To ensure correct positioning of the pin in the connecting rod, a device with stop pin is to be used.


Whether the rings have safely locked into the grooves can be checked by slightly turning them. The joint of the retention must always be in direction of the piston stroke.

Checking the piston rings

Check whether the rings can be freely (turned) rotated in the ring grooves.
Checking the piston rings
For piston rings marked with “TOP”, the marking must point to the piston crown. This ensures the intended function is working.
Checking the piston rings

Spiral expander oil control rings

The joint ends of the spiral expander should always be exactly opposite the ring joint for spiral expander rings. For spiral expanders with Teflon sheath, the sheath rests against the ring joint. In addition, for spiral expander rings with locating hook it is important that the locating hook is locked into the oil slot.

Spiral expander ring with locating hook

3-part steel rail oil control rings

During transport the spiral ends are untightened and can slip one above another. The position might need to be corrected before installation. Both colour markings at the spiral ends must be visible. If they are not visible, the spiral has overlapped and the ring is not working. The ring joints of the 3-part oil control ring (the two steel rails and the expander spring) must be turned against each other by 120° each before installation.

3-part steel rail oil control rings

Inserting the piston into the cylinder liner

Clean the cylinder block thoroughly. Make sure that all gliding surfaces are free from dirt and well oiled. Press the piston rings together with a squeezer to enable the piston gliding into the cylinder liner without resistance. For Diesel engines measure the gap dimension or piston's amount of protrusion and always adhere to manufacturer's specifications.
Inserting the piston into the cylinder liner

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