Step 1: Clean pistons:

First clean the pistons thoroughly and remove all carbon deposits from the ring grooves. Use a twist drill and tap wrench to remove the carbon deposit from the oil drain holes. Replace cracked or deformed and worn pistons.

Step 2: Check piston ring grooves:

If a clearance of 0.12 mm or more is measured between a new, parallelsided compression ring and the associated groove wall, this means that the piston is excessively worn and has to be replaced.

Groove clearance (mm)	Piston usage
0.05 - 0.10	Piston can be re-used without restrictions
0.11 - 0.12	More caution necessary
> 0.12	Fitment of new pistons essential

Step 3: Check the cylinder wear:

If the cylinder wear exceeds 0.1 mm for SI engines and 0.15 mm for diesel engines, the cylinder also has to be exchanged (top ring reversal bore wear).

Step 4: Clean the cylinders:

Remove carbon deposits from the top area of the cylinder bore, above the ring travel zone.

Step 5: Check the ring set components:

When fitting the pistons with new rings, we recommend in principle to exchange the complete set. Check the ring height by means of a measuring gauge. It is recommended to compare with our Catalogue data. 

The diameter may be checked by means of a measuring ring or of a re-worked cylinder, the ring gap on the basis of subjective assessment or using a feeler gauge. When verifying the ring diameter in worn cylinders / cylinder liners, it should be remembered that the ring get may have larger values.

Insert piston rings in the associated piston ring groove using the right assembly tool! Avoid excessive opening of the piston rings on fitting as this would cause permanent deformation and impair the performance of the piston rings.

Piston rings marked "TOP" have to be fitted with a particular side up. The mark "TOP" should point towards the piston crown so that the scraping effect is directed to the skirt lower end. If the rings are not fitted accurately, there is danger of oil being pumped from the crankcase to the combustion chamber and the function of the ring set would no longer be ensured.

When fitting rings with spiral expander the spring ends should always be positioned opposite the ring gap. Some spiral expanders pass through a teflon tube, which is located opposite the spring ends and therefore directly beneath the ring gap.

Attention! In the case of certain three-piece oil control rings the spring has a coloured dot at each end. Each of these coloured dots must still be visible after fitting the ring to the piston. This ensures that the spring ends butt up to each other and do not overlap. 

Pistons for 2-stroke engines whose rings are prevented from turning by a small pin, must not be rotated when being introduced into the cylinder. The securing pin could otherwise slip under the ring as it springs outwards into a cylinder port. The ring would then break off at the port edge.

Attention! Chromium-plated piston rings must not be fitted to chromiumplated cylinder liners.

Step 6: Function test / Turning the piston rings:

After fitting the piston rings, make sure that they can be freely moved. Position the ring gaps with 120° off-set to the next ring.

Step 7: Fitting the piston into the cylinder bore:

Oil the piston rings and the piston appropriately and use a ring compressor or a conical KS assembly sleeve in order to prevent damage to the piston rings.

Ring compressors / Assembly sleeves

KS-Art.-Nr.	Description
50009816	Piston ring compressor for ø 57 - 125 mm
50009828	Piston ring compressor for ø 90 - 175 mm
50009865	Assembly sleeve for ø 86,0 mm
50009877	Assembly sleeve for ø 94,4 mm
50009878	Assembly sleeve for ø 94,8 mm
50009866	Assembly sleeve for ø 97,0 mm
50009874	Assembly sleeve for ø 100,0 mm
50009875	Assembly sleeve for ø 102,0 mm
50009867	Assembly sleeve for ø 121,0 mm
50009868	Assembly sleeve for ø 125,0 mm
50009869	Assembly sleeve for ø 127,0 mm
50009870	Assembly sleeve for ø 128,0 mm
50009876	Assembly sleeve for ø 130,0 mm