When a cylinder head is overhauled, it is almost always machined. To prevent the compression ratio from becoming too high, it is compensated for by shims placed between the cylinder and the cylinder head. Many revision companies put a number in the bottom of the cylinder head that indicates how many millimeters the cylinder head is flattened.
These rings can also be used to set the correct capacity and thus the compression ratio when, for example, different cylinder heads are used than those originally fitted to the engine.
Never use 2 rings on top of each other. If you need more than one ring, fit 1 between the cylinder and cylinder head and 1 between the crankcase and cylinder (refer to the option tab).
To calculate the compression ratio correctly, we have an "engine calculator", which you can find in the main menu under the button "Documentation", then "Technical data".
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