HOW TO | this is how you install a piston

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Only when you install a piston safely and properly do you get its full quality and reliability. In this blog you will learn tips and tricks on how to successfully install the piston. And at the same time, you expand your knowledge about pistons. If you have any further questions, please do not hesitate to contact us. You can find our contact details at the end of the post.

Determination of piston diameter

First of all you determine the piston diameter. The nominal size of the piston is measured at room temperature on the piston skirt, 90° and approx. 10mm above the lower edge. The installation clearance should be determined as follows depending on the cylinder material, cooling and power range:

Aluminum cylinder: 0.6 – 1.4‰ of the nominal diameter

Cast iron cylinder: 1.2 – 2.0‰ of the nominal diameter

Here's an example:

The measured cylinder diameter is 39.00mm

The installation clearance at 1‰ is then: 39mm*0.001 = 0.039mm

Result: A piston with a diameter of 38.96 mm is to be used.

Note: Piston coatings such as the Blue Saphir coating have a thickness of approx. 10-20μm and are not taken into account in the installation clearance. If the installation clearance selected is too high, the running noise and wear will increase. If the clearance selected is too small, cold welding can occur between the piston and the raceway. It is therefore important to determine the installation clearance as precisely as possible.

ring kick game

The next step is to calculate the ring kick game. This can be determined by installing the piston ring without the piston in the cylinder. Note: The piston ring must be orthogonal to the raceway, otherwise incorrect measurements may occur.

The ring joint play can now be spied out using a feeler gauge. It should be at least 4‰ of the nominal diameter.

Here is an example:

The nominal diameter is: 39.00mm

The ring gap clearance at 4‰ would be: 39mm * 0.004 = 0.156mm

If the clearance selected is too small, thermal expansion will cause stresses in the ring. The piston rings are pressed against the raceway with increased pressure. Wear increases and the piston ring can break. If the clearance is too high, the compression is minimized. So, here too it is very important to carry out the measurement as precisely as possible so that there is no unwanted loss of quality.

Installation direction of the piston

The installation direction of the piston is indicated by an arrow on the piston crown. The arrow must point in the direction of the cylinder outlet.

Assembly preparation

Please check your delivered components for completeness and condition. Make sure to keep the components and your assembly area clean. Always moisten pistons, rings, gudgeon pins and cylinder bores with a light film of oil during assembly, which increases the service life of the parts.

Do not drive in the gudgeon pin, if it is stiff, heat the piston slightly.

You can find important information about piston rings in our blog post “ How to – piston rings ”.

butt clip

When installing the piston clips, note the following:

Plunger clips must not be pressed together for insertion into the puncture! By compressing the preload can be reduced. As a result, the clips can fall out more easily or hold more poorly in the groove. Therefore: first place one end of the clip in the groove. Then insert the clip into the puncture in a spiral motion. The openings and lugs of the clips must point in the running direction of the piston. Otherwise the clips will start to wobble at high acceleration and may break.

We strongly recommend to always use new clips. You can also find them in our online shop in the usual BARIKIT quality.

Everything should be clear now, right? If you have any questions or need help with installation, please contact us! We are glad to help you.

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