The measure of engineering precision is called “tolerance.” Tolerance can be a plus or minus number, and refers to the measurement of a specific engine part, such as the thickness of a cylinder wall, for instance. There is also clearance to consider. In the automotive engines’ world, this refers to the space between engine parts. For example, the space between the cylinder wall and the piston housed within it. 

Long ago, in classic cars, tolerance and clearance was not as precise as it is today. Modern manufacturing has come a very long way since then, resulting in more capable and longer-living engines. Today’s cars can thrive far beyond the mileage once expected of classic car models from the 1950s, because they are built with more precision than ever before. 

What is the purpose of Tolerance?

So, we know in the grand scheme of things that the right tolerances and clearances make for a better engine. However, let’s talk about why exactly this is. Engine bearings, for example, must maintain a very sensitive level of clearance. If tolerance is too loose, it could result in an oil leak. However, if this measurement is too tight, it may cause too much difference in oil temperature (think friction). Tolerance and clearance really matters for engine parts when an upset in the balance may lead to engine damage and malfunction. Pistons, piston rings, and other components must be carefully spaced to achieve the desired, optimal result within an engine. The amount of clearance and tolerance a part has directly influences the load distribution on that part, which in turn affects the lifespan of that part.  Not setting a tolerance in a critical component may cause that part to become unusable for it’s intended function.

top piston ring

Why do YOU need to know this and other important measurements?

When you are searching for and ordering engine parts for a particular application, it’s important to know your bore size and other important measurements like compression height. There are so many critical measurements that work together to create a functional engine. Another common part this applies to are piston rings. Piston rings must have the correct ring back clearance for suitable engine performance, as well as the correct axial width, adequate side clearance, and optimal gap.

It’s important to know what you are ordering, and if that part’s measurements are compatible with your engine, and all its other measurements.

We Can Help.

Your local machine shop can assist you in determining measurements, like bore size, etc. Once you have those measurements, it’s much easier to find the right parts for your engine rebuild. For more in-depth information about our product lines, visit our product pages under the “Products” drop down menu. These pages give general information about each product line. For specs and dimensions of a part number, you can visit our catalog website at: and search for a specific part number to find everything you need. Still stuck? Drop us a line on our contact us page or call 1(800) 869 – 8711 for more information. Enginetech products are available at auto part retailers nation-wide.

Don’t see us on the shelf at your local auto parts store? – tell them you want Enginetech!


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