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Mixing bearing shells

Practical Engine Building

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When mixing a STD size bearing with a +1 or -1 thou bearing. Is it absolutely required to do the same mix on every journal?

Or is it acceptable to mix some but not all?

The situation I've got is the tolerances in one or two are slightly off from the rest. But I can 'normalize' them by using full STD shells in some journals, and a STD and a +1 in others.

The goal is to get proper oil clearances. It doesn't really matter how you get it done. For instance, I personally always file bearings to some extent in order to get required clearance for particular application since i do not have the option of having different size bearings in stock as they do at factory. If you do it properly the engine will stay healthy for very long time and can withstand lots of abuse... I would say that getting the proper oil clearance is priority number one when building an engine.

You can mix and match as you like. ACL has some guidelines in their catalog regarding the mixing of bearing shells. Here's a link to it : https://www.aclraceseries.com/images/catalog.pdf

Check page 6 and 7 of the PDF for the guidelines!

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