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Thread: Crank Bearing Coatings and Installed Clearances

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    Crank Bearing Coatings and Installed Clearances

    I have a question for a turbo 1.6L Xflow I'm building. I'm working with a guy that builds a lot of drag engines and specializes in coatings. He has sourced new std size King crank bearings for me and has applied a vapor deposition friction coating, which he swears by and does and his usual V8 builds. He works for a military lab and uses the same tech for military engines, so I do not have concerns on the quality of those coatings. However, when checking clearances, I find 0.0005" (0.0127mm) of clearance between these installed bearings and the crank journals. Everything so far in this rebuild has been in pretty good shape, and I don't think any dimensions are especially far from std sizes... which leads me to believe the coating is what makes this so tight. Now my builder wants me to have the crank journals cut down just slightly to make up the difference, shooting for 0.0015-0.0022" (0.0381-0.0559mm).

    The way I see it, the other option is to just bite the cost of the coated bearings I currently have, and get new ones to install as is/no coating. Its only slightly cheaper going this route, but my bigger concern is down the road if I have to replace the bearings again, it would be nice to be able to use the std size off the shelf.

    Is it worth having these coatings? By using them, will I ultimately avoid having to change them later all together so sourcing new ones later wont be a concern? I understand that ideally these bearings work under hydrodynamic conditions, but contact under load is likely and top bearing manufacturers are also providing coatings on their bearings (https://www.dragzine.com/tech-storie...cience-behind/ ; do note my coating is not a polymer).

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    Crank Bearing Coatings and Installed Clearances

    Since the coating cannot guarantee anything I would personally go with std shells.


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    Re: Crank Bearing Coatings and Installed Clearances

    My take - a friction reducing coating on a soft metal bearing is nonsense, there is no contact, the journal runs on an oil film not the bearing surface hence the clearance, the soft metal bearing is sacrificial to protect the crank journal.

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    Re: Crank Bearing Coatings and Installed Clearances

    Quote Originally Posted by Erikmex View Post
    My take - a friction reducing coating on a soft metal bearing is nonsense, there is no contact, the journal runs on an oil film not the bearing surface hence the clearance, the soft metal bearing is sacrificial to protect the crank journal.
    Yes totally agree there

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    Re: Crank Bearing Coatings and Installed Clearances

    I was leaning that way too, thanks for the confidence boost guys.

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