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Why do main bores need a cross hatch finish?

Engine Building Fundamentals

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I was talking to a local machinist who does billet main cap installs, he told me he bores the mains to size and the cross hatch is not required. I see and read about how the main bores need to have the correct cross hatch finish.

Why is a cross hatch finish important on a main bore?


it is not needed in the main bearing tunnels only the cylinder bores

Regards Ross

If I understand your question correctly, the 'cross hatch' is a result of the honing to finished size and isn't something that needs to be strived for, as with cylinder bores.

If anything, a slightly rough (honed?) finish 'may' help the block and cap 'lock into' the shell, and further reduce the chance of spinning a bearing.

However, that's supposition and above my pay grade - I'd just prefer it finished to the smallest bore the tolerance spec's.

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