Summary

In what scenario would I purchase aftermarket mains such as ACL which surely are a one size fits all for the given engine? OK so yeah what you're talking about there is a factory engine where there are gradings stamped on the engine block.

00:00 - Leon has asked, when I built my engine, the main bearing sizes were stamped on the block and I used them to buy the correct sized OEM main bearings.
00:07 In what scenario would I purchase aftermarket mains such as ACL which surely are a one size fits all for the given engine? OK so yeah what you're talking about there is a factory engine where there are gradings stamped on the engine block.
00:22 There will also be gradings stamped on the crankshaft.
00:25 So in the factory workshop manual, what we can do is then use a grid to decide which grade bearing shells we need for a particular journal.
00:34 So this in a way is a factory blueprinting procedure aimed at achieving the required or specified oil clearance on each journal and maintaining it consistent, so this just accounts for the very small machining tolerances that there will inevitably be in every production item.
00:51 In the aftermarket you are quite right, we generally have a one size fits all bearing shell.
00:58 However there are some areas where with popular engines we are able to buy bearing shells in a range of different grades even in the aftermarket.
01:08 What we'll often be doing though is increasing our oil clearance as I've talked about a little bit earlier.
01:15 So what this allows us to do is use an aftermarket bearing shell and then we may make small adjustments or have our machinist make small adjustments to the journal diameters by way of either polishing or grinding those journals on the crankshaft in order to achieve the exact clearances that we particularly want.
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