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Line hone part duex

Practical Engine Building

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Discussion and questions related to the course Practical Engine Building

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Sorry I can't edit my original post. To clarify:

In the LS build worked example. Step 3, minute 1:00 of the machine shop step you mention asking the shop to "perform a line hone with ARP studs attached."

This all makes sense, what doesn't make sense is re-attaching the heads with new gasket and studs just so the machine shop can do this after just having disassembled the heads...

confused, please clarify.

Thanks!

Kevin

It is referring to the line boring/honing of the crankshaft main bearing bores/tunnels.

Most main bearing caps/girdles are retained with coarse threaded bolts (low number of threads per inch) and when these are replaced by studs with a fine thread, for the same applied torque there is an increase in the clamping force exerted by the fasteners. Often the applied torque is increased to take advantage of the higher strength of the fasteners, compounding this.

ALL materials distort under stress (load), and the higher forces applied by the fasteners can cause the block and caps to distort slightly. With some engines this isn't that significant, but where the alloy is used, there isn't a lot of material (thickness) of the cap or block, and/or the fasteners are close to the bore the bearing fit into, that slight distortion can cause the bore to change shape.

That changed shape will, obviously, change the way the bearing fits and, in turn, the clearances around the crankshaft journal. in extreme cases enough to physically clamp the crankshaft solidly in place. In other cases the crankshaft may spin freely but under load the oil film may be compromised and the bearing will fail.

It may also be required for connecting rod big ends for some engines.

Yes, it can also be important for honing cylinders, especially where the head bolts/studs are close to the bores, and when stripping a low mileage and/or well maintained engine down it's not uncommon to see light hone marks still visible in some areas, but close to the fasteners the hone marks have been polished away. This down to them being initially machined and honed without a hone/boring plate, and when the head is bolted down the loadings through the threads have caused the block to distort slightly in those areas.

Hope that helps.

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