The MGA With An Attitude

On January 26,2017, Dale Spooner in Danville, Virginia, USA wrote:
"Concerning line boring versus line honing, they both accomplish the same thing but there is a difference. I consider a line hone mandrel a finish tool. Lots of shops line hone only, I do it myself occasionally. Basically, if the block doesn't need a line bore but the customer wants to start fresh, it gets line honed. Line honing is tricky. One problem is that a mainline with some wide bearing saddles and some narrow, like a B, material gets removed quicker from the narrow ones than the wider ones, as the pressure of the stones is spread over a smaller area. The opposite is true on wide saddles. So often times you'll arrive at size on narrow saddles yet you still have half a thou to remove from the wide ones. Keeping the mandrel true so it will hone equal diameters is hard when you're constantly honing blocks with different size holes that are out of alignment too. The other issue is getting taper across the saddle. Plus you cannot control from where the material is removed, the block or the cap.

IMO it's best to line bore to within .001"-.002" of finish size and then finish hone to size. My reason for this is that many times mainlines can be off a lot not only in diameter but in alignment. After the main caps are cut in prep for machining, you now have a hole that is much smaller but only on one side, the cap side. A boring bar doesn't care about this nor does it care if the bores are out of alignment, it bores a true straight hole on the centerline that you tell it to. So if I set it up to just barely stay off the block side of the bore and take all the meat out of the cap side, then the original crank centerline is not changed. Followed by a finish line hone to final size, an immeasurable amount of material is removed from the block side. Or if there is a bow in the block or some misalignment, then I'll set it up to take the minimum cut out of the block to correct this.

If you can find a shop that does it this way, I think you'll have a better end result. It's more expensive because line boring is a time consuming operation, very little actual machining time but lots of set-up time. Today, shops with a CNC machine can buy tooling to do it on there. I was going to outfit mine for this but unfortunately the tooling will not accommodate a 5 main B block, the saddles are too close together".

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