Case inspection, align bore or not Options

[930cabman]

Recently I had my local good guy machinist make a steel inspection shaft to pickup the main bearing bores leaving a thou or so clearance. Seems to make sense, similar to installing the crank with new bearings and making sure the crank spins smoothly (easy). The next part of the plan would involve fabricating another gauge to pickup the cylinder mounting surfaces. Sure this can all be done with indicators, but I am trying another tack with this process. Thoughts?

I also use Plastigage to check actual (after crush) clearances

Working a 2.7 911 cases I have found the main bearing bores become elongated due to many heat/loading cycles. This is very common to this magnesium case and keeps guys like Ollies in business. Is this elongation also common to our VW/914 cases

TIA

[Superhawk996]

More info use as you see fit.

Align boring is usually done to address elongation of the saddles not to fix “alignment” per se.

The case 1/2’s will have a bit of material taken off the mating surface. This forces the main bearing bores to become oval with the major diameter being on vertical plane of the case seam. The horizontal plane is the minor diameter.

So the 1st step in align boring is to actually make the situation we originally didn’t want (oval bearing saddles) - even worse.

Once that is done, the main bearing bore is recut to be perfectly round to fit the oversize bearing. By default, the bearing bores are then also “aligned” though the primary purpose was to make them round again and to fit the new oversize bearings.

If you haven’t already found this post on your own it’s worth reading and Jake Raby chimes in as well
http://www.914world.com/bbs2/index.php?sho...p;#entry1384278

Note: the OEM machine work is done with more precision than any aftermarket / machine shop align bore will be. Most shops use a pretty hokey boring tool that pilots off the nose bearing / crankshaft seal bores and won’t be as rigid as the OEM tooling was that cut the bores the 1st time. In addition, align bore changes the dimensions between crank center line and the cylinder registers and has cascading implications to compression ratio and valve geometry.

Bottom line - don’t align bore if you don’t have to