[Walt Fricke]

Since you have the case buttoned up and the head studs in, I guess it might make sense to:

A) install the copper gaskets and cylinders (no need for pistons), and torque them down. That is tricky if you don't have some tubular pieces to fill in and act like the heads. But you could cut some tubing and put washers on the lower end so you don't push rough cut tube ends into the head material. And then use your straight edge and feeler gauges or whatnot, and measure variance up where it counts.

B) Then, maybe no matter what, put the heads on, and the cam carriers. I like to give the heads a light torque, then torque the carriers, then insert a cam, then do the full torque on the heads, rotating the cam by hand from time to time as I go. You can see how the cam feels this way. I seem to recall slight binds at first going away as I work through the tightening sequence. Because no sealant, no cam gears, no chains, no pistons, no rockers, etc., this is actually not that time consuming to do.

If you don't get a bind, and persuade yourself that the height variance you measured isn't going to be that big a deal, you can figure out if you want to go on.

The seal I would worry most about is not the spigot seal and some oil weeping. It is the cylinder to head seal. I'm not qualified to say if the differences will lead to CE ring blowout, and perhaps eventually a flame cutting through to the outside, ruining cylinder and head, but probably not blowing up the engine.

But 0.025 mm = 0.000984249 inch, or a bit less than one thousandth. 0.0015" = 0.038 mm. That is rather a large percentage change. I don't have the hands on experience with hundreds of older motors, so I don't know if that change of half a thousandth is or is not that big a deal.

You can't get a regular shim which is less than 0.25mm, right? So to get which is 1.5 thou, or is 0.25 plus 1.5 thou (0.15mm), you are at 0.40mm. So with a 0.5mm shim, you are 0.1 off the other way. Know a custom shim maker? You could possibly have a shop take shim stock of the right thickness and punch out two shims.

But Steve, who has that experience, gave you an opinion. I don't know Magnus other than from these pages over some years, but he sounds like he is a careful, knowledgeable fellow.

It is a shame that, since the machine shop had the case on its mill, the spigots weren't decked at that time. But if they don't do a lot of mag case 911 motors, they may well not have known this has become something to check, and if needed, fix. And the setup for something simple like drilling existing holes and tapping is probably rather less complicated and exacting than that for truing spigot surfaces.