Impossible 0.010" gap under the cylinder hold down plates?

[ArVeeNiner]

I have an O-320 B2B that I got used. I'm in the process of pulling off cylinders to paint them and have a look see.

At the base of my cylinders are two steel hold down plates each. I have both 1/2" and 3/8" nuts holding the cylinders on. The overhaul manual has you put 4 each 0.010" shims near each of the 3/8" nuts. Supposely these are to provide a gap beneath the hold down plates and the flange on the cylinder barrel. I honestly didn't see how there could possibly be a gap remaining after torquing down the nuts.

So, per the instructions, I put the shims in (feeler gauges), torqued up the large nuts to 25 ft-lbs, removed the shims, torqued the large nuts this time to 50 ft-lbs, and finally torqued the smaller nuts to their final torque of 25 ft-lbs. Sure enough, there isn't a gap under the hold down plates. In fact, the remaining cylinders don't have a gap either. What gives? This engine flew for years on a Pitts with no problem and no gaps.

Can you actually get a gap under this plate? Do I need to worry about it at all?

[osxuser]

I never used any gaps when torquing narrow deck cylinders.

[dart flyer]

The shims go between the plates and the cylinder barrel, not the flange. The purpose is to make sure the plates don't ride up on the radius of the flange as the nuts are torqued.

JG

[ArVeeNiner]

Originally Posted by dart flyer

The shims go between the plates and the cylinder barrel, not the flange. The purpose is to make sure the plates don't ride up on the radius of the flange as the nuts are torqued.

JG

Ahhhhhh, I now see the light!! Now that makes sense! Thanks, I'll take a look at that in the morning.