Spigot/head gap?

There should be about .001" difference, so you will see light through the joint before you tighten the nuts, but none when done up tight. Use coarse grinding paste on the wide face, and fine on the spigot and it should work ok.
John
 

Nathan, I agree with John, fine on the spigot and course on the head, put it on both at the same time and lap it like a valve turning it back and forth, lifting it from time to time and rotating it.  It works for me and was how George Cohen showed me how to do it.  The fun bit (not!) is getting rid of all the grit afterwards!

John, is that your plane?  An Auster? I have a friend in BC with a 58 Cessna 170 and a cub. 

Dan 

Hi Dan
yes it is my Auster, VH-KAZ, a J1-b, 1951, which I've owned for about 35 years and restored about 10 years ago.
John
 

If you had a gasket, surely there's much too big a gap to lap down the outer face?  For information: spigot height and recess depth on my OHC Single are 0.375".

Hi Nathan,

   Your engine has a 3/8th (.375) inch spigot as all of the OHV engines with cast-iron heads of this period. This changed to 1/4 (.25) inch when the aluminium heads were used. Both the heads and cylinder barrels were machined accurately to the sizes and the joint was a ground fit in the pre-war years. This was a time consuming operation and an aluminium gasket was introduced to speed up production and aid owners doing their own maintenance.
   Using a gasket spoils the integrity of this joint as there is a corresponding gap between spigot and head which compromises the combustion process until this gap fills up with carbon. Also the soft gasket has to take the full combustion pressure and can fail if it becomes distorted.
   Using coarse and fine paste will automatically give a 1 thou or so differential which is as much as you need to get a good spigot contact. Use a non-hardening sealer sparingly on all faces.