I have just posted a reply to this thread, but on "Comet oil filter woes" I was too lazy to type it all out again, hope it makes sense, it worked fine for me. If anyone can drag it across that would be great.
Here you go
@Peter Holmes:
“OK, I am waiting for all engineers in the club to to start shaking and weeping. My solution to this problem was thus, get yourself 2 x hole saws, good quality ones, you want one hole saw with the internal diameter a very small amount under the diameter of the filter chamber, just a running clearance, the other hole saw with the internal diameter a shade smaller than the internal diameter of the hole in the filter, use the large hole saw to make a circular disc out of a decent piece of fairly thick plywood, good quality, say marine ply 15mm thick, now follow through the centering drill hole with the smaller hole saw, now Araldite the disc that you have made onto the small hole saw, that will ensure that when the hole saw is used to remove the excess casting from the filter housing spigot that the spigot remains concentric with the filter chamber, hold your heads in horror, but it worked for me, you could make a positive stop depth gauge by packing out the internal of the hole saw but I find that unlike twist drills, hole saws do not have a tendency to pull themselves through so not really necessary, you can do the job in very little stages until you happy with the result, clean any swarf out, job done. There you are Clever Trevor, what do you think of that!
This was my solution to the irregular internal oil filter casting on some Comet crankcases, hold your head in your hands, but it worked for me, with the benefit that it can be done in situ without any stripping down. But in the meantime I believe the internal filter diameter has been made a little larger to accommodate the casting irregularity.”