Chainsaw Repair

OK, if you are lucky enough to have a closed port saw, leave it alone. There aren't very many of those around.
What I do is get a Meteor 46mm closed port kit and also a Meteor Stihl 028S 46mm piston (3mm dome), both use a 10mm pin.

Measure the squish with the kit piston and no base gasket, should be around .0365. Then head to your gunsmith or a machine shop with both pistons. Stihl uses a narrower rod small end than Husqvarna. So some metal must be removed from the insides of the piston pin boss in order to fit the Husqvarna rod and provide for oiling of the small end. The easiest way to figure this out is to measure the kit piston and size the 028S piston to match.

So now the 028S piston fits the rod but is 1mm (.040) taller than the stock piston. Which leaves you with .0035 negative squish (not good) .0365-.040! I determine what squish I want and make a custom base gasket out of annealed copper shim stock. I go for .018-.022. Lastly ask your wife for an old tube of lipstick. Coat the dome of the 028 piston with it and put the saw back together, pull it through and pull the jug to make sure you have no lipstick on the head an the plug.

If all is well, put it together. Mine blow around 195PSI. If you have lipstick on the head or plug you increase base gasket thickness.