when filing pistons how do you know how much to file it seems like it would be easy to go to far so how do you know?

 

You put the ring in the bore, making sure it's absolutely straight, and check the gap with a feeler gauge. Repeat as necessary.

 

Yup. If you got a flat top piston, that works well for getting the ring straight like RB was talking about. Just put the ring in the bore, then use the face of the piston to push it in straight.

 

Use a "constant" pressure while filing, then count the number of files. Start with 10 to get a feel with how much filing you need to do. Once the first ring gap has been established, repeat but do a few files short of the number from the last cylinder.

 

buy a ring filer, it'll save you lot of extra effort, but it is easy to go to far if you aren't careful. use a tri square or ring squaring tool to check the end gaps. i use a stepped feeler gage to check end gaps so i know when i'm getting close. i made my squaring tools out of a piece of tefelon pipe in a lathe.