Originally Posted by Gray Beard

You can also look at photo number one where I have the pointer sitting on the casting block showing you the front. I also used to mark the case and housing with a line to match up to, it works but knowing the front from the back is better. I can tell my early engines from my newer ones when I see the mark. At some point knowing the front from the back finally sunk into my head.
I was just out in the shop so took a couple of photos of two different 110s with the guide markings I ground into the case to make sure I had the diaphragm cover on correctly. Another little FYI. Years ago if you sent in your engine to YS servide they had the jig set up and ported the piston for you for free. It was just 4 or 5 little holes drilled in the piston top and the purpose was to put pressure behind the ring for a better seal. It worked so well that the YS factory started doing it on new engines. The 4 ports on the 110 are factory, the other piston is an old .91 without porting. I tossed in a page with an address for you to pull up too.