Deck Height/Squish Clearance Issue

[Todd Rovello]

A while back I sent my Sachs 125 B cylinder out for boring and to have the ports cleaned up. I noticed that the machine shop also milled the top mating surface.. After installing the head and checking squish band clearance, the piston would bump into the squish band and stop at TDC. I added a second base gasket and the engine will now turn over but using the play dough method for checking squish clearance, the clearance is paper thin. There are matching marks on the piston and squish band where there has been slight piston contact. Should I add a third base gasket or will this change port timing too much? Can the combustion chamber and squish area be milled instead or would it be best to start over? I do have an extra cylinder. Any advice appreciated. BTW, what is the proper deck height for this engine? The piston is a Sachs 1st oversize.

[Richard]

I have to ask, but you do have the stock thick head gasket installed, don't you? If you do, I would try adding an additional head gasket made of brass shim stock. Set the cylinder height by aligning the top of the piston with the bottom of the transfer ports when the piston is at bottom dead center, then set the deck height by shimming the head gasket. My reasoning is that if they took material off the top of the cylinder, that is where you need to add it back. As long as the top piston ring isn't in danger of expanding at the top of the cylinder, I don't believe you would need to replace the cylinder.

You could do like you said and have the cylinder head milled but I would bet that would be a lot more expensive and it sounds to me that you know more about your motor than the guys that cut the cylinder do.

[Todd Rovello]

Thanks for the reply Richard. I will let you know how it turns out.

Todd