I'm rebuilding my 300ex and was wondering what size to get my cylinder bored out to. I know the standard bore is 74mm. I don't understand what to order out of the magazine. It says like (.020)and then .5mm after that. To get that piston do you have to get your cylinder bored out to 74.5mm. If that's the case whats the .020 mean? Thanks alot.

 

.020 is twenty thousands of an inch. I would recomend buying a new piston and then bore to the size of the piston. That way you know it is gonna fit.

 

So if I get the piston that is .020 or .5mm what size do I get my cylinder bored out too. Because you have to have a certain amount of clearance don't you.

 

Yes get the piston first then take the piston and the cylinder to a machine shop. They will know what to do. If your cylinder is in real bad shape .020 might not be enough. If the engine ran and you are just freshening it up then .020 will work great.