Bore Size

[Duckhunter71]

What do I need to bore to for an over sized piston?

Mariner 90hp
OC263xxx
Standard L3
3 piston

Engine has not been bored before.

How big do I bore out to? I plan to use a .020 oversized piston.

Do I just find the center of the cyliner hole and add .020 to the diameter? How much do I need to leave for the flex hone?


This is my first engine cylinder bore out. Just need some advice before I start removing metal. Its hard to put back after its gone.

 

[daveswaves]

Re: Bore Size

I think you should talk to a marine machine shop first. Generally you bore just enough to solve whatever problem you have. Picking a .020 over up front is kinda putting the cart before the horse. The hone is not going to remove metal, it is just to cross hatch the surface so that the rings wear in properly. If you are trying to "bore" with a hone you will not get a round cylinder, it will be oval.

 

[TheWoodCrafter]

Re: Bore Size

Your questions are something the machine shop that will do the work should know. All this is up to them.

How did you plan on doing this?

 

[Faztbullet]

Re: Bore Size

From the information post your engine is a 1990 year model. The only cast pistons avaliable for that engine is a .015 &.030. Wiseco offers a .020-.040. When I bore a engine I cut a trueing cut .003-.005 then recenter and due my final 2 cuts . I only remove enough material to either repair damaged area or true cylinder. If I was to bore your engine I would make my final cut @3.3895 and use my sunnen hore to hone to finish size of 3.390+/-.0005. If you wanted Wiseco's(only use if I have to)I add .001 to bore size so finish bore would be 3.391. The reason why is these a forged pistons and expand quicker than a cast piston,thus will cold stick if customer does not let engine warm up. Added bore helps prevent this as when piston expands it will be 0005 bigger. The other post is correct ball hone only good for crosshatch and breaking glaze.