1989 Force 85hp Rebuild Question (case is at the machine shop)

[Leviathan]

As the title says I need some specs for my 89 85 hp motor. I have a set of 0.0030 over pistons for my engine, but I need the spec for the spacing between the piston and bore. Any other specs would be greatly appreciated as I have nothing.

Thanks

 

[Frank Acampora]

Re: 1989 Force 85hp Rebuild Question (case is at the machine shop)

There is no published specification for piston to bore clearance. If your pistons are made by a reputable manufacturer, they should be the correct size for the overbore. The machine shop needs to bore slightly undersized then rough hone and finish hone to .030 over, plus or minus a couple of 10 thousands. A good machinist can hold these tolerances. Stock bore is 3.3125 or 3 5/16. So your machine shop personnel should be able to do the math.

Since manufacturers do make pistons that fit, I'm sure they know the necessary clearance, but it isn't necessary for the shop to know. If the machinist absolutely insists, try calling the piston manufacturer and find out the major and minor diameters.

 

[Leviathan]

Re: 1989 Force 85hp Rebuild Question (case is at the machine shop)

The piston doesn't need to be machined at all... I was just looking for a clearance spec, but the machine shop can just figure it out based on the old piston and bottom of the bore I guess then add the overbore... Seems a little rudimentary, but they've done it a bunch before.