Need Some Info On Floating Pin Clearance On Wrist Pin

[ARPM]

I am in the process of rebuilding my 1968 302 and I have a doubt regarding the Full Floating pin clearance on the stock rods. A few of the guys I have talk said that .001 overbore it's about correct for any application and recommended to drill a hole on the top and bottom of the rod to benefit from splash oiling. another guy that worked in a now disappeared machine shop said that .002 it's the exact overbore and to cut a .010 slot at each side of the bore. and a few others have said that the rod must be bored .050 and the install a .025 wall bushing and hone the bushing for a .005 clearance. Are any ones of these guys correct? Maybe none of the above?

The pistons are new KB115 with 0.9122 pins and are for Floating or press pin installation ( Spiro Locks included) the specs for the pistons mention that they expand less than a conventional piston under the same amount of heat due to the special casting process and materials used, the rods are Ford OEM replacements .

Now, Cat performance has a replacement OEM style rod 5140 part num CR302 that has the following clearance specs.

Small end has 0.0009-0.0015" clearance for floating type.

Small end is 0.0006-0.0009”smaller than pin for press fit.

Side clearance 0.015-0.025".

The rod is a steel non bushed type and is for both applications, press fit and bushed. Maybe this spec will work for my Ford OEM Rods? I will hate to have a small clearance and have the pin lock in to the rod after the heat expands the wrist pin.

Now, assuming these specs apply to my new rods I will deduct that the actual bore size of the new rods can be anywhere from 0.9113 to 0.9116. If we were to bore the new rods for a floating pin 0f 0.9122 we will have to make that bore 0.9128 minimum and .9137 maximum. My question is, with such a small overbore will the rods weaken a lot?

My main reason for opting the Full Floating approach is the easiness of repair when changing rods/pistons or pins.

Thanks for all the help you can provide.

 

[TOM B]

I have a full float setup and had no problems. I have Eagle H-beam rods and Probe forged racing pistons. I would call KB and ask them if you have to do machine work on your rods and I think you would if they were pressed. KB should know how much to ream the rods out to. the pistons should work both ways. your not the first one to do this and it cant be that technical. A hole drilled at the top or top side of the rod does help with spash oiling and I would put them in for a full float setup. The main reason to go to a full float is that you get less piston rock and drag on the side walls and top sides of piston and that means more power less heat.

 

[mustangdave]

Yes, call the manufacturer. There are too many variables such as different rod types. They SHOULD know.