I am in the market for some Eagle connecting rods for a 383 build.
What is the advantages and disadvantages of press fit wrist pins or free floating ones? Thanks again guys!

 

Full floating pins allow for a double pivot point in the event of lack of oil or overheating. The floaters use a bronze bushing and bronze needs little oil for lubrication.

 

Press fit for an engine expected to do high mileage although highway truck diesel engines are all floating pin and they'll do a lot more than a car ever will. I'm currently rebuilding 2 diesels at work and changing pistons is simple with basic hand tools.

My engine has floating pins. It makes engine disassembly very easy. You don't need a press and torch to get the pins out and you have no chance of damaging the piston. Advantages are if I damage a single piston for any reason, I can easily replace it without having to take it to a machine shop to have the pin pressed in and out. When they install the pin, the con rod is heated a lot to get the pin in. I have a set of Scat 4340 rods and the small end around the pin is blue from the heating. You can use a simple bench press to take out pressed in pins if you're not worried about the pistons but if you're trying to save the piston, you need a special jig to hold the piston so it won't be damaged. There's also a special jig to press in the pistons plus a special torch that heats up both sides of the rods at the same time. With proper tools, pressed pin is easy but very few people have the tools.

Downside to floating pin is the snap rings. I have JE pistons and they use a spiral lock ring to hold the pin in. There are 4 on each piston. They double them on both ends. The spiral locks need to be replaced every time you remove the pins from the pistons. 32 in the engine and they're around $1 each. Technically you only need to remove 16 since only one side is removed to get the pin out but if there's a chance of the other side failing and you never bothered to change the snap rings then it's your own fault.

You buy floating pin pistons and rods. Send everything out to get balanced then you can easily do your own engine assembly without having to pay more machine shop labor rates to put the pins in.

 

I always use free floating so I can assemble them myself and not have to pay a machine shop to do it. Both will work just fine. If you get free floating ones you have to be sure to install the locks properly or they could come out, with pressed ones you don't have this concern.

 

I just looked at the write ups on summit and the press fit rods have a rpm rating 500 rpm higher than the free floaters.

http://store.summitracing.com/partde...=KeywordSearch

and


http://store.summitracing.com/partde...=KeywordSearch

 

That's not a complete surprize. The other possible danger with floaters is that the lock rings can be dislodged from the grooves and destroy a piston/cylinder in less than a second. The likelihood of this happening at higher RPM is greater, since the lock rings can simply compress under thieir own mass due to kinetics at high reciprocating rates (high RPM). Oil holes are a must, and even gun-drilled con rods might be worth considering for floaters. I'm sure those diesel and aviation guys have seen those.

 

It sure is hard to find forged pistons, for 6.0 rods, for a 3.75 stroke with press fit pins. On summit any way.

 

Probably why my JE pistons use 2 spiral locks instead of a single snap ring.

 

Regarding pressing in the pins, the guys at my shop have a SnapOn unit, the rod is laid in, electrically heated and the pin taps in. They use it because they had complaints in the past about the discoloration of the rods with a torch. It's not something new, they've had it for at least 15 years that I know of.

 

You could throw the rods in a toaster oven and do the same thing.

 

floating pins will press fit to a rod not bushed for floating pins and work just fine