Full Floating vs. Semi-Floating rods

Learn me?

What exactly is the difference and why is one better than the other? Is it cost-prohibitive or stupid to convert from one to the other?

One is for boats?

LOL...I kill me. Sorry, no help from me.

CGLockRacer wrote: One is for boats? LOL...I kill me. Sorry, no help from me.

Ba dum TISH!!!

I have heard that full floating rods are better for some things. As a mechanical engineer, that makes no sense.

What is more likely? The full floating rods are easier to install.

In reply to tuna55:

+1

What i'm being told is that full floating = less frictional losses.

Another person told me that it can be more durable in cases of the piston distorting slightly, can prevent galling in the pin bores.

Mostly just curious at the moment. Have a semi-floating motor that needs a rebuild, seems i can convert over for next to no money.

semi floating wrist pin - would be the rod is heated, and interference fit wrist pin is fitted so that when the rod cools, the pin is fixed in place. The piston "floats" on the pin, while being fixed to the rod

full floating wrist pin - would be the wrist pin is held in place with small clips on the ends of the wrist pin cavity in the piston. The wrist pin "floats" in both the rod, and the piston.

full floating is superior.... but it really depends on the application as to how much of an advantage.. (incremental... to significant)

my 8000 rpm 4AGE is using semi floating pistons... for what thats worth to you....

Another issue with full floating rods is that sometimes the clips fail and can cause massive damage.

Swank Force One wrote: What i'm being told is that full floating = less frictional losses.

Think about this while holding up a rod/piston assembly. How much does it take to flop over the not-even-oiled piston?

Super Stock engines are at or over ten grand with pressed in pins.

tuna55 wrote:

Swank Force One wrote: What i'm being told is that full floating = less frictional losses.

Think about this while holding up a rod/piston assembly. How much does it take to flop over the not-even-oiled piston? Super Stock engines are at or over ten grand with pressed in pins.

True. I'm not saying i think it'll be a huge difference by any means.

Sometimes i wish this board had a poll feature.

I've seen 2 cases in person where the clips fell out of the wrist pin and did some incredible damage. One was unrepairable as the gouges in the cylinder was too deep to machine out.

Semi floating if it were my engine.

Pretty common in the acvw world to use Teflon buttons to replace the clips on full floating pins so they can't fail.

oldopelguy wrote: Pretty common in the acvw world to use Teflon buttons to replace the clips on full floating pins so they can't fail.

Teflon buttons were what was recommended to me.

turboswede wrote: Another issue with full floating rods is that sometimes the clips fail and can cause massive damage.

True i've seen this tons in motorcycle motors, Most drag car engines i've used teflon buttons instead of clips to prevent that failure.

Anyone have a photo of these teflon buttons?

I use press fit pins - you don't have to bother with circlips or buttons and there is no down side - they aren't going to come loose on you and there is slightly less reciprocating weight than if you use circlips or buttons. What's not to like?

The only issue would be if you are constantly changing pistons, but its hard to imagine that scenario.

Is the thing with Teflon buttons that they won't damage the cylinder walls if the pin moves?

Exactly. There's no snap ring to come out. Spirolocks won't come out but if it's me I'd go with the Teflon buttons.

Spirolocks are in the center of the picture:

Ok, we are talking about wrist pins not rods. OP had me very confused.

Sorry... i brain farted and the wrong odor clearly came out.

44Dwarf wrote:

turboswede wrote: Another issue with full floating rods is that sometimes the clips fail and can cause massive damage.

True i've seen this tons in motorcycle motors, Most drag car engines i've used teflon buttons instead of clips to prevent that failure.

In over 30 years as a mechanic, I've never once seen this happen.

Zomby Woof wrote:

44Dwarf wrote:

turboswede wrote: Another issue with full floating rods is that sometimes the clips fail and can cause massive damage.

True i've seen this tons in motorcycle motors, Most drag car engines i've used teflon buttons instead of clips to prevent that failure.

In over 30 years as a mechanic, I've never once seen this happen.

Have you ever seen a performance benefit to either?

I've seen it in Turbo-Dodge motors. Spiro-locs was the solution at the time. I'd be concerned about the teflon buttons breaking up and getting into the oil pickup, etc. but I suspect that they have been vetted quite thoroughly by now.

Some old engines had a clamp bolt for the pin. Very old.