I see that most pistons come with an option for pressed in piston pins, or full floating piston pins? Which is better, or is there a difference at all?

 

Floating is better. It gives the piston a dual pivot point, so it will not seize as easily when run hot.

 

We have seen guys install the press fit pistons and after a while pull the engines because of noise to find the piston pins were gauling because the pins were to tight .0004 clearance on the ones that were no gauled.

Most wrist pins made today sem to be over size .9278 is the biggest we measured and if the pin was .927 like it was suppose to be there would not have been a problem.

 

"proper" install is to "fit" EVERY new pin to its hole in the piston, and in the con rod..."std" sized pins would make this difficult as fitting is typically done by 'honing' the piston/rod holes OUT, no good way to expand the pin or reduce hole diameters.

floating pins allow "select fitting" to get same deck clearance in every hole (not important with lower compression/street? ratios but critical for high compression engines)

wrist pin preferred clearance varies with intended useage.

 

most cheap pistons come both way, most GOOD ones will be full floating (JE, SRP, Venolia, Diamond, Etc)

 

you can set a full floater, the machine shop just sets the pin in the rod rather than use the clips. this is beneficial if you are doing a motor that does not have bushings in the small end and is thin enough you don't want to risk installing one.

 

oh, I'm well aware of that, however I think I would buy better rods at that point ( provided they were available, and if they weren't thats a whole other can o' worms)

 

Floaters make rebuilds easier. If a motor gets a lot of rebuilds floaters save time.

 

Thanks guys. Seems that floaters are the way to go. I did see that the more expensive pistons are full floaters. I guess it is up to the individual machinst.

Spanky, I don't ever want to see a rebuild on this engine again. By that time, I hope to be trading it in for a C-10 Corvette.

Thanks folks

 

So far all the pins seem to be the same size per set of pistons but seem to be on the high side.

The thing that scares me I have seen very few shops that have the proper bore gauges to check them with. I guess they go by the feel method.

 

All wrist pins "float" in the pistons, the "press" or "float" option applies to the rod fit. For "full floating" pins the pistons need to be cut for retainer clips and the rods need an oil hole drilled in the tip of the small end.

 

this is 100% true. if you are buying rods for a new motor it would only make sense to go full floater. i just finished a build on my DD with a full floater piston pressed on a factory rod. it's a 220bhp honda 1.8 litre. i didnt see a reason to spend coin on eagle rods for a DD engine. had it been designed for track use or high horsepower that would have been another story. this is a motor that revs to 8500rpm and press fits in the rod didn't scare me. in other words if you have press fit rods i wouldn't machine them for a bushing. you are removing material and for little benefit if you never tear the engine down again. when i did my vette i remember the stock chevy rods being thin and the aftermarket being fairly inexpensive for the quality that exists. a few years back the scat 4340 i beams were the best rod for your buck..that is, if you were cost concious. i have no idea what the prices are like today or the HP your engine will make. i remember buying the eagle 5140 i beams for something like $230 in 2003 and they were extremely light. nothing i would want to hit with nitrous but plenty for a 350-375rwhp car. whatever you do, make sure you check clearances and weights. i have yet to come across a set of rods that are machined right or within half a gram of each other. piston wise i can tell you the mahle powerpaks are the most accurate i have weighed. plus minus one gram on all of em.