Non bushed full floating rods?

Was talking to the machinist doing my block today and was asking about getting my rods reamed out to be fitted for bronze bushings since I will be running full floating pins.

My machinist does not recommend the bronze bushings.

What he wants to do is drill a oil hole to lubricate the pins and just slightly hone out the pin bores on the small end of the rod and run the pins bare in the rods.

The machinist said the pins are steel and the rods are steel or cast iron and as long as they have lubricant the steel on steel will wear much better and last longer than the bronze bushings.

As for lubrication I plan to run dry film lubricant on the piston pins anyways.

The machinist says he used to run this setup on his drag boats way back in the day and he sets up alot of small and big block C****'s that way.

I have never heard of running full floating pins and NOT using bushings.

BTW this guy has a good rep and is well known locally. Hes one of those old gearheads who has probably forgotten more than I will ever know.

He is also amused and seems interested in my inline six build.

Not to talk bad about your engine shop, but it seems to me he has given you some bad advice on more than one issue....IMHO! Steel on steel will gall almost immediately, they are not compatable wear surfaces regardless of how much clearance you put on them, and a bronze bushing is the only way to successfully float a wrist pin. If that was the case as he mentioned, then with his logic, Crower and Carrillo and all the steel rod manufacturers would use that method to fit their pins, instead of using bushings.Even many of the Pro Stock and Comp Eliminator guys are putting bushings in their aluminum rods now, as opposed to steel on aluminum as before, because bronze provides a much more stable and durable wear surface for wrist pins, valve guides, pilot bushings and any heavy load situation. I wouldn't recommend to anyone to float a pin with out using a bushing.... You have probably the best race shop east of the Mississippi right in your backyard in Indy, I think you should begin to seek another engine shop.

8) i agree with cnc-dude, you need to bush the small end of the rod if you float the pins. it might have worked with drag boats, and other short race engines because they get torn down between races and checked for damage.

There were some factory rods that were coated and floated without bushings. I have also seen many small and big block Chevys done this way.

I personaly wouldn't do it. There is usualy one or two that will be galled slightly in every set. The up side is, the piston and pin has less friction than the rod and pin, so it works better than one would imagine.

The machinist did point out that he would have to drill a hole to supply oil to teh pin and rod end so it would not be bare metal on bare metal.

Plus I am getting my pins dry film lubricant coated.

your machinist is NOT talking out of his butt.
that was a common mod for many back in the hey day of hot rodding for those rodders who could not afford the extra cost of bushing their rods.

But you must keep in mind that most engine oils today are not your fathers dinosaur sauce and that may play into whether or not this would be a wise choice. Also consider the benefit of floating pins IIRC they will reduce side loading on the rod. the ultimate benefit IMHO is strictly longevity and not extra HP(you might also achieve some smoothness of operation and better responsiveness of the engine)

IMHO Any extra HP with this mod would be realized at a very high RPM and while that may be desirable our L6s don't like the revs (at least the 250ci with its longer stroke doesn't; the 200 ci is a little better)

The bottom line is where do you want your motor to operate and where does the benefit of floating pins come into that operating range be it for longevity / durability or ,if you spin high enough, extra power.

keep sixn'

dan

I like history, and has anyone ever wore out the pins in the pistons are for that matter the pistons and had a failure because of such, other than extreme builds, I did not float them in my build, nor did I use forged pistons because of the extreme reliability of the federal mogul cast if kept under 5500 in the 200, its really a matter of choice, I personally think the two most important things in a 200 build are arp rod bolts and a complete balance and good dampner to start with, because my six is extremely smooth and has less harmonics.

Im going forged as I will be running a turbo and want to run more than 10lbs of boost.

Then go for it, you won't have to think about it later.

Dry film coatings are good for many applications, but they can't compensate for incompatable materials such as this application, I would recommend either press fitting the rods and pistons or float with a bushing. Cameljockey hit on a key issue, and that is durability and dependabilty, and floating it with no bushing wont give you either one of them. As you mentioned before, an oil hole is going to be needed to supply oil to the pin, and that is true. But this isn't an oiling problem, its a material compatability problem, and regardless of what coating or oiling is used, it still doesn't change the metallurgy of the two metals involved, and they just aren't suited for metal to metal contact. I definately wouldn't recommend it for you.

Your machinist is not wrong. You can float the pins by merely honing the small end for clearance and drilling an oil hole. While bushing the rod would be best, it is not a must. Many high end race engines use non-bushed rods for weight saving, but most use DLC or Casidium coated pins.
I have done it both ways with no failures. Look at it this way, if the pin seizes in the rod it is now acting like a pressed in pin

If you want to bush the rods, simply tell him that it would help you sleep at night if they were bushed and that you will be happy to pay for the service. I'm sure he will be happy to bush them for you, he was probably trying to save you some unnessasry labor in his opinion. What every you do, DON'T mention some people on a web forum said you needed them bushed.
BTW, what type of dry film lubricant are you planning to put on the pins?

I would go with the opinions of the engine builders, that actually do this every day, AP has sure impressed me and you said your builder is very reputable, people find out whos good and who's not in this business fast. Everybody on a forum has an opnion.

The machinist I use said he does not have the fixture or something to install the pin bushings but he told me of two places that can install them.

He didnt try to steer me in the direction of running without bushings he simply said this is hiw he used to run them and he has set up many engines this way with no problem.

Even with that I was wary of this and wanted some input.

I am aware of the lack of Zinc and phosphate being reduced to less than 800ppm to protect the emmisions components. I have not selected a motor oil but I will be looking for something over 1200ppm to help protect my motor once its built.

Piston pins made of case-hardened steels and nitrided steels ensure high fatigue, wear, and seizure resistance when in contact with the piston and connecting rod. Bushings in the bores of the pistons and connecting rods further improve the tribological conditions, but also increase both weight and cost. MAHLE's coated piston pins provide the best tribological conditions, allow the elimination of bushings, and thus the weight of the piston and connecting rod to be reduced.

Coatings based on PVD (Physical Vapor Deposition, a high-vacuum vaporization process) have long been proven in motorsport. Diamond-like carbon coatings (DLC) are often used in this context. Friction losses drop significantly with such coatings. Coatings based on chromium nitride are also possible.

For coating temperatures of up to 230 degrees Celsius, casehardened steels can be used as the pin material, for higher temperatures, nitrided steels have better properties. Besides single-layer coatings, MAHLE is also working on multi-layer coating composition. Tests show that a PVD-coated piston pin consistently has greater wear and seizure resistance, with reduced oil lubrication and friction.