I'm looking forward to purchasing one of the latest versions of OS engines in either two or four-stroke configuration, but looking at the parts list I see that the con rods come lacking a bronze bushing on the piston pin end. The question is, are these type con rods long lasting enough to not have to worry about eventual wear and play?

I see a lot of Saitos come this way. Could this trend be due to cost cutting? What's your experience been so far?

Thanks in advance for your advise.

Misterpanda

If you use a fuel with really good oil in it, the rods hold up well, as long as you aren;t trying to use tuned pipes and trying to max the engine out as much as possible. But for sport flying the unbushed rods are fine. I suggest using a fuel with a blend of synthetic and castor oil in it.

The rods are high silicon content aluminum and hold up as well or better than the old 660 bronze bushed rods because of the better heat transfer.

I've never seen a Saito rod get loose, I've seen lots of bronze bushed rods get loose.

In the diesel world PAW the best known, no bushed rod ether and they of course running higher compression increases the load and they hold up fine thus there are two proofs saito glow and PAW diesels martin

Many high performance automotive bearing inserts contain aluminum alloys.

Aluminum has some self lubricating properties & as long as the proper lubricants are present, the harder high silica alloy should outlast the softer bronze bushings.

While some may have a small amount of aluminum it would not be near enough to call it an aluminum alloy. They call the alloy babbit. Perhaps the shells are aluminum, but the bearing surface is babbit.

Note that automotive bearings are constanty fed oil under pressure, the pressure prevents actual metal to metal contact. The soft babbit material asorbs hard debris that get past the oil filter so the soft material is ideal for pressure fed lubrication systems. For our engines the oil is not pressure fed and there is a lot of metal to metal contact so a harder metal (but not too hard) is prefered.

Babbit use has been discontinued for some high load/temperature rod bearing inserts. It is too soft to hold up to the pounding & heat.

Harder alloys that contain aliminum, tin & silicon are employed for some higher load applications. Some of the "embeddability" of the soft babbit has been traded off for the higher load carrying properties.

Since the embedability properties that the added tin impart to the aluminum/silicon alloys is not needed in our applications, the aluminum/silicon allloys used in the conrod construction suffice.

Federal Mogul uses an "AT" prefix to denote aluminum/steel bearing insert construction.

Your replies have been great and I consider them tantamount to a green light to proceed with my intended purchase. I'd been somewhat hesitant because, in their advertisements, many manufacturers emphasize the fact that their engines come equipped with dual bronze-bushed con rods, as a more desirable feature. It's a fact of life that technology keeps moving forward.

Regards,

Misterpanda

I stand corrected, some of these alloys use less than 40% tin, a small amount of silicon, and the rest is aluminum.It has some embedabilityand However, babbit has not been abandoned, it is still widely used, even for some high performance applications.

http://www.federalmogul.com/en/after...eriesbearings/

Yes babbit is still widely used, especially in main bearing applications.

Just wondering if I need to make a new rod, what aluminum to use that is commonly available.

I would like to know that too as I am contemplating having a rod made for a 150 crank journal that is the same C-C length as a 180 rod.

I saw somewhere that Glen Dye (I think ) had some instructions on how to make rods and he said what to use.  He used to make them for guys.  Things may have changed a lot since then.

double post

[quote]ORIGINAL: Sport_Pilot

Not true. The film strength of the oil prevents the metal-to-metal contact. The oil pressure keeps fresh oil flowing through the bearing.
In a connecting rod bearing in an automotive/truck engine, there's nothing but residual oil pressure most of the time.

CR

That would only be true for the wrist pin. The oil pressure indeed prevents metal to metal contact even on the con rod which has pressure. Actually there is occasional metal to metal contact but mostly on start up. On racing engines the bearing clearance is opened up and the oil pump pumps more oil at a higher pressure. However, the larger clearance does cause more contact at low speeds, the intiial acceleration, and startup. Oil clearances in bearings vary from as little as .0005 thousanths of an inch.Film thickness of oil is much smaller about 200 nanometers.