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Fri Feb 23, 2024 5:14 pm

Since we were talking about rod bearings in my other thread and the sealed power ones were brought up, i looked those up which turned out to be a tri metal bearing, then with some other looking & reading id found an interesting post ( see below ) then , of course, saw contradictory posts from people saying the complete opposite of the quote below. ( taken from a mopar forum )
What do yall think ?

“this is old school but probably still applies. micro/babbit bearing has a 2200psi rating, alum/bi-metal 5500psi rating, tri-metal/clevite 77 7700psi rating. micro's have the best embedability and conformability. all the street wedge engines that i've taken apart had them for the mains. alum/bi-metal is basically like the old federal mogul aluminum bearing. stronger than the micro but giving up some embedability and conformability. the tri-metal (steel back, copper overlay, with babbit coating) is strongest but doesn't like dirty oil.
they will score a crank journal with dirty oil because they have the least embedability and conformability. all factory wedges that have taken apart had tri-metal rod bearings and hemi's had tri-metal mains and rods. micro bearings are easy on the crank but need to be changed often in a race set-up. fuelers used to use micros. tri-meatals will take the most beating but can be hard on parts if the oil doesn't stay clean and alum/bi-metal is somewhere between them both.”

Fri Feb 23, 2024 5:56 pm

I could talk about this all day.
Both types can claim better embedability, becase that depends on WHAT is getting embedded and under what conditions.
The aluminum bearings can handle LARGER chunks of dirt because the aluminum layer is just that much deeper so it can TAKE bigger chunks, while the tri-metal the babbit layer is softer so it can more easily absorb junk with less damage to the crank, but only up to a certain size and amount, but to me that's all a wash.
Nobody plans of what particle size of dirt to feed the engine, or at least that's a secondary consideration.
Babbitt still rules in THE short TERM, OR, When testing the limits.
Aluminum wins in the long term, becuase of corrosion resistance and lower cost.

These are the reasons for why engine builders still preferring tri-metal bearings
1- because they work well on soft steel cranks (lead is soft , duh)
2- because they have the better conformability to adapt to flex and distortion
3-becase they are less likely to completely destroy the crank and block in a sudden lock up if the engine loses oil flow.

Sat Feb 24, 2024 11:55 am

And strangely enough you can mix them.
Cummins later model 5.9 uses a tri-metal bearing in the rod side and an aluminum shell in the rod cap.
And I've done that with several other engines too, works fine, might even work better. :shock:

Sat Feb 24, 2024 3:05 pm

modok wrote: And strangely enough you can mix them.
Cummins later model 5.9 uses a tri-metal bearing in the rod side and an aluminum shell in the rod cap.
And I've done that with several other engines too, works fine, might even work better. :shock:

Now that’s interesting

Sun Feb 25, 2024 11:54 am

And also in either type of bearing there can be different thicknesses of the layers.
Thinner is stronger but thicker gives more ability to conform and take dirt.
And the harder the overlay the thicker it can be.
If the surface layer is thick enough then the bearing can be bored to larger sizes.
The catalogs used to specify what bearings are resizable and which aren't, but they don't anymore.