Have you ever heard the phrase “old wives’ tales”? My father used it all the time whenever something didn’t seem to make sense to him for the moment. For instance, most everyone knows these: “Don’t cross your eyes or they’ll stay that way” and “feed a cold, starve a fever.”
Like I said, they’re “old wives’ tales.” They can be a lot of fun but eventually you get to where the truth needs to be known. So, as the cartoon character Popeye would say just before his head would blow and his pipe would turn into a steam whistle, “that’s all I can stands and I can’t stands no more!”
That is exactly the way I feel about how many people are confused about rod bearings without locator tabs or tangs.
But before we attempt to address that subject there are a couple of prerequisites that we have to get out of the way. Every once in a while you have to go back to the basics. I am going to give you an abbreviated “Cliffs Notes” explanation on two points, but I strongly recommend that you get this information in much greater detail from any of the major engine bearing manufacturers. Verify for yourself that what I am telling you is no “old wives’ tale.”
The term “crush” refers to the outward force created by the portion of the bearing that extends above the housing bore when the bearing halves are set into place. This “extra” material (see Figure 1) holds the outside diameter of the bearings firmly against the housing bore when the assembly is torqued to specification. By increasing the surface contact between the bearing and connecting rod housing bore, crush minimizes bearing movement, helps to compensate for bore distortion and aids in heat transfer.
In simple terms: bearing crush is what holds the bearing in place. Think of it as putting 10 lbs. of something into a 5-lb. bag. The tang or locator tab on the shell that fits the saddle is only for locating the bearing during assembly.
“Eccentricity” refers to the variation in the inside diameter of a bearing assembly (Figure 2) when it is measured at different points around its bore. A properly designed engine bearing is not truly “round” when it is installed in the connecting rod or engine block. Under operating loads, a rod or main housing bore will distort, pulling inward at the parting line between the upper and lower halves. To keep the bearing from contacting the crankshaft in these areas, most designs include additional clearance at each parting end of the bearing. As engine loads increase, so does the amount of distortion, thus race and heavy-duty bearings require greater eccentricity than do passenger car bearings.
The Chrysler 4.7L and 3.7L engines have transitioned to the “no tab” rod bearings, but, as best I have been able to ascertain, the part numbers stayed the same. The “no tab” bearing is the service replacement as well as new production for these engines. They are the exact same bearing as can be seen in Figure 3. The aftermarket has also followed suit with the “no tab” bearing update, so everyone needs to get a grip and realize that the locator tab may be a thing of the past.
Here is an old wives’ tale I’ve been hearing within the engine building segment: “The bearing tab keeps the rod bearing from spinning.” NOT! Tab-less connecting rod bearings are here to stay and will become the bearing style of choice for many OEs in the near future. If you’re wondering why these bearings and connecting rods have been changed, there’s a simple explanation: it’s less expensive to manufacture a bearing and connecting rod without a tab. You may actually find yourself in a position of having to install both types in the same engine because of inventory depletion of the early style tang-type bearings. Fear not: it’s no big thing and the engine will never know the difference.
Eliminating The Low Oil Pressure Gremlin
And while we’re on the subject of bearings, I’d like to discuss something that has reared its ugly head for as long as I have been around the industry. I can also say that the solution has been the most effective in solving a problem that seems to creep up on engine builders everywhere and has an effect on the shops that install engines — both in time and warranty issues.
“Low Oil Pressure” is the frightening gremlin of which I speak! Here is the situation: your customer just got his vehicle back with your newly installed rebuilt engine. But wait: as he returns home, as far as he can tell there is either no more — or possibly less — oil pressure than the old engine had. Or, perhaps they notice that dreaded hot idle oil light flicker, even though the engine meets the minimum pressure allowed by the OE.
What does the innocent consumer believe? Defective workmanship, trying to get away with something, taking short cuts — no matter what the reality is, they feel like you took advantage of them!
Even though every component was machined to exacting specifications and tolerances, this problem rises up and grabs you like a mad pit bull with a death grip on your throat. In more instances than I like to hear about, the engine is replaced with another and everything appears to be fine.
Once the engine in question is returned, all kinds of diagnostics then take place, from oil bleed testing to complete disassembly and re-measurement of all of the components. Oil pump and pick up testing is conducted. Cam bearing oil hole locations are examined, yet invariably, nothing stands out as being a problem.
The components from that engine may be put back into the system and never see each other again as a complete unit. Yet none of the components are ever identified as a problem for any other assembly.
So how do you explain the oil pressure gremlin? More often than not you can’t, and you just move on to “it happened” and that is that.
I can’t give you a foolproof solution, but how about one that has been extremely helpful in eliminating the oil pressure gremlins from many an engine?
Before I give you that however, let’s take a quick moment to talk about what happens at the OE level when an engine is assembled. There was a time when the words “select fit” was limited to import engine applications and it allowed them to install select fit engine bearings that were slightly larger and smaller in size so that the optimum minimum bearing clearance could be obtained on each individual crankshaft journal be it connecting rod or main bearing. Well that procedure exists in nearly every engine application being assembled worldwide today.
Regardless of how stringent the procedures and quality control are on the engine rebuilding side, the use of select fit bearings is neither feasible, economically sound or even available in undersize bearings.
But rising up again, as if from the dead, is the undying entrepreneurial spirit of the “engine builder.” What do I mean by that? It’s no trick – and for many situations they’re proving to be the perfect treat: main bearings that seem to completely eliminate the low oil pressure issue.
No, they are not some voodoo magic but they are a way to address and combat the possible low oil pressure issues described above. What exactly are they? They are main bearings in which the oil grove is terminated prior to getting to the parting line.
As you see in Figure 4, the oil groove terminates before it gets to the bearing parting line. This style of main bearing has accounted for a 15% or more increase in hot idle oil pressure.
So if your shop is the one that does the engine rebuild, and if you’re looking to eliminate some of those unexplained low oil pressure gremlins, contact your bearing manufacturer and ask about this style bearing and availability for the engine applications that you are building for your customer.
A special note of thanks goes out to the engineering people of ProFormance Engines, Springfield, MO, and in particular Reggie Gray.