[fjurassic]

Morning everyone!

I'm supposed to be replacing my connecting rod bearings next weekend. When I went to order parts today, I was told there were 4 possible sizes of bearings for my engine and that "I wouldn't know what I needed until it was ripped apart". Only trouble is, parts are 4 days out and I don't have a week to leave my rig in pieces. I also have a hard time believing that no one at Toyota would know what the stock size is?

Has anyone replaced connecting rod bearings on an '07 4WD AT? I found information that said it could be "standard size" or one of three other sizes (.25mm, .50mm, .75mm). If anyone has resources they could point me to for further research? Or knows what size the OEM bearings are?

I openly admit I don't know much about what I'm looking for... Just sourcing parts and other things for the person doing the work for me.

Helpful answers welcome.

 

[Firemedic831]

If you are replacing bearings its not normal to go back with the original size . There is a reason to be replacing . So to clean up any scouring on the crank they have to turn /polish it down . To make up the tolerance difference they make a plus size bearing . Even new though they can be different , so you will have to Mic the crank to see what you need

 

[LeeA]

To build upon what medic wrote, WHY are you replacing the rod bearings?

If the bearings are worn, then there is probably damage to the corresponding journals of the crankshaft. To eliminate the journal damage, the crankshaft needs to have the journals machined (a.k.a. "turned") to return the surface to a smooth finish. If the damage is minimal, the crank will be turned .25mm undersize (smaller than the original outside diameter).

With a journal that is .25mm smaller (or .50mm or .75), you will need THICKER bearings to provide the proper clearance.

I'll also point out that it is VERY important to properly tighten the rod bolts. Rod bolts are basically progressive-rate springs, and they stretch as you tighten them. IMHO the BEST way to tighten rod bolts is with a stretch gauge attached. It is amazing to me how little effort is required for stretching the bolts for the first couple of thousandths of an inch, and how much to get the last thousandth or so.

Too little stretch, and the bolts will still be easily stretched, resulting in spun/damaged rod bearings. Too much stretch and the bolt will be damaged, and even worse things can result. Some rod bolts are not designed to be reused, as well.

Oh, don't even consider using that 30 year old torque wrench that your father in-law gave you. Not unless it has recently been calibrated.

 

[RocketRob]

Might/should even consider replacing the rod bolts as once torqued/streched they will not return to size.

 

[FJtest]

Seems like there might be a lot of "guessing" going on here as far as advice ...

The 1GR-FE engine uses EXTREMELY tight tolerances for crankshaft main and rod bearing clearances.

It is physically impossible to grind crank bearing journals and connecting rod big ends to the required tolerances at a reasonable cost, so Toyota selects different bearing sizes during initial engine assembly to achieve the required oil clearance.

There are FOUR different "standard" rod bearings that MAY be used in a single engine; these different sizes are designated #1 through #4 . Each bearing # increases diameter by 3 MICRONS (that's .000118 inch!).

The rod bearing "size" that was selected at initial engine assembly is marked on the side of the connecting rod near one of the rod bolts. The OD of each bearing shell is also marked with the "size" designation. You won't know which bearing size was originally used until you open up the engine and can see the markings on the con rods.

Even then, you need to VERY, VERY accurately measure the crank journals to see if there is any wear or taper, and then select the appropriate bearing size which MAY be different from the original bearing size.

VERY, VERY few individuals or shops have the correct measurement equipment that can make measurements at the micron-level; your old thimble-style micrometer won't do it. If you want the engine to "last", you are going to have to take the crankshaft to a very modern, well equipped auto machine shop that has the required equipment to accurately measure journal diameter, and have a mechanic that's astute enough to know how to interpret those numbers when selecting bearing shells.