Rod / rod bearing replacements

Bukowski · 07-13-2013, 08:34 AM

87 944 NA

If the rod bearings are replaced but not the rods - i.e. in an oil pan gasket job - should the rod bearings also be replaced when the rods themselves are replaced?

That is, will the process of removing the rod bearings and nuts and then reassembling with new rods alter any of these parts to be out-of-spec.

ideola · ideola's Garage

At minimum, when replacing the rods, you absolutely should plastigauge the assembly to make sure the rod+bearing+crank journal combination are within spec. Any time one of those variables are changed, you should verify that the assembly is still within spec.

In any event, rod bearings are so cheap, why would you go to the trouble of replacing the rods, and not just replace the bearings while you were at it?

TibetanT · TibetanT's Garage

Not sure what you are asking here, but "Yes" the rod bearings can be replaced without removing the rods. Engine will need to be supported from above so the cross member can be removed from below to allow access.

If you replace just the rod bearings, also replace the rod bolts. I think you are also going to replace the oil pan gasket, which is standard procedure when down there.

Now, to answer the other question with regard to the rods themselves, I would make sure the rods are balanced...just my opinion here. Also, if it were me, I would probably be doing alot more such as: piston rings, crankshaft polish and other stuff since this is a teardown process.

Hope this helps.

Bukowski · 07-13-2013, 08:55 AM

thanks - FYI I didn't want/mean to get into HOW rods are replaced here - merely to get the idea that WHEN they are replaced, then do the bearings.

ideola, when you say "balanced", do you mean measure the mass of the rod on a scale?

mytrplseven · mytrplseven's Garage

Bukowski: He's talking about a lot of things we, who have built high performance motors, do when "blue -printing" a motor. The entire rotating mass of crankshaft, rods/pistons, flywheel, damper, clutch, etc. are balanced at a special shop. Typically these extra steps are taken when you spend most of your life around redline and want to ensure the motor will last and not "grenade" in that lofty region.