Originally posted by Horse:
really easy- first of all the Cobra R ditched the powdered rods in favor of forged Manley rods because they knew the rods were junk. the Noble M12 GTO uses steel rods- also the its new M12 GTO 3R uses the 3L with the same turbo setup for 400 hp.
The connecting rods made of sintered metal are made from powdered metal forged together- sintered metal is notoriously weak. they are made in one piece and then the big rod end is broken so that it can be used around the crank without using a modular crank- which is VERY expensive and not as strong as a forging. when you get machined sintered metal around its large crank bearing that has been broken to split it around the crank, it is very weak. (remember we are talking in relative terms here) Forged steel for instance is a large quantity of either molten steel or an ingot of some type- which is then forged (smashed) into shape- the density and strength charictaristics of forgings are amazing! Sintered metal is a step above a casting but a step below a true forging.
when the rods are weak in their large end they will tend to "mutate" from a round bearing surface to an oval one. (again this is relative- mabey a few hundred thou) this change in shape does not allow the metal bearings to function correctly. for those who dont know the bearings are called a Plain Metal Bearing- or depending on the makeup they can be called Tri-Metal bearings. they are about 1/16 inch thick - almost like a metal shim- and when the big rod end ovals it bites the bearings- and spins them- this creates many many problems- if youll refere to my other post- youll see which bearing did what-
When I say the rod bites the bearing you must understand that the con-rod has two grooves and it does indeed hold the two bearing halves in place- they are stationary in the rod and the crank bearing surfaces rotate within the rod end- so when the rod end bites the bearings it presses them into the crank which actually spins the bearings- and the two little teeth that sit in the rod end grooves get wiped off by the rod - then there is nothing to stop the bearings from free spinning within the rod end, where they either get chewed up by the rod end or the crank. (or in my case two welded themselves to the crank journals and one chewed up a rod end, and one set got so chewed up they spun into each other spoon style, and continued to get eaten away.
These powdered metal rods are made at the Lima Engine plant in Ohio. Their advantage is that they are all the exact same weight, so every single rod is balanced right after they are forged, since they pour exactly the correct amount of mass into the rod that is necessary.
The tangs on the end of the bearing locate the bearing in the journal, but it's the "bearing crush" that holds them in place. If you were to measure the diameter of the journal once the bearings have been installed and the bolts have been tourqued that the bearing is actually oval. This is again by design because the bearing interferance helps hold it in place. You'll notice that when new bearings are installed , they are a little larger than the jornal. That is by design. What causes a bearing to spin is oil starvation, or incorrect boring and honing of the journal.
