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lineboy55
02-23-2009, 09:30 PM
Accoding to mitchell On Demand, all the main bearing bores are 2.712-2.713" but the Main Journal on the cranks are 1-3 2.5190 - 2.5198 and number 4 is smaller by .010. Doesn't this mean that the bearing for journal 4 is thincker? If you were to buy a set of bearings for a 3.8 N/A, they would all fit in the SC but Journal 4 would have a larger oil clearance and cause low oil pressure at idle or possibly make a knock noise due to the crank banging around and also then possibly explain a rear main leak?

Duffy Floyd
02-23-2009, 09:35 PM
The rear main bearing journal on the crank is 10 thousandth's undersize to prevent mistakes at the engine plant during assembly (tying to install a NA 3.8L crank will not work and the engine builders can easily tell they did something wrong)

lineboy55
02-23-2009, 09:38 PM
But what if you were to use 3.8 N/A bearings with an originall SC Crank
then you would have a large oil clearance

lineboy55
02-23-2009, 09:39 PM
if the journal is smaller and the bore is the same size as the others, that means they used a thicker bearing for the SC, an N/A bearing would fit but not be thick enough for a SC crank.

frdlvr30
02-23-2009, 11:41 PM
Yes, you are correct. It sounds like you have done this on your vehicle? Do you have N/A bearings installed?

Mike Puckett
02-23-2009, 11:49 PM
Don't worry, the bearing manufacturers know all this. When you buy a set of main bearings for an SC one pair of them will be for the undersized journal. They'll be marked differently on the back so you can identify which ones they are. I bought a set of King bearings for a spare short block and it had the undersized pair in the set appropriately marked. And as I discovered (OOPS), if you don't pay attention to what you are doing and accidentally put them in the wrong spot, it will lock up the crank when you cinch the bolts down much less put any torque on them.