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Journal and Bearing tolerances

C

Car Enthusiast

NAXJA Forum User
Location
Columbus Georgia
I have been searching and for the life of me can't seem to find actual number one what main and crank journals should be or what the tolerances to measure. Is there a reference website out there that I can look it up. I looked in my Chilton's manual and can't find anything about the size, only that it shouldn't be .001 outside of spec

I just got my 4.6 back from the machine shop and I want to plastigage the bottom end to make sure it is in the ballpark of what it should be before I put it all back together.
 
Have you had the crank ground and the rods resized? The preferable clearences would be about .015-.003", just start with the plastigauge.
 
New scat crank and rods. The main journals in the block weren't touched and I want to make sure they are within tolerances before I put it together. If not I want to get them align honed.
 
according to my 96 FSM....Main bearing bore dia - 2.691>2.692
Main bearing journal dia #1.#6--2,4996 >2.5001...#7-2.4980> 2.4995
preferred bearing clearance---.002
 
If your spending good money on a crank and rods, I would definitely get the block align bored!
 
Yes they can do it, it has nothing to do with the deck. Did you have the cylinders bored? What about cam bearing installation?
 
What pistons did you buy or plan to use? That will determine how the block is bored! What compression are you shooting for?
 
Cam bearings installed
Bores are .030 over at 3.905
The piston are a set of race techs and they are at 3.9020

The block deck is set up to have the piston .008 out of the hole with a .051 head gasket giving me a .043 piston to head clearance. If the align bore the block after miling the main caps, wouldn't that move the piston high up since the rod would be "deeper" in the block?
 
Car Enthusiast said:
Cam bearings installed
Bores are .030 over at 3.905
The piston are a set of race techs and they are at 3.9020

The block deck is set up to have the piston .008 out of the hole with a .051 head gasket giving me a .043 piston to head clearance. If the align bore the block after miling the main caps, wouldn't that move the piston high up since the rod would be "deeper" in the block?
Click to expand...

NO, the centerline of the crank will not change, just like line boring the cam holes in the block keep the cam centerline the same too.
 
TRCM said:
NO, the centerline of the crank will not change, just like line boring the cam holes in the block keep the cam centerline the same too.
Click to expand...

That's not necessarily true, most shops grind the caps only so they can do std size bearings!
 
RCP Phx said:
That's not necessarily true, most shops grind the caps only so they can do std size bearings!
Click to expand...

If they grind the cap, then to get the hole round again, they will have to bore the cap side of the hole back out....so the centerline will stay in the same place and they can use standard bearings. The cap will not stand as tall off the block tho due to it being ground down.
 
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