odd main bearings?

98zjstroker

98zjstroker

Well-Known Member
Joined
Oct 14, 2009
Location
concord nc
So I just tore down my 4.0 engine and noticed the third journal bearing for my crankshaft looks different then the rest of them. Never seen that before and was worried that something caused this bearing to have to be used (spun main crank bearing) to fix it. I talkd with a mechanic I know and he wasn't sure of what it was and also brought up the same thing.

So I looked up main bearings and saw that all the pictures of bearing sets they have for sale has the one odd looking one and began to think that is normal? Why would it be for the third journal though? Is this in fact normal?

Thanks attaching a pic so you can see what I am talking about so no one thinks im crazy.

 
Yep, what they said. It can be in a different journal on different motors, (Ford vs chevy vs Mopar for example) but It goes on the same one on every version of that motor because the block is machined for it. On your motor it's the third one back, on a Ford 390 it's the middle or third main, on a sbc it's the rear main.

It basically sets the end play on the crankshaft, and it's the reason you should put a manual transmission in neutral and take your foot off the clutch at stop lights. After all the leverage from hydraulic or mechanical linkage the throw out bearing is pressing the crankshaft against that thin thrust bearing with 800 to 1000 lbs of force when the clutch is released.
 
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normally, note the numbers on the journals. Make sure they go back exact the way they came off. Also on the connecting rods, be sure the hole between the two halves point towards the cam.
 
Tim C said:
Yep, what they said. It can be in a different journal on different motors, (Ford vs chevy vs Mopar for example) but It goes on the same one on every version of that motor because the block is machined for it. On your motor it's the third one back, on a Ford 390 it's the middle or third main, on a sbc it's the rear main.

It basically sets the end play on the crankshaft, and it's the reason you should put a manual transmission in neutral and take your foot off the clutch at stop lights. After all the leverage from hydraulic or mechanical linkage the throw out bearing is pressing the crankshaft against that thin thrust bearing with 800 to 1000 lbs of force when the clutch is released.
Click to expand...

That makes sense. I remember seeing a funny looking one like that on my sbc.
 
Jeff B said:
normally, note the numbers on the journals. Make sure they go back exact the way they came off. Also on the connecting rods, be sure the hole between the two halves point towards the cam.
Click to expand...

I will try and remember that once everything comes back from the machine shop
 
Tim C said:
It basically sets the end play on the crankshaft, and it's the reason you should put a manual transmission in neutral and take your foot off the clutch at stop lights. After all the leverage from hydraulic or mechanical linkage the throw out bearing is pressing the crankshaft against that thin thrust bearing with 800 to 1000 lbs of force when the clutch is released.
Click to expand...
All my years of driving, & constantly being in the presence of mechanics, I've never heard that mentioned! Makes sense.
 
Tim C said:
It basically sets the end play on the crankshaft, and it's the reason you should put a manual transmission in neutral and take your foot off the clutch at stop lights. After all the leverage from hydraulic or mechanical linkage the throw out bearing is pressing the crankshaft against that thin thrust bearing with 800 to 1000 lbs of force when the clutch is released.
Click to expand...
never thought about it, but that makes sense! I bet owners manuals don't mention it. Although, who wants to hold a clutch down for 5 minutes while the light cycles?!?
 
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