Main bearing clearances?
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,158
Likes: 9
From: N.E. WA
Main bearing clearances?
I just had my main line honed and my crank turned on my 92 LT1. My main bearing clearance is .003-.004 depending on jounal number. The book recommends something around .002 max on #1-4 and up to .0032 on #5. I used plasti-gauge, but assuming it gave me the correct reading, what do I do now?
Racer
Joined: Sep 2000
Posts: 355
Likes: 0
From: Valdosta Georgia
Re: Main bearing clearances? (ANTI VENOM)
Check with a knowledgeable parts guy. Most bearings can be bought in a .001 oversize which should brig you into the correct clearence range. Hershey :chevy
Race Director
Joined: Jan 2000
Posts: 13,012
Likes: 2,253
From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
2020 Corvette of the Year (performance mods)
C2 of Year Winner (performance mods) 2019
2017 C2 of Year Finalist
Re: Main bearing clearances? (ANTI VENOM)
If they turned the crank to a "normal" dimension,meaning they didn't try to add some extra clearance and the block was just line honed, you shouldn't be having this issue.
Plastigauge takes some real practice and care to get accurate readings.
If i was you, I would install all the main bearings in the block and install the main caps and torque it all down. I would then load it all up and take it to the machine shop you used and have them re-measure the crank and check the actual bore diameter of the inside of the main bearings. This will take them about 5 minutes if you already have the mains torqued. They can walk out to your truck or trunk and do it all right there.
Then you can be absolutely certain something isn't amiss.
Since they got a good ***** of money from you, they shouldn't balk for half a second to come check it out.
You are shooting for something around .001 per inch of journal diameter. That means around .0024 or so on the mains and .0021 or so on the rods. The #5 is typically set in the .003 range.
Let us know how it turns out.
Also pay close attention to timing chain slack. Depending on how much the cut you can get into trouble.
Jim
Plastigauge takes some real practice and care to get accurate readings.
If i was you, I would install all the main bearings in the block and install the main caps and torque it all down. I would then load it all up and take it to the machine shop you used and have them re-measure the crank and check the actual bore diameter of the inside of the main bearings. This will take them about 5 minutes if you already have the mains torqued. They can walk out to your truck or trunk and do it all right there.
Then you can be absolutely certain something isn't amiss.
Since they got a good ***** of money from you, they shouldn't balk for half a second to come check it out.
You are shooting for something around .001 per inch of journal diameter. That means around .0024 or so on the mains and .0021 or so on the rods. The #5 is typically set in the .003 range.
Let us know how it turns out.
Also pay close attention to timing chain slack. Depending on how much the cut you can get into trouble.
Jim
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,158
Likes: 9
From: N.E. WA
Re: Main bearing clearances? (427Hotrod)
I spoke with my machinist today and he said that this is a common problem. He stated that, unless you install the bearings and caps measure them and then custom grind the crank for .0025 clearance, that they nearly always end up with more clearance. He says that this is due to the bearing manufacturers making the bearings with some "extra" tolerance so that the everyday guy doesn't assemble it to tight. He also says that Clevite 77's don't usually run as tight as Federal Mogul. He suggested polishing my main caps were they meet the register and measure the tolerance with a micrometer. I'll keep ya posted if I find some "breaking" news. :rolleyes:
