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Generation III Internal Engine
1997-2006 LS1 | LS6
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Old 01-10-2012, 09:12 PM   #1
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allright my question is if you turn a crank .010 what bearing do you run undersize or oversize can someone explain to me how they get these measurements undersize or oversize

my take is if you turn the crank .010 your tolerance between the crank and main bearing will be greater so you need an undersized bearing smaller inside diameter on the bearing

and if you machine the mains .010 the tolerance between mains a crank is greater so undersized bearing should be used

so when do you need to use an oversize main bearing?

i would guess the crank is a larger diameter than the mains


sorry for going on just like to know how stuff works AND WANT TO ORDER RIGHT BEARINGS FOR ENGINE BUILD
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Old 01-10-2012, 10:12 PM   #2
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If your crank is turned .010 undersize you need .010 oversize.They rate them as .010 thicker so thats how they come up with oversized.
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Old 01-10-2012, 10:29 PM   #3
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so if you machine the crank to a SMALLER tolerance you need an undersized bearing cause i just read on king bearings if you machine the crankshaft the tolerance must be taken up they do this by adding material to the back of the bearing to put the bearing within tolerance and if you align hone the mains you need an oversized bearing they put the material on the inside of the bearing to bring the bearing back within tolerance
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Old 01-10-2012, 11:32 PM   #4
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Before the machinist align hones the main bores, they are supposed to trim the caps so that they will be a smaller ID. This way, they are able to remove material from the bores to get them round again, and also back to spec so that special bearings aren't needed.

Cracked cap rods are a different story though...
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Old 01-11-2012, 02:35 AM   #5
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Yep you 10 thousandths thicker of a bearing, you might even need to use the +\- 1 thousandth half in combo with the new bearings in order to achieve the right oil clearances
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Old 01-11-2012, 06:36 PM   #6
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I just used Clevite MS-2199P-10 bearings where I had the machine shop grind down my crank .010" for my ls6 build.

I so happen to have the box sitting right next to me, so I figured I would add my .02
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Old 01-11-2012, 09:28 PM   #7
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Quote:
Originally Posted by fastazzls1 View Post
allright my question is if you turn a crank .010 what bearing do you run undersize or oversize can someone explain to me how they get these measurements undersize or oversize

my take is if you turn the crank .010 your tolerance between the crank and main bearing will be greater so you need an undersized bearing smaller inside diameter on the bearing

and if you machine the mains .010 the tolerance between mains a crank is greater so undersized bearing should be used

so when do you need to use an oversize main bearing?

i would guess the crank is a larger diameter than the mains


sorry for going on just like to know how stuff works AND WANT TO ORDER RIGHT BEARINGS FOR ENGINE BUILD
Keep in mind that you can go ahead and get .010" under bearings (ie MS 2199H-10) and then measure the ID before you turn the crank. Then, when you do send the crank to be turned, give them the ID measurements and then tell them how much bearing clearance you want, and they will be able to grind the crank to that diameter.
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Old 01-11-2012, 10:30 PM   #8
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A little off topic, but can you simply put in new crank and rod bearings without any machining? As in take the rods and crank out/old bearings, and put stock replacements in and put it back together with new bolts?
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Old 01-11-2012, 11:57 PM   #9
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might not need machining but it is going to need measuring in order to see where youre at no matter what.....if you dont wannna do it again
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Old 01-12-2012, 06:50 PM   #10
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A little off topic, but can you simply put in new crank and rod bearings without any machining? As in take the rods and crank out/old bearings, and put stock replacements in and put it back together with new bolts?
It depends on the condition of the surface. If there are no deep scratches then no or just get away with a polish ($75) and you can use stock sized bearings or if the scratches are deep and cannot be polished out then they will need to be ground ($120-$150) and the use of the oversized bearings will be needed. Either way both the crank and main journals should be measured to establish the clearances. Your local machine shop should be able to tell you if any scratched on the crank need to polished or ground out.
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Old 01-12-2012, 09:11 PM   #11
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its got a small gouge in a main journal so it will have to be turned i will order undersized main bearing the crank is being turned thet said that the mains do not have to be align bored so am i good for just bearings
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Old 01-12-2012, 09:15 PM   #12
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Technically it's best to get align honing of the mAin bores done, but if on a budget you should be fine because the turned down crank will match the bearings:..

I have heard of racers that always turn their cranks on their rebuilds in order to get the main oil clearance perfectly in spec
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Old 01-12-2012, 09:39 PM   #13
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Just an FYI is if You're crank is .010" undersize that is also what they call the bearings .010" unsersize ,,,,,,,,,,,,for rod bearings they have a bearing for LS based gen 3 and 4 chevy small blocks that are .002" oversized for when You have the rods honed out by .002" to make the big end round again especially with ARP rod bolts ,,,,,,the extra clamping force tends to distort the rods a little bit ,,,,,,,,,,,,,,,Clevite has standard inner diameter bearings with .002" oversized outer diameter and Federal Mogule has the .002" oversized outer diam bearings in all the undersizes and in standard inner diam .
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Old 01-12-2012, 10:08 PM   #14
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^^ thanks a lot. I'm just going to bring the rods into the machine shop with the bolts and see if they need to be honed
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