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Old 04-26-2011, 07:32 PM
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crankshaft bearings

ok im building my first engine lt1 twin turbo i have a forged pistons crank and rods im going 4 bolt billit main caps and i was woundering after i get them line bore and hone what typy of bearing do i need i mean like .010 over or so

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Old 04-26-2011, 09:13 PM
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Sure you are.........the "typy" of bearing you need is the correct one that fits the final machined circumference of the rod and main journals. Let your machinist handle it.
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Old 04-27-2011, 02:48 PM
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Originally Posted by malcolmz28
ok im building my first engine lt1 twin turbo i have a forged pistons crank and rods im going 4 bolt billit main caps and i was woundering after i get them line bore and hone what typy of bearing do i need i mean like .010 over or so
Clevite or King tri metal. See link for failure modes analysis, this gives you a pretty good idea of what to pay attention to during assembly.

Measure and clean, clean and measure, remeasure and re-clean. It is not necessary to scrape bearings with your pocket knife nor rub the imbedability layer off with Scotch Brite and do the other useless activities that the popular press would have you believe is some racers secret.

Two really important things:

1) What is important is that the oil hole in the bearing exposes all the oil hole in the block to the bearing. A misaligned hole reduces the area to supply oil to the journal where it's needed and applies oil pressure behind the bearing where it isn't. You may use a high speed grinder and fine stone to carve on the bearing, keep it cool with a compressed air bleed on the cutter. Finish the cut edges with fine sand paper and crocus cloth. Clean it and clean it again.

2) Be doubly sure to use rod bearings whose width is compatible with the cheek radius of the journal. Standard radius is 1/16th or .0625 inch; many performance cranks and reground cranks us 1/8th or .125 inch. Make very sure you're using the correct insert for the crank. Bearing manufacturers are usually careful to call this fit out, but check and when assembling check every damn rod at the journal it goes on. You can get away with bearings for a 1/8th radius on either a 1/16th or 1/8 crank. You cannot get way with 1/16th bearings on a 1/8th crank.

A street driven blower motor that doesn't get wound up very often nor very long can use 3/4 oil grooves on the mains. For an engine that sees a lot of WOT and high RPMs go with a half groove bearing. Make sure the full groove of either type is in the upper saddle, not in the cap.

Clean and measure again and again. That means the saddle, the cap, the side of the bearing that mates here. The journal surface of the bearing and the journals of the crank. The oil passages in the block and crank, and under the damn cam bearings. It is not uncommon for cam bearing installation to peel off some metal that gets into the groove behind the bearing shell that feeds the mains. Figure on blasting the block's passages after the cam bearings are installed with a gallon of WD40 and some high pressure air to force flow around this area to wash out any loose crap.

Believe me this will save the pain of ruined bearings and crank journals when you finally build a fire in this thing.

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