Bearing Clearance
This an age old question - how much bearing clearance should you run in street driven 350 SBC. One common recommendation is:
Rod bearings 0.0020 - 0.0025" , side clearance 0.010 - 0.020" Main bearings 0.0020 - 0.0030" Crankshaft end play 0.005 - 0.007 crankshaft end play I am in a process of putting a budget 350 (880 block, 1peice RMS) Micrometer: Mitutoyo 103-217 (2 to 3", 0.0001 resolution) Bearings: King Bearing 557SI (STD and -001) Mains Measured Plasti-Gauge Plasti-Gauge 103-217 | STD | -001 M1: 2.4500 | 0.002 | n/a M2: 2.4495 | 0.003 | 0.002 M3: 2.4495 | 0.003 | 0.002 M4: 2.4495 | 0.003 | 0.002 M5: 2.4490 | 0.003+ | 0.002 to 0.0015 (Probably 0.0018) Rods R1/2 2.0995 TBD (to be determined) R3/4 2.0995 R5/6 2.0995 R7/8 2.0995 Crank thrust movement: 0.005 to 0.007 depending how hard I pry my bar So I am going with mix set of main bearings - on the mains I am keeping #1 STD and 2 through 5 -0.001" based on platigauge indication. My only concern that #5 Main is a bit on tight side:0.0018" Comments regarding #5 being a bit tight.... //RF |
Re: Bearing Clearance
Was there any machine work done? Was the crank turned or polished? Block line honed? ....or are you just replacing the bearings?
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Re: Bearing Clearance
Crank was polished (it was not turned) - it had 140k on it when I yanked it in favor of 3.75" stroker.
Block probably was line honed at one time or another. Crank turns very nicely with bearings configured in original post. It is a budget build - just tossing new bearings and rings and put it back into service. //RF |
Re: Bearing Clearance
#5 is the thrust bearing right? .0018 is too tight. I always set that one at .0025-.003
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Re: Bearing Clearance
Quote:
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Re: Bearing Clearance
^^ not only that, #5 gets the full flow of oil then sends it on down the line/s. Otherwise clearances look good. You are installing a new pump right? Std volume with high pressure spring.
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Re: Bearing Clearance
If you are that concerned about it being too loose with the standard bearing and too tight with the -.001 bearing, have the machine shop polish it a little more.
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Re: Bearing Clearance
Are you using any lubrication on the bearings or journal when you are measuring? Even a splash of any goo can give you a false reading. Rods are a bit trickier because you can easily distort the strip when you are taking the rod caps off. Is the crank nice and round? Is taper in check, or are you figuring from hi/average? A bit to the looser side will keep you out of danger, a bit on the tight side can get ugly fairly quick. Lots of science to bearing load and oil film, but SBC is somewhat forgiving on clearances.
Good luck! Robert |
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