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Old 04-23-2012, 09:47 PM
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454 Main bearing clearance question

I just got my engine back from the machine shop and so far the first thing I have measure is off. All the mains read .002 except the rear which reads .003, an the #2 main which reads slightly over .003". My question is what should I do? The way I see it, I have a 3 options. The first is to get a set of .011 bearings and install just one on the #2 main journal, or get the crank turned .020 and replace all the bearings. The third option is to run all .011 bearings which should still keep everything within spec, some tighter than the one. The only thing I have against running the one journal with the undersized bearing is that it will be an "H" Clevite bearing instead of the "P" type the rest will be running.

FYI, the engine is a 4 bolt 454 with a .010/.010 forged crank, 11 to 1 compression. The engine will redline at 6K rpm, an I plan on WOT quite a bit. Don't want to do anything that I'll regret later. Thanks!

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Old 04-23-2012, 10:29 PM
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Was the block align honed? Are you measuring w/machinist tools or plastigage? If plastigage, be real sure nothing's under the shells on the tight bearings.

IMO, 0.003" isn't too much oil clearance, and is what I would have spec'd in the first place. 0.002", while a little on the tight side for a BBC engine that's going to be hammered on, will be OK as long as the main line and crank are true, which it should be regardless of the oil clearances.

You could in all probability run it as-is w/o problems, providing the crank and bores are good. The 0.003" clearances will allow more oil to pass through and create more oil windage (this also helps keep the bearings cooler), but providing the pump pressure is adequate there will not be a loss of pressure enough to worry about as long as a higher than stock oil pump relief spring is used. Using a windage tray can help w/oil control- at least that's my opinion, YMMV.

BTW, I think you meant 0.001" bearings. I wouldn't go tighter than 0.002".

Last edited by cobalt327; 04-23-2012 at 10:34 PM.
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Old 04-23-2012, 10:44 PM
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Quote:
Originally Posted by Slomotion34
I just got my engine back from the machine shop and so far the first thing I have measure is off. All the mains read .002 except the rear which reads .003, an the #2 main which reads slightly over .003". My question is what should I do? The way I see it, I have a 3 options. The first is to get a set of .011 bearings and install just one on the #2 main journal, or get the crank turned .020 and replace all the bearings. The third option is to run all .011 bearings which should still keep everything within spec, some tighter than the one. The only thing I have against running the one journal with the undersized bearing is that it will be an "H" Clevite bearing instead of the "P" type the rest will be running.

FYI, the engine is a 4 bolt 454 with a .010/.010 forged crank, 11 to 1 compression. The engine will redline at 6K rpm, an I plan on WOT quite a bit. Don't want to do anything that I'll regret later. Thanks!
I could almost guarantee that is a better fit than the factory.
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Old 04-24-2012, 12:00 AM
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Thanks for the info! I am just going by factory spec's of .0013-.0025. I flipped when I saw .003 on the plastigage. I did it a second time with the .002 -008 range plastigage and it looked like it was a touch over .003. I was just concerned... good to know that they like to be on the higher side when they are going to be pushed a little.

The bearing was for a -.011 turned crank. Would it be optimal to get the thicker bearing? how much would that affect oil pressure?

the block was line honed at the machine shop... so hopefully all trued up.

Thanks again.
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Old 04-24-2012, 06:09 AM
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from my BBC experience, you need to setup a bbc up tighten than a sbc if you want oil pressure when warm.

I use 0.0015 to 0.002 in the mains and rods and 0.0025 to 0.0035 on the rear main. You need a little more on the rear main to allow more oil to go to the top side of the engine.

I recommend you check lifter bore clearance also. With a flat tappet lifter you need around 0.001 to 0.0015, and with a roller lifter 0.0015 to 0.002. Not enough clearance will wipe out a cam lobe.
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