Main/Rod Bearing Clearances
#1233294
05/14/12 05:27 PM
05/14/12 05:27 PM
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Joined: Feb 2003
Posts: 3,456
Out West
408strokerdart
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Out West
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Looking for information on bearing clearances that you have ran in your race engines. Please keep the information related to race only applications since I think it varies to much from street stuff to cross over.
What was the combo (Aluminum rod/Steel Rod, Aluminum Main Caps, etc.)? Journal sizes? Also, successes or failures on oil pressure. Half grooved mains, 3/4 grooved mains, etc..??
I know there are guidelines of so much clearance/inch of journal, but I am looking for real world experiences. I'm not sure if I am right or wrong, but I would assume that you could get away with slighlty tighter tolerances on an aluminum rod or aluminum block or aluminum main engine (due to thermal expansion differences), but I don't know that for sure.
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Re: Main/Rod Bearing Clearances
[Re: 408strokerdart]
#1233297
05/14/12 06:43 PM
05/14/12 06:43 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Master
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Posts: 52,972
Romeo MI
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I use .003 on mains and rods... steel H-beam and chevy rod journals... I never go below .0025... 1/2 groove bearings 
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Re: Main/Rod Bearing Clearances
[Re: Thumperdart]
#1233298
05/15/12 12:20 AM
05/15/12 12:20 AM
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Joined: Feb 2003
Posts: 3,456
Out West
408strokerdart
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Out West
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Quote:
Jason Pettis and I recentlly had this very same conversation and he said he actually saw less wear and could actually re-use the bearings in 6-second big motors by going as loose as .005........... 
Wow....that's alot of clearance!
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Re: Main/Rod Bearing Clearances
[Re: MR_P_BODY]
#1233299
05/15/12 12:24 AM
05/15/12 12:24 AM
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Joined: Feb 2003
Posts: 3,456
Out West
408strokerdart
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OP
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Quote:
I use .003 on mains and rods... steel H-beam and chevy
rod journals... I never go below .0025... 1/2 groove
bearings
Any thoughts on aluminum rods? I sometimes see people add clearance for alum rods, but I would think it would be the other way. Any technical reason why?
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Re: Main/Rod Bearing Clearances
[Re: Cab_Burge]
#1233300
05/15/12 12:28 AM
05/15/12 12:28 AM
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Joined: Feb 2003
Posts: 3,456
Out West
408strokerdart
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Out West
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Quote:
Iron block,BB steel cranskhaft and steelrods, .003+ on the mains and at least .0025 on the rods. More for aluminum rods (.003+) or blocks(.0035+) on both  I like and use the full groove main bearings, Federal Mogul narrow grooves on the iron blocks and the Clevite 426 Hemi wide race main bearings on the aluminum blocks with steel caps 
Cab, I see it often but never see a reason why more clearance is required on aluminum rods. Can you add to this? Thanks.
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Re: Main/Rod Bearing Clearances
[Re: 408strokerdart]
#1233301
05/15/12 12:30 AM
05/15/12 12:30 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
Quote:
I use .003 on mains and rods... steel H-beam and chevy
rod journals... I never go below .0025... 1/2 groove
bearings
Any thoughts on aluminum rods? I sometimes see people add clearance for alum rods, but I would think it would be the other way. Any technical reason why?
I owned a set of BB alum rods and I have heard that
it needs to be larger... it expands in all directions
so it would decrease the clearance also... I sold
those rods so I have never used any alum rods
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Re: Main/Rod Bearing Clearances
[Re: Thumperdart]
#1233303
05/15/12 01:12 AM
05/15/12 01:12 AM
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Joined: Jun 2008
Posts: 186
Middleton, ID
curleysracecars
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member
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Posts: 186
Middleton, ID
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Aluminum rods grow slightly when hot, meaning the diameter of the big end gets smaller, tightening up on the crank. We run .004 in our 820" motor.
Kyle Curley
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Re: Main/Rod Bearing Clearances
[Re: DavidDean]
#1233305
05/15/12 01:23 AM
05/15/12 01:23 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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My brothers SB chevy we ran .006 on the rods BUT you HAD to pre heat the oil before you could fire it... that was some years back so I think the material is alot better now... you can get way more than 300 passes on a set now days
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Re: Main/Rod Bearing Clearances
[Re: curleysracecars]
#1233307
05/15/12 02:59 AM
05/15/12 02:59 AM
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Joined: Feb 2007
Posts: 1,025
Las Vegas, NV
dodgeboy11
super stock
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super stock
Joined: Feb 2007
Posts: 1,025
Las Vegas, NV
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Quote:
Aluminum rods grow slightly when hot, meaning the diameter of the big end gets smaller, tightening up on the crank. We run .004 in our 820" motor.
No offense, but that's wrong. The bore gets bigger. But a drag motor needs more clearance because the oil never really warms up. Thick oil means lots of drag and the potential for spun bearings. I urge you to test me on this. When a rod gets resized I always went over the big number. Once it cooled down, it shrunk to below the big number.
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Re: Main/Rod Bearing Clearances
[Re: 408strokerdart]
#1233308
05/15/12 10:54 AM
05/15/12 10:54 AM
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Joined: Oct 2003
Posts: 7,506
Az
Crizila
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master
Joined: Oct 2003
Posts: 7,506
Az
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My last two ( actually 3 - one was a chevy ) stroked small blocks I have built were tight. .002 on both rods and mains ( all steel ). Along with that I have been running a low viscosity full synthetic oil. Not sure if it is better or worse than going in the other direction? Haven't spun anything. I see less pressure swings with oil temp changes. Also think it helps in the windage / oil control area and makes better use of the newer quality oils that are out there these days. . I'm far from an expert engine builder and don't do it for a living, so - - - - - .
Fastest 300
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Re: Main/Rod Bearing Clearances
[Re: Crizila]
#1233309
05/15/12 11:08 AM
05/15/12 11:08 AM
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Joined: Nov 2003
Posts: 3,060
Western New York
sixpackbee
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master
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Western New York
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I set up clearances by what oil is to be used. In the class engines that run RP No. 9(0/10) or thinner are set at .0015. Street/bracket engines .002-.003. using a 10/30 type oil. I don't mess with real big engines so don't know what I would do there.
1959 Bugeye Sprite
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