Re: Can larger bearing clearances go the distance ?
[Re: hemienvy]
#2988515
11/23/21 11:10 PM
11/23/21 11:10 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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The clearance with conventional oil has been the same for over 100 years: .001" per 1.000" of journal diameter. How do large truck engines last so long? Huge journals; this is not only for inertial mass and stiffness, but determines local oil pressure at the journal surface, it's proportionate to the journal OD. The rod bearings are different, because the journal/shell contact is not constant as to speed, it has load reversals in which the rod beam's motion is added to or subtracted from crank speed. This varies based on rod ratio. The short answer is yes, it should work, but (assuming you have the choice) I would use the largest journals available and the longest rods. Some dims here on my site. Note the Ford 385 FF is 3.000" & 2.500". http://victorylibrary.com/mopar/m-table.htm
Boffin Emeritus
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Re: Can larger bearing clearances go the distance ?
[Re: hemienvy]
#2988520
11/23/21 11:27 PM
11/23/21 11:27 PM
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Joined: Aug 2003
Posts: 43,116 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,116
Bend,OR USA
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I like to have a little bit more bearing to crank clearances than a lot of other engine builders, I do use and like the .0010 per one inch of journal diameter so if I end up .0024 to .00325 on the stock BB Mopar rods and .0028 to .0039 on the mains I'm good I've ran them looser and tighter on both street and race only motors, to tight will spin a bearing a lot sooner than to loose will, mains or rods I like and use both 0W20Wt oil 5W20WT oil in my street cars and I now use the lightest weight VR 1 racing oil I can get, currently 10W30 Wt.
Last edited by Cab_Burge; 11/24/21 03:21 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Can larger bearing clearances go the distance ?
[Re: Cab_Burge]
#2988669
11/24/21 03:18 PM
11/24/21 03:18 PM
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Joined: Jan 2004
Posts: 4,563 Motor City
6PKRTSE
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master
Joined: Jan 2004
Posts: 4,563
Motor City
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I like to have a little bit more bearing to crank clearances than a lot of other engine builders, I do use and like the .0010 per one inch of journal diameter so if I end up .0024 to .00325 on the stock BB Mopar rods and .0028 to .0039 I'm good I've ran them looser and tighter on both street and race only motors, to tight will spin a bearing a lot sooner than to loose will, mains or rods I like and use both 0W20Wt oil 5W20WT oil in my street cars and I now use the lightest weight VR 1 racing oil I can get, currently 10W30 Wt. I agree with Cab. I like my clearances on the higher side also. Plenty of street miles on my Hemi making good power.
1963 Belvedere 440 Max Wedge Tribute 1970 Charger R/T S.E. 440 Six Pack 1970 Challenger R/T, 528 Hemi 1970 Charger 500 S.E. 440 4 BBL 1970 Plymouth Road Runner 383 1974 Chrysler New Yorker 440 1996 2500 RAM 488 V-10 4X4 2004 3500 Dually Cummins 4x4 2012 Challenger R/T Classic.
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Re: Can larger bearing clearances go the distance ?
[Re: hemienvy]
#2988805
11/24/21 09:38 PM
11/24/21 09:38 PM
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Joined: Jun 2012
Posts: 1,899 MYRTLE BEACH SOUTH CAROLINA
ek3
top fuel
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top fuel
Joined: Jun 2012
Posts: 1,899
MYRTLE BEACH SOUTH CAROLINA
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long term ring seal------------- pay to get the bores true and round ! use a hi quality piston such as mahle/je that have much better {fit} machine work in the ring groves! if the cyl. taper is correct and you break it in properly , it will last a long time... some folks build stroker engines that are run with more clearances and heavy oils as they claim it acts as a cushion i like the tighter side when using modern light weight synthetic oils.[ they flow better and drain back faster!] the -truer- the machine work, the better .. the smaller ring sets will live just as long! .
Last edited by ek3; 11/24/21 09:43 PM.
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Re: Can larger bearing clearances go the distance ?
[Re: jwb123]
#2988933
11/25/21 11:18 AM
11/25/21 11:18 AM
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Joined: Jan 2003
Posts: 9,985 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Frostbitefalls MN (Rocky&Bullw...
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.003 to .0035 bearing clearances especially on the mains work just fine, using a thicker oil, say 15w 40 or 20w 50. If using a stock block on a 600 to 700 HP build you want the bigger clearances to help with the mains and the caps moving around under power. If you have tight clearances, the wiggle will cause a bearing to spin, when the crank wipes against it and pushes the oil out of the way. Got to remember those stock blocks were designed for 400HP, so if you increase the power level 70% or more you are really loading the block. All the NASCAR and Prostock engines using those super thin oils, have very rigid blocks, no wiggle. If you look at all the newer V-8's they are designed with a very rigid main cap set up with multiple bolts a lot like aftermarket blocks. Agree'd. On top of the rigid blocks some V8s are running center counter weights as well . Those stock block 5.0 ford's run 8200 rpm STOCK!
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Can larger bearing clearances go the distance ?
[Re: gregsdart]
#2989166
11/25/21 11:56 PM
11/25/21 11:56 PM
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Joined: Jan 2003
Posts: 9,985 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Frostbitefalls MN (Rocky&Bullw...
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I can see where more power and rpm require bigger clearances and heavier oil. Look at what the fuel motor guys use. I believe clearances are much bigger (.006 to . 007?) And oil is straight 70 weight? The amount of flex etc is huge, so big clearances and thick oil let them live.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Can larger bearing clearances go the distance ?
[Re: LA360]
#2989211
11/26/21 06:17 AM
11/26/21 06:17 AM
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Joined: Nov 2020
Posts: 348 Isle of Sheeps
Gtxxjon
enthusiast
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enthusiast
Joined: Nov 2020
Posts: 348
Isle of Sheeps
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Good subject and very important issues for engine builders. High mileage V8 engines are surely 'in the past'? Most engine builders of the V8 variety are for drag racing duties... We know you can't compress oil to less than 0.0005 thousanths so a journal must have a minimum of 0.001. That being the MIN whats the MAX? Me I would say min 0.002 and max 0.003 is a safe working range... Some engines 'rattle' when cold and will quieten down once the oil and parts are warmed up. They have cold clearances in excess of 0.005! I am at a stage now where my race engine may only get 'two or three' runs a year! So the issue is not from wear, but 'lack of use' lol... Not 100,000 miles but a 100,000 inches...(1.58miles)
Last edited by Gtxxjon; 11/26/21 06:20 AM.
Carpe diem, quam minimum credula postero, thanx Horace!
There’s no point trying to fix stuff that ain’t broke,,, 'but if ain’t broke',,, you is not trying hard enough...
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