Previous Thread
Next Thread
Print Thread
Can larger bearing clearances go the distance ? #2988444
11/23/21 09:07 PM
11/23/21 09:07 PM
Joined: Jun 2016
Posts: 735
Washington
H
hemienvy Offline OP
super stock
hemienvy  Offline OP
super stock
H

Joined: Jun 2016
Posts: 735
Washington
Thinking about larger bearing clearances and longevity.
If you were building an 800 HP pump gas motor that you wanted to last 100,000 miles, what are the main things to consider ?

Here's my thinking: An 800-HP street motor is not always at WOT putting out 800 HP, not like a dedicated race motor.
If the oil and oil pump were kept in good shape, you would think the ring seal would be next thing in the shortblock to go away.

The valvetrain parts are another matter entirely.

So there is nothing inherently short-lived about larger bearing clearances, say .003" on 2.750" main bearings, or .003" on the rods ?

I don't have an answer about making ring seal last longer, except maybe by using wider rings ? like the old 5/64" rings ?
I think the wider rings are a horsepower loser, but they would maintain seal longer ?

Re: Can larger bearing clearances go the distance ? [Re: hemienvy] #2988456
11/23/21 09:28 PM
11/23/21 09:28 PM
Joined: Feb 2005
Posts: 931
MI, Lapeer
M
maximus Offline
super stock
maximus  Offline
super stock
M

Joined: Feb 2005
Posts: 931
MI, Lapeer
From my experience, the hardest thing on bearing life is low RPM running. I am talking below 1,800. At slow speeds the bearing is taking a harder beating than at higher RPM's especially on long stroke motors. So, if you run above the RPM stated the extra clearance shouldn't be an issue if you are using good lubrication.

Re: Can larger bearing clearances go the distance ? [Re: hemienvy] #2988515
11/23/21 11:10 PM
11/23/21 11:10 PM
Joined: Oct 2007
Posts: 3,941
New York
polyspheric Offline
master
polyspheric  Offline
master

Joined: Oct 2007
Posts: 3,941
New York
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
Re: Can larger bearing clearances go the distance ? [Re: hemienvy] #2988520
11/23/21 11:27 PM
11/23/21 11:27 PM
Joined: Aug 2003
Posts: 39,049
Bend,OR USA
C
Cab_Burge Offline
I Win
Cab_Burge  Offline
I Win
C

Joined: Aug 2003
Posts: 39,049
Bend,OR USA
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 up
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 shruggy twocents
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. up

Last edited by Cab_Burge; 11/24/21 03:21 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Can larger bearing clearances go the distance ? [Re: Cab_Burge] #2988669
11/24/21 03:18 PM
11/24/21 03:18 PM
Joined: Jan 2004
Posts: 3,900
Motor City
6
6PKRTSE Offline
master
6PKRTSE  Offline
master
6

Joined: Jan 2004
Posts: 3,900
Motor City
Originally Posted by Cab_Burge
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 up
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 shruggy twocents
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. up


I agree with Cab. I like my clearances on the higher side also. Plenty of street miles on my Hemi making good power.

IMG_8664.jpg

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.
Re: Can larger bearing clearances go the distance ? [Re: hemienvy] #2988805
11/24/21 09:38 PM
11/24/21 09:38 PM
Joined: Jun 2012
Posts: 1,867
MYRTLE BEACH SOUTH CAROLINA
E
ek3 Offline
top fuel
ek3  Offline
top fuel
E

Joined: Jun 2012
Posts: 1,867
MYRTLE BEACH SOUTH CAROLINA
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! up.

Last edited by ek3; 11/24/21 09:43 PM.
Re: Can larger bearing clearances go the distance ? [Re: hemienvy] #2988922
11/25/21 10:42 AM
11/25/21 10:42 AM
Joined: Nov 2015
Posts: 642
Missouri
J
jwb123 Offline
mopar
jwb123  Offline
mopar
J

Joined: Nov 2015
Posts: 642
Missouri
.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.

Re: Can larger bearing clearances go the distance ? [Re: jwb123] #2988933
11/25/21 11:18 AM
11/25/21 11:18 AM
Joined: Jan 2003
Posts: 9,444
Frostbitefalls MN (Rocky&Bullw...
gregsdart Offline
master
gregsdart  Offline
master

Joined: Jan 2003
Posts: 9,444
Frostbitefalls MN (Rocky&Bullw...
Originally Posted by jwb123
.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!


8.77 153 mph best, 3055 lbs 528 indy 440-1 alky
Re: Can larger bearing clearances go the distance ? [Re: gregsdart] #2989166
11/25/21 11:56 PM
11/25/21 11:56 PM
Joined: Jan 2003
Posts: 9,444
Frostbitefalls MN (Rocky&Bullw...
gregsdart Offline
master
gregsdart  Offline
master

Joined: Jan 2003
Posts: 9,444
Frostbitefalls MN (Rocky&Bullw...
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.


8.77 153 mph best, 3055 lbs 528 indy 440-1 alky
Re: Can larger bearing clearances go the distance ? [Re: gregsdart] #2989203
11/26/21 03:13 AM
11/26/21 03:13 AM
Joined: Jan 2003
Posts: 5,966
Melbourne , Australia
LA360 Offline
master
LA360  Offline
master

Joined: Jan 2003
Posts: 5,966
Melbourne , Australia
If thicker rings were great for mileage, OEM's would still be using them.


Alan Jones
Re: Can larger bearing clearances go the distance ? [Re: LA360] #2989211
11/26/21 06:17 AM
11/26/21 06:17 AM
Joined: Nov 2020
Posts: 348
Isle of Sheeps
Gtxxjon Offline
enthusiast
Gtxxjon  Offline
enthusiast

Joined: Nov 2020
Posts: 348
Isle of Sheeps
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... thumbs

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... fan

Not 100,000 miles but a 100,000 inches...(1.58miles) Santa5

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...






Powered by UBB.threads™ PHP Forum Software 7.7.1