Mix sbc main bearing question

General engine tech -- Drag Racing to Circle Track

Moderator: Team

User avatar
BOOT
Guru
Guru
Posts: 1333
Joined: Fri Apr 09, 2010 6:23 pm
Location: Michigan

Mix sbc main bearing question

Post by BOOT » Mon Oct 02, 2017 6:17 am

I'm replacing all the bearings and bought a full set already and something just occurred to me. I've had a set of sbc main bearings(same brand/size/part number) that the rear was used so just the 4 narrow upper n lowers. Now I'm no bearing expert but could I use just uppers so I'd have a full groove? Next question, how much narrower are the HP style bearings? This is not a fresh high dollar engine just a worn sbc, so I don't plan on getting a ton of miles out of it and if I can ghetto narrow bearing by having a full groove. I'd never buy two sets to do it on purpose but if I got em already and one set is incomplete anyway. Also installing a 10% more volume pump I have.
I know as much as I can learn and try to keep an open mind to anything!

If I didn't overthink stuff I wouldn't be on speedtalk!

User avatar
bigblockmopar
New Member
New Member
Posts: 47
Joined: Fri Mar 25, 2016 8:53 pm
Location: Netherlands
Contact:

Re: Mix sbc main bearing question

Post by bigblockmopar » Mon Oct 02, 2017 6:28 am

I've used another set of bearings before to make a fully grooved set of them in a build.
This was on a bigblock Mopar but as long as the bearings spec out right against eachother.

mag2555
Guru
Guru
Posts: 2062
Joined: Sun Sep 18, 2011 11:31 am

Re: Mix sbc main bearing question

Post by mag2555 » Mon Oct 02, 2017 7:00 am

First off if the Crank is fully crossdrilled you do not need fully grooved main bearings and you would just be wasting some oil pressure and volume on them not to mention likely making oil windage control harder!

Warp Speed
Guru
Guru
Posts: 2060
Joined: Wed Jun 25, 2008 1:46 pm
Location: NC

Re: Mix sbc main bearing question

Post by Warp Speed » Mon Oct 02, 2017 10:34 am

mag2555 wrote:
Mon Oct 02, 2017 7:00 am
First off if the Crank is fully crossdrilled you do not need fully grooved main bearings and you would just be wasting some oil pressure and volume on them not to mention likely making oil windage control harder!
Same can be said about fully grooved main bearings no matter the crank oiling strategy!

User avatar
BOOT
Guru
Guru
Posts: 1333
Joined: Fri Apr 09, 2010 6:23 pm
Location: Michigan

Re: Mix sbc main bearing question

Post by BOOT » Mon Oct 02, 2017 2:16 pm

Crank is not cross drill, engine has tray and custom baffling.
I know as much as I can learn and try to keep an open mind to anything!

If I didn't overthink stuff I wouldn't be on speedtalk!

Warp Speed
Guru
Guru
Posts: 2060
Joined: Wed Jun 25, 2008 1:46 pm
Location: NC

Re: Mix sbc main bearing question

Post by Warp Speed » Mon Oct 02, 2017 2:29 pm

BOOT wrote:
Mon Oct 02, 2017 2:16 pm
Crank is not cross drill, engine has tray and custom baffling.
Why do you want a full groove?

User avatar
BOOT
Guru
Guru
Posts: 1333
Joined: Fri Apr 09, 2010 6:23 pm
Location: Michigan

Re: Mix sbc main bearing question

Post by BOOT » Mon Oct 02, 2017 2:31 pm

Reduction in friction just like narrow bearings
I know as much as I can learn and try to keep an open mind to anything!

If I didn't overthink stuff I wouldn't be on speedtalk!

allencr267
Member
Member
Posts: 110
Joined: Wed Nov 07, 2012 6:28 pm
Location: Tallahassee Florida USofA

Re: Mix sbc main bearing question

Post by allencr267 » Mon Oct 02, 2017 3:22 pm

is there less friction with a grooved bearing Vs a narrower bearing if they both have the same surface area/squareinx". 2 different then a single on the only bearing half that really has any load.

Warp Speed
Guru
Guru
Posts: 2060
Joined: Wed Jun 25, 2008 1:46 pm
Location: NC

Re: Mix sbc main bearing question

Post by Warp Speed » Mon Oct 02, 2017 3:34 pm

BOOT wrote:
Mon Oct 02, 2017 2:31 pm
Reduction in friction just like narrow bearings
It doesn't really work like that, and the loss of oil control will negate any frictional gains if there were any.

Circlotron
Expert
Expert
Posts: 561
Joined: Tue Feb 05, 2013 6:56 am
Location: Melbourne, Straya

Re: Mix sbc main bearing question

Post by Circlotron » Mon Oct 02, 2017 5:01 pm

Grooved tyres are more able to cut through a film of water and contact the road surface below. A smooth tyre is much more able to have a wedge of water separate it from the road. I can imagine grooved lower main bearing halves are much the same situation as a grooved tyre as regards the ability to cut through a film of liquid so that the two surfaces come in contact.
Last edited by Circlotron on Mon Oct 02, 2017 5:09 pm, edited 1 time in total.

statsystems
Guru
Guru
Posts: 1087
Joined: Sun Apr 03, 2016 1:17 am

Re: Mix sbc main bearing question

Post by statsystems » Mon Oct 02, 2017 5:07 pm

All you are doing is sending oil to the rods all the time. Why do that if you don't need to?

User avatar
BOOT
Guru
Guru
Posts: 1333
Joined: Fri Apr 09, 2010 6:23 pm
Location: Michigan

Re: Mix sbc main bearing question

Post by BOOT » Mon Oct 02, 2017 6:00 pm

allencr267 wrote:
Mon Oct 02, 2017 3:22 pm
is there less friction with a grooved bearing Vs a narrower bearing if they both have the same surface area/squareinx". 2 different then a single on the only bearing half that really has any load.
My thought was to be close to the same, not less than narrow.


As a few have pointed out the oiling could negate the friction reduction, depending on scraper maybe or vac pump.
I know as much as I can learn and try to keep an open mind to anything!

If I didn't overthink stuff I wouldn't be on speedtalk!

ZEOHSIX
Pro
Pro
Posts: 375
Joined: Sun Aug 19, 2012 2:25 am

Re: Mix sbc main bearing question

Post by ZEOHSIX » Mon Oct 02, 2017 8:03 pm

Compromise for everyone's sake just get these Federal Mogul bearings they are 3/4 grooved.....

Link: http://www.jegs.com/i/Sealed-Power/844/ ... 4294829509

Disclaimer....I'm a reformed "Mopar Dude" trying to rev a 340 Duster to higher than 7200RPM levels with a stock oiling system that can give you....Chevreligion.....when your buddies 69 Z/28 regularly SCREEMS to 7500RPMs with no ill effects.....Mopar Dudes LOVE fully grooved main bearings.....Chevy guys know the lower groove greatly reduces the load carrying capacity of the oil wedge between the crank journal and the bearing.....Former Mopar Dudes realize they wasted years of their lives and many dollars trying to make an A motor perform like a Small Block Chevy....given the lousy oil galley routing of the Mopar motor....that was the true cause of all the lost rod bearings....AND even FULLY GROOVY main bearings aren't going to cure crappy engineering :D

engineguyBill
Expert
Expert
Posts: 729
Joined: Fri Feb 26, 2010 11:15 am
Location: Gold Canyon, AZ

Re: Mix sbc main bearing question

Post by engineguyBill » Mon Oct 02, 2017 8:41 pm

Fully grooved main bearings provide no benefit over 180 degree grooved upper shells. As has been pointed out in previous posts, the groove in the lower shell disrupts the formation of oil wedge between the shell and crank journal. This will result in the bearing shell coming into direct contact with the crank journal and this is not a good thing, as the bearings will get wiped out.
In my opinion 3/4 groove main bearings do not result in any performance benefits either. The 180 degree grooved upper shell delivers oil into the eccentric area of the upper and lower shells, whereupon the oil forms a wedge as the crankshaft rotates.
Bill

SAE Member (25+ years)
ASE Master Certified Engine Machinist
AERA Certified Professional Engine Machinist

"Do what you can, with what you have, where you are."
- Theodore Roosevelt

User avatar
BOOT
Guru
Guru
Posts: 1333
Joined: Fri Apr 09, 2010 6:23 pm
Location: Michigan

Re: Mix sbc main bearing question

Post by BOOT » Mon Oct 02, 2017 8:55 pm

So narrow bearings are the devil too :)
I know as much as I can learn and try to keep an open mind to anything!

If I didn't overthink stuff I wouldn't be on speedtalk!

Post Reply