Mix sbc main bearing question

General engine tech -- Drag Racing to Circle Track

Moderator: Team

jsgarage
Expert
Expert
Posts: 677
Joined: Tue Jul 13, 2010 2:54 pm

Re: Mix sbc main bearing question

Post by jsgarage » Mon Oct 02, 2017 10:04 pm

IMHO, Narrow bearings are not the same as small diameter bearings as far as friction reduction. At high rpms, smaller dia but wider bearings (SBC) work better (longer engine life) than slightly larger dia but narrower bearings (SBF) that are virtually the same surface area. Probably has something to do with the spread rate of oil being fed into the bearings but thats just a guess.

RCJ
Expert
Expert
Posts: 566
Joined: Wed Jul 25, 2007 6:15 am
Location: Oklahoma

Re: Mix sbc main bearing question

Post by RCJ » Tue Oct 03, 2017 7:46 am

Bearing have more clearance at the parting line, when the oil groove extends in to that area there is more leakage. There are bearing with grooves that don't extend to the parting line.

engineguyBill
Expert
Expert
Posts: 736
Joined: Fri Feb 26, 2010 11:15 am
Location: Gold Canyon, AZ

Re: Mix sbc main bearing question

Post by engineguyBill » Tue Oct 03, 2017 9:47 am

Boot,
No, narrowed bearing will reduce friction in high RPM, maximum effort race engines. The narrow bearings will still form an effective oil wedge between the bearing shell and crank pin. As with anything else, bearing narrowing must be done conservatively - a bearing that is excessively narrowed will not be able to provide necessary support.
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

engineguyBill
Expert
Expert
Posts: 736
Joined: Fri Feb 26, 2010 11:15 am
Location: Gold Canyon, AZ

Re: Mix sbc main bearing question

Post by engineguyBill » Tue Oct 03, 2017 9:59 am

RCJ wrote:
Tue Oct 03, 2017 7:46 am
Bearing have more clearance at the parting line, when the oil groove extends in to that area there is more leakage. There are bearing with grooves that don't extend to the parting line.
The area adjacent to the parting line has more clearance, due to the eccentric shape of the bearing shells. This area acts as a reservoir for oil to form the hydrodynamic wedge as the crankshaft rotates. The function of the groove in the upper bearing shell is to deliver oil to the eccentric (reservoir) area of the bearing.
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

Warp Speed
Guru
Guru
Posts: 2066
Joined: Wed Jun 25, 2008 1:46 pm
Location: NC

Re: Mix sbc main bearing question

Post by Warp Speed » Tue Oct 03, 2017 10:06 am

engineguyBill wrote:
Tue Oct 03, 2017 9:59 am
RCJ wrote:
Tue Oct 03, 2017 7:46 am
Bearing have more clearance at the parting line, when the oil groove extends in to that area there is more leakage. There are bearing with grooves that don't extend to the parting line.
The area adjacent to the parting line has more clearance, due to the eccentric shape of the bearing shells. This area acts as a reservoir for oil to form the hydrodynamic wedge as the crankshaft rotates. The function of the groove in the upper bearing shell is to deliver oil to the eccentric (reservoir) area of the bearing.
The groove does not need to extend to the parting line/largest eccentric area to form this wedge you speak of....

DaveMcLain
Guru
Guru
Posts: 2685
Joined: Thu Jan 06, 2011 8:57 am

Re: Mix sbc main bearing question

Post by DaveMcLain » Tue Oct 03, 2017 11:17 am

How is it that a cam bearing which is fully round with no eccentricity built in manages to form a hydrodynamic wedge to separate the rotating cam journal from the block. Most of the time doing so with a simple oil hole.

engineguyBill
Expert
Expert
Posts: 736
Joined: Fri Feb 26, 2010 11:15 am
Location: Gold Canyon, AZ

Re: Mix sbc main bearing question

Post by engineguyBill » Wed Oct 04, 2017 9:13 am

DaveMcLain wrote:
Tue Oct 03, 2017 11:17 am
How is it that a cam bearing which is fully round with no eccentricity built in manages to form a hydrodynamic wedge to separate the rotating cam journal from the block. Most of the time doing so with a simple oil hole.
Even though the camshaft is subject to the forces and pressure of followers, pushrods, rocker arms and valve springs, this pressure is much less than that encountered by rod and main bearings during the various cycles. The amount of oil delivered to the cam bearing journals is sufficient to keep this area lubricated.
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

RCJ
Expert
Expert
Posts: 566
Joined: Wed Jul 25, 2007 6:15 am
Location: Oklahoma

Re: Mix sbc main bearing question

Post by RCJ » Wed Oct 04, 2017 12:35 pm

Check out callies Daido bearings.Havn't tried them , going to on the next motor.

Post Reply