I’m getting ready to build 4” stoke small block using a Molnar crank and rods. The thought just hit me that I may need the narrow bearings because of the radius on the crank? I have not taken the crank out of the box yet. Anyone know and have the part number for the narrow bearings if needed? I want fully grooved mains. I’ve got a new set of P bearings but I bet they are too wide.
Thanks

I just chamfered my big block bearings with a burr.

What brand of bearings are those? They look coated. Are you afraid they might flake off?

Clevite MS1266HG is what you are looking for if running a 360 sized main.
Doug

340 mains

MS540H 1/2 groove. MS540HK 1/2 groove coated Personally I prefer the 1/2 groove. They feature more surface area in the loaded posistion. It looks like 360 main are full groove only. 340 main are 1/2 groove only Read this from Clevites tech page.
Doug

Various forms of main bearing grooving have
been used over the years. We are frequently
asked what difference grooving makes.
First, it’s essential to understand that bearings
depend on a film of oil to keep them separated
from the shaft surface. This oil film is developed
by shaft rotation. As the shaft rotates it pulls oil
into the loaded area of the bearing and rides up
on this film much like a tire hydroplaning on wet
pavement. Grooving in a bearing acts like tread
in a tire to break up the oil film. While you want
your tires to grip the road, you don’t want your
bearings to grip the shaft.
The primary reason for having any grooving in a
main bearing is to provide oil to the connecting
rods. Without rod bearings to feed, a simple
oil hole would be sufficient to lubricate a main
bearing. Many early engines used full grooved
bearings and some even used multiple grooves.
As engine and bearing technology developed,
bearing grooving was removed from modern
lower main bearings. The result is in a thicker
film of oil for the shaft to ride on. This provides a
greater safety margin and improved bearing life.
Upper main shells, which see lower loads than
the lowers, have retained a groove to supply the
connecting rods with oil.
In an effort to develop the best possible main
bearing designs for performance engines, we’ve
investigated the effects of main bearing grooving
on bearing performance. The graphs illustrate
that a simple 180 degree groove in the upper
main shell is still the best overall design.
While a slightly shorter groove of 140 degrees
provides a marginal gain, most of the benefit
is to the upper shell, which doesn’t need
improvement. On the other hand, extending
the groove into the lower half, even as little as
20 degrees at each parting line (220 degrees
in total), takes away from upper bearing
performance without providing any benefit to
the lower half. It’s also interesting to note that as
groove length increases so do horsepower loss
and peak oil film pressure which is transmitted
directly to the bearing.

Hmm. That’s an interesting read on a commonly discussed topic here. I guess if that is what the people think that make the bearings, I should pay attention. Thanks for the information.

I might be old school or believe in sasquatch. But I am sticking with 3/4 or narrow full grove mains in my stuff.....

Same. Theories are good but how often have you seen a lower that was bombed out because you KNOW it was load bearing insufficiency. Maybe in severe hp applications. I'll take full time rod oiling.

I don't think this is a theory. This is either the same, or similar info that came out of a Chrysler dyno study years ago. We can't see the graph here, but not a lot of graphs are simply made up, they are results on paper. Both full and partial grooves have been around a long time, and both work. One maybe better than the other.

[quote} Theories are good but how often have you seen a lower that was bombed out because you KNOW it was load bearing insufficiency. Maybe in severe hp applications. I'll take full time rod oiling. [/quote]

My take. My race motor runs 3/4 groove. Has close to 850 passes. 4.5" stroke@7300. There was one issue when we bent the pan and broke a windage tray injuring a rod bearing. Every other rod bearing that has been removed has looked like new. Though it's never hurt a main a few have certainly not looked like new. Especially #4. Same on my sons turbo small block. Rods are always nice. Mains not as good. As far as theory. I would bet the bearing manufacturer knows just a little bit more about bearings than any of us.
Doug

I know what you are saying. Wrong choice of words in my part. I am sure big hp applications it's an issue. But in lower hp it might as well be a theory

I have never seen carnage from a main, but have seen some from rods. But won't deny the article...just sticking with my preference .