KING MAIN BEARING CLEARANCE'S AT PARTING LINE..?

rmcomprandy wrote:

IDT-572 wrote:I can't remember the last time I didn't have to use more than one set to get to where I needed to be.

It really helps to have a crank grinder near who can hit your numbers, spot on ... LOL.

You know any good ones????

rmcomprandy wrote:

IDT-572 wrote:I can't remember the last time I didn't have to use more than one set to get to where I needed to be.

It really helps to have a crank grinder near who can hit your numbers, spot on ... LOL.

I wish I had one in my back door like you do.................... But it would have to be a class act like the one that does yours..............

IDT-572 wrote:I can't remember the last time I didn't have to use more than one set to get to where I needed to be.

X2

as long as you have all the half shells either on top or bottom you will be fine but dont have some on top and some on the bottom on the mains,

I looked through this thread, and in case I overlooked another's comments, one rule of thumb must be followed. The bearing half, upper or lower (which ever is which), the half that has an oil hole or oil slot that passes completely through the bearing shell I believe needs to be located near the hole in the block that provides oil to the crankshaft! I find this true with most main bearing applications and some rod bearings (rods w/pin oilers) as well.

This seems silly to mention, but I have found when trying to re-invent sliced bread the simplest things can be overlooked!

Just my $0.02,
Dave.

cool40 wrote:

feetfirst wrote:My current motor, I tried king/clevite rod halves mixed together, it ran with no issues. Tore it down after a few runs, and reinstalled kings for more clearance, as I wasn't happy with the clearance.....

I also have 0.002 + more side clearance at the main halves...king bearings.

ok,found this on mine today.the main bore is .003@the line.with king bearings its .002 so it's in the bearing........why? i've built a lot of stock stuff and never had a line bore or hone,if it aint broke dont fix it,so this is new to me.the 12-6 o'clock, as Lem put it,checks out good@ .0015 and the crank is dead on ..002 under.=.0035.just tryen to learn something++++++++

Replaceable bearing shells have had an elliptical shape when torqued for at least the last 30 years ... some more and some less.

cool40 wrote:

rmcomprandy wrote:

cool40 wrote:

feetfirst wrote:My current motor, I tried king/clevite rod halves mixed together, it ran with no issues. Tore it down after a few runs, and reinstalled kings for more clearance, as I wasn't happy with the clearance.....

I also have 0.002 + more side clearance at the main halves...king bearings.

ok,found this on mine today.the main bore is .003@the line.with king bearings its .002 so it's in the bearing........why? i've built a lot of stock stuff and never had a line bore or hone,if it aint broke dont fix it,so this is new to me.the 12-6 o'clock, as Lem put it,checks out good@ .0015 and the crank is dead on ..002 under.=.0035.just tryen to learn something++++++++

Replaceable bearing shells have had an elliptical shape when torqued for at least the last 30 years ... some more and some less.

yep,got that part,but why?

There are a bunch of reasons but, the main one is to accommodate bearing bore distortion under high loading.

More clearance was added at the parting lines years ago when stock rods were the norm in racing conditions (grass roots). As a rod is over loaded at the top of the stroke when it changed directions, the big end tends to distort, in this case elongate top to bottom.

When this happens the rod bore gets more narrow at the parting line and longer top to bottom. When the bore narrows it takes up the oil clearance at the parting line and pinches the bearing wiping the oil off and causing bearing failure.

I think most of us now could get by with out it (eccentric) with the rods we have now. (quality tons better) We probably for the most part don't stress the rods to that point. I would say they still change but not to the degree they did years ago. I havent noticed the bearings changing in that department.

The same rods most of us are using to make 800 hp are used in engines making over 1000 hp and turning more rpm.

The eccentricity profile in the bearing serves a couple purposes. One, as mentioned, it to allow for bore distortion under load in the rod. Even a very good rod will experience a fair degree of deformation under high RPM loads. They turn into something of a peanut shape. The added clearance prevents bearing shell contact to the crank at the parting line edges.

The eccentricity also works as a pump, helps the oil to form a hydrodynamic wedge. The larger clearance fills with oil which is essentially dragged into the smaller clearance area by the rotating crank, greatly increasing effective pressure at the loaded portion of the bearing.