Update: ID main bearing size?

Posted by jdemaris on January 08, 2010 at 07:46:58 from (72.171.0.149):

In Reply to: How to ID main bearing size? posted by jdemaris on January 06, 2010 at 18:36:41:

I think I figured out what my bearings are. Part of my confusion seems to be some incorrect information I got from a machine shop.

I clamped my two thrust bearing halves together and brought them down to a machine shop. I did that since I don't have a good inside mike, just outside. So, when I measure, I use inside calipers then re-measuse with an outiside mike.

So, went to the machine shop. The guy laughed a little at me having such a problem that was so "simple." He measured with his inside mike ad told me the bearing ID is 2.24". OK. The standard crank journal is 2.25. He said my bearings are .010" under. I then asked how clearance figures in, and he said his measurements are probably just off by a little.
So, I did not feel comfortable with his "expert" measurement since it did not conincide with my bearing shell thickness measurements.

So, after thinking about many comments made here, this is what I did.

I searched through my big engine manual (not the shorter ITT). Found specs. for main bearing bore in the main saddles.

Bearing mount ID is: 2.437"
Standard crank journal is: 2.250"

Now, I'm no math wiz, but I figured the following.
Space between bearing mount and standard journal is .187". Subtract .002" for clearnace and that comes to .185" Then split in half (thickness of each bearing half) and I get .0925" thickness for a standard bearing. Exactly what Earl-IL stated.

I took a ball bearing and miked it at: .311"

I used the ball against the inside of the bearing shell along with a 1" outside mike. Got a measurement of .413".

So, subtract the ball ID from the total and I get .102" bearing shell thickness.

Going by bearing mount ID versus standard journal, and allowing .002" clearance, I come up with these specs for thickness of bearing shells:

.010" undersize - .0975" thick
.020" undersize - .1025" thick
.030" undersize - .1075" thick
.040" undersize - .1175" thick

So, at this point I am going to assume that my crankshaft if .020 undersize and the machine shop screwed up. So much for hiring "professionals."
And, if I find out I'm wrong, well . . at least I don't claim to be a machinist. Just a grease-monkey.

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