Rod bearing question

pburchett · Mar 15, 2019

Is this a 0.001 over-sized connector rod bearing? It came out of my 640 Ford.

David G · Mar 15, 2019

I would guess .001 "undersize"

T.R.K. · Mar 15, 2019

At one time you could get .001 or .002 undersize rod bearings for a lot of the older engines. I think some engines had .001 and .002 main
bearings offered as well. This was an aid if there was just a bit too much clearance on a worn crank pin.

On some new engines where they goofed up machining the crank they came from the factory with undersize bearings too. It was a way to avoid
scrapping an otherwise perfectly good and rather expensive crank. And the actual measured diameters of the crank pin and the bearing didn't
matter as long as the clearance between them was correct.

Mike(NEOhio) · Mar 15, 2019

It's undersize not oversize. Main and rod bearings are undersized. .001 or .002 are to compensate for wear when the journal is still in good shape. .010, .020, etc. are used after regrinding the crank. Pistons come oversized for a rebored cylinder. Those terms are commonly misused in these forums, just like freeze plugs.

gene bender · Mar 15, 2019

thicker bearings are OVERSIZE they make up the distance when grinding the crank down to make it round again so you have a crank 10 under you will need OVERSIZE and thicker bearings. 10 under means the crank has been ground 10 thous then comes the thicker bearings 10 OVER to fill the void

John Deere D · Mar 16, 2019

To be sure of the Brg. Shell required...Measure the connecting Rod Crankshaft Journal.

Take NOTE of Journal Diameter....compare Micrometer readings with diameter of Journal specifications of 640 Ford.

Probably .001US "One thousand Undersized BRG. Shell"

If the Connecting Rods are removed...you could assemble BRG. Shells back into respective connecting Rods & Caps...Torque caps and check I/D with inside
micrometer:

Bob...

<img src="https://www.yesterdaystractors.com/cvphotos/cvphoto16757.jpg"

K Effective · Mar 16, 2019

thicker bearings are OVERSIZE they make up the distance when grinding the crank down to make it round again so you have a crank 10 under you will need OVERSIZE and thicker bearings. 10 under means the crank has been ground 10 thous then comes the thicker bearings 10 OVER to fill the void

I learned the exact opposite of the above post- the bearing is marked .001Undersized because the crank is undersized. As stated in another post, .010US is more common after turning to remove a defect, .001US on new cranks.

jimg.allentown · Mar 16, 2019

Engine bearings are sized based on the inside diameter. Smaller crankshaft journal takes a smaller inside diameter hence undersized.

I see your logic in saying that more material/thicker bearing seems to be oversize, but the bearing size is determined by the inside dimension. You may call them whatever you like, but the industry standard still calls them undersize. There has to be some uniform method of describing them or engine rebuilders would have continual problems making things fit.

ditchwitch · Mar 16, 2019

The bearing you have is call a (oversized) bearing because your crankshaft is (under sized) (worn) by .001 . I use to grind crankshafts back
in the 80s .

Welding man · Mar 16, 2019

A .001 or .002 bearing is to compensate for normal wear on a crankshaft that really don't need grinding or one that just needs a light polishing. No crankshaft grinder will ever set up a crank and grind it .001..010 will be the minimum you will see one ground.

Brian G. NY · Mar 16, 2019

(quoted from post at 13:50:29 03/16/19) The bearing you have is call a (oversized) bearing because your crankshaft is (under sized) (worn) by .001 . I use to grind crankshafts back
in the 80s .

I'm really surprised!

Even Federal-Mogul refers to them as undersized.

Bob · Mar 16, 2019

(quoted from post at 10:34:20 03/16/19)

(quoted from post at 13:50:29 03/16/19) The bearing you have is call a (oversized) bearing because your crankshaft is (under sized) (worn) by .001 . I use to grind crankshafts back
in the 80s .

Click to expand...

I'm really surprised!

Even Federal-Mogul refers to them as undersized.

You don't SUPPOSE FM got it RIGHT do you? (LOL!)

There always be one or two that can't accept what 98% the rest of the world accepts as "convention".
If you dig deep enough into this, you will find that "oversize" bearing inserts are actually larger OUTSIDE DIAMETER, and are used in certain situations where the rod or main bearing bore is greater than "spec", to "save" the part.

ONE example would be "cracked" rods, where the mating surface can't be ground in the reconditioning process.

Less the "cracked rod" thing starts a new round of argument, see link.

https://www.enginebuildermag.com/2015/09/connecting-rods/

Also, " For powdered-metal “cracked cap” rods, depending on the amount of out-of-roundness that must be corrected, and depending on what thickness rod bearings are available, you may be able to hone to a round condition and install oversize bearings, which will provide the OE I.D. to accommodate oil clearance at the crank, while featuring a thicker wall (and larger O.D.) to use with the overhoned rod big end."

SOURCE: https://www.motor.com/magazine-summary/performance-perspectives-connecting-rod-inspection/

Rod bearing question

pburchett

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David G

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T.R.K.

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Mike(NEOhio)

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gene bender

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John Deere D

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K Effective

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jimg.allentown

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ditchwitch

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Welding man

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Brian G. NY

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Bob

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