8BA NOS Ford rod bearings

[russcc]

Got a call from the machine shop putting the 59L together. Merc crank, .010 under, mains & rods, 8BA rods, magged, resized, rebushed. The rod journals are 2.1280. The shop says the rod inserts id is .002 to .003 oversize. Is that excessive ? I thought you needed good clearance for the oil to flow through, promoting cooling. I measured the thickness of a bunch of the Ford NOS inserts in the original unopened boxes marked OBA-6211-C, .010 U.S. and came up with .106 thickness. Any opinions ? Thank you Fordbarners.

[34PKUP]

Assemble the rods and bearings to their locations using PLASTIGAGE to check actual clearance. (Stop guessing)

[flatheadmurre]

If the shop did the crank and the rods they should have it under control ending up on a value you agreed on.
If you grind the crank on the low side and hone the rods on the high side it´s easy to end up out of spec...

[cas3]

thickness of the bearing shell is irrelevant, its crank clearance you want, plastigauge it

[40 Deluxe]

Originally Posted by russcc

Got a call from the machine shop putting the 59L together. Merc crank, .010 under, mains & rods, 8BA rods, magged, resized, rebushed. The rod journals are 2.1280. The shop says the rod inserts id is .002 to .003 oversize. Is that excessive ? I thought you needed good clearance for the oil to flow through, promoting cooling. I measured the thickness of a bunch of the Ford NOS inserts in the original unopened boxes marked OBA-6211-C, .010 U.S. and came up with .106 thickness. Any opinions ? Thank you Fordbarners.

This would result in about .004" to .006" oil clearance, which is out of spec on the high side. Factory oil clearance spec is .0018", per 1959 Chilton Manual. While you want oil flow for cooling, too much will flood the cylinder walls and the rings won't keep up, resulting in burning oil.

[russcc]

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Thank you all. The machine shop is not guessing, the use a bore gauge not plastiguage.

[GOSFAST]

Originally Posted by russcc

Got a call from the machine shop putting the 59L together. Merc crank, .010 under, mains & rods, 8BA rods, magged, resized, rebushed. The rod journals are 2.1280. The shop says the rod inserts id is .002 to .003 oversize. Is that excessive ? I thought you needed good clearance for the oil to flow through, promoting cooling. I measured the thickness of a bunch of the Ford NOS inserts in the original unopened boxes marked OBA-6211-C, .010 U.S. and came up with .106 thickness. Any opinions ? Thank you Fordbarners.

Hi Russ, your crank is considered "10-low", .002" to .003" is fine, the .003" is on the high but will not be an issue!

We send them all out of here with those sizes!

Thanks, Gary in N.Y.

P.S. You're always better off having an extra "thou" (and still be in specs), will never hurt and may actually help depending on how "hard" you plan to run it? Too tight and you may come to regret it?? The recommended low is .0009", this isn't acceptable over here, especially on a performance build

[Ol' Ron]

Gary X2. .0025 is perfect, But???

[rotorwrench]

A little loose is no problem. A little too tight is a problem. I never use a bore gauge on a new bearing surface since it might scratch the crap out of it. Plastigage is the only way to go or just fit it to a journal with some oil on it. There is always a possibility that parts have been mismarked. Try fitting the rod to a journal and see if it's too loose. A lot of play will be evident.

My 1949 thru 51 Lincoln/Mercury Overhaul Manual lists the clearance or .0005" to .003" so the clearances are like the other guys have already mentioned. I would be happy with .0025" clearance but even .003" is acceptable.

[russcc]

Thank you all for the info. I like the idea of .0025 to .003.

[Kohnke Rebabbitting]

Originally Posted by russcc

Thank you all. The machine shop is not guessing, the use a bore gauge not plastiguage.

The use of a Bore Gauge, is haphazard, at best!

If you want to be sure of the correct size, to a 1/10 of a thousandths , use a post Mic, or, also called an Inside Mic. Then use an out side Mic, to read the inside Mic's reading.

Also the use of Plastigage, works fine, but you have to use oil, as it will give false readings dry. Dry won't let the Plastigage spread out correctly. Always read the Plastigage reading, on the crank, not on the bearing.

Also, Telescoping Gauges are not good enough for accurate bearing Sizing!

[russcc]

Are we confusing a bore gauge with a telescoping gauge ? There is a huge difference in results. Also, what is meant by "reading the plastiguage on the crank, not the bearing ?

[Ol' Ron]

I use a bearing mic for floaters and a toy hammer. Works great.

[flatheadmurre]

T-mike is as good as the operator using it...Boregauge is better but a bit tricky on a soft surface like a bearing.
I use a tripoint micrometer they have a bigger contact surface and you can control the force aplied to the bearing surface.
Plastiguage is a good indicator for what´s going on and can show issues like if the main bore is not in line...but it also is as good as the operator using it...

[Ol' Ron]

When I'm all done setting up the bearings I use a fine scuff pad to remove the shine and add some roughness to the surface to retain oil. Then wash them in soapy water. Some builders don't like this, but it just becomes a habit for an old fart