.002 Undersize Main Bearings

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thomasfouraker

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Took my 4" Crank to a local machine shop to get polished for my 408 Magnum refresh.

Machinist mic'd each journal in three spots and with the specs I provided said it would clean up and still fall within spec, on the lower end.

I picked it up and took it to my brother in laws machine shop (non automotive) to have him mic the journals after the polish. Two of my mains are .002/.0015 below spec, coming in a 2.8070 and 2.8075.

The rest of the mains and rods are within a .001 of spec and I can get my clearance with standard or +.001 bearings.

Do they make a +.002 bearing for the mains that anyone knows of? They must have at one point because my Magnum Motor book by Larry Shepard talks about it but I can't find any manufacture that shows it available.

Trying to shy away from having the crankshaft ground .010 because quite frankly I don't have much faith in the shops around here.

Going to go ahead and buy some +.001 mains and check clearances. If I am under .003 I will probably just roll with it.

Thanks!

Thomas
 
Excerpt from the book

*I think there is a typo, where they gave the v6 magnum main diameter
image.jpg
 
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I used .002 under main bearings (I think from michigan) but that was on a big block, I don't know if they are, or were, available for a small block.
I used them as a shortcut, so I wouldn't have to grind a hard chromed fueler crank, and I was very disappointed in the final oil control, and I never ran the engine.
I think you will be happier if you can find a decent machine shop, and get it ground, rather than look for bearings that might not exist.
 
33IMP said:
I used .002 under main bearings (I think from michigan) but that was on a big block, I don't know if they are, or were, available for a small block.
I used them as a shortcut, so I wouldn't have to grind a hard chromed fueler crank, and I was very disappointed in the final oil control, and I never ran the engine.
I think you will be happier if you can find a decent machine shop, and get it ground, rather than look for bearings that might not exist.
Click to expand...

Thank you for that reply. After researching online I can't even find old part numbers, or literature suggesting +.002 bearings were available for 360s.

I have read enough I feel if I can keep all my clearances consistent, and under .003 I will feel comfortable running those. Hughes suggest running .0022-.0030 on their mains and to shoot for .0020-.0025 on rods. I think the .0005-.0025 of factory spec is rather broad.

I did call a place local today that will grind and polish all the mains to 2.800 for $85. Thats pretty darn cheap but it makes me feel I need to be over their shoulder with a mic helping them.
 
The fueler crank I was trying to use was used to running 60wt oil, changed every lap, so it had HUGE bearing clearance. With .001 under rods, and .002 under mains, I still had .0035 on the rods, and .004+ on the mains. I could get good oil pressure cold, or hot, never both.
I now shoot for .0025 rods, and .003 mains on my big blocks. You know what they say.... build it loose, and you will know, build it too tight, EVERYBODY will know!
 
33IMP said:
The fueler crank I was trying to use was used to running 60wt oil, changed every lap, so it had HUGE bearing clearance. With .001 under rods, and .002 under mains, I still had .0035 on the rods, and .004+ on the mains. I could get good oil pressure cold, or hot, never both.
I now shoot for .0025 rods, and .003 mains on my big blocks. You know what they say.... build it loose, and you will know, build it too tight, EVERYBODY will know!
Click to expand...

Going to order the +.001 Main Bearings and check. Worst case I can get it reground and go for the +.010.

Thanks again for the replies!
 
check your crank to see if you need thin bearing the 4'' cranks I've seen have a radius on the journals requiring special bearings
 
You can mix and match bearing shells/sizes to get your required clearances
 
thomasfouraker said:
Thank you for that reply. After researching online I can't even find old part numbers, or literature suggesting +.002 bearings were available for 360s.

I have read enough I feel if I can keep all my clearances consistent, and under .003 I will feel comfortable running those. Hughes suggest running .0022-.0030 on their mains and to shoot for .0020-.0025 on rods. I think the .0005-.0025 of factory spec is rather broad.

I did call a place local today that will grind and polish all the mains to 2.800 for $85. Thats pretty darn cheap but it makes me feel I need to be over their shoulder with a mic helping them.
Click to expand...
I recommend .0015-.0018 no.1 main , other mains .0021-.0024 mains and around .0021rods
 
Pretty sure I can dial in my Rods right where I need to with buying half Std and half +.001 Rod Bearings.

The bearings that came out where Trimetal Clevite 77 P's, not the H series so normal width should be fine on the mains. Not sure if I get the mains ground how the radius will look......or if that will effect the bearing I can run.
 
Another option that I'm considering in a similar situation is Calico Coatings. Coated Bearings | Calico Coatings

I looked them up and read a little about their coatings then contacted them for further details since they have multiple coating types. For my application (with the main goal of clearance reduction) they recommend their CT-1 coating which has a standard thickness of is 0.00025” per shell. Their heavy thickness is 0.0005” per shell. Cost for a full set of mains coated heavy is about $53. This may be the easiest solution for me if I'm not able to purchase .011 bearings off the shelf.
 
Why not try some simple brass shin stock under one bearing shell? McMaster has it in .005 thickness.

Personally i believe you have nothing to worry about.
 
If it’s .003 I’d run it. Don’t mix shell halves, if that was what was suggested.
 
I checked all my mains and I am under .002 on all my mains except the number 3 thrust I am hovering just below .003.

If I am going to mix/match bearings it will be STD and .001 on the rods. That's common practice to dial in bearing clearances and often you can even mix and match STD bearings and get varying clearances to lose or gain .0005
 
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