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Sanding/scotch brite to increase bearing clearance?

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Sanding/scotch brite to increase bearing clearance?

Postby mshred » Mon Mar 11, 2013 10:05 pm

Is it safe to do? My clearances are on the tight side, and I would really like to see a half thou more. I don't want to grind my brand new crank that is near perfect and would like to be able to use my standard size bearings that I have already bought and installed IF I it safe to increase clearance in this way... I seem to find mixed opinions on this, but woul really like it if people would share their experience with doing it and whether or not it is safe or even worth doing
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Re: Sanding/scotch brite to increase bearing clearance?

Postby governor » Mon Mar 11, 2013 10:18 pm

don't do it, buy a set of extra clearance bearings and put 1/2 of the set in the upper portion of the rod.

You will frick it up, so don't even think about it.

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Re: Sanding/scotch brite to increase bearing clearance?

Postby ProPower engines » Tue Mar 12, 2013 12:03 am

X2
Don't even go there. ](*,) ](*,)
You should be able to get bearings to do the job correctly. This is not a place to cheap out and worry about spending $100 extra to get it right.
What kind and size of engine are you working on and what brand of crank is it?? What bearing part number are you using now? that may be part of the problem??
That way part numbers can be recomended to correct the problem.
Post some more details on what you have and are working with
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Re: Sanding/scotch brite to increase bearing clearance?

Postby Greenlight » Tue Mar 12, 2013 1:47 am

You can try:

Option 1:
Bring the crank to a local crank grinder and have them polish the journals. They can remove from 0.0001" to 0.0015" from the journals. If you let them know how much smaller you want the journals they can usually get the crank within 0.0003" or so of what you want. Then you can use standard bearings and get the required clearance.

Option 2: (not the preferred option, but better than using scotch brite on the bearings)
Use 400 grit, then 600 grit sanding cloth on the crank and polish it down to size yourself.

I've done both.
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Re: Sanding/scotch brite to increase bearing clearance?

Postby vwchuck » Tue Mar 12, 2013 6:41 am

Which bearings(rods,mains) and what is the clearance? What RPM with this engine see?
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Re: Sanding/scotch brite to increase bearing clearance?

Postby mshred » Tue Mar 12, 2013 1:30 pm

Thanks for the info everyone! I have decided against it. I have ordered a set of bearings that will get me the clearances I need. Thanks all!
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Re: Sanding/scotch brite to increase bearing clearance?

Postby Dan Timberlake » Tue Mar 12, 2013 1:43 pm

It takes special efforts and many confirming measurements to not polish measurable taper into a crank, if these HD tolerances are required/desired.
http://www.studebaker-info.org/tech/Bea ... -3-402.pdf

I'm not sure what is more dangerous in a borderline situation. 1/2 thou less than ideal clearance, bearing clearance 0.004 inch tight at one edge due to rod bore barrel on a polished, tapered journal, or a nodular or nitrided crank polished in the wrong direction.
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Re: Sanding/scotch brite to increase bearing clearance?

Postby BrazilianZ28Camaro » Tue Mar 12, 2013 4:52 pm

Extra clearance bearings are the correct decision, but sometimes we just haven't the time to wait for new ones.

Have somebody ever tried to sand the back of the bearing, say, .0004" to increase the clearance?
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Re: Sanding/scotch brite to increase bearing clearance?

Postby robert1 » Tue Mar 12, 2013 5:12 pm

I have sanded the backs. I don't like it but I have gotten as much as .0005" that way. As mentioned NEVER EVER polish the id.
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Re: Sanding/scotch brite to increase bearing clearance?

Postby af2 » Tue Mar 12, 2013 5:24 pm

robert1 wrote:I As mentioned NEVER EVER polish the id.


You don't like copper showing??? LOL
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Re: Sanding/scotch brite to increase bearing clearance?

Postby Walter R. Malik » Tue Mar 12, 2013 5:33 pm

mshred wrote:Thanks for the info everyone! I have decided against it. I have ordered a set of bearings that will get me the clearances I need. Thanks all!


Good move ... ! :wink:
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Re: Sanding/scotch brite to increase bearing clearance?

Postby Strange Magic » Tue Mar 12, 2013 5:38 pm

The correct way to increase clearance in a journal is a few ways, everything else is just a hack job and you will end up with junk in almost all cases. Lets assume that you do not have the option of a .001 under bearing, then below is what you might want to consider.

1. You either puff hone the housing bore, reset the bearing back into place, torque and take a measurement with a dial bore gauge once again. This method can be done if your looking for an additional .0003-.0006.

2. If you need a solid .001-.0012, then you can have your crank grinder remove .0018-.002, coat the bearings and you should net out that .001-.0012. It's very tough for a crank grinder to take tenths or even 1 thou.

I would never recommend that you sand out material for additional clearance on a bearing and I would never recommend that you micro polish material out for additional clearance. If so, YOUR A HACK AND YOU BEST MIGHT BE SUITED FOR EMPLOYMENT AT THE LOCAL BUTCHER SHOP
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Re: Sanding/scotch brite to increase bearing clearance?

Postby fdicrasto » Tue Mar 12, 2013 5:57 pm

FYI, get a magnifying glass,a new,expendable rod bearing, do the scotch bright then look at the bearing surface. I will guarantee you will not do this to YOUR bearings in YOUR engine. Phil D.
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Re: Sanding/scotch brite to increase bearing clearance?

Postby machine shop tom » Thu Mar 14, 2013 3:18 pm

Some time ago, there was a featured article in Popular Hot Rodding magazine that touted a particular engine builder's talents at building a 360 Chrysler engines. The "guru" discussed how he "Scotch-Brighted" the bearing to remove the initial coating to prevent it from flaking off.

I wrote a letter to the editor of the mag pointing out that I thought it was a bad idea to rub abrasives into a bearing and that the bearing designers would probably agree with me and that I thought if the builder wanted race bearings, he should use them.

The gist of the editor's reply was that this guy was a "somebody" and the I was a "nobody", so the builder in question was right.

#-o

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Re: Sanding/scotch brite to increase bearing clearance?

Postby wyrmrider » Thu Mar 14, 2013 7:55 pm

Babbitt or aluminum bearings you could line bore
put some more shims in the rods?
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