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Rod journal polishing


i6pwr's Avatar
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06-21-09, 07:32 AM   #1  
Rod journal polishing

Replacing the rod on the EX-30 Robin engine, should I hit the journal with some 000 steel wool and would it need a mirror polish to it or would this be a fine enough finish?

Don't want to ruin a new rod.

 
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06-21-09, 08:49 AM   #2  
What I did was took some 000 wool and lightly went over the journal. Just not sure if I need to go over again with some metal polish or the likes or leave it be. I've always had and seen mirror finishes but for a generator application is it critical?

 
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06-21-09, 09:34 AM   #3  
You will be fine removing any aluminum deposits left by the rod. Check for scoring and mike it to ensure it is not out of round.

 
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06-21-09, 09:40 AM   #4  
The problem with what you're doing is the direction of the microgrooves you're creating in the crank. When a machine shop grinds and polishes a crank the grooves run in the direction of turn of the crank - for the most part exactly perpendicular to the center line of the crank and the grooves are perfectly parallel to each other.

When you touch up or polish a crank by hand those grooves are very random and have to be worn out by the softer metal of the connecting rod. The application of the engine is really immaterial.

If the crank was needing a touch up because of the previous connecting rod, a machine shop is the best one to touch it up or resurface it.

If everything is within tolerances (plastic gauging) and and you have an unmarred finish on the journal, it'll probably work fine. You will have to take special care to remove any remnants of the steel wool, making sure the crank is perfectly clean before assembly.

 
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06-21-09, 11:54 AM   #5  
I did plastigage the journal and it's right in the middle of the specs. My process was I took a 6" strip of the 000 wool and lightly pulled both ends back and forth in the direction of rotation but not "one" direction. I rotated the crank about 45 deg each time I made a few passes to try to ensure a complete "even" amount of polishing.

The surface isn't a mirror, but it's smooth and appears to have less of a glaze than the bore after a light honing. I am worried about anything less than a mirror finish on a steel crank turning against an aluminum rod, but have heard others perform this with great results.

 
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06-21-09, 12:12 PM   #6  
No expert on small engines..but back when I was a motorhead and rebuilt several hot rod engines, we would use superfine (600? 800?) emory or wet/dry sandpaper with oil on it and buff the journals of the cranks like you were doing a professional shoeshine. Then we'd clean off everything using a spray degreaser or brake cleaner.

Normally IIRC you didn't want to go too fine as you needed some pores to hold the oil for the break in period. Of course these engines all had bearings.

Just a thought......


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06-21-09, 01:13 PM   #7  
Yeah, the whole thought of a glaze rather than a shine just doesn't sit well with me. I hit it with some Mothers Billet metal polish and what a difference. Used some strips of T-shirt and it worked great...will post a pic later.

 
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06-21-09, 02:22 PM   #8  
Before I hit it with some degreaser, looks much better than before.


 
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