308 A/C tensioner - bearing spec | FerrariChat

308 A/C tensioner - bearing spec

Discussion in 'Technical Q&A' started by Peter, Apr 8, 2019.

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  1. Peter

    Peter F1 Veteran
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    Dec 21, 2000
    6,430
    B.C., Canada
    I've had issues with this over the years.

    I'm in the midst of doing my timing belts right now. I've removed most of the front accessories including the A/C system. When I removed the tensioner, I rolled the tensioner pulley with my fingers and it doesn't feel right. No perceptible drag or roughness, but it does make a noise. Bearings shouldn't make noises.

    I've replaced these bearings before. The originals were, according to my notes, NSK 6002-C3. Many years ago when I was at my industrial bearing supplier, I was given the equivalent in size, but not in running/service clearance (which is designated by the suffix). It wasn't long after that it seized while driving, grenading the belt (scared the $#@! out of me when that happened). Went back to the supplier, in not a very happy mood and was given these as replacements. It's given me years of service, but it's time to be replaced.

    The other bearings, like the water pump, alternator, etc, all turn beautifully by hand. Except this.

    Based on the designation, is there any other grade of bearing that will give a more durable service? I'm not sure, but if I remember correctly, the 6002-C3 was obsolete and that's why I was given this (6002-V). NSK bearings are very good quality, so I don't think that's the issue. I've always tried to tension the belt at an appropriate amount (mind you without a tensioner, but, with a steady "feel". Not too loose and not too tight. I've done the neighboring water pump belt the same way and pump and alternator roll butter-smooth. Always have).

    Any suggestions?

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  2. Ricambi America

    Ricambi America F1 World Champ
    Sponsor Owner

    6002-2RS1/C3 - It should be 'butter smooth', but certainly not free-wheeling and spin multiple rotations when you flick it with your fingers.
     
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  3. Peter

    Peter F1 Veteran
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    Yeah, exactly. This set is almost like the free-wheeling condition you describe and yes, that means it's done. Thanks for the P/N...
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #4 Steve Magnusson, Apr 8, 2019
    Last edited: Apr 8, 2019
    Not really, but there are more factors than just the basic size and internal clearance. The part number that Daniel gave is for an SKF brand steel, deep-groove ball bearing (15x32x9) with seals on both sides:

    SKF 6002-2RS1/C3...(but there'd be even more part number gibberish appended to this defining the lube type and amount of lube fill)

    I believe the corresponding NSK part number would be:

    NSK 6002VV/C3...(and this would also have the same additional gibberish).

    Unfortunately, they usually only print the full part number on the box (not the bearing itself) so you might try to decode this at the SKF or NSK website to confirm the lube is something appropriate for this application if you get new ones -- just a thought...
     
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  5. Peter

    Peter F1 Veteran
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    Thanks as always Steve.

    So, would the lubricant make that much of a difference? Is the fact that the A/C compressor is soft-mounted (via rubber cone bushings) would put a side load on this pulley?
     
  6. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    It could if a bearing was supplied with no lubricant in it at all ;). Usually an off-the-shelf sealed bearing is loaded with a reasonable amount of grease that would work fine here so I'd be more suspicious that the bearing you had that failed was a (cheap) counterfeit. This bearing set hasn't been reported as being super-troublesome so I don't think that you'll need to get overly fussy, but this is always an issue when just matching the bearing basic size.
     
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  7. Peter

    Peter F1 Veteran
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    I can’t have control over what my supplier gets... At least it’s easy to get at, so I’ll just have to regularly change it out.
     
  8. WaltP

    WaltP Formula 3

    Nov 1, 2003
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    Don't lose the washer between the bearings on the inner race, it's surprisingly Ferrari costly;)
     
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  9. Peter

    Peter F1 Veteran
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    I haven't lost that spacer, but that's what lathes are for if I ever do! ;)

    FWIW, I picked up SKF 6002-2RSH/C3 bearings from my supplier and installed them.

    One thing I noticed is that the interference fit was quite tight. About 0.02mm between pulley ID and bearing OD. I "relaxed" the fit by passing a small hone to open the pulley ID by 0.01mm. Pressing the new bearings in wasn't as much of a fight in previous repairs, so that should help extend the life of the bearings (by not squeezing the bearing's outer race. I figured the tight interference fit may have had influence on the bearing's running clearance, even considering the "C3" tolerance).
     
  10. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    +1 -- You did rightly - especially since the "housing" in this case is a relatively massive block of steel with a much greater stiffness than the outer race of the bearing (i.e., most of the interference will work to reduce the internal clearance rather than expand the housing). SKF's rule-of-thumb fit table for this bearing size/application says 5 um loose to 20 um tight so you are now much more in the middle.

    Had to look up those "RSH" seals = new and improved over RS1 so all goodness there.

    Was there any additional PN suffix information given?
     
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  11. Peter

    Peter F1 Veteran
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    Unfortunately, no. All the box says is:

    SKF Explorer 095P
    6002-2RSH/C3
    29-Made in Italy 12
    (UPC code):7 316571 814643
     

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