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Discussion Starter · #1 ·
I had my wrist pins coated, clearanced .0015 as I'm going to use a vacuum pump. A well known So Cal engine builder is recommending using coated bearings and says the clearances would be tighter. Why would coated wrist pins be clearanced looser but coated bearings clearanced tighter? Anyone out there have experience with coated bearings, how much clearance did you have and how did they wear?

I plan to use a 5-30 synthetic oil...
 

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steelcomp was here
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All depends on the applications. Some builders say to add wrist pin clearance due to vac pump, depending on amount of vac., HP, rpm, etc.
IMO coatings on bearings are for insurance, and shouldn't dictate clearances.
 

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Sit N' Spin
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It sounds to me like what he meant is that coated bearings are the same size as regular non-coated bearings, but the coating will tighten up the overall size of the bearing. If this is what he meant, you may have to take off an extra thou or two off the crank to achieve proper clearance.

Does that sound right?
 

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B1 Racing
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Coated wrist pins have been good to us, we had alot of wrist pins galling on us, we went to different clearances, stiffer pins and DLC coatings and we have been good to go since then.

The Clevite Tri-Armor coated bearings were very tight when we messed around with them, couldnt use them at all. Ended up with some Calico coating bearings and the clearances came right in.
 

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B1 Racing
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It sounds to me like what he meant is that coated bearings are the same size as regular non-coated bearings, but the coating will tighten up the overall size of the bearing. If this is what he meant, you may have to take off an extra thou or two off the crank to achieve proper clearance.

Does that sound right?
Yes but I wouldnt do that to a crank over an $80 set of bearings, get different bearings.
 

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I have not run a uncoated bearing in about 4 years now, and in that time I have learned a couple of things. The coating will close up your clearances about .0005. If you are already on the tight side of where you want to be before the coating, you may want to go a half set(.0005) to a full set(.001) size over. There no comparison between Calico, Specialty Coatings, or Embee Performance Coatings bearings and Speed Pro, and Clevites. Every Clevite/Speed Pro coated bearing I have used has chipped, and the coating a left long before the other "custom" coated deals. The coating does not have to be visually there to still have some benefit, but the bearing can't worn into the top bearing material. By that time the coating is completely gone. There is approx. 10 hrs at WOT 7000+ on these bearings(Calico), and another 10 hrs of warm up, and testing time. Not to mention about 25 or 30 WOT dead engine starts, which is the biggest reason I run coated bearings. Since I can make 1 call to Calico and get what I want, thats where I get them. If I need something they don't stock, then I take bearings I aquired to Specialty or Embee.



 

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