Tapered needles?

[pontiacjack]

This isn't actually a driveline question, but it concerns roller-element bearings, so I'm guessing that members of this forum have the appropriate expertise. Nor is it a "need to know" question- just trying to learn something.

An ad for Crower's latest roller lifters mentions "polished and tapered needle bearings". Huh? As I see it, a PAIR of tapered-element bearings (complete with races) would be required for such a configuration- but with a roller wheel of no more than 3/8" width, I can't believe there's enough room. So... not being a bearing designer, I wonder if they are referring to nominally "straight" needles that are shaped with a tiny amount of taper near their ends?

 

[tbuelna]

pontiacjack,

I believe they meant "crowned" rollers not "tapered". The "taper" on a crowned roller would be a very slight lengthwise profile (usually a radius) on about the last 10 to 20 percent of each end. This prevents roller edge loading under shaft misalignments. Rollers with a large L/D aspect ratio, like needle rollers, tend to edge load and skew quite easily.

A crowned roller will have less capacity than an uncrowned roller, so the amount of crowning is a compromise between load capacity and misalignment tolerance.

Hope that helped.
Terry

 

[patprimmer]

I am not aware of the bearings in question and roller bearings is not an area I know a lot about.

To my knowledge, Bruce Crower retired quite a few years ago. Bruce was a real racer and a gifted engineer who made excellent products and some insightful developments and built a business with a strong reputation for real and worthwhile innovation and quality.

When he retired, his daughter gained control. I think she has no engineering ability whatsoever and has a marketing or management degree. Since then, Crower has been more into spin and marketing hype than innovation, at least in my opinion.

Regards
Pat
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[Tmoose]

I think part of your stated concern is axial loads, no matter how small. They must be guided, at the very least.

I suspect needles and rollers are always made with a subtle crown these days. A carefully crowned profile can reduce the deadly edge loading to the point the bearing's load rating is better than a "straight" roller would be, even if perfect alignment was attainable.

http://www.digitalmetrology.com/images/RollerProfiles.jpg

For a few decades Harley used cylindrical, square cut rollers.

http://www.howardscustoms.com/catalog/VTwin_2-Classic_445.pdf

Sometimes the crankpins would initiate spalling at the roller edges.

By the 70s Harley had moved to fewer (17 per row from 19?) crowned rollers in aluminum cages. I don't recall seeing any edge spalling, and fewer failures overall. No idea hat's inside the EVO and TC motors.

 

[pontiacjack]

Thanks guys. The consensus seems to be that Crower meant to say "crowned" needles.