Needle bearings or solid bushings?
Post Reply   Forum
Posted by: bjamesw

08/18/2003, 11:08:50

Author Profile Mail author Edit

Hello,

May I get a little advise to settle a dispute?  What relative advantages apply to rolling and to friction type bearings? Why would a designer opt for solid bushings at the journal end of a connecting rod in a compressor pump or automobile engine for instance if not simply for cost savings?  I  understand that needle bearings here can drastically reduce rolling resistance but may have a shorter service life.  Is a needle bearing in this application distinctly better (assuming both bearings types chosen are of highest quality available)?

thank you very much

Brad Williamson







Post Reply | Recommend | Alert View All   | Next |

Replies to this message


Re: Needle bearings or solid bushings?
Re: Needle bearings or solid bushings? -- bjamesw Post Reply Top of thread Forum
Posted by: randykimball
Barney
11/05/2005, 01:22:50

Author Profile Mail author Edit
Shell (or bushing) bearings do not touch the shaft. Oil supplied by a pump assures that oil is forced between the shell and the shaft. Thus the weight and friction is carried by liquid. This is why it takes many miles to wear out a modern set of main bearings. And as they do wear oil pressure drops and clues the operator in that the bearings are needing replaced... as well as the oil pump.

Needles in a heavy pounding situation tend to get flat spots and tend to make rounded splines around the shaft. This would be started also by the split in the sleeve. Needles are as mentioned in another post are hard to install and replace in a journal where they can't be slipped over the end. Many cases studies have ended in faiure. Engines are a harsh condition, one reason is that needles need an endless ring to run in, ... in order to install one on a crank it must be split, ... now you have a seam somewhere, not so kool. Needle bearings need clean pure oil. The carbon deposits that carry through an engine will flow through a shell/journal connection but crush and deposit in a roller needle action. This damages the needles.




The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them.


Post Reply | Recommend | Alert Where am I? Original Top of thread
Re: Needle bearings or solid bushings?
Re: Needle bearings or solid bushings? -- bjamesw Post Reply Top of thread Forum
Posted by: diemeister
Huckleberry
10/18/2003, 17:30:18

Author Profile Mail author Edit
i'm not familiar with all varibles specific in general solid have less vibration and are stronger






Post Reply | Recommend | Alert Where am I? Original Top of thread | |
Re: Needle bearings or solid bushings?
Re: Re: Needle bearings or solid bushings? -- diemeister Post Reply Top of thread Forum
Posted by: frankiepoos

12/18/2003, 18:18:25

Author Profile Mail author Edit

As far as auto engines are concerned, the use of needle bearings is fraught with problems. Whilst the rolling friction is seemingly low, assembly is complicated by the need to fit a needle roller round a journal which may be several webs along a crankshaft rather than at each end (as in a 2 stroke moped engine) Nomatter the lubrication pressure supplied, any wear which accumulates at a journal is uncushioned by oil and crankshaft rumble and overreaching of the con rod follows with chatter exacerbating the problem and eventual reduction of bumping clearance to nil. At rest, the bearing quickly drains down of residual oil and the exposed rollers and face surfaces are rapidly attacked by corrosive combustion by-products remaining in the crankcase. For a regularly used low cost and disposable moped engine the deterioration is acceptable but for those engines used infrequently (for example in a light aircraft) the extent and rapidity of bearing failure compromises apparent economy of installation and leads to unreliability.

By contrast, a shell bearing is easy to assemble and renew, cushions heavy thrust reversals all the time adequate oil is provided and accommodates and tolerates considerable wear. At rest the assembled bearing retains oil which inhibits corrosion of the journal even when exposed to corrosive atmospheres.

One disadvantage of shell bearings is the low tolerance to high temperatures and loads which break the oil cushion, in those cases the shell lining material, popularly known as white metal may reach melting temperature.

Low stressed engines use a white metal alloy mainly of  lead and tin while high load engines use alloys including aluminium for greater strength, though tougher white metals demand nitrided crank journals for longevity.

Roller thrust bearings are notoriously unreliable in auto applications as failure leads to speedy engine destruction while white metal thrust bearings continue to carry thrust loads even when the white metal is worn down to the steel backing.

Most British Leyland (Austin Morris) 1100s power unit failures arose from the collapse of the 2 needle roller bearings which supported the idler gear between the engine and underslung gearbox. Needles which sat beneath the oil surface in the gearbox/sump survived corrosion until they were damaged by circulating swarf in the lubricating oil shared with the dirty engine.







Post Reply | Recommend | Alert Where am I? Original Top of thread | |
Re: Needle bearings or solid bushings?
Re: Re: Needle bearings or solid bushings? -- frankiepoos Post Reply Top of thread Forum
Posted by: charleschin

11/04/2005, 11:11:19

Author Profile Mail author Edit
Help needed!

My company is looking for a possible customized machine that can do:

Assemble (insert) 54 needle bearings into one pin bore (both sides, each side has 27). There are total 4 pin bores on one object. Those needle bearings will surround the bore surface. There is a spacer between two rows of needle bearings. After assembling those needle bearings, then someone will drive the pinions inside the pin bores, which means that the pinion would be surrounded by those 54 (27 each row) needle bearings.

Anyone who knows what company could offer this service, please email to chaochunchin@gmail.com to talk about more detail.






Modified by charleschin at Fri, Nov 04, 2005, 11:25:14

Post Reply | Recommend | Alert Where am I? Original Top of thread
Re: Needle bearings or solid bushings?
Re: Re: Needle bearings or solid bushings? -- frankiepoos Post Reply Top of thread Forum
Posted by: Cragyon
Bart
12/22/2003, 06:53:54

Author Profile Mail author Edit

Very informative post frankiepoos, good reading!







Post Reply | Recommend | Alert Where am I? Original Top of thread | |

Powered by Engineers Edge

© Copyright 2000 - 2018, by Engineers Edge, LLC All rights reserved.  Disclaimer