roller bearings vs plain bearings

[Jay]

Why would anyone use ball or roller bearings as main bearings in a 4-stroke engine? It seems to me that plain bearings are simpler, cheaper, stronger, longer-lasting, easier to service, and have much less friction than roller bearings. What advantages do roller bearings have in this application?

I ask because I'm interested in getting a KTM motorcycle and KTM uses ball or roller main bearings in their 4-stroke LC4 engines. I believe the cams turn on ball bearings also.

 

[Al]

Actually roller bearings probably will have less friction under many conditions. That's probably their main claim to fame. The other advantage is that they maintain position of the shaft better than plain bearings. I guess there are advantages of each type. The min problem to anti-friction bearings is they are really susceptable to dirt.

 

[whizzerdave]

I believe most all high performance motorcycle engines these days have roller bearing cranks. From my experience the plain bearing cranks tend to wear out faster and need bearing replacement more often.

 

[XS650]

quote:

---

Originally posted by whizzerdave:
I believe most all high performance motorcycle engines these days have roller bearing cranks. From my experience the plain bearing cranks tend to wear out faster and need bearing replacement more often.

---

Do any modern mainstream motorcycle engines have roller bering cranks?

AFAIK, even the cost no object road race bikes are plain bearings.

I am under the impression that only a few throwbacks like the Harley Anachronism and some small manufacturers used roller bearing cranks on 4 stroke engines anymore.

 

[tom slick]

as far as i know any dirtbike you buy, 2 or 4 stroke will have roller bearing rods and ball bearing cranks. you'll wear the rings out before you need new bearings, it really isn't an issue to concern your purchase preference with. my modern drz400 has roller and ball bearings on it's crank assy.
one benefit is that it doesn't require nearly as much oil pressure, splash lubrication is sufficent although these bikes do have oil pumps.

if it helps you any i rode with a guy this weekend that has 26,000 unrebuilt miles on his ktm 640 lc4 engine, the bike is a 2002 model! he races regularly including pre-running the baja 1000. that is a testament to ktm durability.

[ March 14, 2004, 01:06 AM: Message edited by: tom slick ]

 

[Chris142]

quote:

---

Originally posted by XS650:

quote:

---

Originally posted by whizzerdave:
I believe most all high performance motorcycle engines these days have roller bearing cranks. From my experience the plain bearing cranks tend to wear out faster and need bearing replacement more often.

---

Do any modern mainstream motorcycle engines have roller bering cranks?

AFAIK, even the cost no object road race bikes are plain bearings.

I am under the impression that only a few throwbacks like the Harley Anachronism and some small manufacturers used roller bearing cranks on 4 stroke engines anymore.

---

All the atv's and dirt bikes I have ever owned had roller bearings. I remember my 1980 atc 110 had a roller crank and main bearings.

 

[sub_zero]

Most design work on MC engines is still a throwback to the twostroke era when you needed needle bearings at the small and big end of the rod. In alot of cases it's probably don't fix what ain't broke thinking. Factor in what it costs to produce the bearings in a proven design vs. the design cost and risk of a new design.


plain bearings are much more shock resistant and better in the rod application than anti-friction roller elemet types. High performance streetbikes use a plain rod and main bearings.

 

[XS650]

quote:

---

Originally posted by sub_zero:
Most design work on MC engines is still a throwback to the twostroke era when you needed needle bearings at the small and big end of the rod. ....

plain bearings are much more shock resistant and better in the rod application than anti-friction roller elemet types. High performance streetbikes use a plain rod and main bearings.

---

I think the majority of current production MC engines except dirt bikes and a few throwbacks are modern engine designs.

If you consider the relatively small complication of a built up anti-friction bearing crankshaft in a single cylinder engine vs a proper oiling system that will function in all the wierd attitudes a dirt bike sees, rolling element bearings in a one cylinder dirt bike make some sense. They don't make as much sense in a high speed high performance street or road race engine.

 

[Jared H]

Roller bearings don't require "constant" pressure lubrication in order to do the job whereas plain bearings usually do or they wear and will ultimately seize up if given enough time with out oil pressure.

As mentioned above, the strange angles seen with offroad dirtbikes could justify the use of roller bearings in crank and rod applications due to difficulty in oiling.