Explain to me crank bearings/cranks

[bwringer]

There's a reason these GS engines go for so many miles... I don't see a plain bearing crank going for that many miles but maybe I'm wrong

My 210,000 mile Toyota would like a word with you about the reliability of plain bearings...

 

[Jethro]

The theory behind using roller crank bearings (as it was explained to me years ago by a wise old man), is that they are better at handling uneven loads. The longevity of the crank bearings are mostly dependent on cylinder health and crank balance. If the cylinder tolerances are out of spec, or the crank is poorly balanced, it causes vibration, which as we all know will kill the crank bearings quick. Roller bearings are SUPPOSED to be better at combating this. Suzuki, in their desperate and futile chase of Honda, used roller bearings in hopes that they could speed production, which was expected to result in poorer manufacturing tolerances.

In short, the reason they used roller bearings is because they were trying to "cheap" on the rest of the engine manufacturing. Basically an expensive solution to a problem that really didn't exist. Typical of engineers.

 

[Nessism]

The theory behind using roller crank bearings (as it was explained to me years ago by a wise old man), is that they are better at handling uneven loads. The longevity of the crank bearings are mostly dependent on cylinder health and crank balance. If the cylinder tolerances are out of spec, or the crank is poorly balanced, it causes vibration, which as we all know will kill the crank bearings quick. Roller bearings are SUPPOSED to be better at combating this. Suzuki, in their desperate and futile chase of Honda, used roller bearings in hopes that they could speed production, which was expected to result in poorer manufacturing tolerances.

In short, the reason they used roller bearings is because they were trying to "cheap" on the rest of the engine manufacturing. Basically an expensive solution to a problem that really didn't exist. Typical of engineers.

The GS engines were Suzuki’s first four-cycle engines; prior to that they built two strokes, which naturally required roller bearing cranks. Of course this is speculation on my part but I think Suzuki choose the roller crank to speed development of the engines since they were familiar with the technology. The top end borrowed heavily from the Kawasaki DOHC design and the roller crank also provided some separation from possible allegations of outright design plagiarism.

Edit: Josh corrected me in his post below: early DOHC Kawasaki engines had roller bearing cranks just like Suzuki GS engines. Hate to say it but it sure looks like Suzuki copied Kawasaki on these engines…but I still think the cranks came from these companies two stroke pasts.

The business about roller cranks being more fault tolerant of poor machining tolerances is an interesting theory but doesn’t sound right to me since rolling element bearings are very unforgiving to misalignment. Rolling element bearings have a grading system which specifies how much internal clearance a bearing can have and Suzuki would have to use some pretty loose bearings if they wanted to take advantage of any cost savings brought on by loose tolerancing. And if Suzuki wanted to save money on machine work tolerances they certainly wouldn’t have chosen a multi piece crank, with all the tolerance stack up concerns this brings into play. The fact that GS engines are so durable also flys in the face of any claims that Suzuki fit together the engines with sloppy tolerances. Interesting theory, but just doesn’t seem right.

 

[Calvin Blackmore]

Suzuki started with a warehouse of roller bearings ( and crappy front brakelight switches ) and had to use em
when they ran out of these they switched to plain bearings

OK not a likely scenario

Plain bearings also allow for higher RPM running do they not?
I recall a great articel in MC or some such magazine that detiled the pros and cons but that was 25 yrs ago and my mond lacks total recall

 

[TheCafeKid]

The GS engines were Suzuki?s first four-cycle engines; prior to that they built two strokes, which naturally required roller bearing cranks. Of course this is speculation on my part but I think Suzuki choose the roller crank to speed development of the engines since they were familiar with the technology. The top end borrowed heavily from the Kawasaki DOHC design and the roller crank also provided some separation from possible allegations of outright design plagiarism.

The business about roller cranks being more fault tolerant of poor machining tolerances is an interesting theory but doesn?t sound right to me since rolling element bearings are very unforgiving to misalignment. Rolling element bearings have a grading system which specifies how much internal clearance a bearing can have and Suzuki would have to use some pretty loose bearings if they wanted to take advantage of any cost savings brought on by loose tolerancing. And if Suzuki wanted to save money on machine work tolerances they certainly wouldn?t have chosen a multi piece crank, with all the tolerance stack up concerns this brings into play. The fact that GS engines are so durable also flys in the face of any claims that Suzuki fit together the engines with sloppy tolerances. Interesting theory, but just doesn?t seem right.

Uhhhmm...Ed, The early Z1 and KZ motor might as well be in our GSes. There is nearly NOTHING that isnt the same, right down to the roller bearing crank.

 

[Nessism]

Uhhhmm...Ed, The early Z1 and KZ motor might as well be in our GSes. There is nearly NOTHING that isnt the same, right down to the roller bearing crank.

Oops, guess you?re right.
Both Kawasaki and Suzuki were primarily two stroke engine companies so I assume that?s where the roller cranks came from.

 

[TheCafeKid]

Oops, guess you’re right.
Both Kawasaki and Suzuki were primarily two stroke engine companies so I assume that’s where the roller cranks came from.

There are those of us that love to tout the "unbreakable-ness" of the roller bearing crank, and, were i to have my choice between the two, I would in fact choose roller bearing over plain bearing, simply for the fact that you state. The roller bearing design developed with the two stroke. Those things had GOBS of power, all at HIGH RPM, LOW torque. Its much comparable to todays sportybikes. They are junk down low compared to a grunt meister like a big CC v-twin, but once they get into that rev range...SEE YA! I would suggest, based on this reality, that this is why early Kaw and Zook motors were designed with the roller bearing, COUPLED with their previous knowlege of the set up within their two stroke designs. They werent exactly going for torque monsters with the GS and KZ, they were trying to design four stroke sport bikes. The fact that there is a decent torque curve to the GS/KZ design is simply a by product of the overall design of their fourstroke DOHC set up. Kaw had LONG destroyed the CB in terms of a FAST sport bike (its too bad they had frames that felt like they had a hinge in the middle of them) and the GS came along and more or less used the same powerplant, almost to the letter, but refined the handling and balance of the machine. It was the best of both worlds. If a CB and KZ had a baby, it would be a GS. Now, I cant explain in technical terms why I think they found this design to be fruitful, and why it gained the torque over the twostroke design (other than the fact that MOST of the bikes by then, with exception of the Widowmaker H2 were larger mills than most two stroke machines) because *I* am not to THAT point yet in my understanding of the properties of the design. I can fix it, because I can see what its SUPPOSED to do and how its SUPPOSED to go together, but i cant always tell you WHY...lol

Having said this, I think a plain bearing crank can hold its own. Thats never been a big gripe with me on the 550 650 and 750 plain bearing motors, for me its the 750s inability to properly deliver oil thru its system, as evidenced by the fairly numerous members who've had a problem with these motors. But, I have one on the bench downstairs, waiting to be split over this winter when i get bored, so maybe I might be able to shed a little light on it??

 

[catbed]

roller bearing cranks theoretically dont have a rev limit either. plain bearings do. its just the cams and chain and such that cant handle the rotation.

 

[Calvin Blackmore]

roller bearing cranks theoretically dont have a rev limit either. plain bearings do. its just the cams and chain and such that cant handle the rotation.

Please explain what you mean by rev limit.
I looked up the gt 750 which was a 2 strokeand it had a 7500 RPM redline not exactly stellar but with twice the rate of impulse a two stroke would not need to rev exceedignly high to make good power.

If plain bearing shave enough oil pressure supplied they can sustain high RPMs
It is the oil that the shafts float in is it not?

I assume the oil film integrity is alos a limiting factor in roller bearing systems. Do the older bikes with roller bearing have high or low pressure oiling sytems?

does the superiority of the roller bearing bikes in terms of longevity not come formt he fact that the bearing materila itself is far more wear resistant being hardened steel as opposed to the soft babbit metal of palin bearings?

 

[TheCafeKid]

Please explain what you mean by rev limit.
I looked up the gt 750 which was a 2 strokeand it had a 7500 RPM redline not exactly stellar but with twice the rate of impulse a two stroke would not need to rev exceedignly high to make good power.

If plain bearing shave enough oil pressure supplied they can sustain high RPMs
It is the oil that the shafts float in is it not?

I assume the oil film integrity is alos a limiting factor in roller bearing systems. Do the older bikes with roller bearing have high or low pressure oiling sytems?

does the superiority of the roller bearing bikes in terms of longevity not come formt he fact that the bearing materila itself is far more wear resistant being hardened steel as opposed to the soft babbit metal of palin bearings?

I think all of the bikes with roller bearing cranks had low pressure systems, not sure about the two strokes, but I would assume so..

 

[Nessism]

I think all of the bikes with roller bearing cranks had low pressure systems, not sure about the two strokes, but I would assume so..

Two strokes have a NO pressure oiling system. They either use premix or a total loss oil injection system.

 

[TheCafeKid]

Two strokes have a NO pressure oiling system. They either use premix or a total loss oil injection system.

Oh yeah...DUH

 

[Suzuki_Don]

Do the older bikes with roller bearing have high or low pressure oiling sytems??

Low pressure, high volume.