Author Topic: Oil for Crankshaft Bearings  (Read 1235 times)

Online Dellortoman

  • Hero Member
  • *****
  • Posts: 10286
  • My wolf mate 6/5/1996 - 3/1/2011
Re: Oil for Crankshaft Bearings
« Reply #15 on: December 07, 2017, 01:10 »
I'm not a mechanic ......... but wouldn't the small ends be under almost the same load as big ends?

No.

I dunno whether being a mechanic would improve your understanding, but being a physicist might help.

The con-rod is a simple pin-jointed element so loads can only be lengthways between the pins. That means any load at the small end is delivered directly to the big end along the rod. If the system was static, you'd be correct. The force at each end of the rod would be the same.

But the system is dynamic, so there are inertial loads to consider. This is why mechanical engineers have to be smarter than structural engineers (that was a standard piss-take between the engineering faculties when I was a student ;D)

The small end reciprocates in a straight line while the big end moves in a circle.

The small end carries the reciprocating inertial forces of the piston and gudgeon pin, which are transferred to the big end via the rod as described above. The big end pin not only has to carry those transferred reciprocating forces but also the additional reciprocating loads imposed by the inertia of the con-rod itself. Added to that are the centrifugal loads imposed by the bottom half of the con-rod flying around in a circular path.
Location: Tasmania, Approx 42°53’S 147°23’E

Offline Grant

  • Hero Member
  • *****
  • Posts: 15164
Re: Oil for Crankshaft Bearings
« Reply #16 on: December 07, 2017, 01:49 »
Mechanical engineers build weapons, structural engineers build targets.  ;D
www.clublaverda.com
Check out the daily blog

Offline chrisk

  • Hero Member
  • *****
  • Posts: 7594
  • I'd like to write something here: SOMETHING
Re: Oil for Crankshaft Bearings
« Reply #17 on: December 07, 2017, 03:41 »
No.

I dunno whether being a mechanic would improve your understanding, but being a physicist might help.

The con-rod is a simple pin-jointed element so loads can only be lengthways between the pins. That means any load at the small end is delivered directly to the big end along the rod. If the system was static, you'd be correct. The force at each end of the rod would be the same.

But the system is dynamic, so there are inertial loads to consider. This is why mechanical engineers have to be smarter than structural engineers (that was a standard piss-take between the engineering faculties when I was a student ;D)

The small end reciprocates in a straight line while the big end moves in a circle.

The small end carries the reciprocating inertial forces of the piston and gudgeon pin, which are transferred to the big end via the rod as described above. The big end pin not only has to carry those transferred reciprocating forces but also the additional reciprocating loads imposed by the inertia of the con-rod itself. Added to that are the centrifugal loads imposed by the bottom half of the con-rod flying around in a circular path.

 ::) OK thanks Cam, I understood your first two sentences, perfectly. 
The initial attraction to motorcycling inflicts people for various reasons and at different stages in their lives. But once someone experiences the elation of riding a motorcycle there’s no denying the nearly spiritual effect it has.

Offline hochkoenig

  • Sr. Member
  • ****
  • Posts: 341
Re: Oil for Crankshaft Bearings
« Reply #18 on: December 07, 2017, 08:22 »
But as bigger a Bearing, more Friction is in it. I think that the Big bearings survive its because coincidentally the Bearings are Oversized and the RPM on Lavs are quite slow.
They constructet all just by Feelings and experiences, nothing calculated here.....
 8)

Offline CLEMTOG

  • Hero Member
  • *****
  • Posts: 3766
Re: Oil for Crankshaft Bearings
« Reply #19 on: December 07, 2017, 09:34 »
ah yes but
the big ends rotate a full 360 degrees at all times, the small end bearing "rock" back and forth only about 10 degrees probably a lot less, so the forces are concentrated at the top and bottom of the stroke always on the same thrust faces of the bearing, causing ovality and rattles, with the rest doing not much at all, weirdly they don't shag out much! relative to the rest of the motor.
CLEM
« Last Edit: December 07, 2017, 11:06 by CLEMTOG »

Offline Piranha Brother 2

  • Hero Member
  • *****
  • Posts: 924
  • It was once a 1973 SF750
Re: Oil for Crankshaft Bearings
« Reply #20 on: December 07, 2017, 09:35 »
But as bigger a Bearing, more Friction is in it. I think that the Big bearings survive its because coincidentally the Bearings are Oversized and the RPM on Lavs are quite slow.
They constructet all just by Feelings and experiences, nothing calculated here.....
 8)
Yep, it's called overbuilding - and lucky for Lav (Breganazanian) twin owners, there's more of it in our agriberthas than you'll find in a triple  8)
What ... leave it standard??!!

Offline Tippie

  • Hero Member
  • *****
  • Posts: 1625
Re: Oil for Crankshaft Bearings
« Reply #21 on: December 07, 2017, 12:25 »
"The big end pin not only has to carry......Added to that are the centrifugal loads imposed by the bottom half of the con-rod flying around in a circular path."
Aha! So that is ehy the big end is bigger.
SF2 17483 (race)
SF2 17424 (road)
An Australian living near Oslo in Norway

Offline nick7

  • Hero Member
  • *****
  • Posts: 1219
Re: Oil for Crankshaft Bearings
« Reply #22 on: December 07, 2017, 14:11 »
Well i dunno..will ask my MEng son.Did like tge oil lube assisting grooves in the phosper bronze bushes put in when the crank was fully redone...seems like a nice idea though whether necessary or not who knows?😁

Offline CLEMTOG

  • Hero Member
  • *****
  • Posts: 3766
Re: Oil for Crankshaft Bearings
« Reply #23 on: December 07, 2017, 16:21 »
I now don't think of them as being a good idea Nick, the oil hole at the top gets the oil right where it is needed, and even forms a tiny reservoir and those spiral grooves might even create a stress concentration point, plus undesirable "edges" the next one gets plain small ends as factory
CLEM

Offline nick7

  • Hero Member
  • *****
  • Posts: 1219
Re: Oil for Crankshaft Bearings
« Reply #24 on: December 07, 2017, 16:46 »
When she blows I will let you know Clem😉

Offline hochkoenig

  • Sr. Member
  • ****
  • Posts: 341
Re: Oil for Crankshaft Bearings
« Reply #25 on: December 07, 2017, 17:13 »
"The big end pin not only has to carry......Added to that are the centrifugal loads imposed by the bottom half of the con-rod flying around in a circular path."
Aha! So that is ehy the big end is bigger.

Hm, yes its a good Question, why the Conrods have differend Diameters, maybe it looks mor professionel then? ;) But serious, I remember the KTM Factory struggeld with bending Pistinon Pins.... (What they thought, but how can you proof....) thats why they start to use not "Pipes" but full round Material as Pistonpins! (At the LC4)

Anyway, I think Laverda was looking if the Engine would be usefull for a Agrar Machine also or something...

Online sfcpiet

  • Administrator
  • Hero Member
  • *****
  • Posts: 7113
  • NRW, Germany
Re: Oil for Crankshaft Bearings
« Reply #26 on: December 07, 2017, 20:21 »
But as bigger a Bearing, more Friction is in it. I think that the Big bearings survive its because coincidentally the Bearings are Oversized and the RPM on Lavs are quite slow.
They constructet all just by Feelings and experiences, nothing calculated here.....
 8)

Oh dear... ::)

Of course the engineers in Breganze calculated before they built.  That sort of thing may have happened in the Stone Age, but since the beginning of the industrial revolution, engineers have had to save pennies were ever they could, therefore careful planning and calculating preceeds any construction, if the exercise is to work as planned (and they were to earn a $ or 2).  Experience plays a part, but is only a small part of mechanics.  Just about everything can be calculated beforehand, computers make this a doddle these days (I still had to learn that with formulae, a calculator, pen and paper).

If KTM had to revert to solid piston pins after breakages, somebody seriously fucked up in the first place.  But bikes these days are throw-aways, once knackered they are often not rebuildable (or it simply isn't viable), so it doesn't really matter much. ;D

We should be glad the boys of Breganze did things the way they did, otherwise our machines would have gone the way of the Dodo long ago, or wouldn't have even attained the popularity they enjoy today.  I think planning future repairs and overhauls into the intial draft is the key here, a matter of course when producing agricultural machines.

rant over...
piet
180s feel quick, 120s are...      If it ain't broke, fix it till it is.

"A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics"  Georg Fitch 1916

Offline chrisk

  • Hero Member
  • *****
  • Posts: 7594
  • I'd like to write something here: SOMETHING
Re: Oil for Crankshaft Bearings
« Reply #27 on: December 07, 2017, 21:38 »
Piet
A couple of years ago, I had a spit at one of our Italian machine manufacturers, when, we couldn't remove an M10 bolt, which located a rod end (that needed a 1 turn adjustment) from it's location. A 12mm aluminium beam was in the way and all the bolt needed was about another three turns to get it out.

Almost a days work of stripping the entire area, to remove the bolt and make one turn on the rod end wasn't appreciated. (liken it to removing a Laverda triple motor from a custom frame to get the cam cover off ;) )

They came back, and said they hadn't thought of the issue at design and mfr.  ::)

They now have a suitable hole through the aluminium plate, to remove the bolt. 

 
The initial attraction to motorcycling inflicts people for various reasons and at different stages in their lives. But once someone experiences the elation of riding a motorcycle there’s no denying the nearly spiritual effect it has.

Offline Grant

  • Hero Member
  • *****
  • Posts: 15164
Re: Oil for Crankshaft Bearings
« Reply #28 on: December 07, 2017, 21:43 »
Did they send you the hole then?
www.clublaverda.com
Check out the daily blog

Offline Shajota

  • Hero Member
  • *****
  • Posts: 987
Re: Oil for Crankshaft Bearings
« Reply #29 on: December 07, 2017, 21:53 »
Did they send you the hole then?

or perhaps a drill bit??
PETER