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Roller bearings in bottom end #5233696 10/08/19 09:10 AM
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supton Offline OP
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While killing time over the weekend I went looking up why the Germans used inverted V12's on their WWII aircraft. [Long story short--I still have no idea. Why they did nor why I was looking.] Anyhow. Came across a tidbit: while I had seen split end con-rods I don't think I've ever seen roller bearings in the big end. I always assumed that the forces were too great for roller bearings. Small engines sure, 2 stroke sure. But big engines with lots of stress? Guess I was wrong.

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Re: Roller bearings in bottom end [Re: supton] #5233701 10/08/19 09:22 AM
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At first thought , I find it puzzling , for the roller bearings would have had to be split too ? Did they also have split inner and outer races ? Again , it seems like they would have had to ?

Makes me wonder , what the average engine life , in hours , was ? Were conventional insert bearings wearing out in that time period ? If not , what was the point in using roller bearings ?

As were as the engines being an inverted V , maybe it had to do with the aerodynamics of the nose of the airplane ?

I have read , every thing else being equal , an inline or V , liquid cooled engine had less frontal area than a comparable radial engine . Thus ending up with an airplane with less drag and greater speed .

Comparing the Bf109 to the FW190 , the radial engine in the FW190 had enough extra hp to make it faster , anyway .


Wyr
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Re: Roller bearings in bottom end [Re: WyrTwister] #5233705 10/08/19 09:38 AM
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Originally Posted by WyrTwister
At first thought , I find it puzzling , for the roller bearings would have had to be split too ? Did they also have split inner and outer races ? Again , it seems like they would have had to ?

Makes me wonder , what the average engine life , in hours , was ? Were conventional insert bearings wearing out in that time period ? If not , what was the point in using roller bearings ?

As were as the engines being an inverted V , maybe it had to do with the aerodynamics of the nose of the airplane ?

I have read , every thing else being equal , an inline or V , liquid cooled engine had less frontal area than a comparable radial engine . Thus ending up with an airplane with less drag and greater speed .

Comparing the Bf109 to the FW190 , the radial engine in the FW190 had enough extra hp to make it faster , anyway .



No split races, the big end of the rod was the race. The rollers rolled directly on the cap and rod and the rollers are loose just like in an old transmission.

Re: Roller bearings in bottom end [Re: WyrTwister] #5233714 10/08/19 09:54 AM
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supton Offline OP
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Originally Posted by WyrTwister
At first thought , I find it puzzling , for the roller bearings would have had to be split too ? Did they also have split inner and outer races ? Again , it seems like they would have had to ?


The rods do have "rotations" separate from each other. Not a full rotation but as the crank spins the rods would turn slightly different; if you pick one rod as a reference point, at times the other would be rotating clockwise, then counterclockwise. Thus the roller for each rod surface would have to be separate, to allow for the rotation necessary.

Quote
Makes me wonder , what the average engine life , in hours , was ? Were conventional insert bearings wearing out in that time period ? If not , what was the point in using roller bearings ?


I don't think it was very high at all. At least for us, we used high amounts of lead, and these were carb engines on what we'd think of as lousy motor oil.

The recent B-17 crash had me look it up; the one that crashed was painted to look like a real B-17 from the war. From the "real" Nine-o-Nine:
https://en.wikipedia.org/wiki/Nine-O-Nine
Quote

Her first bombing raid was on Augsburg, Germany, on February 25, 1944. She made 18 bombing raids on Berlin. In all she flew 1,129 hours and dropped 562,000lb (225 tonnes) of bombs. She had 21 engine changes, four wing panel changes, 15 main gas tank changes, and 18 changes of Tokyo tanks (long-range fuel tanks).


I'm not sure if that 1,129 hours is flight time to/from Germany, or total. But if total... she needed a new engine every 54 hours. 4 engines so that's what, 220 hours MTBF? Cruising speed of 250 mph, so engine lifespan of 55,000 miles? time for the aero guys to chime in, they know more than I do.


2011 Toyota Camry, base, 2.5L/6MT, 193k, hers
2010 Toyota Tundra DC, 4.6L/6AT, 155k, ours
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Re: Roller bearings in bottom end [Re: supton] #5233724 10/08/19 10:14 AM
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Vercingetorix Offline
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Porsche used roller bearing crankshafts in the 1950s.

Re: Roller bearings in bottom end [Re: supton] #5233730 10/08/19 10:28 AM
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So , did the rollers roll directly on the crankshaft ?

As far as engine life , if the plane gets shot down or suffers severe engine battle damage , before it wears out , it has fulfilled its task . Any increase in expense / complexity to extent engine life is pointless .

If , on the other hand , if the engine wears out before it id lost to battle damage , some benefit would occur , by expending more money to extend engine life .

The variations would be huge . A new plane could be shot down / lost on the first combat mission . Compared to a plane that flew until it was completely worn out . That would be where averages / statistical analysis might come in .

Then there is the matter of how much does it cost and how much time does an overhaul take ?


Wyr
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Re: Roller bearings in bottom end [Re: supton] #5233803 10/08/19 11:26 AM
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ragtoplvr Offline
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Millions of Harleys used and still use this arrangement, called knife and fork. Rather than a removable cap, they use pressed together crank.

Re: Roller bearings in bottom end [Re: supton] #5233818 10/08/19 11:41 AM
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Every dirt bike and ATV has roller bearings.


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Re: Roller bearings in bottom end [Re: supton] #5233826 10/08/19 11:51 AM
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another advantage to roller bearings if if the plane is shot up and looses oil, a roller will run at reduced power on residual oil for some time before failing. A extra minute or 2 may be all it take to complete the mission. Maybe even let the crew bail out.

Re: Roller bearings in bottom end [Re: WyrTwister] #5233834 10/08/19 11:59 AM
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Many of the last highest horsepower radials were not built to last many missions, They might only have 2 or 3 hours of takeoff power when they are the heaviest. That could only be a few missions. But returning bombers shot up with good engines were donors. Dad also told of his ship in the Navy carrying loads of crated bomber engines, as well as other bomber parts. They liked that, much safer than the loads of bombs.

Rod

Re: Roller bearings in bottom end [Re: Chris142] #5233850 10/08/19 12:20 PM
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Originally Posted by Chris142
Every dirt bike and ATV has roller bearings.



Yes, some are definitely potent engines. Very little oil needed to keep them happy.


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Re: Roller bearings in bottom end [Re: supton] #5233851 10/08/19 12:20 PM
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Today's Rotax aircraft engines use roller bearings for the connecting rods. The claim was that it extended the time the engine could run without oil pressure.

[Linked Image from forums.matronics.com]


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Re: Roller bearings in bottom end [Re: supton] #5233920 10/08/19 01:46 PM
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supton Offline OP
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Guess I live a sheltered life then. Just haven't seen them in any conventional auto (or heavy truck) engine.


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2010 Toyota Tundra DC, 4.6L/6AT, 155k, ours
1999 Toyota Camry LE, 2.2L/4AT, 214k, his
Re: Roller bearings in bottom end [Re: supton] #5233989 10/08/19 03:17 PM
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bdcardinal Offline
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I have only seen roller cam bearings, looks pretty cool though.


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Re: Roller bearings in bottom end [Re: supton] #5234047 10/08/19 04:34 PM
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Originally Posted by supton
While killing time over the weekend I went looking up why the Germans used inverted V12's on their WWII aircraft. [Long story short--I still have no idea. Why they did nor why I was looking.] Anyhow. Came across a tidbit: while I had seen split end con-rods I don't think I've ever seen roller bearings in the big end. I always assumed that the forces were too great for roller bearings. Small engines sure, 2 stroke sure. But big engines with lots of stress? Guess I was wrong.

Link

[Linked Image]


"High Thrust Line" is the term I remember for the Germans using inverted V12's in WW2. Something about reducing drag.


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