Position of Main Rod On Steam Locomotive

@tigger posted:

Why is the main rod in a different position on steam freight and passenger locomotives.  Example:

Berkshire, mikado - main rod on third axle

Northern, mountain - main rod on second axle

Does it have to do with speed?  Just curious.

Generally, yes plus the passenger 4-8-4s and 4-8-2s have larger diameter drivers.

Thanks

And the Northerns and Mountains have a pony truck wheel (engine truck, I guess, for Hot) in between cylinders and first driver.  The angle at TDC and BDC is critical.

@bob2 posted:

And the Northerns and Mountains have a pony truck wheel (engine truck, I guess, for Hot) in between cylinders and first driver.

So, you are saying that the Berkshires and Mikados don't have a "pony truck"? Besides, the "pony" or Engine truck has nothing to do with the design of the cylinders and the bore & stroke relationship to where the main crankpin is located. Piston speed also is a major factor.

 The angle at TDC and BDC is critical.

Maybe on a model.

@bob2 posted:

And the Northerns and Mountains have a pony truck wheel (engine truck, I guess, for Hot) in between cylinders and first driver.  The angle at TDC and BDC is critical.

If I'm not mistaken passenger locomotives used a 4 wheel pilot truck for stability at speed, where as freight locomotives used a 2 wheel pilot truck as they weren't running at high speeds. Freight locomotives didn't nee the "wheel between the cylinder and front driver" (4 wheel pilot truck)  as they didn't operate at as high a speed as passenger locomotives. Correct me if I'm wrong here. 

There are exceptions to the rule. UP's 4-8-8-4 Big Boy was a freight locomotive with a 4 wheel pilot truck.  

@Lou1985 posted:

If I'm not mistaken passenger locomotives used a 4 wheel pilot truck for stability at speed, where as freight locomotives used a 2 wheel pilot truck as they weren't running at high speeds.

Way too much of a generalization.  Also, the correct name for the two axle "pilot truck" is Engine Truck, and was developed for increased weight support and much better guidence into curves. The two axle Engine Truck goes all the back to the 1860s 4-4-0, 4-6-0 and 4-8-0 locomotives, and then into the 4-6-0, 4-6-2, 4-6-4, 4-8-2, and 4-8-4.

Freight locomotives didn't nee the "wheel between the cylinder and front driver" (4 wheel pilot truck)  as they didn't operate at as high a speed as passenger locomotives. Correct me if I'm wrong here. 

OK, you are wrong. How about the 4-6-6-4 Cjallenger types that were used in both freight AND passenger service at speeds above 70 MPH? Again, the primary reason for the two axle Engine Truck was for support of increased frontend weight.

There are exceptions to the rule. UP's 4-8-8-4 Big Boy was a freight locomotive with a 4 wheel pilot truck.  

Lets not forget the the PRR 4-4-4-4, and 4-4-6-4 locomotives, i.e. one passenger and the other freight.

@Hot Water posted:

 

@Lou1985 posted:

If I'm not mistaken passenger locomotives used a 4 wheel pilot truck for stability at speed, where as freight locomotives used a 2 wheel pilot truck as they weren't running at high speeds.

Way too much of a generalization.  Also, the correct name for the two axle "pilot truck" is Engine Truck, and was developed for increased weight support and much better guidence into curves. The two axle Engine Truck goes all the back to the 1860s 4-4-0, 4-6-0 and 4-8-0 locomotives, and then into the 4-6-0, 4-6-2, 4-6-4, 4-8-2, and 4-8-4.

Freight locomotives didn't nee the "wheel between the cylinder and front driver" (4 wheel pilot truck)  as they didn't operate at as high a speed as passenger locomotives. Correct me if I'm wrong here. 

OK, you are wrong. How about the 4-6-6-4 Cjallenger types that were used in both freight AND passenger service at speeds above 70 MPH? Again, the primary reason for the two axle Engine Truck was for support of increased frontend weight.

There are exceptions to the rule. UP's 4-8-8-4 Big Boy was a freight locomotive with a 4 wheel pilot truck.  

Needless to say a lot of 4-8-2's and 4-8-4's on various roads saw regular freight service. 

Then there were 4-10-2's and UP's 4-12-2's that were essentially freight only.

Rusty

@Lou1985 posted:

If I'm not mistaken passenger locomotives used a 4 wheel pilot truck for stability at speed, where as freight locomotives used a 2 wheel pilot truck as they weren't running at high speeds. Freight locomotives didn't nee the "wheel between the cylinder and front driver" (4 wheel pilot truck)  as they didn't operate at as high a speed as passenger locomotives. Correct me if I'm wrong here. 

There are exceptions to the rule. UP's 4-8-8-4 Big Boy was a freight locomotive with a 4 wheel pilot truck.  

The function of the lead truck was literally to pilot the locomotive around curves.  IT had a spring system that exerted a lateral force on the front of the the main engine as it entered a curve.  At higher speeds the force was greater, thus the need for another pair of wheels.

@Rusty Traque posted:

Needless to say a lot of 4-8-2's and 4-8-4's on various roads saw regular freight service. 

Then there were 4-10-2's and UP's 4-12-2's that were essentially freight only.

Rusty

The 4-10-2's and 4-12-2's were fast freight locomotives that could pull reefer blocks at 60 along the Platte River Valley(UP)  or on the long straight and flat parts of the Sunset Route (SP).  In those conditions, you wanted plenty of lateral force going into curves.

If you are interested in learning more about the parts of the steam locomotive, there is an excellent reference book available.  On eBay, look for THE STEAM LOCOMOTIVE IN AMERICA BY ALFRED W. BRUCE.  IT's written in simple English and can be understood by anyone with a modicum of mechanical aptitude.  It's available for $20 to $40.  IT's the reference for the comments I posted a few minutes ago.

@mlaughlinnyc posted:

The function of the lead truck was literally to pilot the locomotive around curves.  IT had a spring system that exerted a lateral force on the front of the the main engine as it entered a curve.  At higher speeds the force was greater, thus the need for another pair of wheels.

I worked on a worn out engine truck once and there was quite a bit to it.  It had “heart” links that act like cams,  which increase both the vertical and horizontal force on the engine truck wheel on the outside of the curve. This has the effect of trying to push the front of the locomotive toward the inside of the curve.   This would reduce the lateral force on the outside of the curve lead driver. 

@mlaughlinnyc posted:

The 4-10-2's and 4-12-2's were fast freight locomotives that could pull reefer blocks at 60 along the Platte River Valley(UP)  or on the long straight and flat parts of the Sunset Route (SP).  In those conditions, you wanted plenty of lateral force going into curves.

I thought the 4-10-2's for the SP were built for Donner Pass.  However, they had issues with the track.  Hence they were taken off the mountain.  However these were 3 cylinder locomotives.  Could that have contributed to the problem?

@Dominic Mazoch posted:

I thought the 4-10-2's for the SP were built for Donner Pass.  However, they had issues with the track.  Hence they were taken off the mountain.  However these were 3 cylinder locomotives.  Could that have contributed to the problem?

What "problem"? 

@Hot Water posted:

 

The article from THE SP BULLETIN stated that the 4-10-2 "ate out" snake looking pieces of metal from the rails, and one could see these "snakes" as hot metal at night.

Truth or myth?

@Dominic Mazoch posted:

The article from THE SP BULLETIN stated that the 4-10-2 "ate out" snake looking pieces of metal from the rails, and one could see these "snakes" as hot metal at night.

Truth or myth?

Probably related to the many, MANY very sharp curves on such a steep grade. Wonder why the SP 2-10-2 locomotives didn't exhibit the same issue? Also, the lateral on the 3-cylinder 4-10-2 locomotives may have been a bit tighter, due to the 3-cylinder drive arrangement.

Meanwhile the Norfolk & Western and Seaboard Air Line ran 2-6-6-4's on fast freights with a two wheel lead truck.

Stuart

I think I shall disagree with my friend Hot above.  The length and angles a main rod must be held to are critical, even if top and bottom dead center are mid-stroke.  If you have larger drivers and a two axle engine truck, you can connect to the number two driver - but if you are a 63" drivered Mike or consolidation, critical angles might be exceeded by connecting to #2.

Note that the SP class connected to #3, even with a two axle engine truck.  Also note how long those crosshead guides are, and that at front dead center you still see a lot of piston rod.  The center rod indeed connects to #2, so perhaps that is the reason for extending the outer main rods?

@Stuart posted:

Meanwhile the Norfolk & Western and Seaboard Air Line ran 2-6-6-4's on fast freights with a two wheel lead truck.

Stuart

I believe I have read that the N&W operated those engines at 60 but I could be wrong.  A typical fast freight speed in the 40's and 50's was 50 mph.  The term "fast freight" didn't actually refer to actual engine speed.  A fast freight was a train the got expedited handling at terminals and was given priority over other freight trains.  A few minutes less running time wasn't important for freight trains.  What was important was whether a car got in and out of a yard in three or four hours rather than 12 or more.  From a customer perspective, hours didn't matter at all.  Their only concern was on what day a car would arrive.  Railroads saved days by prompt handling at yards and sell planned blocking and scheduling.

As for the Seaboard using 2-6-6-4's on fast freights, that didn't mean fast running.  Look at their grade and curve profile between Richmond and Savannah and you'll not see a railroad suited to high speed.

@Hot Water posted:

Probably related to the many, MANY very sharp curves on such a steep grade. Wonder why the SP 2-10-2 locomotives didn't exhibit the same issue? Also, the lateral on the 3-cylinder 4-10-2 locomotives may have been a bit tighter, due to the 3-cylinder drive arrangement.

Donner Pass doesn't have to explain the four wheel truck.  Those locomotives were designed for use also in situations that required more speed than a 2-10-2 could deliver.

@bob2 posted:

I think I shall disagree with my friend Hot above.  The length and angles a main rod must be held to are critical, even if top and bottom dead center are mid-stroke.  If you have larger drivers and a two axle engine truck, you can connect to the number two driver - but if you are a 63" drivered Mike or consolidation, critical angles might be exceeded by connecting to #2.

Note that the SP class connected to #3, even with a two axle engine truck.  Also note how long those crosshead guides are, and that at front dead center you still see a lot of piston rod.  The center rod indeed connects to #2, so perhaps that is the reason for extending the outer main rods?

Those SP engines had a THIRD CYLINDER?

A long rod ratio provides less wear at the guide rails and rod pinnings with improvement in the thrust angles on the wheel during stroke

(Huge rod ratio is motor design 101.)

NKP 2-8-4's ran at speed, both freight and passenger.  765 was set up so she could pull passenger, and there is a picture of 765 leading a passenger train.

One cannot rule out that an engine cannot run at speed if it only has 2 wheels for an engine truck.

@bob2 posted:

I think I shall disagree with my friend Hot above.  The length and angles a main rod must be held to are critical, even if top and bottom dead center are mid-stroke.  If you have larger drivers and a two axle engine truck, you can connect to the number two driver - but if you are a 63" drivered Mike or consolidation, critical angles might be exceeded by connecting to #2.

Note that the SP class connected to #3, even with a two axle engine truck.  Also note how long those crosshead guides are, and that at front dead center you still see a lot of piston rod.  The center rod indeed connects to #2, so perhaps that is the reason for extending the outer main rods?

OK, lets try and clear-up some of the misconceptions and missinformation. I contacted my steam locomotive engineering expert, Mr. W.D.Camp, long time Chief Mechanical Officer for Ross Rowland's High Iron Co., and essentially the man behind the selection of SP 4449 for the American Freedom Train. In addition to Wes' Mechanical Engineering BS degree, there really is no person still alive in the U.S. with as much hands-on steam locomotive experience & knowledge, as he.

I quote:

"The connection of the main rod to the 3rd driver derives from the days of the 2-8-0s,,,,,,,drivers were small diameters and train speeds were lower. The 2-8-0 was an enlargement of the 2-6-0, back when almost every loco in the U.S. was a 4-4-0, and they preferred the equalizing lever to the front (Engine) truck, thus allowing a smaller driver diameter and 3 driving axles under the same basic boiler as a 4-4-0. Then the 4th drive axle was added and derived the common standard 2-8-0.

The use of the main driver being the 3rd driver evolved because the "short/stubby" main rod had "leverage problems" when under starting forces. The challenge with the 2-8-0 was that the grate area was small when confined between the rear two driver sets. The solution was adding a trailing truck (from the 2-6-2), and thus putting the grate area aft of the drivers,,,,,,,,,yielding the 2-8-2.  Large casting techniques were not yet perfected on the manufacturing industry, so the 2-8-2 tended to have smaller driver diameters for low speed freight engines.

A subtle design problem was the location of the Center-Of-Gravity in the 2-8-0/2-8-2 whole engine mass. The C.O.G. of those engines was in the region a little ahead of the 4th driving axle, and at about the belly of the boiler.

What shakes the C.O.G, shakes the whole engine structure. Thus, as freight locomotives attempted to go faster, the whole engine was bounced around by the imbalance of the driver counterweights. The heaviest counterweights were right at the C.O.G.!

When the 2-8-4 came along (Erie, NKP, C&O, etc.) the much larger grate area gave rise to much higher speed capabilities of those locomotives, but they were very rough riders, and would pound your teeth out! The small drivers of the Berks could grow in size,,,and freight train speeds could increases, but shaking was a very big problem (especially with light trains).

Manufacturing processes improved in the 1920s & 1930s, so that much larger castings like one-piece cast engine beds, trailing trucks, etc., were very possible.

Designers then moved the main driver to the #2 axle (from the #3 axle), thus moving the imbalanced main driver away from the Center-Of-Gravity. But,,,,that also moved the main cylinders forward, and again would have resulted in a too-short main rod. Thus, the two axle (4 wheel) Engine truck was perfected, in order to support the increased weight, as well as providing greater "leading into a curve" guidance. The end result was the huge 4-8-4s.

So, the concept of moving the main crankpins, from #3 to #2 driver axle, had a LOT of sophisticated engineering and research behind it. One concept was that at higher crank RPM speeds, the counterweights didn't have to be as massive, in order to obtain good counter-balance effects. Thus, the 4-8-4s could run like the wind, and ride as smooth a a baby carriage."

HW: EXCELLENT explanation, as always!

To illustrate what Wes Camp and Hot Water are saying about the angular leverage problem with a short-coupled main rod, look at these crude diagrams.

The N&W K3 class Mountains, nicknamed "Water Buffalos" were a group of 10 locomotives designed for fast manifest trains on the more level portions of the railroad. They had 63" drivers with crankpins on the #3 axle.

They proved to be rough riders, suffering from severe dynamic augment. They were slapped with a 35 MPH speed restriction and were sold off eventually to the RF&P (6) and D&RGW (4), proving that even almighty Roanoke didn't get it right 100% of the time.

@Rich Melvin posted:

To illustrate what Wes Camp and Hot Water are saying about the angular leverage problem with a short-coupled main rod, look at these crude diagrams.

These drawings are misleading in that the eccentric offset on the #3-axle diagram is less than on the #2-axle diagram. Therefore, the drawings overstate the angular advantage of the main rod motion for the #3-axle case, although the reduction in angle is beneficial in terms of torque delivered to the crankpin and piston side-thrust. The disadvantage of the #3-axle setup is that the main rod is 50% longer and more than 50% heavier. Therefore, the counterbalance weight required on the main driver is also increased and, as Mr. Chillianis says, the dynamic augment will be larger for the same locomotive speed. Therefore, the #3-axle locomotive would have to be operated at reduced speed to get the same dynamic augment, as apparently was found by the N&W. Thus, for equal wheel diameters, the #2-axle setup would appear to be better for a high-speed (passenger) locomotive than for a low-speed (freight) locomotive. A full evaluation of these effects also requires that wheel diameter and piston stroke be taken into account.

MELGAR

Take T&P 610.  It is a 2-10-4.  Pin on third axle.  Even with the, Baldwin disk (?) and better counterbalancing placed on it before WWII, did it damage track?  Is there anybody here who was in the cab operating the locomotive as AFT 610 or SOU 610? 

@Dominic Mazoch posted:

Take T&P 610.  It is a 2-10-4.  Pin on third axle.  Even with the, Baldwin disk (?) and better counterbalancing placed on it before WWII, did it damage track? 

No.

Is there anybody here who was in the cab operating the locomotive as AFT 610 or SOU 610? 

I was in the cab on the Southern Rwy, teaching them how to properly fire an oil burner. She rode pretty good at 55  to 60 MPH with Bill Purdy at the throttle. 

@MELGAR posted:

These drawings are misleading

I agree that the drawings are misleading for the main rod attached to the third axle. Take a look at NKP 756 and N&W 1218 and note how close the #1 driver is to the back of the cylinder. Now compare that to a 4-X-X.

@Big Jim posted:

I agree that the drawings are misleading for the main rod attached to the third axle...

@MELGAR posted:

These drawings are misleading in that the eccentric offset on the #3-axle diagram is less than on the #2-axle diagram...

What part of "... look at these crude diagrams...."  did you guys not understand? Good grief. And the rod I show in that crude drawing is not the eccentric rod. It's the main rod. Honestly, some of you guys could over-complicate a one-car funeral. 

I wish I hadn't even bothered to do this... 

Looking at the “crude diagrams”, I see that one lists the main Rod swing as 10 deg, the other as 20 deg... seems clear enough to me, one is twice the other, QED? 

To me, Rich's diagram seemed to back up what I was trying (apparently unsuccessfully) to say.  I did not find it confusing or over- simplified.

Hot's comments about center of gravity make sense too - but the first place to start in my opinion is Rich's diagram.  If you think about it, there is some synergy between the two issues.

Synergy, already? LOL!

@Dominic Mazoch posted:

Take T&P 610.  It is a 2-10-4.  Pin on third axle.  Even with the, Baldwin disk (?) and better counterbalancing placed on it before WWII, did it damage track?  Is there anybody here who was in the cab operating the locomotive as AFT 610 or SOU 610? 

Before the Baldwin counterbalancing, the engines were very rough.  There are articles that said it was bad enough that you could see daylight under the 3rd driver at speed.  T&P decided that wasn't going to cut it, and the engines needed to be able to run faster at speeds, so they went to Baldwin.  The work extended beyond the Baldwin disc driver.  Lots of counterbalancing.  After that, the class was a very smooth rider and regularly operated at 70mph, including passenger trains.

There was an article in Railfan & Railroad during the Southern lease where there was a writeup from Dick Yager of the SP 4449 crew who got to fire 610, and he said it rode as smoothly as the Daylight did.....and this was with over a million miles on the running gear--which is kinda what doomed the engine with SR.  The engine got a "make it steam" rebuild for the Freedom Train, and Southern wasn't going to pay for a major running gear rebuild that it desperately needed by that point.  There's some videos from the Southern trips and the running gear was slop wore out by that point.  To answer the question quickly though....it's no harder on the track than the 765 is.  Actually, the axle loadings are a bit less.  The rebuild and counterbalancing work made it a very good riding engine.

@kgdjpubs posted:

Before the Baldwin counterbalancing, the engines were very rough.  There are articles that said it was bad enough that you could see daylight under the 3rd driver at speed.  T&P decided that wasn't going to cut it, and the engines needed to be able to run faster at speeds, so they went to Baldwin.  The work extended beyond the Baldwin disc driver.  Lots of counterbalancing.  After that, the class was a very smooth rider and regularly operated at 70mph, including passenger trains.

There was an article in Railfan & Railroad during the Southern lease where there was a writeup from Dick Yager of the SP 4449 crew who got to fire 610, and he said it rode as smoothly as the Daylight did

Right. My buddy Dick was down there a week or two prior to my going down, in oder to show them, help them, fire an oil burner. Bill Purdy want to know if I wanted to fire, and I politely declined as they wouldn't be learning anything, if did the firing. As I posted earlier, she rode very smooth, but the sounds of the rods was most times louder than the exhaust from the stack! Being a bit loose, the rod bearings never ran hot.

.....and this was with over a million miles on the running gear--which is kinda what doomed the engine with SR.  The engine got a "make it steam" rebuild for the Freedom Train, and Southern wasn't going to pay for a major running gear rebuild that it desperately needed by that point.  There's some videos from the Southern trips and the running gear was slop wore out by that point.  To answer the question quickly though....it's no harder on the track than the 765 is.  Actually, the axle loadings are a bit less.  The rebuild and counterbalancing work made it a very good riding engine.

610 I thought was to do Austin-Houston-DFW on the AFT, and no real long term plans to run her until the SOU needed extra and larger steamers.

I do not remember if it was TRAINS or R&R, but the higher ups at the T&P foresaw WWII, and wanted the Texas engines to run faster.

Now at Sierra Blanca, T&P had trackage rights on the T&NO.  Was there a difference in track geometry which could affect the T&P 600's?

@Dominic Mazoch posted:

610 I thought was to do Austin-Houston-DFW on the AFT, and no real long term plans to run her until the SOU needed extra and larger steamers.

I do not remember if it was TRAINS or R&R, but the higher ups at the T&P foresaw WWII, and wanted the Texas engines to run faster.

Now at Sierra Blanca, T&P had trackage rights on the T&NO.  Was there a difference in track geometry which could affect the T&P 600's?

If memory serves, the 610 was supposed to take over at an earlier stop and missed the deadline.  Either way, a lot of money to get it steaming for not a lot of intended use.  They are lucky Southern wanted a bigger engine.

the article in Trains mentions that SP used a bit more rounded rail contour than the T&P did, which made the 600s a bit slippery on that track.  Wouldn't affect the ride though.  Just adhesion.

@Hot Water posted:

 As I posted earlier, she rode very smooth, but the sounds of the rods was most times louder than the exhaust from the stack! Being a bit loose, the rod bearings never ran hot.

yea, I've got some video from an Alexandria to Charlottesville, VA trip in '78 with some pacing and the sound with the engine coasting isn't much quieter than it working.  It was going to need some money sunk into it if they had kept it.

It's an odd feeling to see what you would think would be a drag freight engine with that frankenstein articulated frame gliding along at 60mph or more.  Lima superpower changed quite a bit between the 610 (which is basically just a lengthened A-1 with a combustion chamber) and the better known, later designs.