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Steam & Excursion > Subtle aspects of noisy, plain-bearing side rods.


Date: 02/17/21 15:50
Subtle aspects of noisy, plain-bearing side rods.
Author: wcamp1472

Back in September of 1968, HICO & 759 made our first fan trip together.
it was the first trip that 759 had made & its 1st high speed road trip, since rebuilding
a decade earlier, in 1958.

About 2 hours into the trip, the left main crankpin overheated, and got smoking, smelling hot.
We, stopped, cooled it down, applied lots of 'pin grease' and proceeded at reduced speeds to Buffalo.

After watering and servicing, leaving Buffalo, we plodded along on the way back to Conneaut.  
After about 40 minutes the NKP engineer called me over to his side of the cab.  
He explained that the slow speed was risking continued over-heating of the crankpin.  
He proposed running at track speed, since in his experience he had run engines in the
past with 'sensitive' bearings .... he knew how to run them safely and asked me to allow
him to run 759 faster...  I, of course, agreed.  

I asked for a short stop to check the rod bearings'  temp; then, if cool, we  go as fast as
he was comfortable...   All was cool to the touch ..  I gave the enginer the high-ball, and
away we went... track speed.  Neeedless to say, it was a smooth run home, from then-on.
Little throttle, & hooked-up, "under the chin"!!  
The engineer relaxed, smiled and away we went!
At Conneaut,, later that night,  all was cold😃

At the roundhouse we explored the reasons behind the overheated crankpin incident.  
Nothing was obvious as a putative cause.  

But, the N&W ( NKP) roundhouse foreman, Harry Reets, ( machinist by trade) 
suggested that a common cause could be a critical radius-area ( mis-match)
used on the bronze rod bushings, where they fit at the crankpin.

Reets described the problem as being at the inner, flat,  face of the crank pin.  
Crank pins have several samaller diameter, concentric, bearing surfaces.
However, the crankpins must be carefully machined --- so that sharp right-angles
at the smaller diameters must be avoided at all costs.  
Sharp right-angles are a "root cause" of originating  cracks at the juncture,
and later , 'breaking-off'  there.

So, crank pins are machined with wide-radius curves at the point where the smaller
diameter matches the larger diameter of the the crank pin.

The heating problem can come from a bronze bushing with a radius that rubs on the crankpin 
at that crucial transition region.  A properly fitted bronze bearing will only contact
the crankpin at two places: the cylindrical surface of the crankpin,  AND the flat surface
on the crankpin face.  

There should be NO contact between the bushing radius and the pin's radius.

A subtle source of overheated crankpins IS the "hard rubbing"  of the two interfering
radii on the crankpin.

An easy test : from auto parts stores get quick-drying 'bluing' used for qualifying 
plain bearings fits on auto engines.  Paint one of the radius regions: either on the
bronze bushing OR  on the radius of the crankpin, with the 'bluing'..

When dry, rub the two together... then examine both radius regions---- there should be 
NO TRANSFER of the "bluing"  to BOTH surfaces.   If there is "transfer"/ staining,
the easiest remedy is to re-chuck the bushing in a lathe and remove more metal from
the radius region, then re-check with another 'bluing'  transfer test.

There should only contact of the bushings and the crankpins should be on the cylindrical
surface, and the flat 'face' of the crankpin that absorbs the lateral impacts.  
There should be NO rubbing between the two, wide-radius regions of the two components.

Before fitting-up new/replacement bronze bushings, use the 'bluing'" dye-test ( as above) to ensure the 
proper clearances at the  "interference regions" .....

One other important point:  many plain bearings are fitted with bronze bearings that are
drilled with lubrication-holes fitted around the whole bushing.  When renewing them its  important
to manually pack ALL the lubrication holes  with pin-grease before application.  
I cannot stress too strongly the importance of this step.  
Failure to do so, invariably leads to overheated crankpins..

Now you know...

W.



Edited 11 time(s). Last edit at 02/17/21 19:02 by wcamp1472.



Date: 02/17/21 16:42
Re: Subtle aspects of noisy, plain-bearing side rods.
Author: ChooChooDennis

What the engineer and the shopman said is precious empirical knowledge that is golden. So sadly, it vanishes when the men pass. That is why oral history or writing down like you do Wes is so very, very, important.

Dennis Livesey
New York, NY



Date: 02/17/21 17:05
Re: Subtle aspects of noisy, plain-bearing side rods.
Author: wcamp1472

Yes, we were very lucky to have the guidance of many experienced RRers, from Conneaut,
to Hagerstown, to Harmon, to Roanoke, Hoboken ( E-L), and E'port...

We would never have discovered that possible cause, on our own.
We had new, replacement brasses made in Staten Island,  and 
made sure that we had no potential "interference problems".

We had ready-access to old-time skills... and experiences.
As youngsters, we eagerly sought advice and input about all 
sorts of 'steam mysteries'.... 

It was wonderful spending 2 weeks in Roanoke Shops, October 1968...
At first, there was a lot of reluctance to approach us, but soon that thawed...
we learned so much from them.

W.



Edited 2 time(s). Last edit at 02/17/21 17:39 by wcamp1472.



Date: 02/18/21 06:13
Re: Subtle aspects of noisy, plain-bearing side rods.
Author: Kimball

Great post Wes!  Very interesting.  Just yesterday at work I red-lined a young engineer's drawings for the same issue.  However, can you please explain to us:
How did fast running avoid the radius-radius concentrated load problem?  Had it just worn itself in by then?
Why do you need to handpack the grease holes, assuming you would always shoot them full before running the loco?



Date: 02/18/21 07:01
Re: Subtle aspects of noisy, plain-bearing side rods.
Author: Frisco1522

A lot of times, if everything on the bearing doesn't have a radiused edge, etc, it becomes a wiper.  Make them fit right.



Date: 02/18/21 08:45
Re: Subtle aspects of noisy, plain-bearing side rods.
Author: wcamp1472

Great questions!

I'm speculating here....

1.
Overheating causes localized swelling of the rubbing components,
That swelling aggravates the friction.   If there is enough time, the swelling
can expand ---- and everybody and things should calm down.... the operative word is 'should'.

In practice, the localized heat builds rapidly affecting local regions only...and you get the grease
smoking & smelling...  If you're smart, you stop and cool everything down...using grease-and-air ONLY.

NEVER try applying water ---- you could embrittle the steel, setting the stage for shattering
and breaking the 'case-hardened steel'.

So, my suspicion is that, once cooled-down, and with so few cars ( 15 or so?) we completed trip
to Buffalo without incident.   At Buffalo, while taking on water, we used the Alemite gun to add
rod grease at all the crankpins.

With slow speeds, the presumption is that you're unnecessarily laboring the engine; while at
cruising speeds, and superheated steam you apply small shots of steam ( at 'admission' )
with greater expansive effect, thus applying less total pressure.  On level, tangent track,
the speeding mass of the flying cars in the train requires very little 'steady strain' on the
tender drawbar --- the engine is "generally coasting"  at the 70-mph speeds we were going.

Excursion trains are no serious strain on the Berks ---- they were built to sail along easily
at better than 60-per with 70 to 80 loaded freight cars in tow...NOW, that's a TRAIN.
15 to 22 coaches is no 'load' for a Big Engine..

2.
Filling in the holes of new brasses is necessary because the stiffness of the applied
rod grease will not flow when forced through the one grease-entry passage
drilled through the steel of the siderod, or through the crankpin.   Rod grease is about as stiff
as a  tall size candle, at room temperature--- when pumped under extreme pressure
into the rod, it dies not 'flow' very easily, and will not fill-in the 'reservoir holes' drilled 
into bushings.

( Rod pin-grease is designed to only soften when heated.... that way, fresh grease
becomes a beneficial lubricant only when soft enough to flow.... at cooler temps,
it 'stays put' and does not run-out.  It becomes a self-regulating lube- system,
flowing only a little bit, & only when needed.  You can expect that all rod pins will
have an elevated temperature when running.... that would be their optimal  'running temperature'.    
Typically it can be in the region of 120 F to 180 F , that would be perfectly normal...
Rods with more clank, will typically run at cooler temps, rods with no clunking, or silence,
will run hotter, until more  thoroughly 'broken-in'.)

?During service stops, what is the chance that an empty 'grease hole' in the bronze bushing will line-up
exactly with a single  supply-hole in the siderod?  
Slim and none!  And Slim has left town..

Typically, bronze floating-bushings will have 12 to 24 grease holes in
a spiral pattern, drilled into the circumference.   Manuallly packing them full at
the time of application,  means that subsequent re-application of fresh grease fills-in the
voids and spaces around  the crankpin.  A few of the bushing's grease holes near the
Alemite fitting port will benefit from a little bit of new grease that gets forced-in.

When applying the grease with the Alemite gun you can see the rod shift & move on the pin,
as the grease takes up the spaces.  As the voids in the free-spaces of the bearings fill with
fresh grease, a tiny amount adds to & fills-in a few of the lube-holes, at each re-application
of fresh grease.

Bare, new holes will NEVER virtually fill-in, by themselves.... the probability of
the one lube-hole through the steel siderod, or crankpin, getting to the all the holes
in the floating bushing is impossible, ---- with cold, stiff rod grease.

Typically, amateur "Alemite-gun newbies" feed-in more grease after the 'rod-shift' --- that excess pin
grease is later flung free ( all up & under the running boards, etc.) after reaching track speeds
above 15-mph..

Hope this helps.

W.
 



Edited 3 time(s). Last edit at 02/18/21 09:58 by wcamp1472.



Date: 02/18/21 09:32
Re: Subtle aspects of noisy, plain-bearing side rods.
Author: wcamp1472

Frisco 1522 is right!

On new bronze bushings all corners and holes should be slightly beveled,
or have 'broken' edges.

This especially true of applying new plain journal, babbitt-lined 'brasses' 
applied at the axle journals.  The long edges of the babbitt need to be scraped to form 
a slight angle ---- forming a wedge to squeeze the oil film evenly between the brass
and the journal*.  When running, the oil film entirely separates the axle from the 'brass'.
Many cars, not in "revenue service", or not offered at interchange, continue to use
reliable, plain bearing journals and journal lubricating components. 

When running, if ever the two components touch each other, overheating and a 'hot box'  
will be the result.

Back when infrared journal scanning ( hot box detectors) were common, 
it was typical that rolling-element journals run at hotter ( infrared) temps than plain bearing,
oil lubricated journals which operated at colder temps --- simply because the two plain-bearing
surfaces were separated by the oil film.

With the exclusive use of roller bearings on all axles, ALL plain journal  bearings were banned
from AAR interchange rules, by the time a rolling-element bearing began to run HOT,
and when the axle failure occurred was typically under about a mile!   
So, 'hot box' detectors were not effective at reporting endangered roller bearings, fast enough.

But, rolling element bearings emit high-frequency sound waves ( inaudible) when running,
a bearing that is in danger of failing will emit ultrasound frequencies that typical of endangered 
bearings ( ultrasonic 'screaming').  All these bearings emit ultrasonic frequencies,
but endangered bearings squeal at a distinct level, and the detectors react & report those
dangerous frequencies, that are out-of-spec.

In today's world,  ultrasound train motion monitoring ( microphone)  is used to give
early warning of endangered. bearings.  The high frequency detection system typically gives
a couple of hundred miles of warning, before ultimately having a critical failure.  
The system is very effective at reporting specific axles that are endangered.  
Your human responses may vary.

W.

* See Frisco1522's 'wiper' comment, in above post...
 



Edited 5 time(s). Last edit at 02/18/21 10:05 by wcamp1472.



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