My brass steam loco surges - any ideas?

[Loren Perry]

I'll cut right to the chase: My 20 year old (like-new condition and  rarely used) Hallmark/Samhongsa ATSF 4-8-4 (No. 3751) has a very slight surge when running forward. The surge is in time with the driver rotation and does not occur when running in reverse. It is more noticeable when pulling a load and while running at a low speed. The main giveaway is coupler slack running in and out of the trailing passenger cars in time to the drivers' rotation. But at track speed the surge is almost undetectable.

The engine's second driver axle is gear driven from the motor's worm; the third axle has rubber traction tires although I removed the tire from the engineer's side to improve electrical pickup. Axles 1, 3, and 4 are rod driven.

At the point in driver rotation when the speed drops off to almost zero, I have stopped the engine and checked for rod binding. At this point, the side rods between axles 2 (gear driven) and 3 (rod driven) have no slack action at all. All other rods and valve gear are loose.

This engine has no separate bronze axle bearing blocks. All driver axles run in holes drilled into the frame sides and have little to no slop. No adjustments are possible without major disassembly and surgery. I have lubricated all gears, axles, and rods with LaBelle's light oil.

The drivers' quartering all match on each side. When the left side rod pins are at 6 o'clock, the rod pins on the right side are at ten o'clock, not quite prototypical, but close.

My personal modifications to the engine (besides the aforementioned traction tire removal) include adding maximum ballast in the boiler using Tungsten putty and a light weathering job. All wheels are perfectly in gauge according to my NMRA and Micro-Trains wheel gauges. The engine easily handles a twelve car train of heavyweight passenger cars up a curving two percent grade.

I'm tempted to slightly elongate the hole in one end of the side rod between axles 2 and 3 (possible doing this to both sides), but I want to hear from more experienced steam experts first. After all, if I do this and it doesn't work, there's no going back other than to somehow find replacement rods somewhere.

Any suggestions, please?

[peteski]

That still sounds like a quartering problem.  It could be caused by the 6-10 o'clock quartering setup. I assume that this is not a new problem but one which was there since you owned the model, correct?

When the problem occurs (loco stalls and the rod  between driver 2 and 3 has no slack) what position is the crank pin (describe it as a clock-hand position).  Also is the tightness on the 2-3 rod on both sides or on one side only?

Having traction-tire on a non-gear-driven driver is not the best design, but there isn't a good way to fix that.  Also, when you removed the tire on one side (exposing the groove in the thread), since the driver axles are in fixed in holes in the frame, that seems like that drive will not contribute much to the electrical pickup.  The groove for the traction will leave that wheel floating above the railhead.

[victor miranda]

like this? click for grainey video.



after no little tinkering with one from a while ago....

I recall spending a lot of time on this one to get it to pretty smooth.
I replaced one axle and re-quartered it and re-bushed the siderods after carefully fitting

This is my conclusion....
after all I did, I am pretty sure that the siderods centers are off a whisker or two.
or that the cranks are somehow off a little.
you can start there because that is easiest.
make sure you keep the siderods straint for where they go.
there are 6 and they are not really interchangeable

after the work... click


I am still working on the tender to get effective pick-ups in it.

victor

[mmagliaro]

Did you re-test this with the missing traction tire replaced?   I agree it still sounds like quartering or the rod/crank hole lengths being off a little.  But having a tire on only one side will exacerbate the problem because that wheel is likely to float too much and not provide the same "push/pull" on one side compared to the other.

I saw the same phenomenon in one I fixed up.   It was generally weak on pulling and hills anyway, so I
did my standard Faulhaber + gearhead maneuver, and the problem went away, but that's because I overwhelmed it with torque.

I would not recommend egg-shaping or enlarging the holes.  Usually that alleviates one bind and causes more binds at another point in the rotation.

BTW on the pickups and stalling...
I fixed one of these up, and had NWSL make me some custom 42" wheelsets that are
live on one side and insulated on the other.  Those will replace the pilot and trailing truck wheelsets in this engine,
and get you some pickup on the engine-side rail so you no longer have just the 3 non-traction-tire drivers providing pickup there.  Getting 4 more wheels on that side really helps.  You have to make sure to clean off any paint on the axle slots and on the frame and truck "tongue", and add a phosphor bronze washer under the screws that hold the two trucks on, but it really helps.  It cost about $32 for 8 wheelsets.  Not exactly cheap, but in
an engine like this, not bad.

[Loren Perry]

Thanks for all your great suggestions, gentlemen. They give me some good ideas to try out.

I removed the one traction tire because its thickness was just enough to raise the other three drivers on that side to the point that the loco would stall on turnout frogs when going through them at very low speeds, and yes, all my turnout frogs are live, ie. wired for power and not plastic frogs (they're all Peco Code 55 Electro-frogs.) I solved a similar problem with two brass Yulim SP 2-8-2's by adding all-wheel pickups to their Vanderbilt tenders.

The groove in the driver's metal tire doesn't seem to be a factor here because the other three drivers hold it level on the rails. All the axles are rigidly fitted into holes drilled through the frame sides so there's zero vertical play. And the surging occurs on straight as well as curved track.

As for the odd quartering arrangement, yes, this is the way it came from the factory. I haven't changed it. The only re-quartering I ever did was on a Key 4-8-8-2 Southern Pacific AC-12 and that was many years ago. Very tricky job, but I managed to pull it off that time. I'd rather not do it again.

I tend to agree with Victor that my problem is rod-related and will take a closer look there. Based on all of your guidance, I'll hold off elongating the rod holes this time but will see about realigning the rods in some fashion. And yes, the rods connecting axles 2 and 3 do seem to tighten up simultaneously on both sides.

[peteski]

But at what specific position of the cranks do they seem to lock up (on each side)?  That might give some extra clue?  Assuming 12-o'clock would be the topmost position.

[victor miranda]

you may want to look at this thread from a while back...
http://forum.atlasrr.com/forum/topic.asp?TOPIC_ID=61165

I am surprised where it went.

fixing siderods....

you are heading toward a precision problem.
the way I 'repaired' or moved the side rod holes
was to confirm the side rods were off the proper centers
I filed oblong holes to test the fit
I reamed out the oblong holes and then red loc-tited in
bushings I made on my little lathe.

the bushings were tiny and I had to re-ream them
after the loc-tite cured.

I have to mention this,
if you want to move the hole in the siderod,
you have to file at one side of the hole.
I have met many siderods just reamed out round.
it will work, sorta, and the hole stays centered.


the loco is/was on the tight side and it has since loosened
during my tender testing.


when I started,
I had no confidence the siderods were the problem
They are close to correct.
so I eliminated causes until there was no other reason left.

building a press jig to get the drivers apart was the hardest part.
then I made a quartering jig...

use good oil on the axles.
there is not much room to add bushings.

try making the holes a little oblong and see if the bind  is eliminated. 
from your description the side-rods  are close to good.

victor

[Cajonpassfan]

Agree with everything said here. I would add that in my experience with these, and I own seven, is that the motors are underpowered and deliver marginal amount of torque. As a result, the least amount of mechanical imperfection or uneven friction will impact smooth performance. I repowered three of them, one with a 16 mm Sagami (which is a very tight fit and a bit of overkill) and two with 14 mm, and along with added weight, the improvement is dramatic.
Improving electrical pickup is also key to success, and I'm still searching for a practical all-wheel tender pickup solution.
Otto K.

Amended: oh, Max, somehow I missed your previous remotor comment 
                Yes, more torque will go a long way.

[mmagliaro]

One more tip.

In that engine, as in many brass locos, it's not too hard to take the motor out.  So you can do that, and then
roll the chassis on some track, or just hold the chassis in your hand and roll the drivers to feel just where the spot is where it is binding.

Loren, if you need them, I have pics of what I did to this 4-8-4 regarding a motor and extra pickups.  If you give a shout, I'll post them in here.

[strummer]

....would you consider a "shout" from me? 

I'd like to see those pix...

Mark in Oregon

[mmagliaro]

....would you consider a "shout" from me? 

I'd like to see those pix...

Mark in Oregon

LOL!   Certainly.   I have no secrets!
But I threw them into a separate thread so I wouldn't clutter this one up.  None of my fixup on this engine was really related
to the quartering/binding issue that Loren is facing. 

They are here:
https://www.therailwire.net/forum/index.php?topic=35983.0

[Loren Perry]

I just took a close look at the side rods and found that there is a little bit of freeplay (slop) in the holes that connect the rod ends to axles 2 and 3. The rest of the rods have virtually no slop at all. So elongating the rod holes won't be necessary as they already have a little freeplay as-is. Maybe this is the problem? The engine is like new with very little mileage (footage?) on it, perhaps one or two hours maximum running time, so I doubt that they have been worn in to this level. I know there's a connection between the surging and the fact that the geared axle drives the traction-tire axle through the rods. Also, when I slowly start the engine using pulse power, the geared axle (No. 2) drivers start to turn a bit before any other axle rotates, in either forward or reverse.

The "binding" seems to occur when the rods reach the 12 o'clock position as viewed from the left (fireman's) side. My engine's quartering anomaly matches that on the chassis shown in the link Victor supplied to his above-mentioned thread. Victor's solution involving the precise machining of bushings goes far beyond my desire to keep this simple. I've done similar work in the past and still have a Unimat 3 lathe/milling machine do do it with, but I haven't used it in over a decade. Max's idea of substituting a geared Faulhaber motor to "muscle through" the problem sounds more do-able.

Where can I obtain such a gearmotor, Max?

[mmagliaro]

I just took a close look at the side rods and found that there is a little bit of freeplay (slop) in the holes that connect the rod ends to axles 2 and 3. The rest of the rods have virtually no slop at all. So elongating the rod holes won't be necessary as they already have a little freeplay as-is. Maybe this is the problem? The engine is like new with very little mileage (footage?) on it, perhaps one or two hours maximum running time, so I doubt that they have been worn in to this level. I know there's a connection between the surging and the fact that the geared axle drives the traction-tire axle through the rods. Also, when I slowly start the engine using pulse power, the geared axle (No. 2) drivers start to turn a bit before any other axle rotates, in either forward or reverse.

The "binding" seems to occur when the rods reach the 12 o'clock position as viewed from the left (fireman's) side. My engine's quartering anomaly matches that on the chassis shown in the link Victor supplied to his above-mentioned thread. Victor's solution involving the precise machining of bushings goes far beyond my desire to keep this simple. I've done similar work in the past and still have a Unimat 3 lathe/milling machine do do it with, but I haven't used it in over a decade. Max's idea of substituting a geared Faulhaber motor to "muscle through" the problem sounds more do-able.

Where can I obtain such a gearmotor, Max?

That is a Faulhaber 1016, 6 volt, with a 10mm Faulhaber 4:1 gearhead.  You can get that set up by contacting
motorman (micro loco motion).  But please realize that even with lots of motor muscle, you may still see a hesitation or unevenness
in the rotation.  Maybe, maybe not.  It all depends on how severe your problem really is.   

Also realize that your top speed on the engine will  be about 40 mph.  Personally, I like that, but not everybody does.

I think before I did that, I would take out the old motor and carefully roll the chassis to see if I could feel a trouble spot
in the rotation with my fingers.   I might also try removing pairs of rods and seeing how the motion changes
or improves to help narrow it down.

 If it's got more than a very slight bind, no motor in the world will compensate for it.
I was going to change the motor anyway for other reasons as I described.  I don't think I would have done it just
to fix a binding issue.  I just kind of got lucky on that one.

[peteski]

Loren posted his solution to this problem in a separate thread. Further discussion ensued there.
For continuity here is a link to that thread.