Model Power Pacific 4-6-2 Improvement: Fixing a Disaster and making a Pearl

[u18b]

So… I now have two running Pacifics…. But they were not the same.    I was disappointed that the second ran louder than the first conversion.

In doing all this work, I made an important discovery.

And I came to a conclusion that there is indeed a difference between mechanisms.

In the reviews of @spookshow, Mark said- he couldn’t see any significant differences in runs.

Well, here is one I discovered.  It turns out to be huge.


I have three Pacifics. 
2 have a boiler that is all metal (save details pressed on).

But one has a plastic cover on the bottom of the boiler between the motor and the worm. (that’s the one I worked on first).

Let me show you.

Two of the boiler bottoms look like this.  All metal.



I’ll highlight the area in question for you.




But the third has a plastic plate screwed on.  The metal is open, and the cover is now plastic.

As in here...



And I can tell you this.   The one with the plastic cover runs much quieter than the all-metal boilers, and I’ve discovered that the plastic cover is the revision and thus a later run.  The all metal boiler is an earlier run.

I think you will see that the earlier all metal boiler is LESS desirable.   If shopping, look for the plastic plate.

[u18b]

Spookshow quotes the MR review, saying:  “The locomotive runs well but is a bit noisy. “   Well now I know why.  I took all the locos apart again to document this issue.

So I pulled the motor on my good loco.  You will see why next.




I removed the screw from the plastic plate but could not pull the plate out.




I eventually found if I rotated it 90 degrees, it would come out.




Now you can see this is more that a cover plate.  The motor goes through this piece.









Now, this is not really a bearing because I don’t think the flyworm actually touches it.  And so I’m not really sure I know what this does beside keep dirt out.




Here is the motor reinserted without the cover plate.  Look how huge the hole is.




I then inserted the motor in the parts loco.  The metal comes all the way to the worm.






When I removed the motor, that’s when I made a discovery.  Do you see those round marks?




Those are wear marks where the flyworm is rubbing against metal.  THIS is where the excess noise is coming from.




I then looked at the motor and you can see a wear pattern on the flyworm.  There is a wear line just right of the worm.   Did Model Power envision this metal as a “bearing”?  If so, it was a bad idea.  If not, then the tolerances are poor and the boiler is too close.





So here is what I plan in the future.  If I can get motor tool bits in there, I will remover a lot of metal away from this spot on the flyworm.   If this works, noise will go down and friction will be reduced.

I’ll keep you posted.

[nickelplate759]

Maybe a little too late, but wouldn't it have been easier to just graft on the entire Bachmann tender?
That's what I did here:



Or did you need to keep the factory painted tender?

[u18b]

Oh.  One more thing.  I was VERY disappointed that when I reassembled the good loco it would not run.  What?!

Here is the cover plate with its screw.



Here is no cover plate and you can see that the hole for the screw is right over the flywheel.   If that screw is too tight, then you may hit the flywheel.



I'll probably add a tiny bit of ACC to the screw head to hold it in place.

[u18b]

Maybe a little too late, but wouldn't it have been easier to just graft on the entire Bachmann tender?
That's what I did here:



Or did you need to keep the factory painted tender?

George,
I have one of those tenders, but I think it is too large for the prototype.
Too long but not tall enough.



The stock tender was closer in my thinking.

[Chris333]

I know on some MP steam the newer versions have grey gears and I think the drivers were keyed to the axles so they wouldn't spin. I remember staring at auction photos to make sure I saw grey gears.

[u18b]

Here is a video of the better running Pacific.

Slow speed is almost silent.  As smooth and quiet as Kato Mikado.   Does not creep as well as Kato, but not bad.    Will pull seven passengers cars for a nice excursion train.

[spookshow]

Ron, you don't think that extra part was added to keep the flywheel from hitting the shell? I can't imagine what other purpose it might serve.

-Mark

[peteski]

By the way, the second mechanism did NOT have gears go out of mesh- so I did not cut on the bearing slots.

Hmmm, I'm curious what the explanation would be.  They all use the same frame castings. I believe the holes for all  the gear axles are molded (not drilled later to possibly introduce an error). Are the drive axle bearing slots machined?

[peteski]

Oh.  One more thing.  I was VERY disappointed that when I reassembled the good loco it would not run.  What?!
Here is the cover plate with its screw.
Here is no cover plate and you can see that the hole for the screw is right over the flywheel.   If that screw is too tight, then you may hit the flywheel.
I'll probably add a tiny bit of ACC to the screw head to hold it in place.

Why not grind the end of the screw a bit (using a Dremell tool?) to  shorten it so it doesn't touch the flywheel when tight?  I regularly shorten small screws if needed.

[Mark5]

Ron,

Thanks for this thread!  (bookmarked)

An embarrassing number of years ago I piked up one of these for a kitbash. It ran fine when purchased, so we'll how that pans out. I am using a different tender, so at least that part shouldn't be a challenge.

Mark

[nickelplate759]

George,
...

The stock tender was closer in my thinking.

The "medium USRA" Bachmann tender is the same prototype as the Model Power tender.  Bachmann does also offer a longer one, which would look goofy behind a Pacific.

[u18b]

Hmmm, I'm curious what the explanation would be.  They all use the same frame castings. I believe the holes for all  the gear axles are molded (not drilled later to possibly introduce an error). Are the drive axle bearing slots machined?

Yeah.  This is curious to me too.
Are gears the same- or different?   
They are All black.  Look the same to me.

[u18b]

The "medium USRA" Bachmann tender is the same prototype as the Model Power tender.  Bachmann does also offer a longer one, which would look goofy behind a Pacific.

I think I have one off a Berk.  So it is long but not as tall.

I may steal the trucks off of it since mine are wrong.   Year ago, when Bachmann was dumping $50 tenders for like 15, I bought about 4 or 5.

[jwaldo]

Hmmm, I'm curious what the explanation would be.  They all use the same frame castings. I believe the holes for all  the gear axles are molded (not drilled later to possibly introduce an error). Are the drive axle bearing slots machined?

My guess is Ajin was using a die with multiple mold cavities and/or multiple dies in order to produce more than one copy of the part at a time. If some of the mold cavities had better/worse tolerances than others it'd be easy to end up with some parts being better/worse than others despite being identical on paper.