GS-4 General Problem Observations

[peteski]

Actually, now that I've had some of these apart, there are small metal "fins" on the half-axles that are pushed into the plastic tubes, so Kato thought of that.  Unless the tube cracks, the wheels would not go out of quarter.

That is good to know (I didn't actually take the old wheel set apart).  But creating scoring on the inside of the tube could have also contributed to wakening those tubes, causing cracking.

I'm surprised they didn't just make a new plastic tube out of a different material that wouldn't crack.
I suppose they decided it was tough to know exactly what would hold up in that application.

I think the problem here is the huge diameter of the wheels with the axle tube still having dimensions similar to what is used in the passenger cars with scale 36" wheels.  After all, how many cracked axle tubes have you heard of on the passenger cars?  Putting even moderate pressure on those wheels by being ham-handed while re-railing the model will cause a lot of stress on those axle tubes (since the large diameter wheels act like levers).  Kato replacing them with solid axles came up with IMO the optimal solution.

I realize that you aren't bashing Kato - you are just critiquing their workaround and finding some unusual problems with the chassis/bearings.  And I'm playing a devil's advocate as I usually like to do. 

[mmagliaro]

Victor's suggestion about a sleeve over the axle (what I called the "faux" axle tube) would work.
I considered that when I was fixing these.  I really didn't want to pull the wheel to put it on, however.
Then I considered just putting two styrene half-round pieces over the axle clam-shell style,
and gluing the seams with liquid cement.  I think that would work too.  The plastic sleeve doesn't have to
be all that precise.  It just has to not rattle or flop around too badly.  Heck, I bet even a very
thin-walled thing, like those thin straws you stir coffee with, slit lengthwise, and then just
snapped over the axle, would work.  (Hey... that's not a bad.. idea....)

Peteski, I hear you about ham-fisted shoving and stressing of the big drivers.

But man, having played with these... the old bearings were so much freer. 

You just have a polished hardened steel axle sliding in the bearing hole.   
On the new ones, the nub on the back of the wheel spins in
the axle hole instead, and no way is that as smooth as the axle.   Moreover, on the old ones,
the axle was always entirely inside the bearing (obviously, there's nowhere else for it to be!)
But in the new ones, those wheel-back nubs move in and out of the bearings.  Sometimes the whole
nub is inside the bearing.  Sometimes only part of it.  So there is sliding friction and spinning friction, and
I had that problem with the nub sliding over so far in the bearing that just the very edge
of the nub was in the bearing hole, so it would sag and get stuck ("Con-Cor 2-10-2 disease")

I think if I owned one of these, I would rework the axle tubes and keep my old bearings.
There's a good bit of room in that frame.   I could grind out some more clearance under where the tube
goes, and grind some off the inside of the gear cover plate where it sits above the tube,
to allow for a larger tube diameter.

Then sleeve a brass tube right over the plastic tube.   It would be like Victor's brass collar solution, only
it would be a little easier to do, I think, because it's just a single sleeve, no milling of the plastic tube edges,
or cutting tiny collars, etc.   This assumes I would have the advantage of doing this BEFORE the tube
actually fails.

If you catch them before they break and reenforce them, they should last forever.

So... you really think these break a lot because people are shoving on them on the track, eh?
Boy.   People need to take better care of their engines.

[carlso]

Max and all,

I have really enjoyed this discussion about the GS-4. I have one from the 1st run and, knock on wood, it runs fairly well with no broken tubes at this point. The only problem was the rapid failure of the "tires". I do not place it on the track and push/pull to check that it is indeed on the rails. So, possibly that does have the cause/effect talked about. I have set up N Trak modules all over the country, including many times at the large OK City show in December of every year.
Without hesitation, I can say I have seen adult men place a steamer on the tracks and push or pull it to check for correct rolling. You will see them slide diesels along the rails too, so a habit it formed. Wow, they then complain about the darned traction tire broke or fell off. To be fair about my comment I guess I need to qualify that statement by saying "many newbies", not all, do that.

Carl

[peteski]

The only problem was the rapid failure of the "tires". I do not place it on the track and push/pull to check that it is indeed on the rails.

Carl, pick up the "new" traction tires (for FEF-3 and GS-4) available direct from Kato USA.  They are much improved.  They fit tighter and seem to be made from a harder material.

[peteski]

Victor's suggestion about a sleeve over the axle (what I called the "faux" axle tube) would work.
I considered that when I was fixing these. 

I agree that it is an excellent idea.  Remember the thread from few years ago going all the way to making those tubes out of carbon fiber?  It was fun re-reading that thread (and hitting many points covered again here).

https://www.therailwire.net/forum/index.php?topic=27691.0 (page 4 for carbon fiber info)

But man, having played with these... the old bearings were so much freer.
You just have a polished hardened steel axle sliding in the bearing hole.   

Absolutely!
I mentioned that way back in 2012, before thre revised drivers were introduced.
https://www.therailwire.net/forum/index.php?topic=27691.msg286259#msg286259

I think if I owned one of these, I would rework the axle tubes and keep my old bearings.
There's a good bit of room in that frame.   I could grind out some more clearance under where the tube
goes, and grind some off the inside of the gear cover plate where it sits above the tube,
to allow for a larger tube diameter.

Then sleeve a brass tube right over the plastic tube.   It would be like Victor's brass collar solution, only
it would be a little easier to do, I think, because it's just a single sleeve, no milling of the plastic tube edges,
or cutting tiny collars, etc.   This assumes I would have the advantage of doing this BEFORE the tube
actually fails.
If you catch them before they break and reenforce them, they should last forever.

I agree again. But this type of a permanent factory-produced revised axle set, this would be too labor and part intensive.  Remember, the companies are all about making profit.

So... you really think these break a lot because people are shoving on them on the track, eh?
Boy.   People need to take better care of their engines.

A big resounding "YES!"  It is amazing what grown men are capable of doing to these delicate models.

[mmagliaro]

One thing to realize...
These engines also come right out of the box new with cracked axle tubes sometimes.
Not cracked enough to operationally fail, but clear stress cracks nonetheless.

So I would bet the the root cause of all this trouble is that the axle tubes themselves cannot take
the stress of the inserted metal axle - either because the plastic is too inflexible, or the hole is bored a little
too small (or both).    Maybe ham-fisted operators exacerbate the problem, but I think
the part itself is really the problem.

[peteski]

One thing to realize...
These engines also come right out of the box new with cracked axle tubes sometimes.
Not cracked enough to operationally fail, but clear stress cracks nonetheless.

So I would bet the the root cause of all this trouble is that the axle tubes themselves cannot take
the stress of the inserted metal axle - either because the plastic is too inflexible, or the hole is bored a little
too small (or both).    Maybe ham-fisted operators exacerbate the problem, but I think
the part itself is really the problem.

It might have been aided by the (anti-twist) knurling on the axle ends which created a convenient place for the crack to start. Kind of like when a small rock hits a windshield and that spiders out into a major crack.

[victor miranda]

oooof.

Kato decided they had enough process control to hold an important specification

I looked at the axle half shafts and thought they could crack if not carefully made
and I decided Kato knows what they are doing.  (engineering calculations, and modulus of elasticity
expected forces...etc.)
now I am thinking they tried it and decided it works.  On to the next part.

plastic can have pretty high tensile strength.  Nylon is close to steel in tension I have  read somewhere....
where the concept fails is that molding plastic often cracks where the flow
into the mold touches and it is pressed to final shape.

plastic for insulation, metal collars for clamping to keep the plastic from cracking (further)

It may be the correct fix is to use one of the original drivers in slot 4
and the #3 to absolutely be from the new batch... the other 2 can be either...

btw, the collars are easy to install.

victor