Author Topic: Kato GS4 Driver Replacement Tutorial  (Read 10992 times)

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victor miranda

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #15 on: March 11, 2015, 04:03:07 PM »
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the gs-4 is now 7 years past the initial run.
the plastic axle centers are doing what I have seen many plastics do.
shrink with age.

if we ignore what Kato should have anticipated....
there is a lot of merit to the small bearing surface in the axle design.

from all I can gather I think the Kato gs-4 is about at 20 percent failure rate.
at more time passes that will go up, I think in another 7 years
all the were ever going to fail will have failed.

lets guess that will be a 50 pecent failure rate...

is that good or bad?
 

mmagliaro

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #16 on: March 11, 2015, 04:32:21 PM »
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Victor, I would say that even 20% is pretty bad, especially when the repair isn't something that the owner can do
themselves.   But I have no way of knowing if that 20% is even accurate.
The mere fact that Kato redesigned the part implies that the failure rate must be quite high,
so I think 20% is a good guess.

Peteski, I think the fix has already been shown: Victor's collars.
The new part could have had the same diameter plastic axle tube, with the ends reduced a little, with steel or brass
rings snapped over the ends.  Yes, it means a few more parts.    But not much more.  Really, the plastic
tube mold would have to be changed, and then there is an added assembly step to snap the collars on

But instead, they made a new bearing, new wheel center with a tab to lock it into the wheel rim, and they beefed
up the plastic axle gear too.

Golly, if they had just made the bearing ears a little bigger and the bearings them selves a little wider, even that would
have worked (but not as good as the original bearings  ;)  )

I understand, Kato had to make a design choice and a business decision: what was the most expeditious, "safe" way
to make a retrofit part to address this problem. 
But I don't follow the reasoning that led them to the parts they made, and I am not at all happy with the QC they did
on the replacement parts, especially considering that they were making them to address a defect.

There are two other problems with the new wheelsets that I haven't mentioned because I was afraid it would be taken
as "too much bashing", but:

So far, out of 5 sets of replacement drivers, not only are they all too narrow in gauge, but at least one
plastic wheel center in every set has not been snapped all the way into the rim, making the wheel roll with a wobble
and making the gauge even more narrow.   The rim can be squeezed back over the center where it belongs, but
this worries me too.  There isn't much holding it in place and that is probably why some are coming through that are not
all the way on.

Second:  On the geared driver.... All 5 of those on the replacements have the wheels mounted on the geared axle
such that they are not quite perpendicular to the axle.  If you roll the wheelset on a workbench, you can see the flanges
wobbling in and out as it rolls.  It is enough that the flanges will be in gauge on the NMRA plate at some points
around the rim, too wide at others, and too narrow at others.  You have to "game it" when you regauge this one
so that every point around the rim is in gauge, even though some places are narrower than others. Yes, yes, I know,
it functions,  but come on.  This is the sort of thing that might happen to me if I were screwing around
with one of my own engines and could only get it "good enough".   But in a production part?

In a very back-handed way (I admit), part of the reason I am so hard on this issue is that this is a Kato product,
and I expected better.  They are always so thorough, and so good at engineering and design, that I just expected
better.


peteski

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #17 on: March 11, 2015, 05:03:53 PM »
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To me it sounds like it would be very beneficial to everybody if model companies would consult "expert" modelers when they were designing their models (or fixes for poor designs).  That would be good idea all around , but there is no way to make everybody happy.
. . . 42 . . .

victor miranda

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #18 on: March 11, 2015, 05:25:31 PM »
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from the thread about gs-4 issues
https://www.therailwire.net/forum/index.php?topic=35463.0

my guess is that Kato made more than 3000.
we got 10 locos we KNOW had cracks

the ... thread had maybe 10 responses
I did a SWAG.

tiny survey 80 percent hits for cracks
and a measureed guess about the relation of the silent majority
to the responders....

plus last time I looked at my gs-4 it had no cracks...

I am thinking it is enough of a problem that Kato made a fix
I am thinking the problem is not 100 percent
and we have 20 known to 3000 guesstimated units
plus they are not on the bay in droves

bake in the half oven for an hour...

I am pretty sure over 10 percent warranty work causes 'fixes'
and while we here are vociferous, I tend to think the cause to complain is
a good reason to post.

so I SWAGed more than 10 and less than 50.
and decided 20 percent would do.

when the geared axle breaks... the loco will stop.
my guess on the matter is that 60 percent have at least one crack
just not the geared axle...

k?

towl1996

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #19 on: March 11, 2015, 05:57:12 PM »
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I don't own one of these locos, but Excellent tutorial! I'd like to nominate this thread for "best of".

Is it possible to do one on quartering? Thanks

Never argue with idiots; they'll drag you down to their level, then beat you with experience.

mmagliaro

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #20 on: March 11, 2015, 06:35:50 PM »
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Victor, I think you went through a reasoned approach to come up with a good guess on the failure rate.
Remember, however, that if any of the 4 tubes crack enough to let the axle loosen and spin,
the engine will stop.  It doesn't only have to be the geared axle.   Granted, that is the one with the most stress
on it.

mmagliaro

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #21 on: March 11, 2015, 08:11:46 PM »
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Say... Just read up on something: plastic annealing
Delrin annealing can be done by gradually heating up the part to 310 - 320 degrees F over 4 hours, holding it there
for 30 minutes for each 1/4" of thickness, and then cooling it at 50 deg F per hour.

For the little axle tubes, I'm thinking you only have to hold it there for 10 minutes or so.

Since all the rest of the original drivers are metal, I wonder if the wheelset could be put in an oven
and processed this way, before the tube ever cracks, to anneal it and thereby relieve any stress on it.

victor miranda

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #22 on: March 11, 2015, 09:32:20 PM »
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not a bad idea.
I am not sure the plastic is an acetal like delrin.

my guess is nylon... then perhaps ABS.

and I have not tried to determine what kind it is.
hmmmmm....

victor

peteski

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #23 on: March 11, 2015, 09:43:56 PM »
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The axle tubes are definitely not ABS. Probably not Delrin either. Nylon - maybe.  But I would worry about the plastic driver faces (and whatever they are made of) distorting in a 300 degree heat. If annealing was to be done, it woudl be safer to just do that to the axle tubes.
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mmagliaro

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #24 on: March 11, 2015, 10:15:27 PM »
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The axle tubes are definitely not ABS. Probably not Delrin either. Nylon - maybe.  But I would worry about the plastic driver faces (and whatever they are made of) distorting in a 300 degree heat. If annealing was to be done, it woudl be safer to just do that to the axle tubes.
Yeah, I thought about that.  I was thinking it would be nice to do it with the axles in place so you didn't have to worry about
getting them requartered.   I don't know.   Can plastics take heat up to 300 degrees?  I would guess not.

peteski

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #25 on: March 11, 2015, 10:23:34 PM »
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Can plastics take heat up to 300 degrees?  I would guess not.

Some can - others can't. Unless we know exactly what plastic was used, I wouldn't not stick it in a 300 degree oven.
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victor miranda

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #26 on: March 11, 2015, 11:54:52 PM »
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I am pretty sure that delrin is soft at 300 degrees.

the annealing process has got to be done in the mold.
I can't see that working any other way.

about the cracks...

if we assume that the new part is close to the tensile strength of the plastic...
any shrinking will cause the plastic to exceed the limit.
almost a guarantee to cause a crack. 

Max, I know the loco can stop if any axle fails
it is just that there is so little  pressure on the non-geared axles
that they may not fail even is there is a crack
and that is pointedly not the case with the geared axle.

victor

delamaize

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #27 on: March 12, 2015, 11:58:29 PM »
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from the thread about gs-4 issues
https://www.therailwire.net/forum/index.php?topic=35463.0

my guess is that Kato made more than 3000.
we got 10 locos we KNOW had cracks

the ... thread had maybe 10 responses
I did a SWAG.

tiny survey 80 percent hits for cracks
and a measureed guess about the relation of the silent majority
to the responders....

plus last time I looked at my gs-4 it had no cracks...

I am thinking it is enough of a problem that Kato made a fix
I am thinking the problem is not 100 percent
and we have 20 known to 3000 guesstimated units
plus they are not on the bay in droves

bake in the half oven for an hour...

I am pretty sure over 10 percent warranty work causes 'fixes'
and while we here are vociferous, I tend to think the cause to complain is
a good reason to post.

so I SWAGed more than 10 and less than 50.
and decided 20 percent would do.

when the geared axle breaks... the loco will stop.
my guess on the matter is that 60 percent have at least one crack
just not the geared axle...

k?

Shear curiosity, do you count my 3 that had cracked axles?
Mike

Northern Pacific, Tacoma Division, 4th subdivision "The Prarie Line" (still in planning stages)

victor miranda

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #28 on: March 13, 2015, 08:50:40 AM »
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hi Delamaize,

you were part of the 10 responses.

believe me my  guess is mostly made in ignorance of real facts.

do you know how many gs-4 Kato made?
that would give us a better guess about the silent majority.

from what I have seen if a loco has one crack it has all axles cracked.
the other piece is that we have given Kato a lot of benefit of a lot of doubt.

once you get to "it is a Known problem" do we really need to know
how many are affected?

victor

up1950s

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Re: Kato GS4 Driver Replacement Tutorial
« Reply #29 on: March 13, 2015, 10:08:22 AM »
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The cracking of plastic sleeves , collars , gears , etc with a pressed in metal axle is a common occurrence . Would it not be better if the plastic isolation piece was under compression . . The metal wheels swaged to metal axles with holes drilled in the ends . Then a plastic gear with molded on pins would be the driven wheel center piece . The other wheels would be joined with a plastic rolling pin shaped piece . Yes the metal axles would need to be a larger diameter , and that cost . But doesn't it cost money and a reputation to have this cracking failure . 


Richie Dost