Kato GS4 Driver Replacement Tutorial

[victor miranda]

Hi Up1950s,

what you advocate is effectively how Kato constructed the new style gs4 axles.
(ok not the plastic rolling pin...)

there are a good number of ways to build a durable n-scale driver set.

what they all have in common is a minimum bearing size of about 2mm.

(a 1mm metal axle and a .25mm plastic sleeve and then a .25mm metal bearing nub
this get us to a diameter of 2mm)
this is true if you want to use a vertical split frame and get the benefits
of the drivers as electrical pick-up.

what Kato attempted was to get a 1mm axle bearing.
in terms of smoothness and efficiency this is very desireable.
it also makes the siderods more tolerant of small errors in quartering.

when I think of Kato, I think they are a company that goes
the extra mile to build superlative mechanisms.

you are looking at an example of that Kato thinking.

the Diesel Axles don't split right?

so they 'forgot' that the metal axle halves of a steam engine have more leverage on
the plastic centers.  They also did not seem to take into account those diesels
have outside bearings.

it is a serious oversight.

If they had put a metal sleeve over the plastic axle centers
we would not be having this conversation.

I suspect we would be wondering why Kato used a different style
of axle in the FEF

victor

[peteski]

I have no numbers to back my theory up but I think the GS-4 split axle problem was severe enough for Kato to redesign the drivers to their current design.  They are probably being used by Kato's repair staff to fix models sent to them broken. Then they also decided to offer them to the public, but  I think the majority of the new drivers are used in-house for repairs.  We seem to forget that the modelers who tinker with their own steam (or any for that matter) N scale locos are very small percentage of the N scale modeler population.

When the retrofit drivers were first announced I thought they were simply FEF-3 drivers sold for GS-4.  But once those drivers and the FEF-3 came out I realized that they were separate and distinct designs.

Speaking of hollow tube axles which do not seem to crack are all of Kato passenger trucks:  There are lots of those out there (as compared to the number of GS-4 locos), yet I have never seen or heard of one of those cracking. Even though they have small diameter which should be prone to cracking.  Go figure.

[victor miranda]

Hi Peteski.

the cracking, or lack there of, is a leverage  thing.



warning! actual numbers and ratios will be used...

you may want to compare a diesel axle rather
than a passenger car axle to the gs4  axle.

let get dimensions
the axle center for a passenger car is 7mm
the metal stub is 1mm diameter and
about 3.2 mm from the back of the wheel.
the bearing is about 2mm away from the plastic
and the impulse from the wheel is shared with the bearing.
the wheel has about a 2.5mm leverage arm.

the gs4 has some tricks in it.(from memory
Anyone who wants to measure the driver can and I'll use those numbers)
the metal stub is a 4.2 mm from the inside of the driver
the bearing is about 1 mm inside the wheel back
the bearing is 2m mm thick
the absoulute longest the plastic sleeve can be is 6mm
(inside of driver to inside of driver is 10mm)
there is some side to side play so the plastic axle center is
a little shorter than 6mm.

so we have the axle stub 2.8mm into the plastic sleeve
and we have a 6mm leverage arm.

the gs4 has about a 2 to 1 advantage to bend the axle over a passenger car
or even a diesel.
this is ignoring the bearing of the gs4 is acting as the pivot point.

I suspect the passenger car axles are not as stressed.

I have seen a cracked diesel axle. the driver was not out of gauge.
it is a rare failure in my experience.
part of the reason we don't hear about it may be as simple as it is cheap and easy to fix
and a failure is not going to stop the loco.

victor

[mmagliaro]

Peteski, I think you have it right.  The problem had to be severe enough, and common enough, that Kato
designed a new axle because the old ones were becoming a constant headache.  Again, I don't know anybody
at Kato and I cannot prove this, but it is the only answer that makes economic and practical sense to me.

They almost got it right.   

Kato:  If you are reading this.  Here is my suggestion:

1. On the new drivers, add a plastic spacer tube between the bearings, just to keep the bearings from tipping and wobbling
out of the frame.
2. Adjust the press so the gauge on the drivers isn't quite so narrow.  Just get them into the NMRA notches.
And make sure the wheel centers are fully pressed into the rims.

If they do that, these replacement sets would truly
become "drop in".

[peteski]

Victor,
earlier in the thread it has been hypothesized that the splitting of the plastic axle was due to the plastic sleeve being too tight and the inserted metal axle was exerting too much pressure on the inside of the tube, splitting the plastic.

In your latest writeup you seem to be leaning towards the leverage theory - the axle tubes simply split because they are being snapped by the half-axles (possibly by ham-fisted modelers putting too much pressure on the model while rerailing it or just in general handling).

Either way, the axles do seem to split, indicating less-than-ideal design, with Kato providing a retrofit parts.

Max,  I highly doubt that Kato will redesign their retrofit parts (yet again).  It would be totally unrealistic to think that. I suspect that if and when they re-run GS-4 again, they will either use the revised GS-4 drivers or if they are really ambitious, they will redesign the chassis to utilize the FEF-3 drivers.  I guess we will have to wait and see.

As far as the tight gauge is concerned, AFAIK all of Kato offerings are tight in gauge (using NMRA gauge as a reference).  I also don't see that changing. Actually quite a few N scale manufacturers produce models that are tight in gauge.

[victor miranda]

the splitting is all of that.

there is no doubt the tension on the plastic is high.
that by itself can be all the sole reason.

you noted that the passenger cars don't crack

and I explained why.
now you have a second reason to put collars on your gs4.

victor
 

[mmagliaro]

Since I know at least one person who has taken multiple brand new GS4's out of their box, opened
the cover plate, and seen cracks on the axle tubes, we can pretty well see that the cracking
is not just caused by handling of owners.  They may make the problem worse, but the cracking
is definitely also happening just as a by-product of the tightness or the assembly procedure.

As for the gauge... yes, a lot of people make their stuff too narrow.  ( And they need to quit it     )

What I'm saying is that these are *worse* than the original drivers.  The original drivers were just
on the "okay" side of narrow and could make it into the notches.  The new ones are NOT.  They are narrower
still and are not in the notches.

One must be very careful, when introducing a fix to a problem, not to introduce other new problems.
And these new drivers do introduce new problems.
In fact, to be quite honest, given the situation, if I owned one of these (and could not do repairs
myself), I would buy a set of drivers
and sit on the sidelines with them.  If the axles never crack enough to stop my engine,
I would enjoy my superior GS4, and worry about replacing them if and when they fail.
OR, I would send my set to Victor and let him put collars on as a precautionary measure,
and then keep running my old axles.

[up1950s]

When I was in HO I had some Brass Alco Models diesels . They had a nylon gears on metal shaft that was prone to cracking . NWSL made metal replacements . That was 1975 ish .

[victor miranda]

back around 1990 Lifelike had an HO BL2 that had gears crack and fail.

I recall fixing  one loco...

wow that is a blast from the past.

it seems such things have to be re-learned every so often.

victor

[victor miranda]

Hi Max,

I love your tutorial. good clear photos and good text go go with them

I am sticking to one item. I strongly urge anyone with a gs4 to get a new driver set.
the new driver design for the geared axle is much better than the old style.

Get a collar on the #4 driver if you have a problem with the newer set
in position #4.

victor

[mmagliaro]

Hi Max,

I love your tutorial. good clear photos and good text go go with them

I am sticking to one item. I strongly urge anyone with a gs4 to get a new driver set.
the new driver design for the geared axle is much better than the old style.

Get a collar on the #4 driver if you have a problem with the newer set
in position #4.

victor

EDIT: How ungrateful     
First, Thank you, Victor
END EDIT
Now...

Now that this has gone around and around for a while, and we have all spoken our minds on it,
I tend to agree with what you suggest here.

I think the geared driver on the new set is a big improvement.  The bearings
stay put nicely. and it is heavier so it won't crack.     
Replacing just that one, and collaring one original one for the 4th position, should make for a reliable engine.

[victor miranda]

you post is quite funny.
well it got me laughing anyway.

the 5 you fixed
the three delamaize did
the 2 I did
and 18 for superturbine
1 for up1950s

that is 26...

(I hope I got those right)
hmmmmm

[peteski]

back around 1990 Lifelike had an HO BL2 that had gears crack and fail.

I recall fixing  one loco...

wow that is a blast from the past.

it seems such things have to be re-learned every so often.

victor

Funny how nobody yet mentioned the infamous Bachmann white nylon axle sleeve/gear used in all Bachmann locos from the 80s.  They were infamous for splitting.  Unfortunately they used to split right at the gear.

[carlso]

Good evening my friends,

I wanted to resurrect this thread to add some additional information to the KATO GS-4 replacement drivers. As you know, Max did the replacement for me, and prepared this excellent tutorial using my GS-4 mechanism. Max sent me a short video of the mechanism and tender running on his layout and all looked good. However, I have discovered an issue that was just touched on by Victor and others. I have discussed this post with Max and he has no problem with me passing on what I have found, so I am not bashing Max, he is top notch in my book.

When I received the loco back from Max, I did not touch it until I decided to re-motor it with a gearhead set up. Last Friday I partially re-assembled the loco and tested it on my rollers stand. The drivers did not look right with a lot of wobbling which may be partially attributed to the roller stand. I turned it upside down, removed the driver retaining plate and I found a problem with the #2 axle. The bearing from the fireman's side of the chassis had come out of its seat and migrated all the way across the metal axle and was freewheeling against the opposite side bearing. Well , the axle was sitting at an angle and it is a wonder that the damned thing ran at all. The #2 driver has the crank on it and I think that the rotation of the crank caused the axle to "bounce" thus lifting the bearing out of slots. No wonder it wobbled. I think I shall try the Max upside down "U" on this axle as well. I shall see! BTW, the #4 axle with the "U" on it was/is OK.

I am a KATO lover but I find this fiasco to be a very poor product and attempt to correct a problem for purchasers of the GS-4's. On the positive side, the Maxon motor/Faulhaber gearbox started very slow and ran quite smooth. I think I will be happy with it because I will make it run or croke trying. I did find a problem with my motor install but found and fixed that issue.

I found the speculations about the percentages of GS-4's with problems to be intriguing and I think Peteski made the comment that most likely the majority of owners would just shrug the problem off and make a shelf queen out of the loco.

Thanks for listening and I hope this tidbit helps others who are having issues.

Carl

[victor miranda]

oh.. dingit.

Hi Carlso,

well, I wondered if the  #2 driver bearings could escape.
It seems they can.

the u-channel trick should work for that axle as well as the #4 axle.

I have to comment about the shelf queen idea...
I am curious about what guys do.
I first thought was that such locos get sold.
... they are not on the bay with any regularity...
selling them enmasse does not/has not happened as far as I can tell.
I'd been expecting to get ones to fix and re-sell.

then, I thought a whole lot of these locos were purchased as display items.
For a while brass gs-4 were cheapish.

The guys who have them do not seem to have a problem with the
idea of using a gs-4 as a display piece.

victor