1995 version of Bachmann 'trainset grade' SD40-2

[peteski]

The wheel set construction is similar to Kato wheels. The wheels have integral half-axles protruding out of the backs of the wheels. Those half-axles then installed in a plastic tube whic has the gear molded on it. That is why those gears/axle-tubes are prone to cracking.

[Doug G.]

Yes, that's why I wanted to know if they use that type of construction. If it were the other way, cracking would be unlikely.

I don't subscribe to the "shrinking plastic" theory. I believe the problem is merely pressure from the larger diameter bosses inserted into the smaller diameter holes in the axles. Then the weak spot(s) in the plastic give way eventually. There are always parting lines and gate lines in injection-molded plastic parts. Those are the weak spots.

Incidently, Kato (Sekisui) originally used the opposite method with the wheel and partial axle having the hole and the center plastic insulator/axle having the bosseswhich inserted into the wheels. The original Alco PA/DL109 was made that way. No cracking at all. The design used the other way as in the Bachmanns is very poor.

Doug

[peteski]

Incidently, Kato (Sekisui) originally used the opposite method with the wheel and partial axle having the hole and the center plastic insulator/axle having the bosseswhich inserted into the wheels. The original Alco PA/DL109 was made that way. No cracking at all. The design used the other way as in the Bachmanns is very poor.

Doug

Actually, other manufacturers used that type of design too. One that comes to mind is the old Mehano N scale Diesel locos.  I think  those were sold by Model Power and Life Like.

But the Design used by Bachmann is not really all that bad - Kato and most of the other manufacturers that use the low-friction design copied from Kato have metal half-axles pressed into plastic tubular axle without cracking.  So, I wouldn't call it poor - it was just poorly implemented by Bachmann. Not sure it it was the material they use or tolerances, but something makes them crack.

[daniel_leavitt2000]

These were pretty disappointing to all who came in contact with them. And for years, they were still the best SD40-2 available.

Such an important engine to get so very wrong.

[bman]

That was the most disappointing locomotive release ever for me. SD40-2s, right in the prime of it's service life when it was still go to mainline equipment, just beginning to be bumped by the SD50/60 or Dash 8s from GE.

It was the last loco I have pre ordered from Bachmann sight unseen. Never again from them. Never again. Amazingly disappointed in performance and appearance.

Ride height, thick handrails, clunky paint. It had it all. Like a Pinto.

Minus the bondo.  I think even with all the rust my 1971 weighed more when I owned it than new from the show room.  But when your 16 and it's given to you you take it and make it run.  Wish I could say the same for the Bachman  SD40-2 I bought in the late 80's. 

[Doug G.]

Actually, other manufacturers used that type of design too. One that comes to mind is the old Mehano N scale Diesel locos.  I think  those were sold by Model Power and Life Like.

But the Design used by Bachmann is not really all that bad - Kato and most of the other manufacturers that use the low-friction design copied from Kato have metal half-axles pressed into plastic tubular axle without cracking.  So, I wouldn't call it poor - it was just poorly implemented by Bachmann. Not sure it it was the material they use or tolerances, but something makes them crack.

Yeah, I have plenty of old Mehanos. Atlas was about the earliest importer of them to the US. And of course, material selection is a big factor too. Not enough flexibility and it's going to crack. A problem inserting a relatively unyielding object into one which DOES yield.

Doug

[scaro]

I'm struggling to understand what a 'boss' is in this context.  I'm no expert.

The wheel and stub axle are one part.  The stub axle starts at one diameter and is stepped down to a narrower diameter and it is this part of the stub axle that is pressed into a hole in the white gear.

It is a 'friction' fit and that is why the white gears are prone to crack, as the material ages and loses elasticity.

[peteski]

I'm struggling to understand what a 'boss' is in this context.  I'm no expert.

The wheel and stub axle are one part.  The stub axle starts at one diameter and is stepped down to a narrower diameter and it is this part of the stub axle that is pressed into a hole in the white gear.

It is a 'friction' fit and that is why the white gears are prone to crack, as the material ages and loses elasticity.

Boss, half-axle, stub-axle - are all the same thing.
But as as said, there are many other models from several manufacturers using the same type of design but do not suffer the cracking.

[scaro]

Here's a picture of it.