I'm having a devil of a time with six wheeled diesels on curves

[NorsemanJack]

The only engines I ever bought that had all the wheelsets properly gauged from the factory were all of my Kato FEF's and all of the brass LIK GS's my son had.

That's odd.  I've never messed with the gauging of wheelsets from the factory (other then those crappy LL SW1200's), and never had any problems on UniTrack.  I suspect the OP's minimum radii is just too small for large locomotives.

[Steveruger45]

My layout is unitrack with min radius 11” and no easements. None of my six axle locos (including many many Kato units, have a problem derailing at all.  I don’t think the “radius too small” idea is the culprit here. 
To add detail for perspective, The longest loco’s I have are Kato sd70’s amd atlas sd60’s.
I don’t have any #4 turnouts.  My track is also not perfect, there are some rail height differences at the unitrack joins.

I would recommend to closely inspect the “problem” locos trucks and wheel sets and freedom of the trucks to rotate side to side in the first instance.

[nkalanaga]

For sharp curves, it's possible that the problem is that the middle axles ARE gauged correctly.  Most older Kato locos that I bought had the center axles gauge too narrow, probably for "lateral" on curves.  I regauged them, as they don't need it on my curves, but on sharper curves that could be an issue.

That's part of the reason most European and Japanese track still uses wide flangeways - to handle narrow-gauged wheelsets needed for sharp curves.

Prototype steam locos were built with "lateral motion" in middle axles, and some were even built with "blind" flangeless drivers, just to take extra-sharp curves.  I've seen a few pictures, on industrial track, where the curve is so sharp they had to install an extra rail, on the outside of the inside rail, so that the "blind" drivers wouldn't drop off the running rail, onto the ties.

[thomasjmdavis]

@voldemort - would be most helpful if you could post WHICH specific locos you are having problems with and/or some of your photos or video of the problem areas.  This could help (a) jog our memories of having similar problems with a similar loco and (b) someone may spot something in the photos that might be contributing to the problem.

Not all Katos and BLIs are created equal.

PS- given how far out a coupler trip pin would be on an E6 on an 11" curve, you might want to look at that as well.  If it is an E6, and not an SD-70, giving you a problem.

[EJN]

FWIW - my Kato PA-1 and SDP40F both run fine on an 11.5" radius curve, no easement - Atlas code 80 flex track.

[robert3985]

That's odd.  I've never messed with the gauging of wheelsets from the factory (other then those crappy LL SW1200's), and never had any problems on UniTrack.  I suspect the OP's minimum radii is just too small for large locomotives.

It's not "odd" for me since I build all of my turnouts on the bench to "tight" NMRA standards, which require everything that runs on my layout to be perfectly and properly gauged.  This causes me to make sure that all of my engines are in gauge, because if they're not, they'll hop on my turnouts at the check gauge between the frog and guard rails, and catch a flange at the smaller-than-Kato-Unitrack gap between the point toes and adjacent stock rails at the turnout headblocks. 

However, there's a logic train (pun recognized) to finding out what causes derailment problems, and the logical place to start is to verify that the problem car/locomotive is properly gauged. 

With Kato Unitrack, it's probably okay to assume that if the engines are properly gauged, they should run without derailing through properly snapped together, undamaged, uncluttered curved Kato sectional track since another assumption is that the track is engineered for engines from the parent company to run well on, even with C trucks.

However, I could be mistaken in making that assumption since Mr. Kato is well-known for his lack of logic concerning certain manufacturing and marketing decisions.

I'm gonna bet that the problem isn't with the gauge of the wheelsets, but with drawbar length, or dangling coupler dongles (dangling dongles), or edges of the engines' carbodies rubbing when they enter the sharp curves.

We shall see.

Cheerio!
Bob Gilmore

[u18b]

There's been almost two days worth of discussion.... but @voldemort still hasn't gotten back to us yet.

[CRL]

There’s one more gauging issue to worry about on 3 axle trucks. You need to put a straightedge between all 3 wheels on one side of the truck and be sure each wheel lines up with other wheels on the truck. If one axles wheels are skewed to one side from the other 2 axles, the wheels on that axle may be perfectly gauged relative to each other, but out of alignment with the other axles.

This can happen on 2 axle trucks also, but the loco will still track ok in most situations.

[peteski]

There’s one more gauging issue to worry about on 3 axle trucks. You need to put a straightedge between all 3 wheels on one side of the truck and be sure each wheel lines up with other wheels on the truck. If one axles wheels are skewed to one side from the other 2 axles, the wheels on that axle may be perfectly gauged relative to each other, but out of alignment with the other axles.

This can happen on 2 axle trucks also, but the loco will still track ok in most situations.

While that is a valid concern, the way Kato wheelsets are designed, that type of a defect would be extremely rare.

[nkalanaga]

Bob:  To add to your comment, that points out the importance of following standards. 

In your case, everything is NMRA-standard, and it all works well together.  Wheelsets made to match Kato-Unitrack-standard would also work fine on that.  But likely neither wheelset would work well on the other track.

Most N scale sectional track is made to something similar to European NEM standards, from the 1960s.  That works fine with matching wheels.  But today's narrower treads and smaller flanges don't always play well with the looser track standards, just as NEM wheels (pizza cutters, mostly) don't like NMRA track.  That's why many N scalers have to shim the guardrails on Peco turnouts.

[nscalbitz]

Kato wheels- sets get out of alignment it seems as we had that problem on old friends unitrack layout, nearly all SD's and big GE's... one driver set would lose its parallel and when they hit a curve (and we had contour changes of up to 25mm as well) the friction of one dragging caused the front pair to lift and rise up sideways; or conversely the front pair to dig in and twist the truck so the rear axle came off, still merrily chugging down the line of course.

Invariably a mild pull down found detritus in the axles heads and/ or gears; as well as a different gauging between axles sometimes.
Different problem to drag from too long adjacent cars...
cheers