Hornby locos shorting on points

[MikeHunter]

Hi All. I have a newly installed DCC power bus, track is Peco code 75. Most of my locos run fine. I have over 20 1930s era LMS locos in my fleet, all are either Hornby or Bachmann, with a mixture of decoders. All run fine on my old layout, which is code 100 Peco track with insulfrog points, including a double slip. 

 

I bought a new layout second hand, and have had it professionally wired. Most of my stock is fine, but I have two Hornby locos causing problems. One is the Stanier 2-6-4 tank, and the other is the previous generation streamlined Duchess (to the one just released). The Duchess has the fixed Cartazzi trailing axle. Has anyone had similar problems with either of these locos?

 

Its only a couple of points which are affected, but I'd like to know whether there are any issues from the loco wheels before looking at the wiring. Both locos have modern wheel profiles.

[Guest teacupteacup]

Have you checked the back to backs?  Thats the first thing I check if Im getting a short

[lennie]

Can't give you a positive answer, but, might be worth checking the Back to Back of ALL WHEELS as a starting point.

[MikeHunter]

Thanks for the swift replies. I'll check. Think its likely to be the cartazzi on the Duchess, as it doesn't move, but would like to know if anyone else with a Duchess has had the same problem.

[34theletterbetweenB&D]

d

 

There are two main potentials for shorting on RTR pointwork. Descriptions below when loco is approaching a facing point.

 

If the points where the shorts occur are 'live crossing' (Peco's electrofrog) then bridging of the closure rails just before the crossing is possible, as Hornby have quite a wide tyre on some wheelsets, and the trailing truck unflanged wheel of the pacific is always a disaster in waiting.

 

If the points where the shorts occur are 'dead crossing' (Peco's insulfrog) then bridging just after the crossing is possible, as Hornby have quite a wide tyre on some wheelsets, and the trailing truck unflanged wheel of the pacific is always a disaster in waiting.

 

You can spot where the shorting occurs by running with the room dark, the sparks will be clearly visible. You may even see a few more wheelsets sparking. (Run for long enough, and the location will be visible by spark erosion of the rail surface.)

 

This has been going on for years in DC operation which is tolerant of shorts, and there hasn't been the design effort to revise both track and wheel standards to better match the requirements for DCC, which has a much reduced tolerance for short circuits. We have to fix it ourselves for now, typically by fitting better profiled wheels. The flanged wheelsets that Hornby (hopefully continue to) supply with their pacifics do the job for me, albeit with alteration of the mounting. Or just remove the flangeless wheelset as a simpler fix.. Other wheelsets, if the problem cannot be fixed by the gauging adjustment already suggested, buy and install kit replacements.

[MikeHunter]

d

 

There are two main potentials for shorting on RTR pointwork. Descriptions below when loco is approaching a facing point.

 

If the points where the shorts occur are 'live crossing' (Peco's electrofrog) then bridging of the closure rails just before the crossing is possible, as Hornby have quite a wide tyre on some wheelsets, and the trailing truck unflanged wheel of the pacific is always a disaster in waiting.

 

If the points where the shorts occur are 'dead crossing' (Peco's insulfrog) then bridging just after the crossing is possible, as Hornby have quite a wide tyre on some wheelsets, and the trailing truck unflanged wheel of the pacific is always a disaster in waiting.

 

You can spot where the shorting occurs by running with the room dark, the sparks will be clearly visible. You may even see a few more wheelsets sparking. (Run for long enough, and the location will be visible by spark erosion of the rail surface.)

 

This has been going on for years in DC operation which is tolerant of shorts, and there hasn't been the design effort to revise both track and wheel standards to better match the requirements for DCC, which has a much reduced tolerance for short circuits. We have to fix it ourselves for now, typically by fitting better profiled wheels. The flanged wheelsets that Hornby (hopefully continue to) supply with their pacifics do the job for me, albeit with alteration of the mounting. Or just remove the flangeless wheelset as a simpler fix.. Other wheelsets, if the problem cannot be fixed by the gauging adjustment already suggested, buy and install kit replacements.

Thanks for the considered response, it seems to be occurring when running over trailing points only. The points were converted in-situ to frog polarity switching, (as the track was already ballasted), so I don't think the loco is bridging the gap, as the rail is correct polarity for the whole length of the point. I suspect with the cartazzi truck its bridging the gap between the point blade, and the rail section next to it (which are opposite polarity and both live). If its this, the only easy solution may be a new generation Dutchess, without the fixed Cartazzi....

 

Still mystified on the 2-6-4 tank though. My Bachmann Fairburn one runs fine, but the Hornby Stanier one doesn't, its a slightly longer wheelbase. Suspect it may be a back to back issue here.

[Phil S]

As it certainly used to say in the instructions for Peco points - they should be wired with insulated frogs at the V - regardless of whether they are insulfrog or live frog - because the gap on the insulfrog is so small that almost any wheel will bridge it ......ONLY when the other rail is either isolated or live with the same phase as the other rail on the V will you get a short-free crossing!   Other makes use a wider dead-frog or include inbuilt fog switching. ....

The unguided cartessi truck flangeless wheelset simply increases the risk of the short occurring because the wheels are not retained to the line of the track  ..they are probably okay on Hornby set track with a large dead frog.

(This is one reason I changed to Rocoline points - and only have 1 peco diamond crossing left on my layout - because of the angle I needed - and of course - with older |Hornby stock especially - this is a source of momntary shorts on dcc - troublesome even with a PSX breaker - but solvable with a Gaugemaster auto frog switch without human intervention)

[MikeHunter]

As it certainly used to say in the instructions for Peco points - they should be wired with insulated frogs at the V - regardless of whether they are insulfrog or live frog - because the gap on the insulfrog is so small that almost any wheel will bridge it ......ONLY when the other rail is either isolated or live with the same phase as the other rail on the V will you get a short-free crossing!   Other makes use a wider dead-frog or include inbuilt fog switching. ....

The unguided cartessi truck flangeless wheelset simply increases the risk of the short occurring because the wheels are not retained to the line of the track  ..they are probably okay on Hornby set track with a large dead frog.

(This is one reason I changed to Rocoline points - and only have 1 peco diamond crossing left on my layout - because of the angle I needed - and of course - with older |Hornby stock especially - this is a source of momntary shorts on dcc - troublesome even with a PSX breaker - but solvable with a Gaugemaster auto frog switch without human intervention)

 

Hi Phil, thanks for the comments. Changing to Roco points isn't really an option as the layout is already fully scenic, and all the track laid. My insulfrog ponts on my other layout are all short radius, apart from a double slip, and run trouble free without any alteration. The locos which are shorting on the new layout don't cause problems on the old one. The only difference is that the old layout is code 100, not sure whether the tolerences are finer on cod 74. A visual comparison of the two side by side doesn't look like they are (in terms of the V and point blade to rail clearances. 

[DCB]

The Hornby locos with the fixed Cartazzi truck used to come with alternative flanged and non flanged wheel sets to avoid this issue. It always was a stupid idea.  The 2-6-4T has a ridiculously long coupled wheelbase,  The Midland railway which later swallowed and devoured many more efficient and better run railways in 1923 to become the LMS settled on it back in 1850 and all employees had to pledge alleigance to 8 ft plus 8 ft 6 on entry to the sacred portals of Derby works.

I suspect the 2-6-4T is too tight back to back for code 75.  My experience is Code 100 needs 14.2mm plus minus 0.12mm but Code 75 needs 14.5mm plus or minus 0.1.  Both cases a nice sliding fit.