Points -- Advice, please.

I use Peco code 100 track and my layout is controlled by Lenz dcc. I have a number of Peco medium radius live frog points arranged 'back to back' to enable crossing between 2 adjacent parallel lines. All works well apart from one left hand point. Almost all my stock negotiates this point without any problems. The only problem is with my Hornby Merchant Navy and Hornby Battle of Britain pacifics. These cause a short and trip out the controller every time they negotiate this point on the diverging route. They have no problems on my other 7, notionally identical points.
I suppose I could just swap out the point but I would like to understand the problem as it is specific to just 2 locos on just one point.
Any advice or opinions would be gratefully received.
ROB

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check the back to back of the bogie under the cab. This is the most frequent cause of the short. I normally set mine with a clock vernier at 14.5 may be 14.6.

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After investigation I think what is happening is this:
When the loco takes the diverging route (a left turn), the leading driving wheel on the left hand side is contacting the straight switch rail (which is switched out of the way). The front bogie and rear truck seem to negotite the point OK. I do not have a vernier guage but this seems to be because the back to back of the driving wheels is too narrow, thus allowing excessive sideplay and letting the leading driver slew so far across that it touches the straight switch rail.
Is it possible to adjust the back to back of the driving wheels simply, or do I run the risk of permanently damaging the models?
Regards
ROB

"Robert Flint" wrote
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I had a similar porblem with one Peco Code 75 Finescale Electrofrog point, and like you the problem only ever occurred with a Hornby loco.
As I see it it is caused by improperly set back-to-back measurement on some Hornby products, and consequently that in itself can be difficult to solve.
It is however possible to tweak the point slightly to increase clearances - just gradually ease the point blade slightly away from the stock rail until the problem disappears.
John.

Robert Flint wrote:
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As the others have said, its caused by a wide wheel (possibly overgauge) just catching the two rails near the crossing nose (frog) of the turnout.
If you cannot tweak it out by adjusting the wheels on the stock, you could eliminate the problem by a wiring / electrical change. Place insulated rail joints on the rails which leave the crossing nose (frog) where they meet the continuation track (plain line or another turnout). You may need to add a feed to the continuation track from your DCC supply wires (typically a bus running below the layout on most wiring designs I've seen). Power the crossing nose rails from the switch blades (pretty certain all Peco points do this by default).
As only the "active" part of the crossing nose will be receiving power from the "active" blade you should avoid the short. If the short persists, and you were relying on the internal Peco wiring to transmit power from blades to crossing nose rails, then suspect that power is coming through via the "inactive" blade (possibly by catching on another wheel running past the blade?), and you'll have to resort to separate electrical switch connected to the tie-bar movement (ie. the way people who solder-construct track do it), and remove the Peco wiring which is below the crossing nose.
- Nigel