Bachmann Class 37 derailing on points

[Throppers]

I have an OO gauge Bachmann class 37 which de-rails on points (oddly my other identical loco manages them).

 

 

I have done various checks and confirm that the back to back measurements are correct using a spacing tool. There is also no rocking on the bogey, all three axles are level and all 3 pairs of wheels are firm on the rails.

 

 

After doing some further investigation, there appears to be enough bogey swing as when running over the points, the bogey doesn't swing to it's full potential. However, the mechanism of the derailing is the front outside wheel (front left if going over a right turnout and front right when going through a left turnout) jumps off the rail at the gap before the frog, causing it to jump over the frog.

 

The below pics show the loco on approach to the frog and then having jumped off through the gap in the points just before the frog from top and side...

 

Any ideas? I am thinking about what modification I can make to the loco to allow it to manoeuvre over the points. The points are all Peco and Hornby standard radius and it derails on pretty much every set.

 

Thanks in advance.

 

 

 

[Marcyg]

Is the screw holding the bogie on too tight? Bachmann are good at doing this to their Mk1 coaches! Are the pick up wires slack enough? Do they allow free movement of the bogey?

[The Johnster]

I don't know much about setrack points, except the 4th/3rd radius curved one I have at the entrance to my fiddle yard, but that point looks a very tight radius to me.  You say it is 'standard' radius; if this means 1st radius the loco may be simply too big for it.  The lowest radius recommended for the loco will be stated in the user's manual sheet that came with the loco; if you don't have this for any reason it can be downloaded from Baccy's website.  The determining factors are the wheelbase of the bogie and the overall length of the loco; at least we are not dealing with a Class 40 here!  

 

My personal recommendation would be to use pointwork of the next radius up from the recommended minimum, as points produce their own set of potential problems.  But you may be constricted for space and unable to do this.  My only other suggestion is to ensure that the points are laid smoothly to the adjoining rail, as the angle at which the loco approaches the point may have an effect, and ensure that they are absolutely level.

 

Does it happen on one particular set of points, or all of them?  if the former, the loco may not be at fault at all, just a bit more fussy than the others; check the tracklaying and it may be worth replacing the point.  Before you decide on that, though, check that the plastic frog vee has not worn down at the apex, and check that there is no debris in the flangeway (the channel between the rail and the plastic check rail that prevents the wheelset from moving sideways in the gap between the stock rails and the vee) that might be lifting the loco on that side and forcing the wheels to split the points.  I use pound shop children's paintbrushes with stiff nylon bristles to keep these clear on my layout.  

 

Another thing to try is turning the loco around to face the other way and see if that works.  

[Barry O]

Hang on a mo..why are you asking this question again? In the same place just a new thread a day and having had a few responses???

[40F]

_{All set track points are 2nd radius so the loco SHOULD go over them OK. Are you using Hornby or Peco points? Peco points seem to be more tolerant than the Hornby ones} 

[Throppers]

Problem has been resolved by reducing the back to back spacing on all wheels to ~13.9mm. No derailments now even at what would be considered excessive speed for going over points.

 

Barry O - Yes fair point. I started another thread as I realised the title of my original one wasn't very indicative of my problem that needed advice. I found I couldn't change the title so thought I'd start another one with a more obvious title, with the intention of deleting the original thread, which I also then found I couldn't do. Honest mistake, not meaning to clog up the forum. 

[BoD]

For future reference, if you edit your first post you can edit the thread title there.

[The Johnster]

Glad to hear you have had a successful outcome to this, Throppers.

[Knapdale]

Could anyone tell me the best way to reduce the spacing between the wheels on a Bachmann 37? 
 

I have the same problem as the OP, and while I’ve adjusted wheels on rolling stock, I don’t want to do anything that damages a locomotive. 

[DCB]

8 hours ago, Knapdale said:

Could anyone tell me the best way to reduce the spacing between the wheels on a Bachmann 37? 
 

I have the same problem as the OP, and while I’ve adjusted wheels on rolling stock, I don’t want to do anything that damages a locomotive. 

So what is your B to B   The OP quotes his is down to 13.9m    That does not sound right, Hornby Dublo is 14.2 and that's what I use for my stock, as its about as tight as most Peco streamline point check rails can cope with.  That is a nice sliding fit.   If the wheel sets come out putting one axle end in a hole so the wheel supports the wheelset and hitting the other axle end with a hammer works well.  Widening them out again is more difficult.  The OP Tyre profile looks awful, might just be the camera.   Set track points have their place, micro layouts, floor layouts, industrial sidings and the bin, but generally are a PITA.  Might be easier to re design with streamline... 
EDIT  The Set track points are nearer 1st radius through the curved road.  They have a straight bit at the toe end I have a Hornby Dublo point which is first radius but does not have any straight bit at the toe end Laid on a set track point the curvature is very nearly identical

Edited June 2, 2023 by DCB

[Knapdale]

1 hour ago, DCB said:

So what is your B to B   The OP quotes his is down to 13.9m    That does not sound right, Hornby Dublo is 14.2 and that's what I use for my stock, as its about as tight as most Peco streamline point check rails can cope with.  That is a nice sliding fit.   If the wheel sets come out putting one axle end in a hole so the wheel supports the wheelset and hitting the other axle end with a hammer works well.  Widening them out again is more difficult.  The OP Tyre profile looks awful, might just be the camera.   Set track points have their place, micro layouts, floor layouts, industrial sidings and the bin, but generally are a PITA.  Might be easier to re design with streamline... 

One of the axles is 14.5mm and the rest are 14.4mm. The wider one is the one that causes derailment when leading, while the others just cause the loco to slow down in either direction. I just want to narrow the B2B gradually and test after each adjustment. 
 

Unfortunately, my layout is laid so don’t really want to change it at this stage. All my other Co-Co locos (47, 55s and 60) manage no problem, it’s just the recently purchased second-hand 37s that have a problem!

[Il Grifone]

14.2 ± 0.1 mm B2B is correct for Dublo (or other) wheelsets with a 0.8mm flange. Peco Streamline was originally designed when these were still current*, with rather slack tolerances (which have been tightened up since).

Is there sufficient side play on the centre axle? Asking anything to negotiate such tight curves requires a fair amount of side play.

*Adopted by Tri-ang (later Hornby) of course following the takeover.

I adjust back to back with a drill press. Once it's shifted, fine adjustment can usually be done by twisting a wheel on the axle. (Some will shift without the press - others are more recalcitrant!)

Edited June 3, 2023 by Il Grifone

[Knapdale]

On 03/06/2023 at 19:32, Il Grifone said:

14.2 ± 0.1 mm B2B is correct for Dublo (or other) wheelsets with a 0.8mm flange. Peco Streamline was originally designed when these were still current*, with rather slack tolerances (which have been tightened up since).

Is there sufficient side play on the centre axle? Asking anything to negotiate such tight curves requires a fair amount of side play.

*Adopted by Tri-ang (later Hornby) of course following the takeover.

I adjust back to back with a drill press. Once it's shifted, fine adjustment can usually be done by twisting a wheel on the axle. (Some will shift without the press - others are more recalcitrant!)

So after various trials with adjusting back to back gradually without success, I’ve discovered that it is the worm gear covers on the newer model’s gear towers that prevent the bogies from turning as much as the older model’s bogies. The older bogie design doesn’t have a cover for the worm gear, so the bogie can turn a tighter radius. Will try and file down the plastic covers a wee bit where they hit part of the chassis block and see if this solves the issue. 

[Knapdale]

In case anyone else has a problem with their Bachmann 37 on set track R2 curved points, a solution is to cut and file down the two top corners of the worm gear covers in the bogie tower. This will then allow the bogies to swivel slightly more as they go through the curve. Pictures attached show my crude handiwork, but it works.  

I think the radius of curved points must be slightly less than R2, because the bogies don’t have a problem going through the normal R2 points. 

[34theletterbetweenB&D]

22 hours ago, Knapdale said:

I think the radius of curved points must be slightly less than R2, because the bogies don’t have a problem going through the normal R2 points. 

Quite possibly so, though I have not looked at a set track curved point. The LH and RH set track points' curved road is 'substitution radius' for the quoted radius, the sum of straight (tangent) sections and curved sections. The curved sections have to be smaller than R2 for the curved road overall to conform to the R2 plain track radius, and thus able to substitute for the plain track piece.

 

Inverting the matching radius plain track curve over the point curve may assist in detecting where the deviations occur.