Bachmann K27 bogie woes

[KeithT]

Yesterday was a frustrating one. I got out "the beast" only to find that one of my footbridges had 'dropped', either that or the loco had grown since I last used it, entailing taking a jig saw to the bridge. :wits: Next one of the cab window blinds fouled a second bridge. Fortunately in both cases the loco was only crawling - the slow running is superb.
It wouldn't have been at all bad if it stopped at that but the K27 insisted on derailing at numerous places even in a straight line. My recent reballasting and fitting of railclamps must be a contributory cause but it happens mainly because the pony truck on the K27 is so unforgiving. In the past I chamfered the corners of the front coupling support bracket to reduce fouling but that has proved to be insufficient.
There are several things happeneing - or not!
The lateral travel on the bogie is restricted due to the flanges fouling the coupling fixing plate; the truck has insufficient weight to remain 'planted' on the track but worse still seems to be the inadequate vertical play in the truck. On even apparently level track I can see a wheel lift. There is a pressure spring but it is ineffective.
The loco has much vaunted springing on the drivers and trailing truck but this problem arises due to the sheer length of the wheelbase which the pony truck cannot accomodate.
Initially, I will add some lead weight and may try to reduce the depth of the small bracket which house the inner end of the "V" shaped pony truck frame but I imagine this will have minimal effect.
I can't work out what the central metal bar which passes through the "V" is for. Certainly it isn't holding the truck down

Before I begin hacking (cringe) has anyone had and tried to resolve the problem?

EDIT: I think I have just discovered what the 'central metal bar' is - it, is an equalising lever invented by William S Hudson in 1864.
Well, Mr H it doesn't work!!!!

 

[PaulRhB]

Mr Hudsons lever will only work if there's enough play to allow it to work mind you
I've not got a K27 but usually I try to open out the bogie pivot to allow a bit more slop and vertical movement. Padding up the area where the compression spring is, with thin plasticard shims fixed with double sided tape, is also often easier than putting in a harder spring in. Lateral movement is more of a problem due to fouling other detail bits as you mention as it usually means grinding bits that are visible but I suspect as the derailing was minimal before the track alterations that it's vertical rather than lateral problem anyway.

 

[KeithT]

Mr Hudsons lever will only work if there's enough play to allow it to work mind you
I've not got a K27 but usually I try to open out the bogie pivot to allow a bit more slop and vertical movement. Padding up the area where the compression spring is, with thin plasticard shims fixed with double sided tape, is also often easier than putting in a harder spring in. Lateral movement is more of a problem due to fouling other detail bits as you mention as it usually means grinding bits that are visible but I suspect as the derailing was minimal before the track alterations that it's vertical rather than lateral problem anyway.

Yes lack of vertical movement is the prime issue. These parts of the loco are solid metal so I can see me having to do a fair amount of v careful grinding/filing to get more play. The spring fitted is very feeble, I might try a stiffer one but as it operates on a central pin it doesn't apply prssure specifically where it is needed ie over the wheels and just 'slops' one way or t'other.
I intended posting a pic but the camera seems to have gone awol for the minute.
Found it!
First pic shows the fouled coupling plate and the others the V bracket and Hudson bar.

 

[PaulRhB]

Looks like the truck is too snug a fit in the pivot on that metal bar, filing a indent into the truck frame or thinning the edges of the pivot retaining plate might allow more movement vertically and not show up once assembled. Possibly a bigger diameter soft spring might work or using two soft springs, one just inboard of each wheel, with a rubbing plate glued to the top of both to stop them snagging and bending over. Easier than making two mini plungers too.
The balance beam may actually start to work if the pony truck has enough movement.

 

[Woderwick]

Similar to Pauls suggestion, Is it possible to put a pair of shims/washers between the pony retaining plate and the crossmember it is screwed too, in order to free it up a bit ?

 

[PaulRhB]

Good idea Wod, but be careful of the clearance to the railhead as Bachmann tend to get very close to it with underframe bits.

 

[KeithT]

Thanks for the suggestions. I like the idea of a shim rather than 'surgery' at this stage.
I did consider replacing the cross member with a flexible plastic strip but the member looks too structural for that.
The loco is so heavy, unwieldy and fragile in places that I feel that I need an inspection pit to work on it!

 

[trammayo]

I just wondered - do the pony truck wheels hang down lower than the railhead (ie, lower than the driving wheels)? Maybe weight instead of springs is the answer. Springs, plungers, rubbing plates all cause friction. I presume lateral play is not a problem thats why I asked about the verticle deflection.

I run on tight curves with big haulers - weight was the answer to constant derailments and helped cure the Buddy Ls I was having the same problems with. Just a thought.

 

[KeithT]

I just wondered - do the pony truck wheels hang down lower than the railhead (ie, lower than the driving wheels)? Maybe weight instead of springs is the answer. Springs, plungers, rubbing plates all cause friction. I presume lateral play is not a problem thats why I asked about the verticle deflection.

I run on tight curves with big haulers - weight was the answer to constant derailments and helped cure the Buddy Ls I was having the same problems with. Just a thought.

That is a good point Mick, the pony wheels are only a fraction lower than the main wheels. The Hudson bar is one of the culprits , it has very little vertical clearance at it's fixed end added to which there is a bearing pin on the underside which presses onto a frame member and further restricts movement. One option might be to take the bar out altogether.
I have chamfered more off the coupling bracket but that will only help the lateral movement.
A strip of lead is waiting to be fitted to the V bracket.
I shall proceed further with care!

 

[Richie]

Hi Keith
Have had the same problem with my pony truck, it ended up breaking in three places from so many derailments :wits: Had Bachmann replace it with a new one . I have found that the Hudson bar does come out of it's slot when lifting the loco so i always check that it's in place when i put it on the track this has solved my derailments with the pony truck
Was at a friends at the week end he has 4 Bachmann K-27 and all suffered with this problem of the pony truck coming off .

 

[KeithT]

Hi Keith
Have had the same problem with my pony truck, it ended up breaking in three places from so many derailments :wits: Had Bachmann replace it with a new one . I have found that the Hudson bar does come out of it's slot when lifting the loco so i always check that it's in place when i put it on the track this has solved my derailments with the pony truck
Was at a friends at the week end he has 4 Bachmann K-27 and all suffered with this problem of the pony truck coming off .

I wonder if that could be the solution? Certainly it never happened that way originally.
I will find it difficult to check underneath each time I put it on the track, it seems to be getting more and more difficult just to lift it onto the track! :
EDIT: Pity, the Hudson bar is in the slot.

 

[Rhinochugger]

Briefly had a similar problem with my Connie at one spot.

Turned out that where the track had settled or the ground had heaved, or both, there was a dip, and when the back end of the loco dived into the dip, the front end pawed the air, and the pony truck floated away out of akignment with the rails.

My track is no way near perfick for level, but I made sure there was plenty of vertical play in the pony truck mount. The K27 mount doesn't appear to have the same amount of play. How about fitting spacers on those two bolts that hold the restraining top hat shaped bracket so that you space the bracket off its frame a tinsy winsy bit?

 

[KeithT]

Made some progress today in between looking after grandchildren.
I removed the truck and diconnected the equalising bar - with difficulty and filed away most of the bearing pip on the underside of the bar. I couldn't lay my hands on any suitable washers to use as spacers on the top hat retainer but I can always use scraps of plastic instead if necessary.
Before filing the pip the pony truck wheels only dropped down by the depth of the wheel flange , roughly 3mm. Not much when you consider the 37cm wheelbase. After the filing that was doubled. It still needs some lead adding to the "V" frame. I haven't had a chance to test it yet but I would be surprised if that was all I needed to do. Probably I will still need to try removing the equaliser bar. I can't see that it serves any real purpose in model form.