Large Scale Central

Improving the operation of the Bachmann K-27

Problem Solving
#1

I would like to give credit to this idea to Terry Burr who’s idea I adapted in a slightly different way.

The Bachmann K27 has a fantastic equalized suspension that allows it to navigate fairly bad track. The downside is that it can sit back on its rear with the result that the pilot and front driver can lift from the track.

Weight was added to the front of the second production which helped a lot but did not solve the problem.

Terry’s fix was to place a spring on top of the gear box to try to force more pressure on the front driver and pilot.

I have implemented a slightly different solution that has the same effect.

I placed a very short piece (between 1/16 and 1/8 inch) of 1/”16 brass rod inside the two axle springs of the 4th driver. This slightly lifts the rear end and makes it much more difficult to lift the front end.

It takes around 20-30 minutes to take out the 4th driver and perform this modification but is very simple as the 4th driver can be removed without removing any of the other drivers.

I tested this on one of our Ks and the result was very positive. I would be interested in the result of others who try the same approach.

Stan Ames

#2

Stan,

Being as I have never had my K apart, can you elaborate a bit on the “inside the two axle spring” statement. This sound to me like you are limiting the travel (compression) of the springs.

Bob C.

#3

Bob

Because of the weight of the K. In normal operation the springs are compressed, i.e. the springs are not strong enough to lift the locomotive. Instead when the locomotive is lifted slightly (such as uneven track) the spring forces the driver back on the rail.

As it comes from the factory the tendency is for the locomotive to rock between its 3rd and 4th driver. The concept is that by lifting slightly the 4th driver the rock will move to the 4th driver requiring more force to lift on the front driver and pilot

Drivers 1,2 and 4 have 4 springs each. 2 are on the frame just underneath the bearings one on each side, and 2 are further towards the center for the power pickup.

By using spacers to lift slightly the rear end of the locomotive, it takes more force to lift the front part of the locomotive with the result that the spring on the pilot stays compressed more and therefore does its job better. There is still enough spring distance on the 4th driver to maintain equalization.

When you turn the locomotive upside down there are small plastic strips holding the drivers in the frame. The rear 4 screws remove the rear strip to gain access to the 3rd and 4th driver. You also have to unscrew the screw holding the center rigging before the 4th driver can be lifted out. I also first remove the side rod from the 4th driver. Lift the driver slowly so as not to lose the springs.

This is still a concept under experimentation and I welcome feedback from others who try the same idea.

Stan

#4

Stan

Can You get us a pic if you go back to work on it?

#5

Stan,
I understand the balance issue, moving the sprung center of gravity forward providing more down force on the forward portion of the frame by stiffening the rear springs. What I am unclear on is, is the spacer inside the inner diameter of the spring, or is it in between the spring and the frame?
I would interpret this in this way. If the spring in inside the inner diameter of the spring, the rod will allow the spring to act in a natural fashion until it contacts the spacer, therefore lengthening the maximum compression (shortening the compression travel). If the spring is in between the spring and the frame, it will generally perform the same function, but in this case the spring will reach total compression sooner (by the length of the spacer).
Bob C.

#6

Bob Cope said:

Stan,
I understand the balance issue, moving the sprung center of gravity forward providing more down force on the forward portion of the frame by stiffening the rear springs. What I am unclear on is, is the spacer inside the inner diameter of the spring, or is it in between the spring and the frame?
I would interpret this in this way. If the spring in inside the inner diameter of the spring, the rod will allow the spring to act in a natural fashion until it contacts the spacer, therefore lengthening the maximum compression (shortening the compression travel). If the spring is in between the spring and the frame, it will generally perform the same function, but in this case the spring will reach total compression sooner (by the length of the spacer).
Bob C.

Bob

Sorry for the delay. The spacers are placed INSIDE the inner diameter of the spring. Your second paragraph above is correct.

One key point. The spacer on each side needs to be the same length.

Hopefully in the next few weeks I will have time to do a second K and I will take photos.

Stan

#7

Stan,

Thanks for the clarification. I am sure I was not the only ‘confused one’. :slight_smile:

Bob C.

#8

From my observation of the K27 suspension, the difference between 1/16" and 1/8" is a lot.

Is the goal to have a tiny bit of suspension, before “contact”?

If so, what is the criteria?

Greg

#9

Greg,

Quoting Stan above:

This is still a concept under experimentation …

My misunderstanding was in HOW he was limiting the travel, not the concept of limiting the travel. I would interpret “under experimentation” to say that the concept is not completely proven and I believe that there may be differences in the how long may be based on whether you have an early version (single weight stack in the boiler) as I have, or a later version with the double stack as I believe it is Ken Brunt or David Russel.

Terry did his similarly, but instead of limiting travel, he found stiffer springs. Both methods will have pros and cons.

Bob C.

#10

I did understand you Bob, your questions were completely clear, I was hoping Stan would give some some criteria from his experiment.

I’d personally want springs with some progressive increase in force as opposed to a “hard stop”, but that is speculation on my part.

Regards, Greg

#11

Stan,

PING…how about an update on the progress on this project??

I am getting ready to do some major surgery to my K and would be interested in your results before I start.

Bob C.

#12

I have the earlier Aristocraft K-27 in brass so can only make a general comment .

Would it not be better to put a spring on the trailing truck to stop the back end dropping ?

Mike Brit

#13

San,

PING again. Do you happen to know the diameter of the springs?

Bob C.

#14

Mike, mine is currently in the box. My requests are based on Terry’s reworking his with very positive results. I do not know if a heavier spring in the trailing truck would do the trick. Possibly an additional shopping over the winter months. Currently doing a battery, R/C, sound installation to also include Rodney Edington’s gear reduction, removal of smoke unit and fan, and locking of #1 and #4 axles. Currently no plans for additional weight, but again that may come later.

Bob C.

#15

Mike Morgan said:

I have the earlier Aristocraft K-27 in brass so can only make a general comment .

Would it not be better to put a spring on the trailing truck to stop the back end dropping ?

Mike Brit

Mike, If your K27 is brass, surely you mean the Accucraft version? N’est-ce pas?

#16

Oi , Tone ,

We are allowed a senior moment a week .

That was mine . You are right of course , silly me . Thanks for pointing it out , it reminds me to take more care and read what I’ve written .

The Accucraft K27 that I got had no instructions in , and with its full on board sound system it drove me crazy ; every time it moved , bells clanged and whistles blew . I went back to the shop that sold it and he said I must have lost them . He then lost a customer and Garden Railway Specialists at Princess Risborough came to the rescue . They really are most helpful . Using the instructions I stopped the offending noises and the loco is now a pleasure to watch .

Anyway , looking at the rear pony truck , I am convinced that a sprung truck would alleviate the problem outlined above .

I am not being a smart ass here , I believe that is the purpose of the leading and trailing trucks on any loco , to spread the weight . That is the explanation given for them in a few Encyclopaedia , plus the weighted truck leads the loco into sharp curves .

Mike Brit

#17

MY AccuCraft K-27 has a switch in the tender filler cap, where the battery charging jack is also located.

It has an ‘on’ and an ‘off’ position.

I simply select the one I feel like at the time…

tac

#18

tac Foley said:

MY AccuCraft K-27 has a switch in the tender filler cap, where the battery charging jack is also located.

It has an ‘on’ and an ‘off’ position.

I simply select the one I feel like at the time…

tac

Why pay over £2000 for a loco and not use its facilities ? It would be like using an SMLE Mk 4 without the mag .

Mike Brit

#19

With a switch I have the choice whether or not to annoy other folks with the sound. I’m deaf, so it’s a meh to me.

Bleeve it or don’t some folks are really annoyed by the sounds a locomotive makes on a small layout - the real thing appears from the distance, and gradually goes back into it - on a small layout the darn thing just comes around again.

tac
Ottawa Valley GRS

#20

tac Foley said:

With a switch I have the choice whether or not to annoy other folks with the sound. I’m deaf, so it’s a meh to me.

Bleeve it or don’t some folks are really annoyed by the sounds a locomotive makes on a small layout - the real thing appears from the distance, and gradually goes back into it - on a small layout the darn thing just comes around again.

tac
Ottawa Valley GRS

Tac , the bells and hooters (I wish) caused my miserable sod of a neighbour to complain . Fortunately , transporting of anti-social sods to Australia is still in vogue and he is probably annoying half the Antipodes now .

Mike