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Jack Benson

Bachmann N class - unintended 'beat'

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The venerable Bachmann N is a west country staple. However we have never encountered a really smooth runner, ours has a very audible 'beat' that ries/falls with speed, it visibly surges and runs much better after a few minutes trundling around Beaminster Road. The latter sympton is odd as we do not touch the throttle and yet it begins to increase in speed - odd.

 

So we have started the usual checks, no wheel wobble, quartering seems OK and we are not DCC but we are baffled.

 

Are Bachmann N's renowed for running quirks? Understandly, their age is a factor, we don't expect modern performance from a 25+ year old design.

 

Cheers and Stay Safe

 

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Hi,

 

Forgot to ask how to remove the loco body? The front fixing screw is hidden under the pony truck but even after removing the two screws at the rear under the cab, it is solid.

 

Cheers and Stay Safe

 

IMG_1393.JPG.56ae14eaafc51e4d6fa90be7507c010d.JPG

 

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4 hours ago, Jack Benson said:

Forgot to ask how to remove the loco body? The front fixing screw is hidden under the pony truck but even after removing the two screws at the rear under the cab, it is solid.

 

 

The screws you mention hold the cab in place, not the chassis. The second screw (as well as the one under the front wheels) is the one arrowed in this picture.

 

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5 hours ago, Jack Benson said:

, it visibly surges and runs much better after a few minutes trundling around Beaminster Road. The latter sympton is odd as we do not touch the throttle and yet it begins to increase in speed - odd.

 

 

Be sure that all the original grease is removed from the mechanism and relubricate with only a drop of oil. Take care, though, making sure as many pieces go back in as you took out!

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5 hours ago, Jack Benson said:

The venerable Bachmann N is a west country staple. However we have never encountered a really smooth runner, ours has a very audible 'beat' that ries/falls with speed, it visibly surges and runs much better after a few minutes trundling around Beaminster Road. The latter sympton is odd as we do not touch the throttle and yet it begins to increase in speed - odd...

Only ever had one to play with, and it didn't have a beat of this description. Other stuff to look at on the model: a piston rod too long for the cylinder hole, stuck or stiff action on the sprung driving axle (distant memory, think it had one).

 

5 hours ago, Jack Benson said:

 

Are Bachmann N's renowed for running quirks? Understandly, their age is a factor, we don't expect modern performance from a 25+ year old design...

The quirk was the original loco to tender linkage which was a camming design, of needless derailment causing complexity.

 

The good stuff: if it is an early release then every time I have been able to compare the 5 pole Buhler motor that Bach launched with, to the later 3 pole Kader motor subsequently fitted on the same chassis, there was no doubt that the Buhler was the more refined in DC operation. (Happily a good decoder completely masks the difference.)

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IIRC Branchlines once offered a worm wheel so that a Mashima motor could replace the original can.

 

The model is really stiff, absolutely no side play in the two rear coupled axles and I am sure that a 'fix' was discussed for the loco/tender coupling.

 

Thanks

 

Cheers and Stay Safe

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Posted (edited)

I have 3 of the N class - 2 BR and one SR - and all are sweet runners.

I penned an article many years ago on fixing the derailing tendencies of the straight-sided tenders on earlier models, involving a combination of increasing vertical play in the centre axle and rebalancing the weight distribution, plus allowing slightly more vertical movement in the tender coupling. It is still available on the SEMG site, although my diagrams are a bit naff. You can read it here: http://www.semgonline.com/model/ntender.html

Edited by SRman
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On ‎28‎/‎06‎/‎2020 at 20:29, Jack Benson said:

...The model is really stiff, absolutely no side play in the two rear coupled axles...

That's probably the cause of the beat. I would have the keeper plate off and restore both axles free movement.

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Ours has always had a rhythmic thump as if the quartering is out.  It doesn't get used much as the wheels look much too small compared to GWR 5ft 8" wheeled locos, and it would have trouble pulling the water off a ducks back.

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49 minutes ago, DavidCBroad said:

Ours has always had a rhythmic thump as if the quartering is out.  It doesn't get used much as the wheels look much too small compared to GWR 5ft 8" wheeled locos, and it would have trouble pulling the water off a ducks back.

I have half a dozen Ns, all but one bought secondhand on ebay. They have had very little TLC beyond oiling the rods, are currently doing most of the work on the layout, and happily walk away with 9 Hornby Maunsells. 

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I don't have an N Class, originally because I was put off purchasing due to reported Mazak Rot problems years ago. See pinned topic at the head of this section.

The problem appears on 'The List of affected models'  described for " Bachmann 31-152 Southern N Class 31813 - Mainframe disintegrates".

I don't know if that was exclusive to the particular model, but another early symptom of Mazak problems has been generally described as 'swelling of chassis castings, causing axle journals to close around the axles making movement stiff.'

 

I sincerely hope this isn't the problem being encountered by the OP, but might be worth trying to check for.

 

Regards,

 

               John

 

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I have had no Mazak problems with my N Class locos, in contrast to Hornby T9s, bought new at the same sort of time - a decade or so ago, so newer than any of the Ns - at least two of which, 312 and 314, have failed. 

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The Mazak rot seems to be confined to  N class Cat.no  31-152  N class No. 31813, it is the footplate  that is affected, Bachmann will supply a  replacement footplate free, my one was OK when I took it out of the box after a number of years to fit a DCC Decoder, once the body securing screws were tightened, the footplate disintegrated before my eyes, when I brought the loco the original one the dealer opened to test the smoke deflectors fell off,  I have brought a number of the Mazak Rot affected models some for the tender, others for the chassis to replace locos with damaged chassis/valve gear brought cheap on auction sites.

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