Hornby mallard wont reverse

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joshv8
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Hornby mallard wont reverse

Postby joshv8 » Sat Jan 12, 2019 1:52 pm

Pulling out some of my locos to run around our slowly evolving layout Maybe 6- 7 years ago I acquired a hornby loco drive mallard. These were I believe a super detailed item, Chinese manufactured, dcc ready. It was new at the time but has pretty much been in storage.
I have not fitted a dcc chip and am running just a dc setup.
Its been around the track pulling coaches, runs lovely at slow speed.
We tried to reverse it for the first time onto a rake of coaches tonight and it thinks about it, jolts slightly rearward, stops then I can hear the motor just humming. Half power reverse it will run for a few inches then stop, then run a few inches then stop etc etc. It will run backwards full power reverse.
The problem definitely seems to be electrical. Has anyone got any thoughts?

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Bufferstop
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Re: Hornby mallard wont reverse

Postby Bufferstop » Sat Jan 12, 2019 2:37 pm

Josh - before committing to "it's electrical" examine the driving wheels and the pick up wipers after lifting the loco off the track whilst it is refusing to reverse, you are looking for a wiper which has gone between the spokes and is jamming the motor. It might be helpful to use a magnifying glass. If you find one straighten and adjust it so that it is running on the wheel rim just above track level. If you've subsequently run it in reverse at full power you may find it bent over backwards. If this is not the cause then look for other mechanical problems before looking for electrical ones.

First rule of electrical fault diagnosis "Make darned sure it's not a mechanical fault before unpacking the test meter."
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Bigmet
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Re: Hornby mallard wont reverse

Postby Bigmet » Sat Jan 12, 2019 3:19 pm

Another likely cause is in the gear train. For example the pinion driven by the worm moves sideways slightly when the motor direction reverses, and this can lead to this kind of unidirectional stop-go effect. There are further potential causes such as a split in a gear or a poorly profiled/damaged tooth.

If the wheels make a full rotation between each 'stop' in reverse - that is always stops with the wheels in the same position - then most likely the problem is on the wheelsets such as the pick up wiper catching, or the axle gear. But if the wheels stop at varying positions, you are probably looking at a problem elsewhere in the gear train. The difficulty there is that you have to be very careful to get access inside as the screw that holds the combined worm cover and motor clamp on is very apt to strip the thread in the mazak.

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joshv8
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Re: Hornby mallard wont reverse

Postby joshv8 » Sat Jan 12, 2019 10:53 pm

John and Bigmet, thankyou.
I must admit the avenues you've given me to follow aren't ones I had initially thought of.

I think your right John, the magnifying glass may be of some assistance. Ill start with the wipers as thats mostly the easiest check then move on through the suggestions.
Check all mechanical before electrical seems like fair advice.

The only one concern Ive got is there's a connecting rod off the wheelset that attaches to the body. Im not sure on the real life prototype but am I correct in assuming its a modelling of the reversing lever?
To remove the body from the chassis it needs to be disconnected. Ive never had to remove the connecting rods from a wheel set before. From parts breakdowns Ive studied I can just undo the crank pin holding the connecting rod to the wheel to release it?
cameringo_20190113_083521-800x450.jpg


Ill be sure to update on my findings.
Once again, thankyou
Last edited by joshv8 on Sun Jan 13, 2019 1:22 am, edited 1 time in total.

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joshv8
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Re: Hornby mallard wont reverse

Postby joshv8 » Sat Jan 12, 2019 11:33 pm

Seems when you look in the packet you find some instructions and answer your own questions.
20190113_092932-800x600.jpg

Now I need to realise what tool I use to remove the crank pins.
And apparently the assembley is a lubricator or speedo. Id love to know which.

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Re: Hornby mallard wont reverse

Postby End2end » Sun Jan 13, 2019 1:41 am

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Bigmet
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Re: Hornby mallard wont reverse

Postby Bigmet » Sun Jan 13, 2019 7:59 am

You should be able to source local nutspinners. 2.5mm across the flats of the hexheads is what Bachmann and Hornby mostly use. (2mm on the 08s, and 3mm on the connecting rod crankpin of Bachamnn's ROD/O4 2-8-0.) Whether the various others now entering the steam loco market conform I cannot yet tell...

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joshv8
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Re: Hornby mallard wont reverse

Postby joshv8 » Sun Jan 13, 2019 12:06 pm

Good information Bigmet, and thanks End2end. Ill be sure to pick up the correct tools. So far ive managed to remove the crank pin with a small shifting spanner and a lot of undoing by hand.

The wipers are not fouling on the wheels. I can see what is happening however now the bodys off. The gear set moves when going from foward to reverse allowing the gears to bind. Why Im not sure.....

The initial gear set off the worm drive seems to have a split through it
cameringo_20190113_221244-800x450.jpg


Apparently the parts x8849. As far as I can tell its not available from hornby and replacements online are 26 teeth.... I count 25 on mine.
The crack in the gear seems to allow it to walk back and forth on the drive shaft, missaligning the gear set.
Pretty dissapointing considering its basically had 0 use except for a 2 minute run out the box when purchased to make sure it did run. Otherwise its just sat until now. One would assume this was cracked during manufacturing?

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Re: Hornby mallard wont reverse

Postby Bigmet » Sun Jan 13, 2019 11:06 pm

Probably a moulding defect. (I live near the specialist plastic gear manufacturer Davall Gears, and they lay great stress on the process control required in the moulding process - among much else - for moulded gears to be stable 'for life'.)

Contact Hornby time I think, and explain the gear has failed essentially unused.

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Re: Hornby mallard wont reverse

Postby GWR_fan » Sun Jan 13, 2019 11:59 pm

The idler gear split is unusual. Normally in my experience it is the driven gear on the axle that splits. I have seen gears repaired using superglue and baking soda although this would be only if a replacement could not be sourced. The idler gear is most likely a common gear across the range, however, in true Hornby fashion will have a different part number for each specific location.

The cracking will occur even on a zero time model. Stresses raised when pressing on the axle shaft cause it to crack, along with a poor choice of plastic to mould the gear from. Ideally, an engineering plastic should be used, such as Delrin, as was used many years ago on U.S. manufactured locomotives and I cannot recall even a single cracked gear from that era on "h.o." models. Most manufacturers have had their "split gear" moments over time as recycled plastics become more common.

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joshv8
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Re: Hornby mallard wont reverse

Postby joshv8 » Mon Jan 14, 2019 12:16 pm

Im trying to find i hornby as a recommended repairer for their products here in Australia but no dice so far. I might have to make an international call.

GWR_fan interesting on the plastic. Im familiar with Delrin having had timing curve bushes machined from it on the U.S for automotive distributors. Im guessing this is falling in the Chinese rubbish basket. They'll make you the greatest stuff in the world but if you wont pay the dollars for manufacturing they'll also cut every corner and use poor materials to produce what you want at the cost you want.

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Bufferstop
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Re: Hornby mallard wont reverse

Postby Bufferstop » Mon Jan 14, 2019 4:59 pm

Peter's Spares has 52 in stock, probably a different part number but it says for China built Mallard loco drive. It's small enough to get it airmailed.
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joshv8
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Re: Hornby mallard wont reverse

Postby joshv8 » Mon Jan 14, 2019 7:31 pm

Bufferstop wrote:Peter's Spares has 52 in stock, probably a different part number but it says for China built Mallard loco drive. It's small enough to get it airmailed.

Thanks John,
Ive ordered one, its in the mail!

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joshv8
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Re: Hornby mallard wont reverse

Postby joshv8 » Thu Jan 24, 2019 12:46 pm

Bufferstop wrote:Peter's Spares has 52 in stock, probably a different part number but it says for China built Mallard loco drive. It's small enough to get it airmailed.


The gear set arrived yesterday from Peters spares. Part number x8849. Worked perfectly. Beautiful slow reverse. Slow foward has the ever slightest jolt to it but when I get a chance ill fiddle with gear alignment. These gears are much better made then the factory hornby ones. They have a sleeve to stop the gears/ axle from being able to walk side to side in the gear casing, the hornby ones had a lot of play. Really impressed thanks John and everybody !

Bigmet
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Re: Hornby mallard wont reverse

Postby Bigmet » Thu Jan 24, 2019 4:18 pm

Keep in mind that the jolt in moving forward may not be the gears at all. Quite a risk in working on a loco with outside cylinders and valve gear is that a rod gets slightly bent and then catches on either another moving part or on fixed structure. If that is the cause it will only happen at the same position(s) of the driven wheels.


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