Hornby A3 Motor change and added weight

[westaust55]

My Hornby A3 "Flying Scotsman" in NRM LNER format (bought around 2013) has always suffered from a lot of wheel slip when pulling a rake of 6 coaches in a 600 mm radius curve.

For information, my Hornby A4 "Great Snipe" does not exhibit the same wheel slip problem with the same or other rakes of 6 coaches.

 

The A3 has also been a bit jerky under DCC control when operating at slower speeds - less than speed step 10.
Note that a set my decoders using the speed table such that the scale speed (mph) = speed-step / 2 for express passenger locos and = speed-step / 3 for other locos

Early September 2019 I noted that the A3 was also now very noisy (scraping sounds) and even more jerky even at higher speeds.

 

Cleaning the wheels and some light lubrication to axles, connecting rods and even the motor bearings and gears did not solve the noise and jerkiness.

Eventually I removed the intermediate gear and ran the motor alone and found it was noisy (scraping noises) at higher speeds.

 

I decided on a bit of research before buying a replacement Hornby X4026 direct replacement 5-pole motor (refer Hornby Service Sheet HSS 388).

Having previously (March 2019) replaced the 3-pole motors in two Hornby D16/3 locos with motors intended for the Hornby K1 that were 5-pole plus flywheel resulting in far better slow speed running I looked for an alternative to the X4026.

 

From photos the motor (part X6711) for the Hornby Crosti 9F (loco R3273)  appeared to be the same plus a flywheel at the non-gear end. Hornby and many websites were silent on whether this was a 5-pole motor however a couple of Hornby retain outlets did mention 5-pole in the description for the Hornby Crosti 9F.

I took a chance and ordered a Hornby X6711 from Peters Spares in the UK which duly arrived a week ago. I also as a precaution ordered a spare set of the original A3 motor retaining parts in case my change-out idea proved unsuccessful. Comparing the X4026 and the X6711 motors externally they were the same dimensions. Using a torch and counting the pole segments found both were the same - that is 5-pole.

 

This weekend I removed the original X4026 motor from the Hornby A3, modified (cut a slot in) the rear motor retaining so as to allow it to slide over the motor shaft between the motor housing and the flywheel.

The X4026 also have two parallel faces on the sides of the part where the rear of the motor body sides into the rear retainer bracket whereas the X6711 is circular so a judicial easing of the retaining bracket for a good fit.

Then it all went together beautifully. A test run and there was no further sounds and there was no jerkiness at slow speeds.

 

I also undertook a  further minor modification while I had the A3 apart to try and improve the traction and prevent wheel slip when pulling a rake of 6 coaches.

The A3 chassis has a location on top between the front and centre drivers where a decoder could be installed - albeit that the actual 8-pin decoder socket was installed in the tender.

I removed the two stubs intended to hold the decoder socket and in that space placed some steel strips that totalled 20 grams. This combined with 10 grams increase for the flywheel (behind the rear drivers) resulted in a total increase of 30 grams weight.

This has proved to be sufficient to:

(a) prevent wheel slip when pulling a rake of 6 coaches in a 600 mm radius curve, but

(b) if one holds the tender stationary the loco wheels will still slip so that in operation an unforeseen event causing the loco to physically stop cannot stall the motor and potentially lead to a burn-out of the motor windings.

 

Various threads on various websites are mixed on the topic of adding extra weight to locomotives.
Some folks claim it should not be done - primarily because it could overload the motor and cause a motor winding failure (overheating)

Others propose quite significant additions in weight - suggesting they add weight even around 150 grams in some cases.

Some do rightly highlight the need to keep or improve the loco balance with the added weight over the driving wheels - extra weight in the smokebox can be detrimental and reduce the traction of the rear wheels.

I understand that the DCC Concepts "PowerBase" is in fact steel segments placed under the track with a magnet attached to the loco to increase adhesion of the wheels - akin to the old (1960's era) Hornby "Magnahesion"

 

The conclusion from my perspective is that:

(a) changing out the Hornby X4026 motor to an X6711 (5-pole with flywheel) results in smoother slow speed operation, and

(b) a little extra weight (say 30 grams = ~ 1.1ounce) helps prevent wheel slip pulling a rake of 6-coaches in a 600 mm radius curve.

 

I have attached a number of photos here to show what I have done.

 

The Hornby A1 and A4 series also apparently from the respective Service Sheets use the X4026 motors and thus tentatively, subject to space behind the motor, the same motor change-out could be undertaken.

Edited November 3, 2019 by westaust55

[GWR-fan]

I looked into replacement Hornby motors and thought that the following may have been useful for the A1 - A4 range and far less than a Hornby spare.    Looks like a replacement for the Crosti as well.

 

https://www.ebay.com.au/itm/DC-12V-24V-5-Pole-High-Speed-Rotor-Mini-Motor-2mm-Dual-Shaft-DIY-RC-Car-Boat/113232528640?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

 

From a different supplier - 

 

https://www.ebay.com.au/itm/DC-12V-24V-22200RPM-5-Pole-Rotor-Motor-High-Speed-2mm-Dual-Shaft-Carbon-Brush/283139835200?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

 

 

Edited November 3, 2019 by GWR-fan
Additional info

[micklner]

Was the test run with the body on?  Clearances betwen the flywheel and backhead must/might be tight ? Addiing lead strip to the chassis would be heavier than steel.

[34theletterbetweenB&D]

7 hours ago, westaust55 said:

My Hornby A3 "Flying Scotsman" in NRM LNER format (bought around 2013) has always suffered from a lot of wheel slip when pulling a rake of 6 coaches in a 600 mm radius curve.
For information, my Hornby A4 "Great Snipe" does not exhibit the same wheel slip problem with the same or other rakes of 6 coaches...

 

Various threads on various websites are mixed on the topic of adding extra weight to locomotives.
Some folks claim it should not be done - primarily because it could overload the motor and cause a motor winding failure (overheating)

Others propose quite significant additions in weight - suggesting they add weight even around 150 grams in some cases.

Some do rightly highlight the need to keep or improve the loco balance with the added weight over the driving wheels...

The mechanism in the current Hornby A1/A3/A4 is the same, so the models should all perform pretty much alike. Check out the tender off your A3 temporarily behind the A4 and see if that's what is causing the poor haulage. Hornby tenders can be very draggy, the pick up wipers are like brakes, I take them off. Weighted up (see below) the pick up from the coupled wheels is solid as a rock.

 

Adding weight. My A4s are weighted to 600g balanced in the centre of the coupled wheelbase so they will work a 25 coach train (Silver Link took 25 up the 1 in 105 out of Kings Cross unassisted) and I have had no motor trouble in something like fourteen years since my first purchase. (The A3s are a little lighter.) If the wheels will slip when the model is held back, there will be no harm. It is necessary to ensure that all working parts that take load are well lubricated is all.

[westaust55]

22 hours ago, micklner said:

Was the test run with the body on?  Clearances betwen the flywheel and backhead must/might be tight ? Addiing lead strip to the chassis would be heavier than steel.

Hi Micklner,

 

Initial test was without the body but then run with the loco fully assembled.

 

With the Hornby X6711, the flywheel is axially about 7.5 mm long and taking into account the space between motor body and the flywheel it protrudes 11.5 mm beyond the motor housing.

I have prior to purchase determined that I had approx. 15 mm maximum possible length so I have around 4 mm clearance to the backhead.

 

The X6711 rear shaft does not go all the way through the flywheel (about half way I believe) so roughly, the shaft extends 8 or 9 mm  from the rear of the motor body.

That is shorter than the 13 mm in the details in the dimensioned images for the Ebay items GWR-fan has mentioned.

Though I believe that Ebay item would still fit.

 

Agreed that lead is 1.7 times the S.G. of steel however, I had steel strip of the right width to hand and what I have done appears to be sufficient for my situation.
There was sufficient space above that I could have easily added at least 2 or 3 more pieces of steel strip if needed for say another 10 to 15 grams weight.

 

 

On ‎03‎/‎11‎/‎2019 at 19:37, GWR-fan said:

I looked into replacement Hornby motors and thought that the following may have been useful for the A1 - A4 range and far less than a Hornby spare.    Looks like a replacement for the Crosti as well.

 

https://www.ebay.com.au/itm/DC-12V-24V-5-Pole-High-Speed-Rotor-Mini-Motor-2mm-Dual-Shaft-DIY-RC-Car-Boat/113232528640?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

 

Hi GWR-fan,

Agreed that those motors are about quarter the price.  One must also check the prices. I found prices between a couple of UK retailers selling the X6711 to be up to a factor of 4 difference !!

In my case I would also have had to locate a suitable flywheel and need a puller to remove the worm drive from the existing motor and then a careful job to fit the wormgear and flywheel to the far cheaper motor.

The extra parts (flywheel) and tools (puller) would have reduced the cost advantage for a 1 off modification. Nevertheless it is good to know that there are cheaper alternatives out the for the future.

 

 

[31A]

I'd like to thank Mr. Westaus55 for this suggestion, as I have just done the same to one of my A3s and am very pleased with it.  The one I picked had been running poorly for a while and then failed completely with a split drive gear (on the same shaft as the worm wheel), so I replaced that but the running was still 'lumpy' so I also replaced the driving wheels with new ones.

 

But the replacement motor has resulted in a much more smoothly running loco, especially at slow speed.  I found I didn't need to file the upper sides of the motor bracket to accept the new motor - maybe the motor I got was slightly different?

 

Also, as well as removing the DCC circuit board, which I didn't need, I also took out the cast block it sits on and replaced it with a coiled piece of sheet lead inside the boiler, not extending any further forward than the cast block so as not to upset the balance.  So far I've only tested it running light so not sure what improvement the extra weight will bring in terms of haulage, but it's certainly a lot heavier than the standard A3s!

[atom3624]

The flywheel is a dual edged sword, as it were.

 

It can aid over areas of poor pick-up (points, etc) and particularly with locomotives with loco-only pick-up.

 

I would NOT include the flywheel - which permits smoother slow starts (flywheel builds in too much inertia).

I would look into including additional tender current pick-ups to compensate for the smooth passing over points.

 

Al.

[GWR-fan]

On 05/11/2019 at 00:36, westaust55 said:

Hi GWR-fan,

Agreed that those motors are about quarter the price.  One must also check the prices. I found prices between a couple of UK retailers selling the X6711 to be up to a factor of 4 difference !!

In my case I would also have had to locate a suitable flywheel and need a puller to remove the worm drive from the existing motor and then a careful job to fit the wormgear and flywheel to the far cheaper motor.

The extra parts (flywheel) and tools (puller) would have reduced the cost advantage for a 1 off modification. Nevertheless it is good to know that there are cheaper alternatives out the for the future.

 

 

 

I have purchased gear pullers in the past and I have usually found that either the clamping jaws separate or the pin pushing on the end of the shaft will bend.  My simple method (and maybe considered a little butchery) is to insert a pair of long nose pliers between the worm gear and the end of the motor and then clamp the handles of the pliers with elastic bands to keep the jaws closed tight.  The motor is then inserted in a vyce with just sufficient clearance for the motor to move and the jaws of the pliers placed across the opening of the vyce jaws.  A suitable pin punch or perhaps blunted nail is then placed on the upper end of the motor shaft and the shaft is then hammered through the worm gear.  The gears are usually very tight and if a dud motor a little heat may need to be applied to the brass worm gear.  To fit the gear open the vyce sufficiently to insert the motor and worm gear and then carefully close the vyce jaws, holding the motor steady with the free hand.  This will allow the worm to slide onto the shaft.  On finer motors with 1 mm driveshafts there is the possibility of bending the motor shaft while inserting the worm gear.  2 mm shafts have given no trouble. 

Edited March 3, 2020 by GWR-fan
Grammar