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Thursday, 21 April 2016

Mainline 42 Warship Clunking Noise Fix & More

Bachmann used the 1970s Mainline Class 42 Warship body with a few extra details for its own Class 42 and added their own chassis, motor and bogies. Both models are now obsolete, being only available from the after market. The Backmann is about twice the price of the Mainline on Ebay so, with no prior knowledge of what I now know is an appalling motor and gearbox design, I opted for the cheaper Mainline version.

The Ebay seller declared it was untested so there can be no cause for complaint when I ran the locomotive and wondered what the strange clunking noise was. A search for information revealed many comments about the overall poor performance of this model and revealed the cause of the clunking noise.

If you are thinking of buying a Class 42 then take my and everyone else's advice and pay the extra for the Bachmann model. If you have a clunking Mainline version then read on for solutions.

Split Final (wheel axle) Gear

That is the cause of the clunk and if you are unlucky then both axle gears may be broken. To get to the gears the bottom plate of the bogie has to be prised off by inserting a small, flat screwdriver between the bogie body and end panel of the bogie bottom plate and gently prise apart and pull down to release it. This can be done without removing the bogie from the body. The wheel axles can then be pulled straight out.

There is a deep depression in the gear shown circled in the photo caused by the mould tool ejector when it pushed out the part from the mould. This introduces a significant weakness in that area so that under load a split can occur, shown by the white line. That is enough to cause mis-meshing between this and the adjacent gear. Worst case the gear might start slipping on the axle.

This is a common fault, Fortunately replacements can be purchased.

Ultrascale offer a brass replacement, You may need to replace both gears as the number of teeth is one less. This is the most expensive option and on a long lead time when I checked.

On eBay I found a close match sold as a pack of five and being inexpensive with fast delivery I purchased this.

Mainline gear spec: 16 teeth, 8.72mm diameter, 2mm axle.
eBay Seller firstclass4u208 spec: 16 teeth, 9mm diameter, 2 mm axle.

The faulty gear is a two tier arrangement but only the outer teeth are used. The replacement part is a single tier and the eBay model is much thicker. What you have to do is cut it down to the same thickness as the original, i.e. overall thickness of the two tiers, and file the tops of the teeth to bring it down close to the 8.72mm of the original.

To fit the gear first remove a wheel by griping both wheels with combination pliers and twist whilst pulling apart. Eventually one or both wheels should come off the axle. Slide off the old gear and press fit the new gear. I did this in the jaws of a vice with a metal tube over the axle that rested on the gear. As the vice jaws close it pushes on the tube which pushes the gear along the axle. Once on it is possible to slide it into position with finger pressure. It is important to position it so it is always in mesh. Test this with both wheels and the new gear on the axle. Check the sideways travel of the axle in relation to sideways travel of the adjacent gear. Also check the meshing is not too tight compared with the original (file more off the teeth if it is).


You may find the new gear rubs on the base plate because of a raised gear stopper (shown white boxed). You'll need to Dremel/grind that away if necessary.

After I did all that I came across another supplier, Genisis Kits offering a pack of two inexpensive cast gears for the Mainline model. I have no experience of these and I suggest anyone wanting to buy to contact the business first to check stock availability.

Hot armature melting plastic

I was happy the new gear was doing its job but still found other performance issues, sometimes slow running on full speed or stalling. Eventually, the locomotive stopped but motor still running. Why? The spindle turns in a hole in the plastic body, not a proper bearing, and because of this the motor inherently runs hot causing the armature spindle to soften the plastic resulting in it moving out of true and the drive cog going out of mesh, let alone the coils snaring between the magnets causing the motor to lockup, and I'm sure all this lead to teeth being sheared off the centre large gear!

I fabricated a bearing from nylon sprue, opened out the spindle hole and glued the bearing in place. I only did this for one end as the other had not deformed. If you do this make sure the armature spindle spins freely in the bearing.

The gear with sheared teeth was potentially a show stopper. It is two tier 32/9 teeth, which is an unusual specification and none found in the market. The only solution it seemed was to scrap all this work and buy another warship for its motorised bogie. Even if a good one was found the chances are it will eventually fail too.

Some modellers have fitted the reliable Hornby Class 42 motorised bogie but I have cosmetic issues with it, like the brake blocks don't line up with the wheels .Others have fitted the body to a complete Bachmann chassis (May as well buy a complete Bachmann).

I decided to try and repair the missing teeth. Using nylon sprue again I fabricated an insert with file and razor saw and glued this into the gear (shown circled in the photo). Further fettling was required to ensure the two gears meshed freely.

To my surprise the repair held and I had a working locomotive again. Well almost, I find the locomotive needs to warm up to achieve full speed potential and even then its pulling capacity is only four passenger coaches *. I wonder if I should have fitted a bearing for the other end of the armature spindle? For now I have left as is but being concerned about a hot motor I glued on a heatsink designed for an integrated circuit (Maplin RN70).

* Postscript. The cause of this was the bearing axle hole being very slightly off centre placing the axle under stress, which then wore away the nylon making the hole larger and eventually going out of mesh. I replaced the nylon with a brass bearing fabricated from a brass screw shank and took great care to centralise its axle hole acurately. Loco now runs from cold to full speed without faltering and can handle longer trains. I also removed the heatsink as the motor does not get so hot.


One other thing to be aware of is the carbon brush springs. If you need to replace these then make sure they are not too long as the extra pressure on the brushes causes the motor to stop turning. Peters Spares sell replacement brushes and springs but their springs are too long in my opinion.

I'm not hopeful that what I have is a long term solution. I will be on the lookout for a good spare motorised bogie.

By the way, the extra material costs I incurred still makes my purchase far cheaper than a Bachmann.


It is a great looking model don't you think, evocative of the mid 1960s. This one, D824 'Highflyer', is reputed to be the first of its class to run on the Southern main line after the Western took over in 1963.















1 comment:

  1. Split gears is a very common fault with a lot of new models manufactured in China. Main problem is that moulded nylon or acetal shrinks, and it can only shrink so far on the steel/metal axle before it splits. Some new models have split gears within a very short period after manufacture and new out of the box! Solution is to use cut gears in cast nylon, but this becomes expensive, even if you can find somebody to do the job.
    North West Shortline in the USA does supply some replacement gear sets, but I doubt whether they would cover British outline models.

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