Motor mounting with Zamac Rot

[Dad-1]

Over the years I've read about certain models from certain dates having problems
of corroding (Zamac Rot), but as most of my purchases were new with the oldest from
around 2008 I'd not experienced any difficulties.
I suppose the good times had to come to the end !! I'm checking out a deceased friends
stock and cleaning up.
The T9, Ahh I'd heard they had problems and it sat on the track with the motor screaming,
but no motion. Internal check revealed the motor housing had corroded and couldn't hold
the motor onto the gears. Peters Spared used to do a replacement, but out of stock. Will
they be getting more - A question for them on Monday.
The immaculate and checking the wheels, probably never run, Railroad 9F wouldn't move.
Placed on a DCC track the motor hummed, but wouldn't run on '00'. I took to pieces and
found the motor housing was suffering decay and fouling the flywheel. Both mountings
were in a poor and distorted state. Somewhere at the back of my mind I recalled seeing
some reference to Hornby 9F's being affected so decided to look at mine all neatly tucked
away in it's box in the loft. The chassis rolled - Uhhh. Rolled on a flat table top ?? On stripping,
yes, mine also had rot in both motor mountings. This time rather than fouling the flywheel
it had allowed the motor to rise out of contact with the drive gear. I have run it since we moved
to Dorset, I think when I was doing tests to see what locomotives could negotiate 1st radius
curves, I'll have to check the FAQ section, but it's really of no concern that it was fine in 2014 !!

Peters spares, another to add to Mondays enquiry !!

Geoff T.

[Roger (RJ)]

I'll have to check my 9F now. Not been used in a while.



Edit

I must be luckky. Seems to be running OK, not had the top off to look for any rot.

[Bigmet]

There is a very useful list in the opening post, as a PDF here:
https://www.rmweb.co.uk/community/index ... dels-list/

If using the term 'zamac' it is helpful to also include mazak to help with future searches, interchangeable terms for this much used zinc based casting alloy.

The tender drive frame on Hornby 9Fs is on the list.

[Bufferstop]

Afraid that's the way of it. It's all down to what goes into the pot when they mix the alloy. That Hornby got blighted by it in the 21st Century is pretty rich. The original research into what causes it was done by the Ministry of Supply in the early stages of WW2 when Meccano expressed their concerns about producing some aircraft parts as they hadn't at that point solved the problem, pre-war Horby Dublo suffered a few failures, I've read that they scrapped a load of unused castings before recommencing production. Rovex were either aware of the research, or just lucky, as I never heard of failures of the spacing blocks in their loco chassis. So how come Hornby failed to insist on the same quality control when they outsourced production. There's a story, probably a myth, that one source of the problem was traced to the guy who tipped the bags of zinc into the melting pot, he is said to have torn the lead seals of the sacks and tossed them in along with the first batch.

[windcutter9f]

Afraid that's the way of it. It's all down to what goes into the pot when they mix the alloy. That Hornby got blighted by it in the 21st Century is pretty rich. The original research into what causes it was done by the Ministry of Supply in the early stages of WW2 when Meccano expressed their concerns about producing some aircraft parts as they hadn't at that point solved the problem, pre-war Horby Dublo suffered a few failures, I've read that they scrapped a load of unused castings before recommencing production. Rovex were either aware of the research, or just lucky, as I never heard of failures of the spacing blocks in their loco chassis. So how come Hornby failed to insist on the same quality control when they outsourced production. There's a story, probably a myth, that one source of the problem was traced to the guy who tipped the bags of zinc into the melting pot, he is said to have torn the lead seals of the sacks and tossed them in along with the first batch.

Meccano were producing the geodetic fuselage parts for the Wellington bomber,they couldn`t have these parts falling apart during operations.

Ray.

[Bigmet]

...There's a story, probably a myth, that one source of the problem was traced to the guy who tipped the bags of zinc into the melting pot, he is said to have torn the lead seals of the sacks and tossed them in along with the first batch.

No myth, that was a typical identified cause. (Lead is a 'poisoning' element of zinc alloys, and the usual culprit for Mazak rot, as it is so common in a wide range of industrial materials.) The cure for that particular cause is of course to cease using any lead in the alloy packaging. More difficult than it might seem, established 'custom and practise' at the alloy maker's factories had to be systematically driven out. (I had the valuable experience of working with a man who had been part of developing the wartime 'ABC' standards for Allied war production, and he had often been at the sharp end of such activity: and it was very rough work indeed by his description.)

...So how come Hornby failed to insist on the same quality control when they outsourced production...

They probably did, and most likely Sanda Kan were full of assurances that they knew how. But the Mazak cast components are typically sourced from small contracted suppliers engaged by the assembly factory, and how good is the control by the time the work is done there?. All of Bachmann, Heljan and Hornby fell victim to contaminated Mazak in the early 2000s (N class, class 47, class 30/31) and they weren't alone, it occurred in HO product for Europe and North America too.

And for all the knowledge in the UK, I have my FiL's 1942 production date naval dirk, and guess what? The handle is Mazak, and it's cracked and brittle, had begun failing by 1950! Knowing the problem cause is one thing. Eliminating it in a well established manufacturing environment quite another.

[Mountain]

Here is a question. If the issue is chiefly due to the differing standards that are used in the manufacturing process in the Far East then why do so many manufacturers not change their designs in the future to avoid using the material in the first place? It is more then possible not to use mazak as a material, or to only use it where if it did rot, it would not cause a problem. I am thinking of Lima diesels where the metal weight is positioned in such a way that if it was suseptable it is very unlikely to do any damage. Ok, they maybe made to an elderly design, but look how many are still plodding along today, and if they are not plodding along, they are repairable as it is usually a cog or something that has come out of alignment or something like that.

[Firefly16]

Why stop at changing the designs? Why not change the makers? In other words, bring production back to the UK. The T9 compares unfavourably with the two L1s I have, one of which, an ebay rescue, is now an E1. Both bearing the Tri-ang brand they must be getting on for sixty and do not disappoint on the track. The annoying thing about Mazak is that it is not amenable to remedial treatment. The switchback rotted running plate assembly on a Bachmann N I bought as a restoration project completely disintegrated while being tested for workability. Happily, the loco is now restored - with a full length scratchbuilt styrene running plate.

[Bufferstop]

Sanda Kan and others didn't just nip out round to the little local outfits, they put out invitations to tender on a global scale. I had quite a surprise visiting a company not half a mile from home, to see a set of drawings for 4mm scale driving wheels, I presume it was the tools to make them they wanted. No clue as to who they were for (turned out to be Bachmann when the model appeared).

[Bigmet]

Here is a question. If the issue is chiefly due to the differing standards that are used in the manufacturing process in the Far East then why do so many manufacturers not change their designs in the future to avoid using the material in the first place? It is more then possible not to use mazak as a material, or to only use it where if it did rot, it would not cause a problem. I am thinking of Lima diesels where the metal weight is positioned in such a way that if it was susceptible it is very unlikely to do any damage. Ok, they maybe made to an elderly design, but look how many are still plodding along today, and if they are not plodding along, they are repairable as it is usually a cog or something that has come out of alignment or something like that.

The reason why Mazak is used has to be appreciated. It offers a large number of essential characteristics for the purpose of making small castings, at a modest price. If there was a better material at similar cost the manufacturers would move on smartly, but there is not. Hand-held non-destructive test equipment is now available to detect any contamination before components end up in models, so I suspect this problem may now be largely behind us anyway.

Lima went bust which I feel tells you all that is necessary about demand for their 'plodding along' product.

And how serious a problem is this? Twenty years purchasing current RTR OO (since Bachmann really got going with their Blue Riband range in 1999) and no problems so far. It's likely I'll trip over one eventually, but after such a good run I can be philosophical about it.

Actually I have had a benefit, I have been able to buy Hornby's good Brush 2 drives very cheaply as 'Mazak rotted, for spares and repair', and use them to power my old Airfix GMR Brush 2 bodies. It will be easy enough to shift the drive line components onto a DIY brass frame if that is ever required by a cast frame failure. (Given the amount of use my models get, they tend to wear out mechanically before they fail from other causes.)

[Bufferstop]

It's a very intriguing problem, although the root cause is well known, there seem to be other factors involved one of which is a period out of use. The most frequently quoted phrase being it was OK when I packed it away. I wonder if vibration and or cyclic stressing/destressing prevents the forming of crystallisation which causes the cracking and crumbling that is a characteristic of the problem.

[Bigmet]

The only significant environmental factor that I have seen reported for Mazak rot progression is temperature. The shift in crystalline structure which causes the dimensional change that leads to the 'cracking up' is accelerated by lower temperature. Keep Mazak items at as near constant comfortable room temperatures as possible, is the best advice to keep the rate at which it happens as slow as possible. There is no fix.

Long story short, if there is a contaminant such as lead in the Mazak, this failure mode will occur over time. That's entirely consistent with the frequently reported 'on getting my model(s) out of their boxes N years after they were last used, I found the chassis blocks expanding and cracking'.

I haven't gone farther into the literature on Zinc based alloys than that. There may well be varying effect of the concentrations of the contaminant(s), and the rate of the effect may vary with the different Mazak formulations: but the literature is out there for anyone wanting to read up on the subject.

[Bufferstop]

If low temperature is a factor it's no wonder they were they were worried about putting the stuff in aircraft. I ran into it where a die-cast link with a deliberate weak spot had been used in the drive to the paper feeder of a photocopier. The idea being that if the mechanism was fouled the weak spot would break. What happened in practise was the whole thing disintegrated and most of the bits ended up on the chassis bed, where they were likely to remain until the machine was upended to move to a new site. They would then cascade through the machine creating havoc when it was restarted.

[Lysander]

Why stop at changing the designs? Why not change the makers? In other words, bring production back to the UK. The T9 compares unfavourably with the two L1s I have, one of which, an ebay rescue, is now an E1.

I’m updating and improving a Triang L1 right now. Could you post a photo of your E1 conversion?

Tony

[Bufferstop]

I’m updating and improving a Triang L1 right now.
Tony

and very nice it looks too! There were some very nice models hiding beneath the layers of Margate sludge. Cleaned up, a few details added and a good paint job helps overlook some of the conveniently wrong dimensions.