antrobuscp Posted August 25, 2013 Share Posted August 25, 2013 I came to use my 8750 tank yesterday for the first time in quite a while - in the past it has been a smooth performer. It would not start immediately, so I investigated. It would run part of a revolution of the wheels in one direction and then the other and would then bind up. My immediate thoughts were that the quartering was out - but how did that happen when it had been sitting on a shelf - or a split gear. I therefore dismantled the chassis to check the gears and make sure there was no grit in the gear train. Everything appeared fine. The motor ran smoothly out of the chassis with idler gears attached but put it in the chassis and the fault was still there. The axle mounted gear seems fine. There was still binding and this was traced to the front axle which seemed tight to settle into its slot, and tight on revolving. I therefore decided to ease the slot using needle files. This produced an improvement in that the loco would now make progress if extremely jerkily. This morning I decided to have another try. I have a 57xx pannier fitted with the same chassis type, and this loco is working fine. I therefore swapped the wheelset over, and it runs sweetly. I then totally dismantled the 8750 chassis and all the gears, idlers, etc., were in order. At this stage I should mention that when dismantling the chassis I had not realized that the front end weight block which also partially retains the motor is held by 2 small screws. I had applied a small amount of force to try to lever the motor out, and the chassis block had given way at the point where one of the two screws entered. I also tried pushing the un-motored 8750 chassis with the wheelset loosely in place, and it bound up(as it also did with the wheelset from the 57xx). I then set the two chassis castings side by side, and it appears that the 8750 chassis block is 1 - 1.5 millimetres longer between the centre and leading axles than is the 57xx chassis. I have contacted Bachmann service to see if a replacement chassis block is available. Has anyone else had similar difficulties? (edited for clarity) Link to post Share on other sites More sharing options...
Miss Prism Posted August 25, 2013 Share Posted August 25, 2013 I then set the two chassis castings side by side, and it appears that the 8750 chassis block is 1 - 1.5 millimetres longer between the centre and leading axles than is the 57xx chassis. It's been increasingly clear over a number of years that Bachmann chassis' machining is inconsistent, but that kind of error is an appalling situation. Link to post Share on other sites More sharing options...
antrobuscp Posted August 25, 2013 Author Share Posted August 25, 2013 The loco was originally a smooth runner, so I'm not sure original machining would be the cause. I suppose, given the problems arising with some models over the years, I'm suspecting expansion of the casting. Colin Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted August 25, 2013 Share Posted August 25, 2013 Expansion is a pretty sure sign of mazak rot / zinc pest. The catalogue number of your 8750 will help identify if there is a systematic problem affecting a production run. (Typically the contamination which causes this mode of failure in mazak occurs in the melt from which a run of components are then diecast; so usually it is a significant number of models from a production run with parts from that melt that then fail.) Link to post Share on other sites More sharing options...
andyman7 Posted August 25, 2013 Share Posted August 25, 2013 The giving way of the chassis block also points to contaminated mazak used for the casting. I know it gets referred to as mazak rot but as has been pointed out elsewhere, it is actually a chemical process that occurs if impurities are allowed to enter the mazak mix at the time of manufacture. If that happens, eventual deterioration of the component is inevitable and nothing can be done to prevent it. There are various methods for stabilising castings used for decorative purposes (as used by collectors/restorers of pre-WW2 Dinky Toys which are notorious for such failures) but where it is used in structural or mechanical components replacement of the affected parts is the only solution. Link to post Share on other sites More sharing options...
antrobuscp Posted August 25, 2013 Author Share Posted August 25, 2013 Thanks for the last two replies. It is only a suspicion based upon past experience of the N Class, and what I've read about the Hornby 31 and some Heljan 47s. I thought I'd post a topic to see if anyone else had experienced a similar problem because, as you've both suggested, it's unlikely that contamination of the Mazak mix would affect only an isolated model. I wouldn't normally think of it except that a part of the casting seemed weaker than expected and what I'd have thought of as the two more likely causes don't seem to apply. Colin Link to post Share on other sites More sharing options...
Rail-Online Posted August 26, 2013 Share Posted August 26, 2013 Colin, What is the Bachmann stock item number (presumably 32-201?) and the locos running number please? Tony Link to post Share on other sites More sharing options...
stewartingram Posted August 26, 2013 Share Posted August 26, 2013 Just an idle thought, I have a black pannier with another common fault where the quatering of the wheels goes out. From memory (i'm at work so can't check) the split axles are at fault and can't successfully be glued, though possibly a pin might be inserted? As I have heard of a number of these, would the chassis block be similar to yours and easily available as a scrap spare? Stewart Link to post Share on other sites More sharing options...
RMweb Gold The Stationmaster Posted August 26, 2013 RMweb Gold Share Posted August 26, 2013 Just an idle thought, I have a black pannier with another common fault where the quatering of the wheels goes out. From memory (i'm at work so can't check) the split axles are at fault and can't successfully be glued, though possibly a pin might be inserted? As I have heard of a number of these, would the chassis block be similar to yours and easily available as a scrap spare? Stewart The chassis used to be carried as a spare by one Bachmann retailer I know of but I haven't seen one for quite a while. Could well be worth asking Bachmann?r Link to post Share on other sites More sharing options...
RMweb Premium brushman47544 Posted August 26, 2013 RMweb Premium Share Posted August 26, 2013 The chassis used to be carried as a spare by one Bachmann retailer I know of but I haven't seen one for quite a while. Could well be worth asking Bachmann?r I suspect that was the chassis before it was updated to be DCC ready with an 8-pin socket. Are the chassis interchangeable or did Bachmann make minor changes to the body as well? I now only have DCC ready versions so can't check. Link to post Share on other sites More sharing options...
buffalo Posted August 26, 2013 Share Posted August 26, 2013 Colin, What is the Bachmann stock item number (presumably 32-201?) and the locos running number please? Tony A quick google would reveal this, and many other references to and photos of this model number. Nick Link to post Share on other sites More sharing options...
antrobuscp Posted August 26, 2013 Author Share Posted August 26, 2013 Tony, the catalogue number is 32201, and the running number is 8763 - it is the lined black early crest version. The chassis is a later version with solid axles, so I would not have expected the quartering to shift. I had the split axle muffs give way on a Hall some while ago, and I bought a few as spares at that time. I've emailed Bachmann to see if the chassis block is available as a spare, but would buy a chassis if that was the only option. The chassis on the pannier was apparently to be upgraded in 2012, but I don't know if that was done or if it was to be a drop in replacement for the earlier version. In the short run, I've filed down one side of the axle slot, re-assembled everything and the loco is running reasonably well at the moment. If my suspicion is correct, the fault will presumably return at some point. Colin Link to post Share on other sites More sharing options...
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