Lima crab

[legin]

I wonder if someone is able to help me with what is probably a small problem.

I have a Lima crab, bought new in 1986, but which has done little running.  The loco ran  exceptionally smoothly a week or two ago except that it would stall when the leading tender pickup wheel was on some of the dead frogs. The rear wheel was not therefore feeding power to the motor to keep the loco going. There is no problem at all with the loco itself (no Mazak problems) and there is continuity between the earth driving wheels and the tender itself. The loco is DC.. There is also continuity between the motor earth and the connection to the loco. The motor runs well in isolation when current is applied. However, when current is applied to the rear tender pickup wheel, the motor does not turn. It does, however, when current is applied to the front tender pickup wheel. The motor also runs when current is applied to the rear tender wheel wiper,and so that is connected. Both the rear pickup wheel and the wiper have been cleaned with isopropyl and the wiper is making good contact with the wheel.  I am getting a continuity reading between motor and wheel, but none when I apply actual power, which I don't understand. I am not sure of the next step but think that the way forward is to detach the rear tender wheels from the chassis (once the driving cogs are removed from the motor) because those wheels are extremely stiff, despite oiling. The front wheels  move freely. The wheel axles run in fully enclosed plastic holes and so will not come out without being removed from the axle. Will the wheels simply pull  or twist off to get them out without breaking them. I assume that is the only way in which they can have been assembled in manufacturing. I can then give both the offending wheel and its wiper some sanding to see if that is the problem. I have a B2B gauge to reinstall them.

I have looked through the Lima Crab forum posts but cannot see anything on this particular topic. Since the loco is in almost new condition, I would very much like to  get it running properly and convert it to DCC, as  all my other locos. And if anyone has any other ideas about what may be causing a problem other than this particular wheel, I would be very grateful to hear from them.

[roythebus]

Maybe the pick-up wiper is not contacting the wheel properly and needs bending outwards a bit to touch the wheel.

 

[34theletterbetweenB&D]

12 hours ago, legin said:

...The motor also runs when current is applied to the rear tender wheel wiper,and so that is connected. Both the rear pickup wheel and the wiper have been cleaned with isopropyl and the wiper is making good contact with the wheel.  I am getting a continuity reading between motor and wheel, but none when I apply actual power, which I don't understand. I am not sure of the next step but think that the way forward is to detach the rear tender wheels from the chassis (once the driving cogs are removed from the motor) because those wheels are extremely stiff, despite oiling...

You have done a good job of reporting there.

 

There's nothing wrong with the wiper contact on the tender rear pick up wheel, and it has continuity to the motor when tested off track, but doesn't supply current to the motor when on track.

 

The rear tender wheelset you also report as 'stiff' which I take to mean not freely rotating. That I believe is the problem you need to fix.

 

Never seen the construction of this tender, but your information leads me to suspect that the rear tender wheelset is not turning freely because of some deformation in whatever the axle runs in, or how the wheelset is retained, and this deformation also has the effect of lifting the wiper wheel out of contact with the rail. This accounts for what you are reporting.

 

Over to someone who knows the construction, to advise how to fix it.

[legin]

Thanks both. The wiper appears to be making good contact with the inside of the wheel and springs back against it well when pulled inwards by me. I should have said that I tested continuity with a multimeter between motor and wheel and there was good contact. But when I applied power to both the rim and back of the wheel with the loco in the cradle, neither the wheel nor motor turned. I agree that the first port of call should be to remove the rear wheels so that I can look closely at the plastic holes which carry the axle and maybe sand, lightly, the offending wheel as well. It appears to be brass. or some brass amalgam. Another thought is that I don't see how there can be any sort of short between wheel and motor, otherwise the front tender wheel would not turn either. The motor is connected directly to the 2 wipers by one single wire and the wiper assembly is one piece.

[34theletterbetweenB&D]

So if you apply power to the wiper strip, (and complete the circuit on the earth side obviously) with the loco in the cradle, the motor runs and both front and rear wheels turn?

 

I would leave it to run like that for fifteen minutes to polish up the wiper contact, and gently apply a rail offcut to the tyre and outside face of the flange, then retest with the power now directly on the tyre, I think you have an oxide film or two to bust through...

[Brit70053]

Hi legin ,

               As you are aware, this model appears on the list of models affected by Zinc Pest/ Mazak Rot and I note you have concluded your model is not affected by this problem.

I do however wonder if the pick up failure on the rear tender wheel might be a result of the following as detailed on "The list" of Mazak problem models compiled under that specific Topic ?  For the Lima Crab, part of the problem detailed is 'Quote :- " Weight expands in [Loco] chassis, [rubbing] onto driving wheels preventing them turning & Tender ballast weights expand, cracking tender sides. (Weight is easily removed, filed and reinstalled")  

My parenthesis [ ] and Bold 

 

I'm wondering if the tender weight has expanded a little and is bearing on the rear axel pick up wheel which you say is stiff to revolve and is not picking up current correctly in its present state.

Could you try removing the tender ballast and seeing if the tender drive and pick up are any better ? (Traction will obviously be adversely affected with the weight removed).

Just a theory, but might be worth the experiment.

Good luck in resolving this annoying problem.

 

Regards, 

 

               John

Edited January 29, 2020 by Brit70053
repetition

[legin]

Thanks John,

I hadn't thought of this one at all. The tender body goes on easily when the Mazak weights are exactly on position, but I have never looked at the clearance between the top of the rear wheel and the weight. So I will try the loco with weights on and weights off. I think the thing to do first is to attach power to the motor direct, and with it out of the tenderchassis, to see if the wheels turn properly. If they don't, it's not the Mazak but that is not to say that when the loco is actually on the track, with weights installed, they are not fouling the tender driving wheels. The other suggestion above from 34... is also worth a try because the loco has been sitting for so long in my roof that some oxidisation of the wheels could have occurred as well, and possibly on the wiper itself at the point of contact between wiper and wheel. Unfortunately at the moment, I can't find my crocodile clips to attach to the motor, but they must be somewhere!

[legin]

Hi, 

I am hoping this thread is still alive.

I have managed to get contact between the rear tender pickup wheel and motor by sanding the wheel, both tread and rear face, and the wiper at the point of contact with the wheel, with 180 grit paper. There must have been a lot of oxidation on there because isopropyl did not touch it. The wheel still will not spin freely with drive cogs removed. A track test shows no improvement, with stalling still evident when the front tender pickup wheel is on a dead frog, and touching a metal clip between rear wheel and track does not get the loco moving, nor will pressure on the tender rear, nor moving the tender side to side to try and get contact. But I am now really perplexed, because, applying current to the front tender wheel when the loco is in the cradle is fine and both sets of wheels spin indefinitely but applying current to the rear wheel makes it revolve well for a few seconds and then it stops and will not restart. I don't understand this at all because it is obviously nothing to do with contact between wheel and track and there is clearly good contact between wheel and wiper for it to start at all, and between the Peco wheel brush and the tyre for the same reason. The rear tender wheel still needs to come off, somehow, to get it revolving freely, but this now appears to be the least of my worries and not the main cause of the problem.

[legin]

Sorry, John, I forgot to say that there is clear daylight between the tender Mazak weights and the wheels, so this does not appear to be affecting running.

[Il Grifone]

A strange one!

It looks like the next step is to swop the two tender wheelsets if possible (I don't have an example of this chassis) to see if the fault either cures itself or switches to the front wheel not contacting (to confirm whether it is the wheel or wiper failing to make contact. This will require removing the insulated wheel from the axle. IIRC Lima wheels need to be pulled off straight as the axles are splined, but this might not be case with tender wheels.

Lima wheels are rather thick in the tyre and I suspect the correct back to back setting is 14.2mm. (I'll measure a few and report back.

[wasdavetheroad]

Just a thought. If the tender chassis is twisted the pickup axles will not be parallel to the track. Maybe the weight of the tender is concentrated over the front axle so you are only getting 3 wheel contact with the track. Place on a piece of glass to check?

[legin]

Thanks a lot. Swapping the wheels is a great idea, but I was not sure how to get them off because the axles are held and fully enclosed in, the motor underframe. I spoke this morning with a friend who long since gave up model railways, but still has 200 locos!! on most of which he has installed Romford wheels. He too thinks that the tender wheels may be splined and to lever them off with tweezers either side of the axle and pressing equally on the wheel backs..I have spent absolutely ages on the net trying to find out how the wheels are held onto the axle, looking mostly at LIma diesels, but with no result   I suspect that it would have been good practice of Lima to have driven wheels splined rather than simply a push fit on the axle.

I have been suspecting also that the tender chassis might be warped, given its age or alternatively that the engine drawbar is bent ( though it doesn't look like it), forcing the rear of the tender upwards. All 4 tender drivers appear to be ok on my workbench but I haven't tried them on glass, so many thanks for that wasdavetheroad. 

I am still not getting why the rear tender pickup wheel revolves with the loco in the cradle for a few seconds with power applied and then stops. Maybe the wiper is losing contact after a few revolutions, although it seems to be hard against the wheel back. I have tried to sand the wiper with the wheel in situ but that is rather difficult and removing the wheels would allow me to get at it properly and to access properly the back of the wheel.

[wasdavetheroad]

Ah!, it is tender drive? How many axles are driven, is it the front and rear ones? If so it may be a problem with the drive train to that axle, Have you checked the gears.

[Il Grifone]

Lima motor bogies and tender drives usually have a plastic motor/wheel block held in a separate frame, which is detachable for access to the wheels etc.

I've not had split/damaged Lima gears, which is not to say it doesn't happen of course. I wouldn't expect even faulty gears to cause loss of electrical contact however.

[legin]

Apologies for the delay in replying. Tried the day before yesterday but submit button not working.

I have removed the back wheels and thanks for telling me that they were probably splined, They are. The wiper is polished and the back of the pickup wheel shiny, so it appears to be making contact. Once I had moved the wheels slightly, I noticed that they were starting to spin freely so I think that the plastic cog attached to the pickup wheel may have been fouling  the motor body assembly. I shall remove the commutator so that I can see if the plastic cogs going to the offending wheel are moving freely as well. When I removed them all 3 weeks ago, they all appeared to be in new condition and I removed some tiny sprigs from them. I could see on you tube 2 days ago that the drive cogs have caused some jammiing trouble on  LIma models. But when I applied power to the front "good" tender wheel, both wheelsets went round, although perhaps not as quickly as they should. I am still mystified about the loss of drive after a few seconds when the rear "faulty" wheel is powered.

The tender has just the 2 pickup wheels, front and back. Middle is a dummy.

[uax6]

Although this won't necessarily help, you could buy a secondhand Airfix or Hornby tender drive 4F. This will give you a tender of the correct dimensions and all you will then need to do is arrange pick-ups on the insulated side of the loco to have it running nicely. A bit more work will see you fitting Romford drivers, which will make a whole world of difference to the look of the beast! I've done one of my five and the results are worth the effort (I also widened the cab and footplate).

There was an article in the RM years back that showed you how, which I can email you....

 

Andy G

[legin]

Thanks Andy (and everyone else),

I actually have an Airfix 4F, same age as the Crab, but it's my best DCC runner and so unavailable for conversion, I would have to get another one, or maybe even a second Crab and then filch the tender. I'd like to see the article you mention though, if it is not too much trouble, either to modify my Crab or for future reference if I can get this one going. My e-mail is nwhittakerw@outlook.com.

Anyway, I have had some success with the Crab, but discovered I have two problems rather than one.  Having swapped the front wheels to the back and getting the B2Bs around but not more than 14.5mm, all the wheels turn freely now and with everything back together both sets of wheels will turn indefinitely when power is applied to each in turn. So nothing wrong now with the electrics.

The bad news is that I have also put the loco with tender on a piece of glass, as suggested by wasdavetheroad (thanks for that tip) to check whether both tender pickup wheels are resting on it, and they are not. I detached the motor block from the tender chassis and it was rocking very slightly on the wheels, unless minimal finger pressure was applied to the top of the motor when it didn't rock. So I don't know at this stage whether it's the tender chassis or motor block which is distorted. I have loosened the chassis to motor block screws a half turn to allow the motor block and wheels to sit on the track without being held fast by the tender chassis-so when it goes on the circuit tomorrow with all the DCC locos removed, it will be clear if it is the motor block at fault. If it is, then what can be done about it is another problem, but I will report back tomorrow.

[uax6]

As l’m effectively scrapping my Lima tenders, l can dig one out and post it to you if it will help. I’ll try and find one that is at least square (and hopefully runs ok, but l don’t have a layout to test on), and then if push comes to shove you can transfer everything else over.

 

Andy g

[uax6]

With all credits to RM and the author, here is the article:

 

As bought:

 

With romfords (but no coupling rods yet, I'm still waiting to sort the pick-ups out!):

 

Here is the body with white plasticard inserts to widen everything out to the correct width:

 

Andy G

Edited February 8, 2020 by uax6

[Il Grifone]

I've finally managed to find a Lima locomotive and a digital caliper at the same time.

 

A B-B ALCO C420 - B2B: power bogie 14.31mm and 14.34mm; trailing bogie 14.24mm and 14.26mm.

The flanges all measure 0.70mm at the root. which indicates a setting of 14.3mm to give a check gauge of 15mm.

It's possible that the power bogie wheels were intentionally set a fraction wider to compensate for the traction tyres,

which sit proud of the wheel tyres.

 

The drawing of the return crank setting above is in correct. On most  locomotives (Crabs included) it should lean forward (both sides*) and the pivot for the eccentric rod should be on a horizontal line through the wheel centre in the position shown.

 

https://www.youtube.com/watch?v=FDtAiqEsGe0

 

https://en.wikipedia.org/wiki/Walschaerts_valve_gear

 

*Both Bachmann and Hornby seem unaware of this!

 

The recommended Romford drivers have two spokes too many (as is again the case for most locomotives).

 

 

 

[legin]

Hi, Andy,

Many thanks for all your trouble and for the information in relation to the Romfords.

 The good news is that I have had the loco running for an hour now and it runs over all my 22 points bar one without stalling. So both tender pickup wheels are picking up power. It's the first time in 30 years that the loco has run properly, because until 2 years ago, I didn't have the space for a layout. The domestic authorities have relented and allowed me 6 months every year!

I have tweeked the B2Bs on the tender wheels to just short of 14.5mm as you advised, but it's a bit of a guess, since my B2B gauge is exactly 14.5. The wheels, however, are now further apart than they were originally. I think also that the Mazak tender weights might just have worked to counter the slight distortion in the motor block so that the pickup wheels are firmly on the track. It will also thread all the points, a horrible mix of mostly my old Hornby (with modified check rails) and new Peco So far so good, except that the loco is slowing on curves all of which are at least 2nd radius and some points (2nd radius again). Although the drivers appear to be moving freely by hand, there must be some binding when on the track. This is less so when the loco is in reverse,  so I think it might be a slight Mazak problem, fairly easily solved

Tenders: this is a more than generous offer and although it doesn't look at this moment that there is a problem any longer, there was at first some momentary hesitation when the front tender pickup wheel was on a dead frog, so I'm not completely convinced that the pickup difficulty won't reoccur, particularly if there is any more distortion. The other thing is that I cannot get continuity between motor earth terminal and the engine drawbar and so have had to put in a wire direct to the tender drawbar screw. If I have got this right, the motor is supposed to earth directly through the tender chassis. I don't know if you are a DCC man, but I read that type 2 Ringfields have to be isolated from the chassis before a decoder could be fitted, and before I got the layout resurrected 2 years ago, the local model shop converted all my 30 year locos to DCC. I just wonder , since the motor is similar, if they had to do that to mine. I can see under the motor itself that there is a small metal plate which I presume is supposed to contact the brass strip which locates under the tender axles and into which goes the drawbar screw . But it's not happening.

The long and the short of that is that I would love to have one of your tenders, provided that you are really thinking of scrapping them. As you say, I can transfer the motor innards and wheels from my tender if necessary.  Wasdavetheroad suggested that putting the motor block on a piece of glass would reveal whether it was square and this worked for me. I will of course pay the postage and give you something for it. So if you haven't changed your mind,, I will give you my address.

Thanks a lot also for the rmweb article, which I need to read again a lot more carefully. I can take locos to pieces and fashion scratch repairs but that's about it at the moment. I've always been more interested in running trains to a sequence and a timetable.  However, the Crab drivers have always looked completely odd to me and changing them for wheels to scale is something I would like to do, (apart from getting the quartering correct). So with the help of the article, I shall have a go when the layout comes down. I am also fortunate that my neighbour, who gave up model railways years ago, used to work for 3 model rail shops in the midlands and has converted literally hundreds of locos to Romfords, if I get stuck. What a difference it makes to the stance of the Crab, as shown in the article photos-completely transformed.I am slightly puzzled about what you say about the pivot position. Does this mean that when the eccentric is horizontal the pivot should be vertical as opposed to leaning forward at its base?

I think also that some weathering might enhance its looks because it's in MIdland livery and looks a bit plasticky to me but I think that modifying the loco so that it is wider at the cab end than the tender is probably a bridge too far for me.

Regards,

Nigel  (which of course is Legin backwards).

 

[Brit70053]

Well done Nigel (Legin), good to see that your persistence has paid off and that the tender drive is now working as it should. Your topic has also shown RMWeb at its best, with interest and hopefully helpful ideas being freely contributed by members, taking matters beyond the original issue. Most notably, you've had the generous offer of replacement tender unit(s) and inspiration for further detailing work should you wish to undertake any of this.

                Hopefully you'll get more advice on the stiff running of the loco chassis if this persists, though it sounds as though your experienced neighbour would be able to help resolve that. 

                 Happy modelling,

 

                   Regards,

                                    John

[legin]

Thank you john and thank you everyone. You've been brilliant.

All the suggestions have been very worthwhile in that things which were not actually faulty nevertheless needed chalking off and there was much valuable help where things did actually require alteration to get the loco back on the road. Apart from the driving wheels binding on curves, the motor itself runs near silently apart from the loco as a whole crashing over some points as is normal for old heavy locos. All my old ones do it.

As an afterthought, I don't think that the Mazak is causing the centre drivers to bind on curves, and some points, because the plastic keeper plate has not expanded outwards towards the centre drivers and there is good clearance side to side for those wheels.  I only have a small ( but very complex) layout and so trains never go above a scale 20mph but at this speed on the straight, the Crab will stall or nearly stall on some of the tighter curves.So I am not sure what is causing it. I doubt if it is the quartering because I haven't touched it from new and the loco is not rolling eccentrically as it moves along. My 4-6-0s, an Airfix Scot and Mainline standard 4 are fine so I don't think it's the wheelbase at fault. Also on my old layout, many years ago, I think I had some first radius curves which caused the Crab no trouble.

Nigel

 

[uax6]

Drop me a Pm and I can then going looking for tenders for you....

 

Andy G

 

[legin]

Hi, Andy,

I have sent you a PM and due to the number of excellent suggestions I have had, I have unfortunately mixed you up with Il Grifone-David, who dug out the info for the B2Bs and gave me other useful information as well. So many thanks to him as well.

 

Nigel