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Discussion Starter · #1 ·
Hi all, could someone please tell me the cause and remedy for a loco that runs fine but tends to pulse along. It speeds up and backs off speeds up and backs off. Thanking all in advance. cheers PSR
 

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I think we might need a bit more information before someone can help you.

How many locos do you have? If you have more than one, is this the only one exhibiting these symptoms? And are you using DC or DCC?
 

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Discussion Starter · #3 ·
Hi there, layout is DC. Have many locos HO scale. This is an old Lima 38 class that just runs quiet smooth in reverse but in forward won't run smooth and just pulls then backs off pulls backs off. I call it a type of pulsing. Like the engine doesn't run smooth. cheers PSR.
 

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That's usually the product of wear in the drive train, in the direction the loco has had most running. Very frequently seen on a steam tender model that has seen a lot of use, and 95% of it when working hardest pulling a train, running smokebox leading. Top of the list are poorly controlled end float on the motor shaft and wear to the worm and pinion faces.

If you observe the mechanism on the bench with wire connections to the motor, you may be able to see the motor shaft shift fore and aft when direction is changed. If it is possible to restrain the motor shaft so it doesn't shift (a little oil on your thumbnail) and that fixes it, then it's a worn bearing in the motor.

Wear to the worm and pinion: if you can see dust from the worm and pinion materials, there you are. Visual examination with a 5x magnifier you should be able to see the difference between the forward and reverse faces. New gearset is the best solution.

Expedient fix to get the best running in the forward direction that is easily possible if the worm drives directly on the axle gear and the loco has wiper pick up both sides of the driven wheelsets: pull the worm off the motor shaft and turn it around, drop the wheelsets out of the chassis and turn around (usually requires having all the side rods off) and then the better performance will be in the forward direction - for a while. It'll still do the pulsing, but now in reverse of course...
 

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Discussion Starter · #5 ·
That's usually the product of wear in the drive train, in the direction the loco has had most running. Very frequently seen on a steam tender model that has seen a lot of use, and 95% of it when working hardest pulling a train, running smokebox leading. Top of the list are poorly controlled end float on the motor shaft and wear to the worm and pinion faces.

If you observe the mechanism on the bench with wire connections to the motor, you may be able to see the motor shaft shift fore and aft when direction is changed. If it is possible to restrain the motor shaft so it doesn't shift (a little oil on your thumbnail) and that fixes it, then it's a worn bearing in the motor.

Wear to the worm and pinion: if you can see dust from the worm and pinion materials, there you are. Visual examination with a 5x magnifier you should be able to see the difference between the forward and reverse faces. New gearset is the best solution.

Expedient fix to get the best running in the forward direction that is easily possible if the worm drives directly on the axle gear and the loco has wiper pick up both sides of the driven wheelsets: pull the worm off the motor shaft and turn it around, drop the wheelsets out of the chassis and turn around (usually requires having all the side rods off) and then the better performance will be in the forward direction - for a while. It'll still do the pulsing, but now in reverse of course...
Thanking you for the reply, sounds like you've covered all bases. Will pull apart and go over. Thanks again.
 

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Thanking you for the reply, sounds like you've covered all bases...
A thought arose overnight, I realised I hadn't in one significant respect!

Didn't consider the possibility of a pancake motor and spur gear drive line (for the simple reason that I don't have any as they were packed into tenders on RTR OO product and were pretty poor). These will have different problems, but my lack of experience of the breed means no good advice to offer
 

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I had a brand new Crosti 9F that did this so I did the simple things first, ,like cleaning the black wheels, well I have some tough ways of doing this but it took 4 cleaning attempts before they were cleaned and after that it has been OK but there were other things wrong as well, the retailer obviously got it as a return and sold it to be new - naughty box shifter! I had to do some other minor adjustments but the erratic behaviour was down to a severe amount of wheel dirt - probably the worst I have ever seen!
 
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