Loco runs well forward, poorly in reverse

[bluestag]

I know, I know, typically it is the reverse, be grateful.

 

My latest, a LNWR 0-8-0, runs fine forward, but poorly in reverse.   It runs OK in reverse as an 0-6-2.   I've reset the hornguides twice now, and am sure that they match the rods well.   What I might have done is open up the crank pin holes too much.    But would that not affect running in forward as well?

 

The motor is a Canon with a MSC gearbox triple reduction helical gear.  I doubt that the trouble is there.

 

Any thoughts?

 

Kevin

[33C]

Run it backwards, VERY slowly, until it isn't happy. Check for the tight spot. If none is found when in your hand, then the tight spot must disappear when the body weight is taken away. At the very least you know then whether it's a vertical or horizontal problem in the chassis. Also, is the gear pitch/mesh clear and free of grit/dirt in the reverse direction?

[doilum]

Sadly not a solution, more an observation. Of my fifteen or so tank engines, the three with an ABC gearbox and the one RG7 run identically in both directions. The others using an 1833 and fold up single gear all slightly favour one direction and are noticably noisier in the other despite much running in and tweaking.

[33C]

I have found that problem in some motors over the years. The shaft bearings have been found to wear off square. With can motors, I put these in my Scalextric cars, as they only want to run forwards anyway! When this occurs in my open frame motors, I turn the back plate 180° and the problem disappears! 

[bluestag]

1 hour ago, doilum said:

Sadly not a solution, more an observation. Of my fifteen or so tank engines, the three with an ABC gearbox and the one RG7 run identically in both directions. The others using an 1833 and fold up single gear all slightly favour one direction and are noticably noisier in the other despite much running in and tweaking.

The other three of my locos have fold up gear boxes with Mashima motors.   The first one was noisy as hell.    I replaced the steel worm with nylon, and hey presto: silent.   All three run the same regardless of direction.   And silently.

 

 

[bluestag]

2 hours ago, 33C said:

Run it backwards, VERY slowly, until it isn't happy. Check for the tight spot. If none is found when in your hand, then the tight spot must disappear when the body weight is taken away. At the very least you know then whether it's a vertical or horizontal problem in the chassis. Also, is the gear pitch/mesh clear and free of grit/dirt in the reverse direction?

I don't see anything in the gears, but that may mean nothing.    How does grit trouble it in reverse, but not forward?

[doilum]

Not sure if it should make a difference, but my ABC / RG7 locos drive the centre axle. The others all drive the rear axle with the motor vertical in the firebox.

[33C]

57 minutes ago, bluestag said:

I don't see anything in the gears, but that may mean nothing.    How does grit trouble it in reverse, but not forward?

Compressed dirt/grease can mimic the teeth over time making them thicker and changing the pitch. Hornby gear towers suffer from packed grease actually forcing the cover plate off! The S15 especially. A thorough clean out of the gear train cured them like you would not believe!

[Coal Tank]

Hi Kevin, does it free wheel in both directions ok

John 

Ps I have one of those kits

[budgie9]

Try driving on a different axle, that may show  you where what is going wrong. That showed up on my two GWR 8 coupled

[bluestag]

6 hours ago, doilum said:

Not sure if it should make a difference, but my ABC / RG7 locos drive the centre axle. The others all drive the rear axle with the motor vertical in the firebox.

This one is driven on the third axle of four.

5 hours ago, 33C said:

Compressed dirt/grease can mimic the teeth over time making them thicker and changing the pitch. Hornby gear towers suffer from packed grease actually forcing the cover plate off! The S15 especially. A thorough clean out of the gear train cured them like you would not believe!

The gears have not been greased.

[bluestag]

4 hours ago, Coal Tank said:

Hi Kevin, does it free wheel in both directions ok

John 

Ps I have one of those kits

John,

 

How are you getting on with the Cauliflower?   I am looking to you for tips.

 

And I sent Nick a series of observations on this one.    I'll PM some of it to you.   Especially about the smokebox.

 

Kevin

[bluestag]

20 minutes ago, budgie9 said:

Try driving on a different axle, that may show  you where what is going wrong. That showed up on my two GWR 8 coupled

I don't think that possible.    There are frame spacers and a motion plate in the way.

[Michael Edge]

Loosen the grub screw in the gear wheel and turn the wheels by hand, starting with your driven axle. Watch the position of the wheels and note where (if) it feels sticky. You can try with each of the other axles to see if there is any difference.

Going back to your original query it seems to work OK without the rear section of the coupling rods - can you take the front section off and try just the 3rd/4th axle bit?

One more point, I can't tell from your photo but have you spaced the coupling rod away from the trailing wheels to match the thickness of the leading section of the rods?

[doilum]

Does removing the body make a difference? A slightly overtightened body screw can put an amazing amount of twist in the chassis. Just backing it off a tad immediately restores the the previous performance.

[Izzy]

If as seems possible it’s the rear coupled wheelset that is the issue, what current collection is being used with them? It can happen that sometimes that too much drag will cause problems in one direction but not the other. This is especially so with ‘split’ coupling rods and you can’t obviously ‘finesse’ the quartering since they are Slaters self-quartering ones. 

[bluestag]

17 hours ago, doilum said:

Does removing the body make a difference? A slightly overtightened body screw can put an amazing amount of twist in the chassis. Just backing it off a tad immediately restores the the previous performance.

There is a substantial twist in the body.   I was mystified when I would put the body on the chassis and tighten down both nuts.   The loco derailed all over the place.   These days I only tighten down the front nut.

[bluestag]

18 hours ago, Michael Edge said:

Loosen the grub screw in the gear wheel and turn the wheels by hand, starting with your driven axle. Watch the position of the wheels and note where (if) it feels sticky. You can try with each of the other axles to see if there is any difference.

Going back to your original query it seems to work OK without the rear section of the coupling rods - can you take the front section off and try just the 3rd/4th axle bit?

One more point, I can't tell from your photo but have you spaced the coupling rod away from the trailing wheels to match the thickness of the leading section of the rods?

Yes, the rear crank pins have two bushes each.   I tried the chassis as you suggested a long time ago, and detected nothing.   I may try the chassis with only the rear coupling rods on it.    See if it runs at all.

[bluestag]

16 hours ago, Izzy said:

If as seems possible it’s the rear coupled wheelset that is the issue, what current collection is being used with them? It can happen that sometimes that too much drag will cause problems in one direction but not the other. This is especially so with ‘split’ coupling rods and you can’t obviously ‘finesse’ the quartering since they are Slaters self-quartering ones. 

I use Slaters plungers.   I swear by them.    I doubt the drag is excessive, as it is running today as a 0-6-2, and the rear axle revolves without issue.   Fore and aft.

[budgie9]

Check your coupling rods have all the same sized holes. Use drill bits to check the sizes  and see if you have one or two tight ones compared to others.  they should be all be the same size hole. Even them all up being slightly loose is better than tight I find. But not sloppy. 

Use a straight edge to check the crank pins are in a straight line when you run the loco at a very slow speed so it stops or sticks at a point. This will show you if you wheels are quartered correctly, maybe they are out slightly or your coupling rods are too tight. and pushing one wheel out of line.

[bluestag]

19 hours ago, budgie9 said:

Check your coupling rods have all the same sized holes. Use drill bits to check the sizes  and see if you have one or two tight ones compared to others.  they should be all be the same size hole. Even them all up being slightly loose is better than tight I find. But not sloppy. 

Use a straight edge to check the crank pins are in a straight line when you run the loco at a very slow speed so it stops or sticks at a point. This will show you if you wheels are quartered correctly, maybe they are out slightly or your coupling rods are too tight. and pushing one wheel out of line.

I'm using Slaters wheels, which I believe are reliable in the quartering.    At least that is my understanding.

 

None of the crankpin holes are tight.  If anything, the holes in the rear coupling rods are loose.   But I don't understand why that would not also affect forward running.

[Michael Edge]

There shouldn’t be a problem with the quartering, Slater’s axles are very reliable. Try it with just the trailing rods on.

[budgie9]

I have used the fixed Markit wheels in the past but they have run the same as you have described on the one 28XX I have built. I found that using the methods I described above I found helped locate the problem. Michael Edge is telling you to remove the rear coupling rods and that is the next step I would have suggested to you also, but he beat me to it.

I too have used Slater wheels and Ultrascale wheels on my builds and have found that they all have there own pluses. On the 8s I find that the Markits are better as they are far easier to get right.  You only need one tight hole in a rod to get things out of sorts on the 8 coupled believe me.

They can be a pig to get right, here are a couple of other things you may wish to look at. Just don't give up 

Maybe a slight twist in the frame   One bearing can be pushing it out of alignment also. You will need to use a gauge to check the bearings to check this. Check the distance between  the coupling rod pins they need to be the same on both sides of the frame for the same pair of wheels. If not then you have a problem. Are the pins square to the wheels?

Check the frame sitting on some glass to see if it is sitting square perhaps, It may look as if it is running flat to the track, but it may not be doing so at all the time.  Disconnect it from the motor and see if all wheels still sit of the glass without rocking.  Do a full circuit of the wheels.  Run it without the cylinders on the front and see it it is binding there. 

[bluestag]

On 11/02/2022 at 19:06, budgie9 said:

I have used the fixed Markit wheels in the past but they have run the same as you have described on the one 28XX I have built. I found that using the methods I described above I found helped locate the problem. Michael Edge is telling you to remove the rear coupling rods and that is the next step I would have suggested to you also, but he beat me to it.

I too have used Slater wheels and Ultrascale wheels on my builds and have found that they all have there own pluses. On the 8s I find that the Markits are better as they are far easier to get right.  You only need one tight hole in a rod to get things out of sorts on the 8 coupled believe me.

They can be a pig to get right, here are a couple of other things you may wish to look at. Just don't give up 

Maybe a slight twist in the frame   One bearing can be pushing it out of alignment also. You will need to use a gauge to check the bearings to check this. Check the distance between  the coupling rod pins they need to be the same on both sides of the frame for the same pair of wheels. If not then you have a problem. Are the pins square to the wheels?

Check the frame sitting on some glass to see if it is sitting square perhaps, It may look as if it is running flat to the track, but it may not be doing so at all the time.  Disconnect it from the motor and see if all wheels still sit of the glass without rocking.  Do a full circuit of the wheels.  Run it without the cylinders on the front and see it it is binding there. 

I'm pretty sure the coupling rods are the same lengths.    A larger chance is that one of the axles is not parallel to the others.   Hard to see.   The crankpins LOOK square to the wheels, and parallel to the axles.  I need to retract my previous statement that none of the coupling rod holes are tight.    On close observation, there may be room to open one or two out.

 

As I wrote earlier, the body had been twisting the chassis when tightened up both front and rear, with dire results.   Now the body is only secured at the front.

 

Took it to John's running session yesterday.   John has built over 80 7mm locos.  He just cranks them out.   He released the drive gear, and found an occasional conflict between the coupling and connecting rod on one side, with the motion bracket (supports the rear end of the slidebars).   I had filed clearances on it before soldering it to the chassis, and it seems that there was still a problem.   I filed a slight taper on it, and the rods seem to brush past it now.   Which comports to the on again off again nature of the problem.

 

It is running much better, thanks to John's eye.   Perhaps still a little sticky, but nothing like before.  I'm going to look closely at the rods again and see if they want opening out.  A report after I do that.

[budgie9]

I look forward to hearing how you get on with resolving your issues. I am on my last full build, a Martin Finney 51/61xx, of model locos,   going back nearly 50 years.  But I have one more chassis to build on it's way from the UK as I write. It is to go on my well or should I say overly worn out Grange loco. That poor loco has done more miles than I care to think about. so it has to have a complete new chassis and that I think will be the last - unless I find another.

Edited February 15, 2022 by budgie9
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