Roundhouse Bertie valve timing

[Andrew]

Hello!

A while back I carried out some work on my RH Bertie, including adding slide bars, and in the process I think I messed up the valve timing, running becoming impossibly jerky.

I'm finally tying to fix it and have removed the valve chest covers in line with RH's kit-building instructions available online. Unfortunately the instructions relate to the locos fitted with standard RH valve gear rather than the slip eccentric Basic type, and I'm not much of an engineer - so I've got a partially dismantled loco but no idea what to do next. Can anyone advise?

Thanks,

Andrew.

[-steves-]

Is this what you need?

http://www.roundhouse-eng.com/pdf/sevg.pdf

[Andrew]

Aha! That looks promising! I'll give it a shot and let you know - thanks!

Andrew

[Andrew]

Hello again...

Although I'm grateful for the link, I think it refers to a different version of the RH slip eccentric - maybe the old Dylan one? It doesn't seem to match the "Basic" set up...

I just raised steam to see if I'd remembered the symptoms correctly. The last runs ended when a crank-pin worked loose, but I glued that in place yesterday so I was able to get the thing moving but running was far from smooth on a rolling road, a kind of surging fast-slow-fast movement. I risked taking it outside (in the dark, but I'd got steam up and couldn't resist!) and although it did run its performance was distinctly reluctant, despite clearly making a lot of steam...

Any thoughts would be appreciated...

Thanks,

Andrew.

[DLRdan]

Andrew, it is not possible to alter the valve timing on the basic locos as it is part of the wheel. It is possible to change the valve position within the chest by rotating the valve spindle. It should uncover both ports equally when the wheels are rotated.

EDIT: It sounds like you might have glued the eccentric to the wheel. When you turn the wheels the eccentric should slip on the axle before the little pin catches up with it. If some glue has got through it might have stopped this from happening.

[Andrew]

Thanks Dan... I'll double-check the valve position later - it looked OK on the cylinder I opened up, but I didn't check the other one.

I don't think I can have glued up the eccentric because I only applied a little glue to the crank pin last night and the problem arose after the work I did a while ago. That involved removing the rods to paint them as well as adding the slide bars - I wonder whether I just didn't re-assemble terribly well?

I may end up handing the loco over to a professional to get it going smoothly and then stick to strictly cosmetic work - I seem to have very little mechanical aptitude!

Thanks for your thoughts,

Andrew.

[Andrew]

Ah, just realised! If it's not possible to alter the valve timing, that ain't gonna be the cause of my troubles because I can't have messed that up - I told you I'm not mechanically minded! What have I done to the bloomin' thing?! The rods look nice in red mind you...

[DLRdan]

Just a thought, make sure that the cross head isn't binding on the slide bar. It shouldn't do but worth checking. The other thing would be to disconnect the connecting rods from the piston rods and rotate the wheels. They should turn over smoothly with no tight spots. Its also worth checking that there isn't a feather stuck behind the wheel, guess how I know that......

Wouldn't worry too much, they are pretty much bullet proof.

[Andrew]

Thanks, I'll look into that - after I've fed the kids... My wife's away, but I've been using the kitchen table to test Bertie on (strictly forbidden!)instead of cooking the evening meal, oops...

Andrew

[Andrew]

Hmmm...

No binding on the slide bars, the wheels turn freely when the connecting rods are disconnected, and there don't appear to be any stray feathers... I made a slight (token?!) adjustment to the valve position too.

I raised steam again but the jerky movement persisted - the first run (on rollers) again ended with a crank pin working loose, a different one this time, just to make a change. I refitted it and continued for another ten minutes or so, but it's just not running smoothly - at slower speeds, when the wheels aren't a blur, you can see that something's binding somewhere, it bounces around a fair bit on the rolling road...

I might risk a further run at the weekend, but in the meantime any further thoughts are welcome...

Cheers,

Andrew.

[Big Jim]

While I am not familiar with the RH slip eccentric set up. I have had issues on a few models over the years.

Try disconnecting a bit at a time and turn the wheels by hand. The bind should show up via a process of elimination.

[DLRdan]

If it runs freely with the rods disconnected then there is something amiss with the admission of steam into the cylinders. As you have checked the position of the valves then next thing is to look at the eccentrics. If you hold onto the eccentric rod you should be able to turn the wheels almost half a turn one way before the eccentric rod starts to move.

The picture below shows the rear axle of my Millie which uses the same valve gear. The hole just below the axle has a small pin in it.



This pin goes into the slot in the eccentric as seen below






The pin then pushes on one end of the curved slot, turning the eccentric and making the valve move. When the wheels are turned in the opposite direction the eccentric slips on the axle allowing the pin to move to the other end of the slot.

This movement relies on the eccentric being free to move so that the pin can travel to the end of its slot, if not the valve timing will be affected. It is also possible that if the eccentric has become stuck to the wheel some way, often old oil, one side can reverse while the other is still in forward.

Before trying again Andrew, I would fill a tray (or sink if you are feeling brave) with some hot water and a drop of shampoo, just enough to cover the wheels. Leave it to soak for a couple of minutes then slowly roll the loco back and forth a few times. With any luck this should dislodge any foreign bodies that have found their way in and remove any old oil. Rinse the running gear in some clean water, dry and apply a drop of new oil.

The only other thing I can think of is that its worn out, which you can tell by twisting the back axle, like you are trying to make the wheels go in a circle. Its a lot easier explain in person!

[TonyW]

The only other thing I can think of is that its worn out, which you can tell by twisting the back axle, like you are trying to make the wheels go in a circle. Its a lot easier explain in person!

Indeed it could be, and indeed it is! The eccentrics themselves can also wear and affect the running adversely, and they are tricky to replace.

Crankpins coming loose is another sign that all is not well mechanically as they should never be placed under sufficient rotational load to turn, and no Loctite or glue (!) is normally needed to keep them in place. If they do come loose then it is an indication of something binding or the pin taking a bashing from its rod end.

[sstjc]

Following this with interest due to an issue I had on a larger scale engine some years ago.... I'm wondering why Tony if its worn out why this would only show up with the slide bars on ?
Barry

[TonyW]

I'm wondering why Tony if its worn out why this would only show up with the slide bars on ?

Good question ... I've no idea I'm afraid without seeing it, I was just following on from Dan's comment about wear in the back axle.

The slide bars and crossheads on all post about 1984 Roundhouse locos are there for decoration only and they will work fine without them being fitted. The weight and movement of the connecting rod is supported by the piston rod and its gland. If the presence or absence of the slidebars makes a difference then that is the place to look for the problem.

It is the loose crankpins that puzzle me. Shouldn't happen.

[sstjc]

Its crossed my mind that the OP could have taken the connecting or piston rods out, at the same time he fitted the slide bars and put them back on the oposite side thus if the wear is unequal this would cause the binding but I guess that has been disproved by it working ok without the slide bars... Interesting mystery though !

[Andrew]

Thanks for all your thoughts on this folks, much appreciated. I'll try to do some more investigating/testing later. And perhaps a little shampooing...

You might be onto something re the connecting rods. When I fitted the slide bars I also removed and repainted the connecting rods, so could have put them back on the wrong sides.

I didn't think it would matter, BUT, I baked the paint on in the oven, for a hard-wearing finish, and although I used the lowest temperature the rods had lost their slight S bend shape when they came out, which I had to reintroduce - the two rods are no longer exactly the same. I'll try to take a photo later...

Thanks again,

Andrew.

[sstjc]

I which case put on one at a time and adjust until it works
Just a thought
Barry

[Keith S]

Two thoughts:

One, when I assembled my Roundhouse kit engine, the connecting rod bushings needed a slight "dressing" with a needle file in order for the chassis to turn smoothly. Therefore, they might be slightly different from each other, and therefore they must be unique to their respective sides now. I can only imagine this procedure must happen at the factory too, so if you accidentally swapped con-rods, this would surely cause lumpy running. You would notice this when turning the engine over by hand, however.

Also, with your valve rods- if they are different from each other now they will almost certainly have effected the valves. Their stroke will be exactly the same as before, but if their length is even slightly different, then the valve "events" might be happening early or late. You must take the valve covers off and observe the valve moving. Refer to the chapter on fine-tuning the valves in the Roundhouse "Billy" or "Katie" chassis instructions, and turn the valve spindles on the outside of the valve chest to adjust them for proper valve opening and closing. Then with the engine in steam, run it as slow as you can on blocks and make note of where the wheels stop. This will show you which valve stem needs to be lengthened or shortened to eliminate that "sticky spot". No use doing that until you've taken the valve covers off and observed the timing events per the instructions however.

If you do that, you will be able to see if dirt has caused a slip-eccentric to stick in a wrong position on one side, or if you have slightly lengthened or shortened a valve-rod when you re-bent them. I can tell you from experience that a minuscule difference in their length is all it takes to wreck your valve-timing. Happily, it is easily adjusted if you follow the instructions!

[Andrew]

Hello again all!

I'm really very grateful for all your suggestions - I've tried most of them to the best of my ability but in the end had to ask for professional advice... I've just received the loco back from Tony at Rhos Helyg where the dodgy timing and one or two other problems have been resolved, and the loco now runs beautifully - I'll be posting photos on my (Windmill Hill) Welsh highland thread shortly...

Thanks again,

Andrew.