Valve gear problems

[baggo]

Hi all,

Do any of the Black Five builders know if the loco is copied from a 'known' design or if it is Modelworks (or perhaps Winsons) own?

I've spent a couple of hours at the track today helping out a chap who is struggling to get his B5 running properly. He's been playing with it for months now and the problem seems to be the valve gear. It would help if I could see a drawing of the gear and check all the geometry but he says there are no drawings available?

He bought the kits some time ago and has only recently had chance to complete it so possibly it may have originally been from Winsons? The original valves were ceramic but he has since changed the valves and all the valve gear with new parts supplied by Modelworks but this has made little if any difference to the running which is still poor.

Unfortunately he doesn't know much about valve gear so is struggling on his own, hence my interest in helping him out. He's set the gear according to the instructions but if the geometry is all wrong then it's still not going to be right.

If all else fails, I'll take a ruler with me and take a load of measurements and then draw the gear out at home and work from there. The only thing which will be difficult to measure without dismantling is the width of the ports and the width of the valve heads so I can calculate the proper valve travel. Does anyone know what those two measurements are?

Any help would be gratefully received so that we can get this loco running properly

John

[mutley]

Hi John
First of has the builder got all the modification kits for the valve gear and suspension? We have a club member with a MW Black 5 and I have spent some time working through various diffrent problems. The engine only seems to work in full gear or near full gear, trying to notch it up wont work and this is with the valve gear adjusted by MW.
I dont think the drafting is right. MW supplied a replacement blast pipe with a diameter of 6mm some what smaller than the original. I worked the size out as needing to be nearer to 8mm. The superheaters dont do much either. MW sugested that the engines run better without them, which I can believe. I am working on getting them changed to fully radient versions. As supplied the diameter of the coaxial ones doesnt seem to allow much space for gas flow around them.
The final point is that as designed I cant figure out how the injector and pump feed/returns are supposed to work. The tender has three outlets and the boiler has four clacks. Even alowing for the the hand pump and axle pump using the same outlet it is one outlet short. A weekends work saw it re-plumed with seperate feed to all.

Andy

[baggo]

Hi Andy,

I'll have a word with him on Sunday and try and find out just what he has changed. I think he's changed the valve bobbins, radius rods, return cranks, eccentric rods, expansion links, the link brackets, combination levers, and union links!! It seems the new radius rods are fluted on the wrong side (the inside!) and don't line up with the expansion links properly. They are actually at an angle to the centreline of the loco. I did suggest that he'd got the rh and lh crossed over but he says not.

The boiler seems to steam ok from what I've seen but it's difficult to say for certain when it's running so badly.

Your comment that it will only run at full gear suggests to me that the valve travel is not enough. I noticed today when we took off the front valve chest cover off one cylinder that the valve head did not seem to move far enough forward to open the ports anything like fully at full gear. It is possible that the valve bobbin is not set correctly although Roger, the owner, said he had set them. One thing I wasn't impressed with was that the ports are only drilled holes and not rectangular. No wonder the exhaust sounds 'woolly' as the ports will only open very gradually as opposed to snapping open.

It sounds as though the superheaters are strangling the steam flow. Don Young's version uses ½" dia. x 20swg outer tubes and 5/16" x 22swg inners (4 off).

Not sure about the plumbing but I seem to recall Roger saying that one injector and the hand pump (or axle pump?) are teed off the same feed pipe from the tender.

John

[pondok]

Hi guys,

Over the 10-odd years I've been into this hobby, I've taken a fancy to valve gear problems - something about demystifying all those moving bits is so satisfying....

It's not easy to figure out how much the ports are opening when it's all assembled (unless you're lucky enough to have sighting holes), but i've found you can do one really important troubleshoot without taking anything off:

As you mentioned Black 5's, I assume it's walschaerts gear, so when the piston crosshead is at the end of its stroke, (either front or back 'dead centre'), the return crank and eccentric rod absolutely must be placing the expansion link in "mid-swing"

if that sounds complicated, basically the expansion link must form the exact radius of the radius rod, this happens of course at some point in its swing, but it must happen only at dead centre - easy to test by just moving the reverser back and forth .

If the return crank and eccentric rod are placing the expansion link incorrectly at this point, and you move the reverser back and forth, the valve crosshead will be moving slightly (or a lot).

The valve crosshead should not move at all when doing this with the engine in front and back dead centre.

This is so important because otherwise it means the expansion link is swinging one way more than the other, for example, so creating uneven valve travel one way or the other, and no doubt uneven port opening one end from the other.

This is usually caused by the eccentric rod being the wrong length and/or the position of the return crank. It can be a bit of a hassle correcting this because it's the eccentric rod length and the return crank position working together than produce the correct travel of the expansion link so you end up having to take off the eccentric rod and loosen the return crank a bit so you can turn it.

You then take your trusty digital calipers and by trial and error move the engine from front to back dead centre several times, adjusting the return crank position, measuring the imaginary eccentric rod with the calipers (maybe making up small centres to push into the bushes), moving back to the other dead centre and so on until you have an eccentric rod "between-centre" length on your calipers that doesn't change when you move from front to back dead centre.

Then you can maybe resize the rod or make a new one.

A lot of locos built only to drawings have this problem and so notching back is always a problem, as slight deviations from the drawing end up accumulating to maybe 3/32" differences which on 1" scale model valve gear is huge. The eccentric rods seldom end up the same both sides.

Of course, once this is right and the expansion link is at "mid-swing" in front and rear dead centre, and the problem persists, you can then dismantle and check the position on the spindle and dimensions of the valves.

But even if the valve position and dimensions are 100%, notching back will always be a problem as long as the expansion link travel is not exactly the same one way and the other, which in turn ensures the ports open (and close) the same at every stroke.

hope that helps!!

[baggo]

Hi Pondok,

Thanks for your comments. I am thinking that the main problem lies with the return cranks and the eccentric rods.

I studied the drawings for Don Young's version last night and worked out the valve travel etc. Don's version has 3/16" ports and 5/32" lap so the theoretical maximum valve travel is 11/16" (17.46mm). I don't think Roger's B5 has anything like that amount in full gear and I think the ports are a similar size (although the lap may be different).

On the D Y loco the pitch circle diameter for the return crank driving pin is 1.25" (31.74mm). Roger set his according to the Modelworks instructions and his is nowhere near that, hence the lack of valve travel. We did try increasing the throw of the return crank with some improvement but the ends of the expansion link started to foul the end of the lifting arm for the radius rod when in full gear. We did look at the movement of the expansion link either side of the mid position and it does seem to be very unequal.

I could really do with getting the loco in my workshop for a day or so but the owner lives about 50 miles away which makes it a bit awkward.

John

[Deleted]

Hi John,

I've just been through a very similar process with my Modelworks Britannia, which I've described on my website at www.britanniabuilder.co.uk/kit13.htm#25308 . I too found that the correct return crank setting caused the expansion link to foul the lifting arm, but I fixed this by filing the corners a little. I also had to adjust the length of the eccentric rods, and I did this by making off-centre bushes for their front bearings. To be fair to Modelworks, I think eccentric rods need to be measured 'on the job' to take account of slight differences on individual assemblies (eg due to the free play of the bolts in their holes in the frames) - perhaps they should provide a selection of off-centre bushes to allow builders to make fine adjustments?

Regards,

John

[pondok]

Hi Johns,

Totally agree about the eccentric rods - they really always have to be left until everything else on the running chassis is final assembled within reason and done 'on the job'.

If it's very well built often the problem isn't very bad, but it's amazing how much ability to 'notch back' one loses with small discrepancies. If you imagine the port being 3/16" and the valve travel only being a tiny bit out, say 1/16", you are losing fully 30% of your total cut-off so in practice only able to notch back to maybe 50%.

I imagine in bigger scales such small differences would hardly be noticed, full size must have been so easy in comparison.

Maybe such things would only matter in the IMLECs anyway, but that familiar lopsided jerking when notching back is never nice, and it's only with a well notched-back engine that you really get to open the throttle to the roof on these models - otherwise they just slip.

cheers!

[mutley]

I'd go back to first principals and measure everything including cylinders and the relationship of them to the chassis components.


Andy

[baggo]

Roger brought his B5 to the track today and had another run after checking things over.. Apparently he'd got the valves bobbins out by 4mm due to an incorrect measurement!

Had a drive and, although not exactly sparkling, the performance was vastly improved. Still needs a bit of tweaking but at least it runs now

[freddo]

My buddy, the abrasive doc in Malaysia, has the definitive description for determining the return crank offset and eccentric rod lengths on his website (www.dr-john.org) in the tips section. Seems wonderfully simple if you undestand that pythagorus seemed to know something about the squaw on the hippopotamus ......

Freddo

In fact, on page 4 of his pictures in the Simplex section, there is a pic of how he has done the return crank setting - it's got the caption under the little pic of "Wow - the geome....."

[circlip]

Didn't realize that there were any Pythons or Hippopotami in Malaysia ;D ;D ;D

[mikessme]

As these posts are a bit in the past now, I would be interested to hear if anyone has eventually sorted one of these locos out to their satisfaction. I bought a completed but not commissioned B5 last year as I liked the look of the loco. It has taken a lot of time to sort many minor faults but when I first ran it earlier this year it was apparent the valve timing was incorrect and it was also passing a lot of steam through the valves. The timing I think has been sorted as per the walschaerts set up as outlined in this thread above although I have yet to steam it again, and after a close look at the piston valves I have made a new set of CI rings which although very tight appear to run OK on compressed air at 10psi. Mindfull of previous comments re restrictions in the steam passages I worked right through this one and found everything to be of a greater area than the 1/4" bore regulator, except for the steam ports into the cylinders which were very small and have now been opened into a slot rather than the 2 x 3.5mm holes. My loco has the 6mm blast pipe nozzle fitted so I will reserve judgement on this until I see how well it runs, hopefully within the next couple of weeks.

[michaelfive]

Oct 2, 2017 7:45:51 GMT mikessme said:

As these posts are a bit in the past now, I would be interested to hear if anyone has eventually sorted one of these locos out to their satisfaction. I bought a completed but not commissioned B5 last year as I liked the look of the loco. It has taken a lot of time to sort many minor faults but when I first ran it earlier this year it was apparent the valve timing was incorrect and it was also passing a lot of steam through the valves. The timing I think has been sorted as per the walschaerts set up as outlined in this thread above although I have yet to steam it again, and after a close look at the piston valves I have made a new set of CI rings which although very tight appear to run OK on compressed air at 10psi. Mindfull of previous comments re restrictions in the steam passages I worked right through this one and found everything to be of a greater area than the 1/4" bore regulator, except for the steam ports into the cylinders which were very small and have now been opened into a slot rather than the 2 x 3.5mm holes. My loco has the 6mm blast pipe nozzle fitted so I will reserve judgement on this until I see how well it runs, hopefully within the next couple of weeks.

It's been a while since your post, but i wonder how it turned out when you steamed it with your modifications.

[oldnorton]

Michael,

As this is an old thread you are unlikely to get a reply. mikessme has only posted once and that was in 2017. Most of the previous posters from 2008 have now gone.

Just making the comment so you do not get put off by silence :-)

If I am proved wrong then that's great!

Norm

[michaelfive]

Sept 30, 2020 15:26:53 GMT oldnorton said:

Michael,

As this is an old thread you are unlikely to get a reply. mikessme has only posted once and that was in 2017. Most of the previous posters from 2008 have now gone.

Just making the comment so you do not get put off by silence :-)

If I am proved wrong then that's great!

Norm

Thanks for your reply Norm. I was afraid that this might be the case!

[mikessme]

I thought this thread had gone dead so I was pleased to see the new one started by Michael in the General chat. Yes my Black 5 was eventually sorted and now runs well.

Mike