Upgraded MSS loco - expecting too much?

[georgesheppard]

I built a kit MSS loco earlier this year and have recently fitted some upgrades including a RWM Steam regulator, displacement lubricator and ceramic gas burner.

It will plod around the track on it's own but fails to pull anything of note. I was hoping that the gas burner, regulator and lubricator would improve things but it's not much better than when it ran on solid fuel. Am I expecting too much? Last night i whipped out the reverser block and can't see much gunk indicating a blockage. You can see in these YouTube videos that it's quite happy expelling steam via the exhaust!

https://youtu.be/60SJXn5my14
https://youtu.be/tUL5RjAVIH4

Does anyone have any advice on how to diagnose it's lack of pulling power further?

Thanks,

George

[-steves-]

Hi George

Do the cylinders move in and out easily?

Do the loco wheels turn freely with the conrods off?

If the answer to above is yes in both cases I would suggest lapping in the mating faces of the block and cylinder faces, looks like lots of steam escaping there and possibly straight to the exhaust.

[georgesheppard]

Do the cylinders move in and out easily?

Yes, they feel pretty smooth overall. I have an old Mamod I'm working on, the well run in cylinders on that loco feel pretty similar.

Do the loco wheels turn freely with the conrods off?

Yes, no issues there either from what I can see.

If the answer to above is yes in both cases I would suggest lapping in the mating faces of the block and cylinder faces, looks like lots of steam escaping there and possibly straight to the exhaust.

I had a quick google on lapping techniques, it seems like most things there are simple and more complicated approaches! Are there any resources you can recommend specific for lapping steam related parts?

[-steves-]

Some very fine grinding paste and a bit of glass tends to work well. Place some paste on the glass and just rub it around in circles until all of it appears shiny and no major parts are missed. Take off only what you have to, to achieve flat surfaces. New glass tends to have 2 decent flat sides, older glass only tends to have one.

I hope that explains it and I hope it solves it.

Other issues can be badly fitting pipes so check those for leaks too.

I am assuming the exhaust in in correctly as so much steam was coming out of it?

[Wobbly Wheel]

I'd be inclined to try something less aggressive than grinding paste, which is after all meant for steel.

Autosol or liquid metal polish might be better, even cheap toothpaste, all of which should be easier to remove after a lapping process.

For small non ferrous items any surface will do as long as it truly flat, off cuts of aluminum plate for instance.

[Jimmyb]

When i bought my Roundhouse loco earlier this year, the recommendation were the loco would require "running-in" under a light load for a couple of hours. I found that the pulling power was not as good as I was expecting, especially up gradients. However a couple of weeks ago I put the heavier load on to "see what would happen" and was quite surprised and pleased by the improved performance, so "running-in" was the solution, just more than a couple of hours.

[georgesheppard]

I'd be inclined to try something less aggressive than grinding paste, which is after all meant for steel.

Autosol or liquid metal polish might be better, even cheap toothpaste, all of which should be easier to remove after a lapping process.

For small non ferrous items any surface will do as long as it truly flat, off cuts of aluminum plate for instance.

I've got some autosol on order, I'll give it a go. I have a spare cylinder I can practice on too.

When i bought my Roundhouse loco earlier this year, the recommendation were the loco would require "running-in" under a light load for a couple of hours. I found that the pulling power was not as good as I was expecting, especially up gradients. However a couple of weeks ago I put the heavier load on to "see what would happen" and was quite surprised and pleased by the improved performance, so "running-in" was the solution, just more than a couple of hours.

I think that's certainly something to consider, once I've lapped all the required surfaces I think some light loads to run in sounds like a good plan.

[georgesheppard]

I received some autosol and a sheet of glass in the post in the last couple of days so thought I'd take a look at lapping.

Before:

After initial attempt:

The port faces are quite pitted on the rear side. I'm not sure how smooth I need to go? Am I aiming for a smooth mirror like finish?

I have an older Mamod loco I'm also working on - I noticed the reverser block has the ports widened:

Is this something worth doing to my MSS reverser block?

[-steves-]

They look loads better, much shinier and flatter, of course less likely to leak

I wouldn't worry too much about the port sizes, I have never bothered to open the ports out as it can change the "timing" so always left it alone.

[georgesheppard]

After several steam tests later I feel like I'm back to square one! It still fails to pull anything and it's quite erratic in terms of control. I've stripped it down again today and noticed a few things.

Firstly, on the reversing block - is there a trick to help line up the block with the rotating part? I've tried a few times and it seems to have both the inlet & exhaust fully open would require an unobtainable position in terms of rotation and the frame.

Comparing my new MSS reverser block to an old Mamod one, it seem the straight ends of the channels are on different sides? This seems strange. Mamod on the left, MSS on the right.

I've also been looking at the seals between block & frame. It seems the frame and block don't line up very well. How much of a problem could this be? Short of ordering a RWM reverser block - any further advice welcome!

[Chris Cairns]

Whilst considering my reply I found my original photos so have re-instated the missing images in my MSS Kit Build topic here - viewtopic.php?f=44&t=6201

If you have not already found them, this library contains many useful files - www.hglw.co.uk/mamod.html I recommend starting with the top one - Mamod Handbook.

That Handbook recommends drilling out the chassis side frame steam holes to 1/8" or 3mm. Having done that make sure that the cylinder gasket is not covering part of those holes - use a circular file to open out as necessary.

I've drilled out the steam holes here, and the gasket needs a little fettling to clear those holes.


The gasket forms the steam path for the two cylinder ports so make sure the holes are not blocked on the rear of the cylinder backplate.

You can chamfer out the steam holes on the reverser block. On your Mamod one above they've chamfered out the mounting holes as well which will likely cause a steam leak.

Does your upgraded safety valve lift whilst under gas firing? Without a pressure gauge the only way of knowing what pressure you have is when the safety valve lifts (I assume that is a Dream Steam 20 - 25 psi valve). The safety valve is not lifting in either video so your pressure may be a bit low for running in?

Is your chassis free running? If you lift the pistons off the crank pins & fully retract them & rotate the cylinders out of the way you should be able to push the loco to see how far it will travel/free run. Sometimes the mount on the gas burner is too wide which then affects the wheels.

You are correct. The cutout plate on your MSS reverser has been mounted back to front. You could try temporarily fitting the correct fitted one from your Mamod to see if that makes any difference.

Chris Cairns

[georgesheppard]

Chris - thank you for your detailed reply.

Since my last post I gave in and ordered a couple of RWM reverser blocks which arrived this morning. They come with some gasket material on the sides and are obviously are made to a far superior quality. I'm going to fit these over the weekend and see how I get on.

Does your upgraded safety valve lift whilst under gas firing? Without a pressure gauge the only way of knowing what pressure you have is when the safety valve lifts (I assume that is a Dream Steam 20 - 25 psi valve). The safety valve is not lifting in either video so your pressure may be a bit low for running in?

I think the regulator might be leaking steam, I'm going to take it off the boiler and wrap a bit of plumbers mate on some of the threads.

Is your chassis free running? If you lift the pistons off the crank pins & fully retract them & rotate the cylinders out of the way you should be able to push the loco to see how far it will travel/free run. Sometimes the mount on the gas burner is too wide which then affects the wheels.

No issues free running, without the pistons attached it will roll across the table quite happily.

[georgesheppard]

I put the body + chimney stack back on to help stop the boiler wobbling while testing. Please ignore the shoddy slot cut + priming for the regulator!

Testing went well, I'm hoping with a bit more running in the performance will keep improving.



Still doesn't have much pulling power but it feels like the performance is a bit more stable on the track at least.

Goes like the clappers on some improvised blocks.

[georgesheppard]

Could anyone advise if upgraded pistons are worth the money? I was thinking about ordering some from RWM. At £85 for a pair, I'd rather not bother unless I can expect a decent boost!

[-steves-]

Could anyone advise if upgraded pistons are worth the money? I was thinking about ordering some from RWM. At £85 for a pair, I'd rather not bother unless I can expect a decent boost!

Upgraded ones are better or at least the ones I used to have were, however they are not worth the extra £85 IMHO, that's a lot for a small gain.

Nothing beats a good many hours of running in as long as everything is as it should be, that's assuming it's not got something broken or leaking.
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