The New??? Mamod Locomotive Mark II

Chris Cairns · Post by **Chris Cairns** » Thu Oct 03, 2013 8:43 pm

John,

Thank You for posting the photo of a dismantled current Mamod oscillating cylinder.

So what were Mamod thinking of by using 'O' ring pistons without a proper lubricator on the Mamod Train/Mark I locomotive? Glad I managed to fit a dead leg lubricator to mine.

Chris Cairns.

Aizoon · Post by **Aizoon** » Thu Oct 03, 2013 8:44 pm

I pay for lots and lots of space and use it for backups. Well worth it, IMHO.

Aizoon · Post by **Aizoon** » Thu Oct 03, 2013 10:08 pm

Chris Cairns:90083 wrote:John,

Thank You for posting the photo of a dismantled current Mamod oscillating cylinder.

So what were Mamod thinking of by using 'O' ring pistons without a proper lubricator on the Mamod Train/Mark I locomotive? Glad I managed to fit a dead leg lubricator to mine.

Chris Cairns.

Not to mention using a brass piston rod. I wonder what the other one will look like when I dismantle it?

Aizoon · Post by **Aizoon** » Fri Oct 04, 2013 3:02 pm

Aizoon:90088 wrote:
Not to mention using a brass piston rod. I wonder what the other one will look like when I dismantle it?

Much the same, really.

I've replaced the O-ring on one cylinder and the improvement is dramatic, at least when testing the cylinder alone. Can I just ask what type of O-ring I need? I only had one in stock and need to replace the other.

Chris Cairns · Post by **Chris Cairns** » Fri Oct 04, 2013 4:15 pm

John,

As you are the first owner to successfully take apart a new style Mamod oscillating cylinder that I'm aware of then I do not think anyone here will be able to provide you with the correct 'O' size.

From the updates that Mike Wakefield posted regarding the stalled Thomas Telford project Mamod use nitrile 'O' rings. From research on-line and a recommendation from another live steam Club I've found that using viton 'O' rings instead should give better results.

A phone call to Peter Johnston at Mamod should get you the right size, and if he has any in stock I'm sure Peter would post you a couple.

If you do get the correct size posting that information here would be very useful for future reference.

Chris Cairns.

Aizoon · Post by **Aizoon** » Fri Oct 04, 2013 4:47 pm

It wasn't really the size I needed, Chris, it was the type. Of course, due to Sod's Law, the first site I found when searching talked of "Vitron", which I couldn't find. When I realised it was Viton, I ordered 10 each of 5, 6, and 7mm, although I'm pretty sure it's 6mm.

They're dirt cheap anyway,and it's useful to have a range. I'll report back on progress when they arrive.

Aizoon · Post by **Aizoon** » Sat Oct 05, 2013 2:35 pm

Yes, they are 6mm, although M. Sod got his oar in. The first O-ring out of my pack of "6mm" rings was, of course, 7mm. The rest were fine...

Fortunately, I'd seen this trick before, and knew what to do

Chris Cairns · Post by **Chris Cairns** » Sat Oct 05, 2013 7:31 pm

So 6mm Inside Diameter, but what cross section?

You also got your 'O' rings sent very quickly - who do you get them from John?

Chris Cairns.

Aizoon · Post by **Aizoon** » Sat Oct 05, 2013 8:17 pm

On eBay from sealforce53, Chris.

I can now disassemble my cylinders in situ, but still having problems. I'll keep working on it.

Aizoon · Post by **Aizoon** » Sun Oct 06, 2013 6:00 pm

SAGE OF WOOKEY bench tests 6/10/13

RH new cylinder with ordinary 6mm I/D 1.5mm C/S O-ring

LH old cylinder with thicker 6mm I/D 2mm? C/S O-ring

1. Cylinders dead centre - some steam from exhaust. Needs investigation. Reverser in mid kills steam as does regulator.

2. RH Cylinder in forward but not connected LH in dead centre - steam and water persisting from exhaust

3. LH Cylinder in forward but not connected RH in dead centre - some steam from exhaust but not much more than (1)

4. LH pinned and RH cylinder connected - Won't run and steam persisting out of exhaust.

5. RH pinned and LH cylinder connected - Runs well with proportionate exhaust.

Conclusion. O-ring supplied is right I/D but wrong C/S.

Action - get thicker (2mm C/S?) O - ring.

I/D - internal diameter
C/S - cross section

Aizoon · Post by **Aizoon** » Fri Oct 11, 2013 1:03 pm

Well, there you go. A 2mm cross-section O-ring does make the cylinder steam-tight. Unfortunately, it's also too tight to move freely. I tried turning one down slightly, but then the surface is no longer smooth - same problem

In desperation, I turned to my faithful PTFE tape - result! Even with the remains of an ancient roll of tape wound round in the cylinder head groove, eppur si muove - she runs

Have ordered some less manky tape and will try again to tune up the beast. It will be interesting to see how well it lasts.

Later Got some more tape and adjusted the packing. Works like a dream. Hauling twelve axles on my ferocious 14" (355mm) radius heavily graded indoor line, it runs sweetly at a sensible speed.

After some very necessary cosmetic work, SAGE OF WOOKEY will return to service.

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