How to lap Mamod/MSS Pistons

DolwyddelanLightRail · Post by **DolwyddelanLightRail** » Mon Dec 21, 2009 6:12 pm

As some of you may know, I am currently overhauling my inherited Golden Jubillee Mamod, back into service, and I am currently ordering new steam gaskets for it (and also a piston upgrade set for then MSS, Britomart).

I am also going to lap the pistons and forward/revser thingy as well, now what I have been told, is to get a perfectly smooth surface, fine sandpaper and either go in figure 8 or circles until it is all done.

Is there anything else that may need doing or adding to? :? :)

(Oh, and is the pipe that comes with the better reg already in shape, or do I have to bend it???)

Dr. Bond of the DVLR · Post by **Dr. Bond of the DVLR** » Mon Dec 21, 2009 6:36 pm

For lapping I scavenged a nice plate of glass from a scanner at my school (well they had thrown it out!!), it is a great source of flat glass and free! I mounted it is a wood board so now I can put it on my bench when anything needs lapping and store it safely away!

mhlr · Post by **mhlr** » Mon Dec 21, 2009 6:36 pm

When lapping, you need to use wet and dry paper, and I'd use it wet. You correctly said do it in circles, but once you have finished, do 1 very light wipe lengthways across the cylinder port, as it gives the fine scrores you make go in an opposite direction to the way the cylinders move up and down.

made-in-england · Post by **made-in-england** » Mon Dec 21, 2009 6:37 pm

What I do is I get the finest wet and dry paper avaible. get a sharpie and colour in the area you want to lap the move in figure of 8s across the paper till theres no more sharpie... dead even... (PS use a piece of glass as a work surface,, dead flat

)

Also give it a polish with some brasso

DolwyddelanLightRail · Post by **DolwyddelanLightRail** » Mon Dec 21, 2009 7:03 pm

Thanks guys! I'll give it a try when I'm allowed to even look at them again!

That'll be after/just before xmas!

SillyBilly · Post by **SillyBilly** » Mon Dec 21, 2009 7:05 pm

I used fine grinding paste which laps both faces to match.

DolwyddelanLightRail · Post by **DolwyddelanLightRail** » Tue Dec 22, 2009 8:09 am

And before I go on any further:

HOW THE HELL DO YOU DISASEMBLE MAMOD PISTONS??????

made-in-england · Post by **made-in-england** » Tue Dec 22, 2009 11:53 am

What do you mean? to get them out of the loco it should be 4 bolts and the piston and port face come off and undo the trinion bolt and the pistion comes off...

If your asking how to remvove the pistion gently grip the cylinder in a vice and carefully tap the rod to knock one of the end caps off, they should only be a push fit.

DolwyddelanLightRail · Post by **DolwyddelanLightRail** » Tue Dec 22, 2009 11:55 am

I can get them off, it's the dissasembly of them, how do you get the front end (the face that faces the wheels) off as well?

made-in-england · Post by **made-in-england** » Tue Dec 22, 2009 12:13 pm

You really shouldnt have too.. or are you fitting new pistons? if thats the case and you dont need the old one then tap the top out and use a long center punch to pop the bottom one out...

DolwyddelanLightRail · Post by **DolwyddelanLightRail** » Tue Dec 22, 2009 12:15 pm

I was wondering if there was a long thing needed for it, yes I am fitting the upgraded piston set to H.G.Butler's old ones (As I think they are nackered after misuse and not being treated very well!)

SillyBilly · Post by **SillyBilly** » Tue Dec 22, 2009 5:37 pm

made-in-england wrote:use a long center punch to pop the bottom one out...

I'd for a punch rather than a centre punch, that way you can flog the old bits on eBay.

DolwyddelanLightRail wrote:(As I think they are nackered after misuse and not being treated very well!)

They were probably knackered when new...

DolwyddelanLightRail · Post by **DolwyddelanLightRail** » Tue Dec 22, 2009 5:39 pm

SillyBilly wrote:They were probably knackered when new...

I wouldn't be surprised, as the part of it looks slightly chewed to me!

Dr. Bond of the DVLR · Post by **Dr. Bond of the DVLR** » Tue Dec 22, 2009 5:54 pm

I got new cylinders from PPS and they are rubbish.
why are we all writing really small?

DolwyddelanLightRail · Post by **DolwyddelanLightRail** » Tue Dec 22, 2009 6:04 pm

I don't know!

I'm getting them from dream steam

Crackingjob · Post by **Crackingjob** » Wed Dec 23, 2009 1:39 pm

look on Dream Steam site for diagram of how mamod fits together...it will help
Crackingjob

Sir Clothem Cap · Post by **Sir Clothem Cap** » Sun Nov 21, 2010 12:06 pm

I cheated and brought new complete pistons/cylinders from dreamsteam.

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How to lap Mamod/MSS Pistons

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