Rob Roy Build

[philh1aa]

Dear knowledgeable ones,

I am currently in the middle of a Rob Roy build (I will try to add some pictures at some point) but I have a rolling chassis with part machined cylinders.  I am trying to fit the cylinder drain cocks and its operating mechanism.  So the first question;

1. The drain cocks are rather small and look quite fragile.  They also have a round body with no flats for tightening.  So I presume that you should only really fit them finger tight or with a massive amount of care with protected hand tools??  Does anybody have any recommendations for sealing the valve bodies in the cylinder holes whilst achieving the correct orientation i.e., do I use copper washers and adust their thicknesses and or some kind of clever gasket combined with sealant etc?

The second question relates to the operating mechanism and I would imagine it is Rob Roy specific maybe??

2. Why is their a 'kink' at on the operating handle in the cab.  The drawing in the book is less than clear.  I would imagine that Mr Evans was trying to avoid something or bring its handle into easy reach but it just looks an over complication.  Does anybody know?

Phil H

[JonL]

I use loctite 567 as a thread sealant which is quite effective. They don't need to be hugely tight when this sealant is used. My technique (and I'm quite inexperienced) was to use a copper washer and sand it down to reduce the thickness to the point where the drain pointed in the right direction. However this sealant would probably hold the drain cock in the right direction without being fully tightened down.

[smallbrother]

Don't worry about getting them fully tight.

When fitted, the linkage between each pair will keep them in the right position.

Pete.

[Kevan]

Hi, I am also working on a Rob Roy and fitted operating stuff for the drain cocks. I mounted the lever on the same pivot as the reverser and the kink allows it to clear the bits on the reverser. The operating rod runs directly above the frame to avoid everything else hence the step to clear the step in the top edge of the frame. None of it was too difficult to do

[dscott]

I have just decorated the NEW top shelf in the workshop with a Rob Roy running Chassis.
Lovely locomotive and even part built they look nice.

Interestingly on twin sisters 4 pipes lead the water to a bank of draincocks in the middle.
Perhaps in the Docks they were always getting damaged OR this kept the hot stuff away from
the odd Dock worker who was too close.

David and Lily.

[Shawki Shlemon]

Hi , I generally use a thin lock nut .

[philh1aa]

Thanks for the input chaps,

All....apologies for inserting their instead of there in the second question.

Nobby - I will look up the Loctite product and get a few packs of copper washers.

Pete - with most of the operating mechanism in place, one side is ok because the drain cocks have 'bottomed' against the cylinder holes. The other side tightens and untightens as the mechanism is operated. I think mine at least need to be 'nipped' and bottomed. Perhaps my threads are a bit too loose?

Kevan - That is an interesting thought (using the same pivot). I will look into that because my brakes are on the right hand side and the brake stanchion does come quite close to the cylinder drain cock lever.

David and Lily - Yes it is a very nice engine. I will be taking my semi complete engine to the Rob Roy rally in September (Covid allowing of course). Mine is starting to fill out nicely now. I have the brakes fitted and part of the cylinder drain cocks of course - so I would imagine that the chassis is going to be very busy when the valve gear and pumps have been fitted.

Shawki - I suspect that my cylinder drain cock bodies are a bit short to add a locknut but I have noticed that the suggested mods to Rob Roy include thin locknuts for the cylinder and steamchest glands.

Thanks everybody. I posted the same question on the Model Engineers website before posting here and no response. I think that site has too much tumble weed blowing through it.

Phil H

[stevep]

Phil, you don't need to buy copper washers - simply make a washer cutter as follows.

Take a block of steel, and drill and ream a selection of holes - e.g. 3/16", 1/4". 5/16", 3/8, etc. Then make a saw cut through the block (not all the way) to cut across the holes. Make some punches from short pieces of silver steel of the same diameters.

Slide a piece of copper sheet into the slot, and use the appropriate size punch for the inside diameter of your washer to punch a hole through the sheet. Then slide the sheet (and hole) under the hole corresponding to the outside diameter, centralise by eye, and then use the appropriate punch to punch out the washer.

If you want to be posh, relieve the back of the holes so the washers (or discs) drop out easily. You can also reduce the diameter of the punches in the bit behind the business end.

I've had mine for yonks, and works a treat.

[philh1aa]

Steve,

Thanks for that, certainly worth thinking about. I did consider parting off the end of a copper bar but punching might be better.

I am currently making a plumbing list so I will see how scary the costs get. If it is too scary, the list might evolve towards some bronze and stainless rod to make my own. Lets see - I still haven't sorted my silver soldering kit out.

Phil H

[smallbrother]

May 8, 2021 10:53:40 GMT philh1aa said:

Thanks for the input chaps,



Pete - with most of the operating mechanism in place, one side is ok because the drain cocks have 'bottomed' against the cylinder holes. The other side tightens and untightens as the mechanism is operated. I think mine at least need to be 'nipped' and bottomed. Perhaps my threads are a bit too loose?


Phil H

Hi Phil,

Are you saying they somehow unscrew themselves? With the links attached to each pair I can't see how they can rotate.

Pete.

[philh1aa]

Pete,

Yes there is only just enough freedom to notice the bodies rotating as the mechanism moves forwards and backwards. The other side is fine because the valves are 'nipped' and bottomed against the wall of the cylinder.

I think it is just a washer plus a bit of the Loctite gunge that is needed now.

I am on the home straight with the cylinders because I managed to mill the ports and drill the passages successfully. The only other hurdles are the cover drilling and getting the exhaust pipe to line up.

Phil H

[philh1aa]

I managed to solve the loose cylinder drain cocks by having a bit of a think. Sorry if this is completely obvious to you guys but I realised that the thread is 40TPI. That means for every revolution, the threaded part will move 0.025". So if for example, the body of the valve bottoms out 180 degrees out of position, you need a washer that is just over 0.012" thick to get it to bottom out exactly right (metal to metal). Obviously, corresponding thicknesses if it is say 245 degrees or even 90 degrees out.

So, I parted off a couple of skinny bronze washers (I didn't have any copper) and it works brilliantly. Just a bit of minor adjustment with some very fine emery. The valves are now nice and secure so I can carry on making up the operating mechanism with confidence.

[JonL]

May 9, 2021 15:45:36 GMT philh1aa said:

I managed to solve the loose cylinder drain cocks by having a bit of a think. Sorry if this is completely obvious to you guys but I realised that the thread is 40TPI. That means for every revolution, the threaded part will move 0.025". So if for example, the body of the valve bottoms out 180 degrees out of position, you need a washer that is just over 0.012" thick to get it to bottom out exactly right (metal to metal). Obviously, corresponding thicknesses if it is say 245 degrees or even 90 degrees out.

So, I parted off a couple of skinny bronze washers (I didn't have any copper) and it works brilliantly. Just a bit of minor adjustment with some very fine emery. The valves are now nice and secure so I can carry on making up the operating mechanism with confidence.

I actually typed out the first part before and deleted it before sending thinking I was over complicating things! 

I'm glad you have it sorted.

[philh1aa]

Thanks Nobby. By the way, I looked up Loctite 567 and noticed that it was a thread sealant for low pressure. Does the same gunge work on boiler fittings (for when I get there)?

[JonL]

It's the one I use for all boiler fittings (rightly or wrongly). I find it cleans off nicely when you remove them too (coming off the threads as a dry crust).

www.henkel-adhesives.com/uk/en/product/thread-sealants/loctite_567.html

This web page suggests a very high pressure resistance but I suppose it all depends on the size of the thread, length etc. The data sheet itself wasn't that easy for my sluggish brain to interperet this morning. I've not tried loads of different sealants but so far this has been the most effective. Bear in mind I'm one of the less experienced members of this site though.

[philh1aa]

Nobby, Thanks for the link. I have heard of Loctite type of stuff being used for boiler fittings before but not sure which number had been referenced. Perhaps the experience will come along shortly and let us know. On the other hand, I notice that you are giving your William some exercise and if it works - it works.

Phil H

[don9f]

I have used Loctite 577 successfully for years as a thread sealant but have recently thought that when 577 runs out, I’ll try 567 instead. The 577 is fairly easy to dismantle. For flanged fittings, I use 574, also with great success.

Cheers Don

[philh1aa]

Thanks Don.

So we have a strong leaning towards 567 for screwed fittings but that raises another related question or at least confirmation maybe? Lets take items like the steam chests and cylinder covers. I would suggest that the cylinder covers and at least the steam chest cover could do with a gasket method and system that is easy to dismantle? Should they be fitted with paper with some ter gunge or is 574 suitable for those i.e., are the parts easy to 'part' if 574 is used?

Sorry for all the stupid questions but I am going through this the first time. Yes I have used liquid silicon on car parts or cork etc many years ago but they can always be tapped with a mallet to get them apart. Cylinder covers on a small engine would be wrecked.

[smallbrother]

May 11, 2021 18:57:37 GMT philh1aa said:

Thanks Don.

So we have a strong leaning towards 567 for screwed fittings but that raises another related question or at least confirmation maybe? Lets take items like the steam chests and cylinder covers. I would suggest that the cylinder covers and at least the steam chest cover could do with a gasket method and system that is easy to dismantle? Should they be fitted with paper with some ter gunge or is 574 suitable for those i.e., are the parts easy to 'part' if 574 is used?

Sorry for all the stupid questions but I am going through this the first time. Yes I have used liquid silicon on car parts or cork etc many years ago but they can always be tapped with a mallet to get them apart. Cylinder covers on a small engine would be wrecked.

Hi Phil,

I use paper gaskets (bought a big sheet of it some years ago) and a smear of high temp gasket sealant from the local car parts shop. A small sharp screwdriver has always got the old ones off without difficulty.

Pete.

[JonL]

Paper gaskets and making sure you tighten down the covers evenly; remember you don't need to go mad with the tightness of the nuts on the steam chest studs as they are most likely quite small.

I bought a selection pack of paper gasket material from an ebay seller and as Pete says, it will last. I don't use a gasket sealant myself.