A messed up Stuart no.8 Mk I

[Sanjay F]

I took a break from the Clarkson restoration as quite frankly it was driving me bonkers! 
 
This is an MkI no.8 which means it doesn't have a trunk guide, just a single sided crosshead. The original pictures make it look like its done, painted, mounted nicely and someone has even gone to the trouble of labelling it with transfers.

I guessed that wasn't the full story when I got it as it was cheap, so eyes wide open! The engine doesn't run, the valve has been remade and there was an actual nut holding the valve rod tightly in position. The valve also scraped along the port face and the valve chest. The holes from the ports to the cylinder are slots rather then drilled holes and one is particularly wonky. There is also no valve gland and rod goes straight into the valve chest.

So far ......

Machined the valve so it fits without catching
Made a new valve nut to give the valve some float
Drilled out the valve boss and made a valve gland to fit
Drilled/tapped cylinder exhaust to take 5/16" union
Drilled/tapped cylinder so inlet flange can be fixed
Drilled/tapped cylinder for drain cocks
Stripped off paint and repainted base, soleplate, flywheel and valve chest
Drilled oilway in eccentric

The painted items are now in my 'drying' room which is where the boiler is, so nice warm and I can shut the door to stop dust getting onto new paintwork.

Here's the valve after the above changes, made from Ali as opposed to brass, that's clearly a modern modifcation. I also rounded off the valve guide boss on the valve chest

https://www.youtube.com/shorts/7PtdT8y4b2M

[Sanjay F]

More pictures and also I have now detected there's a mix of metric and Imperial

[vtsteam]

Really great what you're doing! That port angle really surprised me. So much so that I thought maybe it was an intended  feature for some reason I didn't understand. Since it's square cornered it must have been cast in place, or was chipped out with a chisel. Probably cast in place with a core.

I've seen good illustrations of those rectangular section steam cylinder port cores and core boxes to make them -- Terry Aspin's drawings. I guess that one must have floated out of position during the iron pour, or partially broken inside the casting and twisted.

What do the ports look like at the steam chest end? Are they aligned there?

[Sanjay F]

That's a good point, I never looked at the steam chest end! The slots continue all the way through to the ports, you can see them on the photos.

This old advert mentions the ports are cast in, I presumed someone had taken an end mill to the casting and it had gone a bit skew!

[Sanjay F]

Made the lagging using Titanium foil to make a template and then drilled through it some copper sheet - it came out okay, a splash of paint and it'll look just like the Stuart lagging 

[vtsteam]

My guess then is that the core broke inside the cylinder and twisted. The passageway stayed connected however because these cores probably had a piece of wire inside to reinforce them. After the pour the sand core falls apart and the wire is withdrawn. Still, if it's a single break there will be some misalignment between the two rectangular channels. I guess the original builder might have cleared some of this with a needle file or other tool, or maybe they had enough overlap to work as is.

[Jasonb]

The Stuart cylinders usually have a "Z" shaped core the comes out into the side of the cored bore rather than the end so it may have moved quite a lot, though being an older engine maybe they did come straight out the end and it has just twisted and not reduced the cross section anywhere along it's length. The other end of the Z forms the port

[Sanjay F]

I'm now trying to visualise what that 'z' shaped core looks like in situ ...... and failing miserably!   

[vtsteam]

From Terry Aspin's The Backyard Foundry:

1.) The port core
2.) The cylinder and port cores assembled -- this is for the type Jason mentioned with the port coming into the side of the cylinder.

(Sanjay, if yours was an older style, per Jason that went to the end - it might have been more "C-shaped" or "L shaped" of  straight segments)

[Sanjay F]

That's what I needed, thank you - spatial 3-d vsiualising is not on my skills list! 

[vtsteam]

I can see why the Z shaped core would be less fragile than the C shape. The former would be cemented into the cylinder core as a whole.

The latter would be floating until laid into it's print hollow. More subject to breakage if anything shifted while ramming, etc.

[Jasonb]

Something like this but with a little bit of a radius on the bends joining the main core for the bore

Also make sure there is no sand left in there.

[Jasonb]

Some photos of the cores for a compound traction engine cylinder, you can see the similar shape of the passages.

https://anutting.co.uk/index.php/gmt-castings-and-parts/

[Charles Lamont]

I have an early kit for a No 8, with slipper crosshead, nickel silver rods, & Whit fasteners, in Christine condition, that's almost pristine, but has been christened by, fortunately, nothing more than facing the sides of the flywheel. Here are a couple of views of the cylinder casting, which, fortunately again, had the passage cores in the right places.   

[Sanjay F]

Thanks all for explaining how cores work, its not something I've delved into, but I'm interested in how these things are manufactured.

@Charles - I'm amazed that you have an untouched kit and the fact they are Whitworth fasterners made me relook at this one. These are Whitworth with an odd metric one here and there!

I finished off by making new gaskets and repacked the glands and we now have a running vintage Stuart no.8, I hope it looks better than when I started and I couldn't look at the name transfer so removed that and cleaned up the plinth

<a href="https://www.youtube.com/watch?v=IlRcmXY8hl8" target="_blank">http://www.youtube.com/watch?v=IlRcmXY8hl8</a>