Britannia 70047 "Derek Stokes"

[dhamblin]

Ok, that's spooky, I think my one has the same problem! Occasionally put it in full forward gear, open the regulator and all you hear is steam escaping up the chimney. Give the loco a 'jerk' forwards and it starts moving with no problem.

Taking the cylinders off this month to do a re-packing exercise and fix the steam leaks, so might find something of interest.

Regards,

Dan

[keith1500]

I had similar problem with my Speedy. The fault was valve sleeve where it was pressed into the block. The steam was short circuiting around it. Most notable when stationary.

I proved this by popping a snug fitting piece of PTFE, long enough to block off the ports. Applied steam or air and found it exiting the blast nozzle. You can open and close the cylinder cocks this will show if the leak involves the cylinder

Keith.

[JonL]

Dan, could your issue be the snifting valve? On a slide valve engine I would suspect the valves were not seating, but as a Brit is piston valves it could be your snifting valve is leaking and it either sounds like your steam is going up the chimney or it really is and you have something amiss with your snifter!

[dhamblin]

Actually, I think Keith has hit the nail on the head. On the rear face of the left hand cylinder assembly, where the piston rod cover meets the valve chest cylinder I noticed the paint had bubbled and indeed was pulsing as the valve gear turned over. That makes me think there is a sealing issue between the valve chest cylinder and the bore it sits in, which would explain how it can bypass the valve arrangement.

Also, I've got a video from the November track test from the moment I started off with the cylinder drains open and an air temperature of around 5 deg C. The left hand cylinder is definitely doing something odd as the right hand one is giving sharp, clean expulsions of steam, whereas the left hand one is doing much shorter less intense bursts for part of each wheel revolution.

Might be worth checking your cylinder for same issue Jon, as it should display similar symptoms?

Regards,

Dan

[JonL]

Yes that does sound quite likely. Oh what fun!

[keith1500]

I wasn’t up for any major rebuilding in order to solve the problems. So, when I had a chance the cylinders came off and the repairs were done in two stages.
The leak to the outside was exhaust to front where the sleeve protrudes beyond the cylinder block. This was solved with soft solder. I run a fillet around all four to ensure all leaks are solved.
The internal leaks were solved by “injecting” liquid PTFE into the leak area. Basically, I filled the port with liquid PTFE and used compressed air to force it into the leak. Then blew the ports passageways clear and cleaned out the gunk with cotton buds etc. Check it for leaks and repeated as necessary or moved to another port.

It seemed to work okay. I haven’t done a lot of running so can not report on the success.

I wrote a short article for the club magazine. I’ll see if I have a copy of that helps?

Keith.

[JonL]

So I used her yesterday and to my astonishment not only is the lubricator now delivering far better the cylinder leakage appears to have sealed itself. After some initial hesitation it ran beautifully all day, with the only minor issue being the reversing shaft drive universal joint slipping. I'm confused but happy...

A friend who owns a Polly 2 drove her and came back astonished at how powerful it is. I guess I hadn't noticed as i've been slowly tweaking it to improve but yes, I think for its size its a decently powerful locomotive now.

Thanks to everyone who answered to help me out above, it is all noted.

[JonL]

I've been spending some time finally doing the detail work I'd been putting off. Handrails, AWS Battery box (made from a solid block of steel... it's all good weight...) and Placards "Built in Crewe" "Tender Capacity" etc all mounted in place. It's funny, they are only little details but they make a culmulative difference. Next up is to get that lining done properly.

[JonL]

Had a nice day steaming but after running for more than a couple of hours the valve timing started to get uneven. I pulled it off the track to investigate and couldn't find anything amiss, so I put it back on the track. Ran fine for another couple of hours then did it again! I think it's probably time I investigated the valves and piston rings anyway, just see if I learn anything.

[JonL]

Checking the valve bobbins one appears to be very slightly loose on its shaft, generating a 7 thou difference in spindle length. I've readjusted it. Meanwhile I'll go round the rest of it and check the geometry.

[JonL]

Made many changes since I last turned up on here.. Valve chest pressure gauge (although someone in the club quite rightly pointed out its actually a wet header pressure gauge, although I am not sure how much difference that will make), I've now relined it using my Beugler pen, added lots of detail such as hand rails, AWS battery box, rolled the top of the smoke deflectors properly (was always too scared to do it...), and most recently have started making better details for the tender. I'm also going through the process of fitting brake gear. however I've no intention of making it work. It's a purely cosmetic exercise which will hopefully add nice detail as well as much needed weight.

[JonL]

Had an odd problem where the water feed pipe between tender and axle pump kept getting popped off as if under pressure. Got the courage up to spin her upside down and drop the axle pump and it turns out the top ball (there are 3 in a Britannia pump) has started to lodge in its outlet. It's never done it before, but I resolved it by adding a 4ba brass screw through the cap above and then screwing it down until the correct lift was gained without blocking the outlet. Then the cap was removed and the brass screw silver soldered in place. Machined off the excess and reassembled. It seems to work under air pressure but as always the proof of the pudding is in the steaming.

[JonL]

Well it worked for a while.... but it's uncovered an issue with the suction clack! Managed to clean up the seat enough to work well enough at the track, but anything over 4mph and the delivery pipe from the tender would blow off with the back pressure. Will be making a new suction clack seat before I steam again. Otherwise managed to do 5 miles of running with good efficiency and smiles.