Bazyle,

Thanks for the reminder. I was aware of it and I have left as much meat on the cylinders (flange face to port face) as possible. Unfortunately, I had already machined the steam chests a long time ago so I will have to see whether the meat I have left on the cylinders will be adequate. If it isn't, I will go with the offset valve cross head.

I will also make another round stretcher close to the bottom of the cylinders and I like the idea of introducing steam to the cylinders/ steam chest at the front face of the steam chest.

I have seen a list of other possible mods including a mod to the blast pipe and some sort of rear axle/ axlebox cover etc. However, reminders would be great – please.

The ones that hurt the most are the modifications to the boiler because I built it in the 1980s to the old drawings complete with threaded longitudinal stay bushes and a screwed top water gauge fitting (ouch). Various people have suggested that I can salvage it but looking at it in a different way… I have done it once – so I can do it again. I still have all the flanging plates that I hacked out of 1/4" steel – oh and I will build it in line with my local club involved this time – once this virus thingy has cleared..

Phil H

Thanks Rex,

I will press on and who knows, maybe I will get my bag of bits to Bromsgrove in September.

I am currently machining the axles to fit the wheel bores at the moment.

I will take a measurement of the cylinder port faces later to see if I am lucky enough.

Phil H

Dave,

Your valve gear issue…… did any of the basic valve gear parts need to be modified or did you simply struggle to get the as designed parts to work properly? I am aware of a blast pipe issue. Is it something about increasing its height slightly? If so, do you know by how much?

I was made aware of the rear axlebox issue some time ago so I have made 'split' rear axleboxes on my engine. I will take a picture. I will also try to arrange a cover – somehow. Do you know if others have made a cover and how?

Rex, yes thanks keep me updated. My chassis looks ok but I feel that I have made about 3 Roy Roy chassis so far. One shown in the pictures above and about 2 others for the scrap bin.

Phil H

Dave,

Thanks for the tips. I have found some online information from Don Ashton. I will definitely study it before diving into the valve gear.

Next issue….As you can see, I am ready to make the bearings and intermediate coupling rod pin. The intermediate pin is turned from rod with a 45 degree (90 degree included angle) head to fit a countersink in the back of the rear section of the coupling rod. I will add a short section of 4BA thread at the front of the pin for a brass washer and 4BA nut. I am assuming that I need to machine the pin so that the washer and nut tighten up to a shoulder on the pin rather than 'pinching' the coupling rod. The same will happen on the trailing crankpin and driving pins. Is that the right approach and if it is – how much clearance – a couple of thou or should it be more?

Also, I was planning to fit plain hexagon nuts. Would round nuts with flats be closer to the real thing? I don't have any 2BA and 4BA nuts anyway, so turning a few round ones would not be an issue.

Baz, thanks – nice tip regarding the slightly long bush – I will do that.

What about the other end – the nut end. How much clearance between the round nut and the coupling rod. The wheels can 'float' side to side. Do the coupling rods need to float also and if so about how much?

Phil H

Dave, thanks.

Believe it or not I have just taken delivery of some laser cut parts that include the David Machin, stainless steel ashpan. I haven't studied the ashpan but do you have any idea how it is an improvement. Does it get the fire working better or prevent the spread of ash – or maybe both?

Some might suggest that laser parts are cheating. Everything so far is traditional build but if I carried on using the traditional methods, I reckon I would be complete by about the year 2100.

Phil H

Thanks Baz,

I've got about 0.005" extra length on the intermediate pin/ nut. but the tongue and slot is quite snug. I was going to allow about 0.005" on the coupling rods but I will now go for 0.010" as you suggest and about 0.010" extra at the back of the coupling rod to prevent rubbing the rods to the wheel hub. I might also double check the wheel hub run-out again to make sure.

Mr Evans did mention a snug fit on the driver crankpin and mentions the need for movement on the leading and trailing pins but doesn't suggest an actual clearance.

I did a few geometry sums and as you say, they must need at least 0.003" before metal to metal contact is made between the pins and bearings and that assumes that the quartering is perfect – so I think you might well be right at 0.005".

I will wait a while before cutting metal just in case somebody comes with a 'yeah but'.

Thanks again,

Phil H

Yes – a good plan. It wont freely roll without coupling rods yet i.e., the wheel bearings are slightly tight. It will roll freely if I put weight onto it though. The coupling rods without bearings are tight but tight all the way round the rotation.

I think I was lucky with the wheel centres which probably helps. With the wheels and axleboxes fitted, I measured across the axles with a big micrometer (M&W – lovely thing), there was no difference from one side to the other – not even a fraction of 0.001"

I like the house brick idea.

I need to beg forgiveness from the late Martin Evans. I hadn't read the section on coupling rod clearance properly.

He says the driving bush should be a good fit to give smooth running but the leading and trailing bushes should be opened out with a letter F drill. Letter F is 0.257".

Phil H

The cylinder/ steam chest studs are 6BA and 3mm rod looks about the right size for 6BA but most suppliers only have 3/32" or 1/8" in mild steel. I do have some 3mm brass. So – is brass no use for this application and or have I overlooked a ME supplier who does 3mm mild steel?

Phil H