If built to the drawings (and I don't think they have been corrected yet), the valve gear and the valve spindles don't line up. The difference is 1/8" (?), and the solution is either to make a stepped valve crosshead, or to make the valve face 1/16" further out from the cylinder, and the valve spindle 1/16" higher in the steam chest. (Thanks, to Steve Papworth.)
Change the pitch of the thread on one end of the valve spindle, to allow the setting of the valves to be more easily modified.
Fit thin locknuts to both valve and piston glands.
The bottom section of the crosshead pump is too close to the cylinders.
The blast pipe is in the wrong position. Increasing the height of the blast pipe by about 3/8" seems to improve draughting.
The dome bushing on the boiler should be 3/4" diameter bore!
CONWAY. 3 1/2" 0-4-0ST by Martin Evans.
The boiler barrel should be 14.1/4" long, not 14" as on early drawings.
BRITANNIA 3 1/2" Pacific locomotive by L.B.S.C.
Drawings L.O. 81 sheet 8. The side of the cab is stated as being 3 5/16" high............ Oh no it's not.......... it should be 3 15/16"
Also take no notice of actual roof dimensions, I had to add 3/16" at the rear and remove almost 1/2" from the front as the angled spectacle plates do not tally with the roof!!
Derby 4F by Don Young. "Some valve gear parts need extra 'swing' clearance". (I suspect that this might vary according to individual constructors, but a point well worth checking as you build.)
Virginia in 3 1/2" by LBSC. 1. The boiler won't fit if made to drawing. The firebox fouls the suspension either working or dummy. I raised the boiler 5/16" and narrowed the firebox and it just fits.
2.The boiler/firebox is too long making it very hard to fit the blowdown valve in the specified position.
3. The crank pins have no shoulder against which the coupling rods can run. This means that the rods would scuff the face of the drive wheels.
Tich by LBSC. Make the brake hangers 1/8th longer than stated otherwise the brake beams foul the frames. The forward break hangers are very close to the cylinders, as the brakes don't do much anyway might be best to leave the front ones off.
Tap the buffer beam when mounting the brake column, don't try and use a nut underneath as it won't fit.
The oil tank bracket doesn't need the "set" in it if you have angle joints in your frames rather than "sifbronzing" the frames.
There isn't a great deal of clearance between the combination lever(?) and the top of the slide bar if I recall in certain positions, I had to "relieve" mine.
Juliet 2. (The Baker valve gear version of Juliet), by LBSC. Peter Hale informs me that:
Crankpin: Too long - the 5/16 dia part should be 5/8 long, not 11/16.
Eccentric Rod: Slot in fork at front end not long enough to clear bottom of Gear Con-rod ("sickle"). Check from job first with sickle at furthest forward position.
Main Con-Rod: seems OK at 6 1/16 between hole centres, as drawing. LBSC "corrected" the length in an M.E. article to 6 1/4, but I didn't know that and mine fits OK!!
Buffer beams should be 7 1/8 long, not 6 1/2, unless you want heavily tapered running boards.
Maisie by LBSC. Stephen Blyth says: As I recall there are two errors on the boiler drawings. As is usual, there is one hollow stay for the blower, but both are shown as hollow somewhere else, to allow for the vacuum brake. The overall length of the boiler is, I think 3/8" longer on the boiler drawing than if scaled from elsewhere. As drawn, it's very hard to get the reverser into full forward gear, without burning your fingers.
Rob Roy by Martin Evans. Ivan Jacoby says:
The blastpipe is too low and the petticoat pipe has a very small bellmouth. I have fitted a multi jet blastpipe with the jets angled at 1 in 12 and a venturi petticoat pipe. I have raised the blastpipe to within 1/2 inch of the petticoat pipe. I have also reduced the chimney choke by about 1/4 inch. The result is that the draughting is much improved on a bench test and the boiler will maintain pressure whatever the throttle position.