The LNER Encyclopedia

Good morning all

I am attempting to build a C7/2 from two D49 bodies.
The chassis is going together nicely, but I’m confused (not difficult) by the Caprotti valve gear.
How is the valve gear driven?
I thought it was through the box that is inline with the RHS front driver, but this box seems to only be connected to a long valve rod. There is a pic in Yeadon’s D49 volume that clearly shows that the box has no connection to the driving axle.
Does this box merely hang from a bracket on the footplate?

There is slender rod driven by a small return crank on the LHS, connected to a lever, which looks like it oscillates. Is this the drive for the valve gear?

Whilst searching for information on Caprotti valve gear, I noticed that four of the six B3’s were rebuilt with it, becoming B7/2, in the 30’s. The B7/2 would be a simpler conversion of the Kay’s B2 than the original B3. However, sourcing nameplates might be a problem.

Earlswood nob

I'm not sure what you're expecting to see of the valve gear, but you may be jumping to a conclusion. The valve gear might be inside the frames, and what you can see is the reverser. I recollect that the earlier LMS Caprotti Black 5s has inside valve gear, and the last 2 plus the Standard 5's, outside. From a photo, the Caprotti B3 apparently had inside valve gear.

Thanks 1H for the reply
Thats produced more thought on Caprotti valve gear. The D49's, the C7/2's, and Cock o' the North have a "drive"? box on the outside of a RHS driving axle, but the B3/2 doesn't. This presumably means that the B3/2 had inside valve gear.
This leads to more thinking that has to be done, whilst cutting and shutting cab windows on the D49 cab; and doing household chores. It is strange that now I've retired, I still tend to follow the same routine that I had while working. Perhaps I feel that modelmaking IS WORKING; it's certainly more enjoyable.
Earlswood nob

Looking at photos of the Lenz gear on D49/2s,(presuming this is similar to the C7 rebuild,) and my limited understanding, the RH side external drive gear box, in line with the leading axle, is driven by a return crank,just visible on photos.Its output shaft rotates to drive the gearing for the cross frame cam shaft within the steam chest. On the LH side the small return crank/rod possibly provides the oscillating movement for the lubricators.Now open to correction!!

G'day all
I think you're getting there ten ten, the drive box driven by a return crank would rotate at the same speed as the driving wheel, and the cross shaft above the cylinders would operate the LHS valves.
It's looking like I'll need a small bracket to hold the drive box in position.
Earlswood nob

Just checked in RCTS volumes 3A (Atlantics) and 4 (D25 to E7).

The C7 rebuilds used Lenz gear rather than Caprotti, and were similar to the D49/2s in principle.Description is on Page 103.
For the D49/2s there is a layout diagram on Page 91.

There is also a section on this very website! See here History of Lenz Valve Gear on British Steam Locomotives

(If you PM me I'll see if I can photograph the diagram for you. Don't want to scan it as it might break the back of the book!)