On the largish vintage engine I'm restoring, (see 'Work in progress' forum) there is a capped tube next to exhaust outlet on the steam chest. About 1 1/2" long and just under 1/2" OD with 1/8" BSP thread each end.
One end screws into the casting the other has a screwed hex brass cap tightly fitted. The bottom feeds a groove in the steam chest casting that leads to the mating surfaces for the slide valve. So obviously a lubricator of some kind.

My query is that as it only has a 1/4" hole drilled straight through, is it simply manual oiling point i.e. before running the engine, unscrew the caps and give them a good squirt from a can?
There is no provision for reservoirs or attachments to hold copper wires for suspending wicks etc and no obvious signs of any type of drip feed needle etc. it's just a straight hole!
If, as I strongly suspect, it's simply a manual oiling point, how long is one good squidge of oil going to last in a hot steam chest? (I suppose that's a bit of a 'how long is a piece of string' type question though).
It is a very early engine that, as far as I know, pre-dates 'fancy' displacement oilers or mechanical feed systems. Unfortunately all the 'ancilliary' bits were missing when I got the engine so I have been working in the dark somewhat.
Perhaps some of the loco building fraternity might be familiar with this sort of thing on early examples?
Any useful comments much appreciated. Regards Mike

Thanks for all the replies chaps, gives me some food for thought. If the pipe had been all there was – i.e. with an open end I might have suspected it may have been connected to some external feed or pipe etc.in the past However, as MichaelG noted – that cap really has the look and feel of well handled brass! It's also a very good fit, internally it is nicely flat to provide an excellent seal against the top of the pipe, which makes me feel it was a regular task of the operator to be using it. Theres not a lot of room around it so any kind of additional reservoir or device wouldn't fit I think.,difficult to see from the pics, but there's only just enough room for your fingers to unscrew the cap.

Still, I appreciate your time and trouble. If anything else comes to mind, I'll be more than happy to hear ideas!

Projects like this don't half help keep you mind active.

regards, Mike