The Home Machinist!

Hello all, I'm looking for a procedure to test my cylinders. And or the quality of the rings. The valves too. (Stephenson valve gear)

Thank you for any help.
Tom

what make and type of cylinders?

I'm sorry they are on my 2-4-2 Columbia they look homemade.

Slide valve i would assume? if they are and I wanted to test the rings, I would make a plate with a seal that i can bolt down on the valve face, then remove a cylinder drain and connect to an air source. if you have any blowby, you will see that out other other end, but be sure the piston is secure so you do not send it through the rear head.
piston valve cylinders will like require a bit more thinking.

Check blowby at either end as well as the limit of piston travel.

I use a piece of plywood with a sheet of rubber on the face...held in place by a c clamp like a sandwich.

Very neanderthal but for something I use once in a decade..why be fancy?

cbrew wrote: ↑Wed Mar 10, 2021 1:36 pm Slide valve i would assume? if they are and I wanted to test the rings, I would make a plate with a seal that i can bolt down on the valve face, then remove a cylinder drain and connect to an air source. if you have any blowby, you will see that out other other end, but be sure the piston is secure so you do not send it through the rear head.
piston valve cylinders will like require a bit more thinking.

When you say any blow by that seems a little strict. I have a cylinder leak down tester (used on race engines) it reads in % what % do you think would be acceptable?

Thank you
Tom

For aircraft we use a leak down test as well. Piston at TCD, pump 80 psi in and see what it holds. 75+ psi is excellent, 70 is ok, and I beleive it can go as low as 60psi before the cylinder comes off. So thats 75% minimum.

Thats for internal combustion of course but maybe it helps.

Assuming you have a two cylinder steam engine--- First easy tests without dismantling, arrange a supply of compressed air at about 20 lbs pressure, feed that to the boiler, jack the engine off the track, or out of gear if a traction engine,Open regulator, motions should spin enthuiastically.
Secondly, stop motions from turning( USE BRAKE or SCREWDRIVER THROUGH SPOKES, NOT FINGERS OR HAND)put one hand over chimney, open regulator, if there is any perceptible blowby you will feel it.
Thirdly, Repeat step 2 at various positions of motions, especially just before each dead centre. IF the blowby hardly changes then it is likely your valves are the culprits. If blowby varies then it is likely then piston, rings or cylinder bore are the problem,
Deciding which cylinder is at fault can be difficult with only these preliminary tests. Try these and report back for more guidance, Regards David Powell.

10-4
Thanks
Tom

The slide valve seems to be the problem. I don't know where to start.