More Minnie help required

[David Bothwell 1Participant @davidbothwell1]

After making a new piston and new endcap and re-assembly of my Minnie cylinder I tested this (held in the vice) by compressed air and hand operating the slide valve, all seemed well so I fixed the cylinder to the boiler and connected the con rod and valve rod. But upon opening the compressed air tap there was no effect on the piston, although there was air and plenty of it through the blower and exhaust. I blocked the blower (with tap made for it) but this still had no effect. i.e. there does not seem to be any pressure on the piston. As I have previously stated I bought this part made. I have noticed that in the base of the cylinder (inlet apeture) there is a hole leading to the blower, no idea why this is there as it does not appear on the drawing. Any help or useful suggestion would be most gratefully received. I have started to remove the cylinder from the boiler. I am mystifed as to how the cylinder appears OK apart from the boiler?

[David Bothwell 1Participant @davidbothwell1]

cylinder and transmission (frustration)

[JasonBModerator @jasonb]

Where did you put the air in when testing it off the engine?

There should be a hole to the blower from the milled cavity in the undersid eof the cylinder, its on my drawing.

[David Bothwell 1Participant @davidbothwell1]

Hello Jason, I placed a pipe directly into the hole in the apeture and fitted the compressed air to the pipe. I was tempted to put a thread into this hole and on the pipe but the pipe was such a snug fit there was no need

[JasonBModerator @jasonb]

It may be the valve is sticking slightly on the nut or rod which is stopping it sitting down onto the portface, it wants to be free to move but not sloppy This will mean the air takes the easiest route into the valve chest and straight out teh exhaust rather than moving the piston.

[David Bothwell 1Participant @davidbothwell1]

Thanks Jason for that suggestion, Is that why it works away from the engine/boiler? If I increase the height of the slide valve (just short of the top of the valve chest) would this have the desired effect? I think I have heard of people fitting a spring to the slide valve, but there is not much room for that.

[JasonBModerator @jasonb]

Keep the height the same. As the minnie does not have drain cocks it is better for the valve to be able to lift and avoid hydralic lock. It just needs to be free enough to find its own way onto the port face once there is some air pressure behind it.

[JasonBModerator @jasonb]

One other thought has the exhaust passage drilling got a plug screwed into it from below?

[David Bothwell 1Participant @davidbothwell1]

Yes the exhaust port has (now) been plugged, I noticed it a week or so ago (unplugged) and thought this was the cause of my problems, Thankyou very much for your replies, very much appreciated, but I cannot see that if I do not alter something (regarding the slide valve) that the problem will go away. I am already removing the cylinder for examination. Decided to strip the motion and possibly alter or remove the motion plate, re-make the cylinder endplate and go the way of the "Fowler" type Minnie (elsewhere on the forum) with angle iron supports for the piston rod etc.,

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