Brian

[ozziemod]

Hi, I am currently building a quarter scale Galloway hit & miss engine from Ministeam plans in which they show a method of locating the ignition trip arm to the push rod using a clamping method.
However on looking at completed models they clearly show a slot in the pushrod for adjustment, question is, is anybody able to give me the dimentions to locate the slot and the pivoting method used?
This seems to be a much better option, any advice would be greatly appreciated thankyou.

 

[Jasonb]

The latest drawings from Mini steam should show the slot, George Britnell redrew all the drawings when he made their test ones when they took over the range.

It uses a stepped bolt and sleeve so the bolt locks onto the shaft but the trip is free to pivot on the bolt

If you are stuck I have the 1/3rd drawings but not the easiest to scale down to 1/4

J

 

[gbritnell]

Hi Brian,
When I built all of the Galloway engines I told the fellows at Ministeam that the drawings were really lacking clarity and ease of machining so they told me to redraw them. One of the areas of concern was how to locate the trip arm on the pushrod. The original design was to 'fit at assembly'. Given the fact that the castings and drawings had been around for some time I would have thought that a hard dimension would have been established for fitting up these two parts.
I did a complete layout of the engine with the pushrod, trip lever, and the rest of the moveable pieces to establish exact points so that the builder could machine the necessary holes. While I was looking at it I thought I would build in a tiny bit of adjustment so that it would be easier to time the trip lever. The outcome was to create a slot from the centerpoint of where the actual pivot would be. In theory the builder could fix the trip lever in the middle of the slot and it would be correct but if the dimensions of the trip were just a bit off then it could be moved a little.
The pushrod is slotted. The trip has a large enough pivot hole to accommodate a bushing through which the fixing bolt goes. By tightening the nut on the inside of the trip it locks the pivot bushing to the pushrod but allows the rocker to pivot freely.
The 1/4 scale Galloway was redrawn by someone else and I'm not sure how he went about mounting the trip to the pushrod.
I did make up a little fixture that had a slot in it that would locate on the pushrod. The fixture had a pivot hole with a removable pin that the trip could be mounted on. The engine was put into the firing position and the fixture was slid along the pushrod until the trip just tripped the ignitor. The fixture was then clamped to the pushrod by a small set/grub screw coming in from the top. The trip and pivot pin were then removed. I then scribed a line in the pivot hole. The pushrod was removed and the hole drilled in the center of the scribed circle.
gbritnell

 

[ozziemod]

Hi gbritnell, Thank you for your reply, most interesting, from the information you give I think I will be able to locate the hole/slot without to much trouble, you have been very helpfull.......Brian