Dusting off my old scratchbuilt engines making them run again.

[Anatol]

Thanks for posting drawings. I was going to ask about the valves. I see (I think) you used a piston type valve for inlet and a poppet type for exhaust. Can you explain why you made those choices?
thanks!

 

[hobby]

Thanks for posting drawings. I was going to ask about the valves. I see (I think) you used a piston type valve for inlet and a poppet type for exhaust. Can you explain why you made those choices?
thanks!

Hi, That is a very good question,
I had to look through the drawings to see why I did it that way, I was woking with a 1 1/8" dia. round bar for the cylinder, with I think a 3/4" bore.
I wouldn't have enough room for both valves made the same way to fit the bore dia.
So I offset the entire cylinder head with the cylinder to accomodate the intake valve and exhaust valve, so the exhaust valve port and intake port can fit inside the inner bore.

Here are some drawings to show that:

 

[Anatol]

Thankyou for explanation and drawings. I see the space problem.
Why did you decide to make the inlet the piston valve and the outlet the poppet?
I can see how/why the exhaust valve lifts - pressure in cylinder I guess, but how/why does the piston valve lift? Is there a spring in the bottom, not indicated in the drawing?
What did you make the valves and seats from? (I guess you're running on air so not so critical as steam?) How did you seal the piston valve? - Rings? or is it just close fit?
Sorry for the probing questions but I'm really interested in this
thanks!

 

[hobby]

Thankyou for explanation and drawings. I see the space problem.
Why did you decide to make the inlet the piston valve and the outlet the poppet?
I can see how/why the exhaust valve lifts - pressure in cylinder I guess, but how/why does the piston valve lift? Is there a spring in the bottom, not indicated in the drawing?
What did you make the valves and seats from? (I guess you're running on air so not so critical as steam?) How did you seal the piston valve? - Rings? or is it just close fit?
Sorry for the probing questions but I'm really interested in this
thanks!

Hi,
The valves were just a matter of choice, I don't think they had anything to do with performance, that I can recall, I went with the inlet being a port hole into the cylinder, mainly because of other engines I built using piston valves for both intake and exhaust.
I probably could have used a piston valve for the exhaust as well, but I think I was under the impression that a poppet valve would give more seal under air pressure in the cylinder during a power stroke, other wise it is possible for the air to escape past a piston valve, when the cylinder is under full pressure. A poppet valve has an inherent way of sealing up the porthole.

Both valves are spring actuated for lifting, the springs are contained in the top of the cylinder head,

the spring retainers slip over the stems of both valves, and tightened on with set screws, with the springs bearing against the underside of the retainers.

The valves were machined from 12L14 steel, and I used I think a large center drill, or countersink, or I made a tooling, to machine the seat for the exhaust valve.
The seat is just machined into the cylinder head.

No sealing was necessary for the valves, in fact I think I had to put a small bleeder hole at the bottom side of the inlet valve housing, so as to allow air to bleed through as the piston valve was depressed into its cylinder, otherwise the piston fit of the valve made it difficult for the rocker arm to push down on the valve, thereby stopping the engine cycle.

The pistons were machined for piston fit to get the greatest amount of compression on the power stroke, but later I had to take the diameters of the pistons down, because if you don't allow some blow by of air past the piston, then the piston will be forced down very hard on the power stroke, and usually does not have enough flywheel momentum to return back up, stopping the engine, so when that happens, the piston needs to be reduced very little until you get smooth flywheel action. In this case piston rings would not be feasible.

No need to apologize, I am happy your interested in this project, I am glad to help out as much as I can.

 

[Anatol]

"for lifting, the springs are contained in the top of the cylinder head,"

ok, so the valve stems are positively pinned to the rockers. I missed that detail.

" ...I had to put a small bleeder hole at the bottom side of the inlet valve housing, so as to allow air to bleed through as the piston valve was depressed into its cylinder,"

yes, I saw it in the drawing.

"then the piston will be forced down very hard on the power stroke, and usually does not have enough flywheel momentum to return back up, stopping the engine,"

right - unless a heavy flywheel.

thanks again!

 

[hobby]

"for lifting, the springs are contained in the top of the cylinder head,"

ok, so the valve stems are positively pinned to the rockers. I missed that detail.

Hi,
The stems are not connected to the rockers, the valve arrangement is pretty much like a combustion engine setup, where the valves are situated in the cylinder head, and the compression spring keeps the valve tight in the valve seat, and the rocker arm pushes down on the valve, but its the spring that keeps the valve seated.
I used the same setup for both valves on my engine.

 

[Longboy]

As you can see there is a lot of things that you need to figure out on your own, that
I just don't have any dimensions or design steps to show, it all has to be built by
your own instincts of problem solving in mechanical design.

Thats how I do modeling too. No step by step plans to follow but making generic engine parts and fitting into a block or frame up as a base. Has worked well in I/C and Stirling for me!