Another Rupnow Air Hit n Miss Engine

[bmac2]

Drilled the holes for the two hinge points. This time making sure I supported them with shims. I do not want to make this part again.

 

[GailInNM]

Fine work Bob. Runs like a charm.
Gail in NM

 

[barnesrickw]

Nice looking engine.

 

[cfellows]

Run's good, Bob. Are you planning to run it on full compressor pressure, like 100 PSI?

Chuck

 

[bmac2]

In the video it’s running at around 20-25 lbs. I use a portable air tank in the basement and the gauge is not terribly accurate. When I increase the pressure it accelerates smoothly until it hits about 45-50 lbs. Then it starts having an asthma attack and jumping all over the bench. Would this be the spring on the exhaust valve? Right now it’s just one out of my small Drawer–O-Springs and I’d rate it at medium to light. The other thing I’ve been thinking about is the flywheels. Their just under 1 lb. each. Would lighter be better?

 

[cfellows]

In the video it’s running at around 20-25 lbs. I use a portable air tank in the basement and the gauge is not terribly accurate. When I increase the pressure it accelerates smoothly until it hits about 45-50 lbs. Then it starts having an asthma attack and jumping all over the bench. Would this be the spring on the exhaust valve? Right now it’s just one out of my small Drawer–O-Springs and I’d rate it at medium to light. The other thing I’ve been thinking about is the flywheels. Their just under 1 lb. each. Would lighter be better?

Bob, I think the flywheels are fine as is, especially if you want the engine to run fairly slowly.

You can't run the engine on full air pressure without the governor, but once it's installed and running in hit n miss mode, you'll want the air pressure as high as you can get it to maximize the number of revolutions between "hits". You may have to experiment with a stronger valve spring to get it to run the way you want.

Chuck

 

[bmac2]

Started working on the governor arms and weights. In the plans it is noted that the weight arms are “File to fit”. These reminded me of doing finish carpentry. A lot of it is “Fit and Fiddle”. Cut it to size and then fiddle with it until it fits.

 

[bmac2]

Cut out the blank and plunge cut the ¼” hole in the center.

 

[bmac2]

I like my Craftex Mini Mill and though it was third hand when I got it, its serves my needs. That being said I think the buyers with Busy Bee Tools must have found a really good restaurant on the day everyone was picking paint colors. Black, Green, and Cannery Yellow must have been all that was left.

 

[bmac2]

Made a quick mandrel to hold the blank on the rotary table.

 

[bmac2]

The mandrel doesn’t go right through the blank so I could use the end mill to align the rotary table and round off the ends.

 

[bmac2]

Used a small square to set it up in the mill to split the two weights.

 

[bmac2]

It’s warming up again so tomorrow I’ll be able to get out to the garage and solder them up.

 

[bmac2]

I was tempted to soft solder the weight arms. But I need the practice silver soldering and it looks like all the reading I’ve done lately has not gone to waist. One of the biggest challenges I have with silver soldering small parts is having the torch blow them out of alignment.

 

[bmac2]

Cleaned up and still square even after having the buffing wheel throw it across the shop at a truly amazing speed. Note to self “time to replace the gloves for the buffer”

 

[bmac2]

The pivot pins for the weight arms are cut from the shank of a dull 1/16” drill bit. I don’t sharpen anything under 1/8”, it’s too easy to just replace them. I just put them in a drawer marked “Dull / Bent” and use them when I need a pin.

 

[bmac2]

AAARG !
I had everything fitted up so off to the garage so I can use the compressor. The governor seems to be working but intermittently. Something is sticking when they start to open.
It was while I was dumping oil on everything and fiddling around that I managed to bash the rocker arm and bend the valve pin. Messed around with it for a couple of minutes before I thought, “It’s only a pin. Make a new one”.

 

[bmac2]

When I cut small pins or screws with a Dremel I like to hold one end in a small vise and the other in a pair of hemostats. Makes it a lot easier to find both pieces.

 

[bmac2]

The governor reinstalled and now it’s down to tuning everything and running it in. Other than that, a good cleaning, some body work on the flywheels and some paint.
I’ll do that tomorrow. It’s nice day outside and I haven’t taken down the Christmas Lights.

 

[cfellows]

Nice, Bob, I'm anxious to hear it running in Hit n Miss mode.

Chuck