Swifty's build of Rupnow engine.

[Brian Rupnow]

Swifty--Congratulations!!! You have done a marvelous job there!!! Adding the hit and miss mechanism will not only slow the engine down, but will also allow the engine to run a lot cooler, as during the "miss cycles" it will be pumping room temperature air through the combustion chamber, cooling it down. I am very happy to see the engine come to life.---Brian

 

[Cogsy]

Congrats Swifty! Looks and sounds sweet mate Thm:Thm:

 

[Path]

Swifty,

Awesome!
woohoo1

Pat H.

 

[Philjoe5]

Nice work Swifty....a great running engineThm:Thm:Thm:

Cheers,
Phil

 

[gus]

Unfortunately today is grandson minding day, been out to the local mall to keep him occupied. He is now having his lunch and then nap time for him, so it's into the shop for me as soon as he's in bed. I have decided to try putting a grub screw between the shaft and flywheel, that should stop it from moving. Will post some pictures later today.

Paul.

Hi Paul,
Gus will go for shrink fit plus your grub screw. Been watching and following your thread. Monkey See .Monkey Do. No worry .
Today will do the C.I. Cylinder. Time now 8am.Will take sweet time.
Will be calm and cool as I have only one C.I. Shaft left.

 

[Swifty]

Hi Gus, just take your time and you will be right. Pinning with a grub screw took no time and its positive, I even added loctite to the screw. I added a shoulder to my small gear to allow for a grub screw instead of using a pin through the gear teeth, I will drill a detent in the axle to really lock it on, and one also for the disc holding the magnet. This will make them easily removable, but will always go back on in the right spot.

Paul.

 

[ELM6061]

I can see a drive and coffee coming up on the calendar. Nice work Paul, a sweet little runner and look forward to smelling some fumes.

On a side note;
Got all the frame uprights welded and have gone through two wire brushes on the drill, cleaning up the frame ready for some paint. Bit shaky yesterday and today, hopefully will fire the spray gun tomorrow. Also moved some plants, so you could say this little snail is picking up speed, has pulled it's head from the shell HaHa.

 

[Swifty]

Hi Eddie, might have to hold off on that visit for a short while as I've taken parts off to complete the governor. Hopefully won't be long before its running again.

Glad that your making progress on your shed, with the weather improving now, it's a bit easier to work outside.

Paul.

 

[Lawijt]

On a hit and miss engine, heat is created when the engine fires. Then during the next 4 to 6 cycles of the engine in "miss " mode where it is not firing, ambient temperature air is sucked in and out through both the intake and exhaust valve, flushing out any residual heat from the cylinder and cooling the surrounding metal. Bottom line is---No, the head doesn't need fins.

That is very interesting Brian. I think never about that. But the engine will still spark than? And what with the fuell it is sucking in?
That fuell is lost than?
But I find it great that the air sucking in & blowing out cool the engine.

Best regards

Barry

 

[Brian Rupnow]

Lawjit--There seems to be a few things you don't know about hit and miss engines. There is no cam or lifter for the intake valve. It is held in the closed position by a very light spring. When the piston moves from top dead center to bottom dead center, it creates a vacuum in the combustion chamber, and this vacuum "sucks" the intake valve open and "sucks" the air/fuel mixture into the cylinder. The intake is what is called an "atmospheric intake valve", because it is actually atmospheric pressure which opens it. When the engine reaches a high enough speed for the governor weights to fly into the "out" position from centrifugal force, the governor mechanism moves a lever into a position that prevents the exhaust valve from closing. Now--the exhaust valve can't close, but the engine is still revolving at a fast rate--but it can not suck the intake valve open, because with the exhaust valve held open no vacuum can be created. This is the "miss" part of a hit and miss engine, when it is coasting. There is still a spark every time the piston comes up to the top, but with no fuel to light, the spark does nothing. After a few revolutions, the engine begins to slow down. When it slows down "enough", the spring on the governor moves the governor into the "in" position, and this moves the lever, allowing the exhaust valve to close. Once the exhaust valve closes, and the engine coasts through one more cycle, it "sucks" in a fresh charge of air/fuel mixture, and the engine fires or "hits" again, starting the process all over again. This is one of the reasons that it is important to put an "anti flow-back" valve in the gas line feeding the carburetor. With the type of carburetor a hit and miss engine uses, the fuel tank/fuel level must always be lower than the carburetor to prevent flooding. Without an "anti flow-back" valve on the gas line, during the miss cycles the fuel can run out of the gas line back into the fuel tank. When this happens, and the engine wants to suck in a fresh charge of air/fuel mixture, if the fuel has all ran out of the gas line back into the tank, the engine may just slow down and come to a complete stop before it can get the fuel back up, through the gas line and carburetor into the combustion chamber.---Brian

 

[Swifty]

I mentioned in an earlier posting that I fastened the small spur gear with a grub screw instead of using a pin through the gear teeth. Of course, this is only applicable if you have a shoulder on the small gear. As I machined the gears myself, I left a shoulder on one end, but it was a very thin walled shoulder as the outside diameter was no larger than the bottom diameter of the tooth form. When I had the gear finished, I machined up a bush which I shrunk onto the existing shoulder, this allowed enough material to tap a hole and use a grub screw.



I'm now proceeding with the manufacture of the governor, I've finished the aluminium block that holds all the pieces, and I am using the mitre gears that I had made previously, they are slightly different in some sizes from bought gears, but I made allowances for this.

For anyone that wants to know how I made the mitre gears, just click on the Articles button on the top banner, and this will take you to the tutorial.



Paul.

 

[Lawijt]

Great work again Paul.

@ Brian. Thanks a lot for the explanation. Now I understand it all. I buy a economy engine from the engineers emporium.
So when putting it togheter I understand already how some thing work. I will make a revieuw from that.

Barry

 

[Brian Rupnow]

Swifty--I like your solution to attaching the small gear better than mine. I will keep that method in mind for the next engine I make.---Brian

 

[gus]

Hi Paul,

Eager Beaver and Eagle Eyes watching the meister. Will be cutting Cone gears too when I get the basic engine started and running.

Gussy.

 

[Swifty]

I turned up a bronze bush that fits in the governor holder, but I made a slight modification by making it a shouldered bush, so that the stem post has a bearing surface where it contacts the body. Of course, I had to allow for the bush head thickness on the post. You can see the head of the bush in the photo.

And of course, I've turned the stem post as you can see. Next, I will have to finish milling the post.



Paul.

 

[Swifty]

Swifty--I like your solution to attaching the small gear better than mine. I will keep that method in mind for the next engine I make.---Brian

I'm glad that you like that idea Brian, it allows you to try different positions for the gear before committing to a fixed position. I plan to drill a shallow indent in the shaft to take the grub screw once I'm happy with the exhaust valve timing.

Paul.

 

[Gurus]

Looking good!

 

[Swifty]

Thought that I better put in an update, I've been machining bits when I have a chance, not far from getting the governor working.



Just a couple of more bits to make, then I will get to work on a fuel tank.

Paul.

 

[Brian Rupnow]

Swifty--that looks really great. I found that on my engine, the rod which extends down thru the center of the stempost wants to rotate.--Which isn't a big problem, but it sets up a friction point where it bears against the lever. My lever was made from brass, and it actually drilled a hole half way through it!!! To make a save, I silver soldered a steel ball bearing into the hole, then ground the top of it flat to avoid any farther wear issues. It seems to have worked alright. I see your lever is made of steel, so you may not have the same problem.---Just put a bit of grease there before your start up.--Brian

 

[Swifty]

Hi Brian, I recalled your problem with the lever, I plan to make a hardened silver steel pad to pin in that area if mine wears a lot.

Paul.