Author Topic: Cam on Bob Shores silver Angel Hit and Miss  (Read 652 times)

Online Brian Rupnow

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Cam on Bob Shores silver Angel Hit and Miss
« on: November 13, 2018, 07:15:50 PM »
The cam on this engine is a circular disc running on a vertical shaft. A roller on the end of the exhaust valve rocker arm runs on this disc, to operate the exhaust valve. I can understand that the flat area on this disk matches the "0 lift" portion of a conventional cam, and that the high point on the disc matches the high spot on a conventional cam, but I'm uncertain of the ramp on both sides of that high spot. I have heard a rumour that a special tool was required to make this cam, but I can't confirm this. If anyone has experience with this engine, or any engine with this style of cam, I would love to learn a bit more about it.---Brian Rupnow

Offline Jasonb

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #1 on: November 13, 2018, 07:19:28 PM »
Domestic Stovepipe uses a similar cam. The special tool I used for the ramp is called a file ;)


Offline stevehuckss396

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #2 on: November 13, 2018, 07:27:23 PM »
Dont know about this engine but other bob shores engines I have built used a fixture to offset turn the camshaft. The difference between his way and mine is he pinned the dish and showed where to start and stop cutting on each lobe. I use a degree wheel and a chart and cut all the lobes at the same time. Not a big deal on a single cylinder but a huge time saver on a V8. This PDF might shed some light on the basics of the fixture.
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Offline michaelr

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #3 on: November 13, 2018, 07:38:08 PM »
Brian, I have no experience of the Silver Angel but this drawing may help you.

Mike.

Online Brian Rupnow

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #4 on: November 13, 2018, 10:47:42 PM »
Yes, I think I have to agree with everybody.--It would be mostly a file job in the end. However, the whole thing can first be turned on a lathe, then all of the ring at the top milled away except for the cam area. The rest could be taken down with a file.  These little hit and miss engines are very forgiving in regards to the profile of the cam. Something that helps immensely is that the cam follower on the end of the rocker arm is round like a bearing, so there would be no danger of it "slapping" against the side of the ramp like a tappet would. I would make this part and the cam follower out of 01 steel, then flame harden and temper it. Probably none of us would live long enough to see it wear out.----Brian

Online Brian Rupnow

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #5 on: November 14, 2018, 12:18:33 AM »
I just did a big rootle thru the internet looking at "Domestic Stovepipe" hit and miss engines. Lots of pictures and videos, but nothing showing on the governor. There appears to be a second shaft running almost parallel to the sideshaft, which operates a bell crank to lock out the exhaust valve lifter, but nowhere did I see a picture of the actual governor. The governor appears to be hidden between the flywheel and the engine frame. Does anybody have clearer pictures of this governor area on the engine?

Offline Jasonb

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #6 on: November 14, 2018, 07:32:29 AM »
You only need to file the external fillet, the rest including the internal fillet can be done by milling.

Keep searching there are clear photos of the governor on the net, you will have to earn your $25 a set of plans on this one ;)

Offline gbritnell

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #7 on: November 14, 2018, 12:40:21 PM »
Hi Brian,
Having done a very thorough investigation of the Domestic side shaft engines in their various iterations when I built my miniature one I will give you the explanation of how the simplest of the mechanisms work. By that I'm saying there is approximately 3 different setups used on the Domestic engines.
You have a helical gear setup on the crankshaft that turns a camshaft which is supported at both the crank and head ends. On the head end is the circular cam that you have been talking about. As it rotates it operates a rocker arm with a roller follower on it which in turn opens the exhaust valve. The rocker arm also has a notch into which the lock-out arm from the governor mechanism fits.
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Offline gbritnell

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #8 on: November 14, 2018, 12:57:42 PM »
Now onto the governor mechanism on the flywheel. This consists of a circular piece which fits over the crankshaft. You take this disc and machine a hole at the center a thou or so larger than the crank diameter. Now you mill a slot from that center hole long enough to provide the required offset to operate the lock-out mechanism. Over top of this disc there is a ring (shown as brass in my picture) This ring has the shaft that runs parallel with the camshaft and operates the lockout mechanism. The eccentric disc has a rod protruding from it that is supported on it's upper end by a bracket on one of the flywheel spokes. It has a spring to return the eccentric disc to center.
How it works is the engine spins and the weight on the rod pulls the disc with the slot off-center thereby creating a cam. As it moves off-center it moves the outer ring with it and this offset moves the lockout shaft back and forth. When the engine slow down the spring pushes the disc back to center reducing the eccentricity.
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Offline gbritnell

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #9 on: November 14, 2018, 01:18:42 PM »
Now the head end. As the lock-out shaft moves forward it operates a lever which engages the rocker arm thereby locking it in the open position just like a normal hit and miss engine. Now to increase the speed of the engine while running a lever is mounted on the head end bracket. It rotates around a boss on the bracket. Attached to the lever and the lockout arm is a spring. As the lever is moved it pulls on the lockout lever and add more spring tension to what is already supplied by the spring on the governor weight. Similar to ordinary hit and miss engines but in a different way.
Now a work about the cam bump on the disc. You can't just take the disc and machine the cam bump with sides produced by radian cuts from center (pie shaped). Well you could but then it would wear out quicker. Let me explain. Lets just say the cam is a rotating disc, no bump. At the centerline of the camshaft and disc but offset is the roller wheel of the rocker arm. As the cam disc rotates the roller runs along it's face, off center. Now we introduce the cam bump. With a radian side the bottom edge of the pie cut will hit the roller first and naturally start moving the rocker arm but this tiny contact area would soon wear and change the valve timing so what needs to be done is machine the edge of the bump off center but parallel with the vertical centerline. This way the whole edge is hitting the rocker arm and providing a more positive movement. The edge of this bump has to be calculated in a manner similar to a conventional camshaft with a roller follower.
The trailing edge of the cam has to have the same configuration, parallel to the vertical centerline, so the rocker arm drops off uniformly.
To look at the cam bump it's still pie shaped but developed in a different way.
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Offline gbritnell

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #10 on: November 14, 2018, 01:25:50 PM »
You can see the cam bump in image 9395. If you imagine a line out from the center of the camshaft you will see that the bump is offset giving a square edge and thus providing a uniform lift to the rocker arm roller.
Here's a video that explains some of what I have tried to write.
gbritnell
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Offline Ye-Ole Steam Dude

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #11 on: November 14, 2018, 02:00:20 PM »
Hello George,

That is a really sweet running little engine.  :ThumbsUp:

Have a great day,
Thomas

Online Brian Rupnow

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #12 on: November 14, 2018, 02:51:35 PM »
George--Thank you ever so much for the pictures and the explanation. I greatly appreciate that. Jason--As I have said before, every engine I build and show on this forum costs me money for raw material and purchased items. The time  invested in making complete sets of plans for one of these engines would run into the thousands of dollars if you had to pay a design engineer to make them. There is  considerable time invested in research before I design and build one of these engines. I have never had a complaint about the price of $25, and never had a complaint about the quality of the drawings.---Brian

Online Brian Rupnow

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #13 on: November 14, 2018, 07:32:57 PM »
George--It took me a while to get my head around this, but I think I have it. Things are not modelled to any particular scale, but that's okay for "show and tell".  Red indicates the flywheel. The light blue indicates the round part which fits over the flywheel with about half a thou radial clearance. The slot milled in the center of that light blue part is long enough to give the offset required. The light blue part has a rod extending from one side of it thru the pink counterweight and thru the spring and thru the light brown bracket. The pink counterweight is firmly attached to the rod. The rod goes thru the light brown bracket with a clearance fit.--Normally, at zero rpm, the spring holds the light blue part centered on the crankshaft. As the rpm increases centrifugal force makes the pink weight want to move away from center, and as it does it pulls the blue part away from center until it is limited by the other end of the slot coming up against the crankshaft. The dark blue eccentric strap and rod which runs out to the bell crank doesn't move at zero rpm. as nothing is eccentric. As rpm's climb and the light blue part becomes more and more eccentric to the crankshaft, the eccentric strap follows it and the rod extending from the eccentric strap moves in a linear motion to operate the bell crank at the far end to lock out the exhaust valve.--Does this sound right to you?---Brian
« Last Edit: November 14, 2018, 07:44:28 PM by Brian Rupnow »

Online Brian Rupnow

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Re: Cam on Bob Shores silver Angel Hit and Miss
« Reply #14 on: November 14, 2018, 08:15:19 PM »
Something about the previous explanation troubles me. Obviously, the counterweight and the light blue part it is attached to have to rotate with the flywheel in order for centrifugal force to pull the light blue part off center. At zero rpm when the light blue part is centered on the crankshaft, the dark blue eccentric strap and attached rod isn't going to move.---But--As soon as the light blue part is pulled off center the eccentric strap is going to follow it, and the rod attached to that eccentric strap is going to move back and forth. Somehow I think that the rod attached to the eccentric strap shouldn't be bopping back and forth to do it's job properly. What am I doing wrong?