Author Topic: Design and build side shaft hit and miss engine from bar stock  (Read 29395 times)

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #390 on: February 08, 2019, 12:01:09 AM »
Here is an interesting fact. The face cam I made for this engine had all of the action imparted to the valve in a 90 degree segment. Because of the 1:2 ratio between the crankshaft and camshaft, that means that all of the valve movement occurred in 180 degrees. The engine ran, and seemed to run relatively well. The new cam, which is patterned after the Odds and Ends hit and miss engine by Philip Duclos has 128 degrees of cam influence, which results in a whopping 256 degrees of crankshaft rotation. Since there are only 180 degrees of crankshaft rotation as the piston moves from bottom dead center to top dead center on the exhaust stroke, that means that the remaining 76 degrees has to be used up before and after the piston is at bottom dead center and then at top dead center. This is normal on internal combustion engines, and is highly theoretical, because when you take the clearance between the rocker arm and the end of the valve stem into consideration, the "lead" and "lag"  of the valve action isn't as much as the theoretical numbers would have you believe. Hit and miss engines are not a high revving engine, so it probably won't make as big a difference, but it will be interesting to see.
« Last Edit: February 08, 2019, 03:50:24 PM by Brian Rupnow »

Offline gbritnell

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #391 on: February 08, 2019, 11:29:13 AM »
HI Brian,
Either your numbers or your explanation are a bit confusing! How can you have 128 degrees of 'cam' influence but 256 degrees of 'valve' influence?
gbritnell
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Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #392 on: February 08, 2019, 01:59:49 PM »
George--Because of the 1:2 ratio between the crankshaft and the camshaft. When I say "cam influence" I mean the cams direct influence on the rocker arm. Cam moves at half the speed of the crankshaft. Consequently, when cam moves thru 128 degrees of rotation, the crankshaft moves thru 256 degrees of rotation.

Offline gbritnell

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #393 on: February 08, 2019, 03:40:56 PM »
It's just in your original explanation you stated that 256 degrees of influence on the valve when you should have said crank degrees.
gbritnell
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Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #394 on: February 08, 2019, 03:46:05 PM »
Okay--I fixed it.

Offline gbritnell

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #395 on: February 08, 2019, 07:46:51 PM »
Brian,
I just looked at your cam lobe drawing and read all the valve event numbers. Being as hit and miss engines rely solely on the intake stroke to open the intake valve the normal timing would be to have the exhaust valve close at TDC or no more than 15 degrees crank rotation past TDC, 7-1/2 degrees camshaft. With your exhaust closing so late you won't be getting a good cylinder fill. On a conventional engine that runs at high rpm's you could get away with a lot of overlap, aiding cylinder scavenging, but I'm afraid it will be detrimental to a hit and miss type. Just my 2 cents worth.
gbritnell
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Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #396 on: February 08, 2019, 09:29:19 PM »
George--I will try it and see what happens. The cam is not hardened, and is not difficult to remake if I have to. I'm deeply into "Try it and see" mode.---Brian

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #397 on: February 08, 2019, 09:29:30 PM »
Today I made the last piece for this engine, and what a snaky piece it it!!! This is the manifold that connects to the base of the cooling reservoir and forms a leakproof seal with the extended tube from the gas tank, and channels fuel through it's many galleries to the anti backflow valve and then to the carburetor. There will be a piece of transparent fuel line connecting the anti-backflow fitting to the carburetor, which allows me to see what's going on with the fuel. Right now the piece has half a dozen brass plugs held in place with J.B. weld, and after it sets up overnight I will add it to the machine and see if it runs.

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #398 on: February 09, 2019, 07:47:03 PM »
Good news--Engine is firing consistently when spun by drill, which eases my mind somewhat about having enough compression to fire with the new head on. (The new head has a larger combustion chamber than the old head had.) Since I also had to make new valve cages for the new cylinder head, (couldn't re-use the old ones) I was concerned about the valves sealing but it seems they are going to seal all right. --The old valves were installed and lapped into the new seats through that access hatch in the top of the cylinder head. Flywheels will bounce back when spun by hand against compression. I have hurt my back, so I'm trying not to do too much for a few days, but I had to try this new configuration out to see what was going to happen. When I had the cylinder head off, I measured the distance from the head of the piston to the end of the cylinder at top dead center, and I have about 0.176" there. If I have to, I can add that much to the top of the piston to bring the compression ratio higher. This is probably all for today, but it's looking quite good so far.---Brian
« Last Edit: February 09, 2019, 07:51:55 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #399 on: February 09, 2019, 09:56:28 PM »
George Britnell--I have studied on this cam profile business, and again, as usual, I believe you are correct. Without getting into a lot of technical poop, I can re-machine the cam I already have to a profile more in line with what you have said.  To change the profile any more than what I am showing would mean setting up to cut a completely new cam, and I don't really want to do that. (Not yet, anyways). The new profile shown here will let me begin opening the exhaust valve 40 degrees before bottom dead center and close exactly at top dead center, or to begin opening the valve 30 degrees before bottom dead center and close 10 degrees after top dead center. Again, this is somewhat theoretical, because it doesn't take the valve lash into account, but it is much closer to the "ideal" than what I currently have.---Brian
« Last Edit: February 10, 2019, 01:00:56 AM by Brian Rupnow »

Offline 10KPete

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #400 on: February 09, 2019, 11:38:48 PM »
 :ThumbsUp: :ThumbsUp:

 :popcorn: :popcorn:

 :cheers:

Pete
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Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #401 on: February 10, 2019, 01:02:40 AM »
I did alter the cam profile this afternoon, on the advice of George Britnell. George is very knowledgeable about design and construction of small engines. I have the engine firing consistently, but not quite to the point where it will take off and run on it's own without the variable speed drill I use as a starter. I have spark, I have fuel, and I have the ignition and valve timing correct. The two things left which would cause the engine to not start are #1--Too much friction as the engine is still quite "stiff" because it is new, and #2-there is a lot more room inside the cylinder head now, which gives lower compression than in the previous design. I have room to add 0.200" to the end of the piston to increase the overall compression, and since that is the easiest thing to do I may do that tomorrow. as far as "stiffness" of the engine, I can always oil everything up good and then drive the engine with a v-belt from my 1/2 HP. electric motor for a couple of hours.

Offline Art K

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #402 on: February 10, 2019, 03:36:39 AM »
Brian,
With your cad you should be able to figure out fairly easily what your compression ratio is. I was able to use the volume on Alibre to determine it's c/r at 7:1. I would imagine with the large circular chamber in the center it dropped it quite a bit. After all it ran quite well before the head switch.
Art
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Offline gbritnell

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #403 on: February 10, 2019, 12:54:40 PM »
Hi Brian,
Art is correct. I have used a lot of CAD programs over the years but never had an occasion to use the volumes part of measuring in Solidworks, that I use now. When I was adjusting tne CR on my flathead engine discovered that function. You can draw any kind of odd-ball shape and select the model and the function and voila, volume!
I'm sure you know from you hot-rodding endeavors that to calculate CR you add the volume of the cylinder at TDC + the volume of the combustion chamber and divide that into the total volume, piston at BDC + combustion chamber and that will give you the CR of the engine.
gbritnell
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Offline Brian Rupnow

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Re: Design and build side shaft hit and miss engine from bar stock
« Reply #404 on: February 10, 2019, 04:14:32 PM »
So--If we want the engine compression to come up higher, we can make the cavity in the cylinder head smaller---OR--we can make the piston longer. In my situation it was much easier to make the piston longer. Using information from my CAD system, I determined how much longer it could be, and what diameter it had to have. The diameter had to be a tiny bit smaller than the actual piston size, because the piston was already designed and lapped as a "precision fit" in the cylinder. I assembled the lengthened piston to the rod and the rod to the crankshaft and turned the engine over by hand to be sure nothing interfered.  Nothing did, so I pulled it apart again, put a dab of J.B.Quickweld on the threads of each bolt and reassembled the lengthened piston. Now I'm off to get some lunch, and by the time I'm finished eating, everything will be ready to go back together.