1" Bore x 1" Stroke Vertical i.c. Engine

[Tim Wescott]

Vietti -- Balancing Small Engines by ET Westbury: Page 2

But no single-cylinder engine is going to be perfectly balanced; the best you can do is minimize the vibration. And some designers purposely under- or over-balance, depending on whether they want the engine vibration to be weighted (as it were) more toward vibrating in a circle or along a line. So doing it b'guess & b'gosh isn't bad -- especially for a light engine.

Brian, the sensitive scales are cheap, and these days you can buy them from Amazon. This means you don't need to go to a head shop and ask for a "cocaine scale".

 

[CFLBob]

Brian, the sensitive scales are cheap, and these days you can buy them from Amazon. This means you don't need to go to a head shop and ask for a "cocaine scale".

Don't overlook Horrible Freight. I got a good gram scale there.

 

[Brian Rupnow]

This morning I remade the fan from 316 stainless. For some reason I found this fan to be difficult to make. It steps outside the bounds of normal machining, and seems to have about a thousand sharp edges that are difficult to get to with anything bigger than an ignition points file. It definitely looks better than the previous fan which I had made from a badly pitted piece of 0.050" metal I had laying around. It tucks in under the exhaust system, which should be enough to keep my fingers out of it.---And before you rush to tell me---I know that the paint isn't going to stay on the o.d. of the flywheel with that o-ring running on it. The plan is to sand all the paint off the outside diameter of the flywheel before I use it.

 

[Brian Rupnow]

CFLBob--Harbor freight doesn't sell in Canada.

 

[Tim Wescott]

Brian, I suspect we have opposite aesthetic sensibilities here, but I'd leave that flywheel painted, and run the engine long enough so that the paint is just naturally worn off by the belt.

Shiny metal surfaces that got that way by honest wear says "this is a hard-working machine" to me.

 

[Brian Rupnow]

And if you wondered where the electrics are, there they are, tucked in behind the flywheel. When the flywheel is installed, they are hidden in behind it.

 

[Brian Rupnow]

The gaskets are all made and installed (except for the one between the crank-case halves). The ignition timing has been set. In this picture I am setting the exhaust valve opening with a printed degree wheel and a pointer attached to the crankshaft. This valve is easy to set. I just loosen off the set screws holding the small gear to the crankshaft, rotate the flywheel until the piston is at the very top of it's stroke (as determined by a a hex wrench down the sparkplug hole resting on top of the piston), this corresponds with the zero degree mark on the degree wheel. Then turn the flywheel until the pointer is pointing at 25 degrees before bottom dead center and lock the crankshaft in position. Then I turn the large gear on the camshaft in the appropriate direction, until the cam just contacts the lifter and starts to move the rocker arm. Then I tighten the set screws in the small gear on the crankshaft in that position. Setting the intake cam position is going to be considerably more difficult, as I have no access to the cam to lock it to the cam shaft. I will have to calculate the degrees of offset between the intake and exhaust valve and remove the camshaft from the engine to set that. For the sake of the picture I have turned the flywheel and crankshaft to a position that shows the pointer.

 

[Brian Rupnow]

I'm doing some pondering here, and it has to do with the rotational position of the intake cam. Both of my cams are exactly the same shape, and both of my valves are exactly the same shape. Top dead center and bottom dead center of the piston are exactly 180 degrees apart. My exhaust valve is set to begin opening 25 degrees before bottom dead center and to close at about 35 degrees after top dead center.--If I position my cams to be exactly 180 degrees apart, then it stands to reason that my intake valve will begin to open about 25 degrees before top dead center and close at approximately 25 degrees after bottom dead center. I'm not certain how this valve timing will effect the performance of the engine, but it certainly makes it a lot easier for me if I can just position the cams to be 180 degrees to each other.--Does anyone have thoughts on this?---Brian

 

[Ghosty]

Brian,
This is the cam layout that I use, may be some help.
Cheers
Andrew

 

[TonyM]

.

 

[Charles Lamont]

IMHO that is too late for the exhaust and too early for the inlet. You would do better to open the exhaust about 40° before bottom dead, and close not later than 20° after top dead. 20° before and 40° after would be OK for the inlet, but a bit later might be better, down to 10° before and 50° after. That would put your cams 210° crankshaft rotation apart, or 105° on the camshaft.

 

[dsage]

I agree with Charles. You're not going to get much vacuum (low intake charge and low power) if you leave the exhaust open that late. A 10 to 20 deg after TDC closing would be more typical and effective. You're just going to be sucking exhaust back into the intake instead of fuel.
Perhaps this explains your comments in the past of your engines not having much power??
Check out Crane Cams (or many others) for typical cam timing specs. Pick one for a stock replacement application.

 

[Brian Rupnow]

Okay, working with the cams I have made, (which have 120 degrees of angular contact ) that means that it affects 240 degrees of crankshaft action. so, I begin to open the intake 15 degrees before top dead center and it closes 45 degrees after bottom dead center. the exhaust begins to open 30 degrees before bottom dead center and closes 30 degrees after top dead center. The angular difference between the cam lobes is approximately 100 degrees when fixed in place on the cam shaft. The following bit of arcane knowledge is something i researched and read about a few years ago when I built my opposed twin i.c. engine.

Now let me see if I can get my head around this. The piston is moving from top dead center to bottom dead center on the power stroke, with both valves closed. 30 degrees before bottom dead center, the exhaust cam which is leading begins to open the exhaust valve. Since there is a 1:2 relationship between crankshaft revolution and camshaft revolution, that translates to 15 degrees of camshaft rotation.

As the piston reaches bottom dead center and begins to travel up on the exhaust stroke, the exhaust valve stays open during the full upwards travel of the piston which represents 180 degrees of crankshaft rotation, or 90 degrees of camshaft rotation. Then as the piston reaches top dead center on the exhaust stroke, the exhaust valve stays open for 30 degrees of crankshaft rotation (15 degrees of camshaft rotation) during the intake stroke before it fully closes. This adds up to a total of 240 degrees of crankshaft rotation, or 120 degrees of camshaft rotation.

So—Let’s back up a little bit to where the piston is coming up to top dead center on the exhaust stroke with the exhaust valve wide open. 15 degrees of crankshaft rotation (7.5 degrees of camshaft rotation) before the piston reaches top dead center, the intake valve begins to open. It stays open thru the full intake stroke of the piston (180 degrees of crankshaft rotation, 90 degrees of camshaft rotation, and then as the piston reaches bottom dead center on the intake stroke and begins to move upward on the compression stroke, the intake valve stays open for an additional 45 degrees of crankshaft rotation, (22.5 degrees of camshaft rotation.)

This adds up to a total of 240 degrees of crankshaft rotation, (120 degrees of camshaft revolution).

So---we see that the exhaust cam and the intake cam must in this case have the same profile, since they must both be “active” an equal number of degrees of rotation. We also see that there is a total of 45 degrees of overlap at top dead center where both intake and exhaust valves are open at the same time.---this is typical of a “mid-range power/speed” engine. Hi speed/ hi-performance engines can have a greater overlap, while slower running engines must have a smaller overlap.

Now, there is a marvelous calculation used to position the intake and exhaust cams rotationally in respect to one and other. I have read this calculation enough times to make my head explode, and will repeat it here:

“Take the total of the valve open periods, divide by 2, subtract the total valve overlap and divide the result by 2”

So—the total of the valve open periods is 480 degrees of crankshaft rotation, divided by 2= 240 degrees.

240 degrees -45 degrees of overlap=195 degrees. Then 195 divided by 2=97.5 degrees of rotational separation between the intake and exhaust cam lobes.

This information was gleaned from a number of sources, but primarily from information found in “Model Four Cycle Gasoline Engines” by C.L. Mason and in “Miniature Internal Combustion Engines” by Malcolm stride.

I laid this out in 3d cad, independently, and came up with a lobe separation of 97.43 degrees, which confirms the long winded mathematical approach.

 

[Tim Wescott]

That seems like an awfully long valve duration for a slow engine. I'm +1 on the suggestion made by @dsage to look at commercial cams -- but to that I'd add that even a boring old stock cam in an automotive application is designed for some degree of extra time to give the valves time to do their work. By the 1950's American engines were designed to idle at 500 RPM, and to turn up to somewhere between 2000 to 3000 RPM depending on how feisty the engine designer was feeling. For engines displacing 30 cubic inches per cylinder that's definitely getting into the range where you need to give the air some time to get a clue that it's supposed to be moving and get underway.

So if you're going to start with a "boring old stock cam" grind, I'd suggest that you don't go any more in overlap or duration for a low-speed motor.

Edit: if you're amenable to just copying full-scale practice, I'd recommend starting with an older lawnmower engine.

 

[Charles Lamont]

I still think you have the exhaust timed too late. Don't worry about opening the exhaust too early.

For example, my E T Wesbury designed Seagull (which you saw over at MEM, on it's second day running, you asked a question) is not designed as a performance engine, but rather as a 'flexible, docile' low compression engine, designed for 'collar work'. It has a 130° exhaust cam, opening 60° before bottom dead, and closing 20° after top dead. The 120° inlet is timed at 10° before TDC, and 50° after BDC.

OTOH, Westbury's Sealion is a performance OHC design, and you can hear the rorty nature of several examples on YouTube. That has a 140° exhaust cam, opening a whole 70 degrees before bottom dead, and closing, yup, 30° after top dead - but as I said, it is a sporty job.

 

[Charles Lamont]

Brian, at a gallop through, I don't understand you calculation. It seems to be unnecessarily complicated anyway, and I am not surprised it is causing brain pain. I have just done a couple of pencil sketch timing diagrams using your (eccentric) timing angles, and they show me the cams are 97.5° apart, as per your calculation. Timed symmetrically 15-45 for both, they would be at 105°.

 

[Brian Rupnow]

I get lost in this cam timing business, and the only thing holding me back from running the engine is setting the cams. I will set it up to run with the last numbers I gave and see what happens. In the best possible case, the engine will run and we'll all be happy. In the worst possible case, the engine won't run, and I'll have to pull it apart to change the cam timing. I do thank you guys for chiming in and helping.---Brian

 

[dsage]

It will run as you have it.
If you want to play afterward adjust the valve lash a bit larger. I'm not sure if your mechanism will tolerate that (push rods need to be in pockets ??) That will make the vales open later and close earlier. I your case you may pick up a bit of power. Of course you'll lose some lift but....

 

[johwen]

For a smooth running engine at lower speeds an inlet opening at 10- degrees BTDC and exhaust closing 15 to 30 ATDC. This allows the inertia of the exhaust to act upon the early opening of the inlet valve to start the intake mixture to start on its way. Opening the exhaust valve early say around 50-60 degrees BBDC is OK as the combustion has done most of its work up to around 100 degrees ATDC. Keep up the great work Brian. Bare in Mind that mild timing will give low end performance and vice versa transfer power higher in the rev range. Because your cams can be individually timed start off with a mild valve overlap and then change the timing varying the overlap with say inlet and then exhaust then both until you are happy with the results. John

 

[Brian Rupnow]

This is another shot of setting the exhaust cam in the correct position, using a degree wheel and a dial indicator. I kept setting it over and over again "by eye", and each time it ended up in a different rotational position. Finally I resorted to a dial indicator so I could actually see the needle start to move when turning the cam gear by hand. I wanted to get the exhaust cam positioned correctly before pulling things apart to set the intake cam. What I have now seems to be repeatable, so I think it's time to pull the engine apart and set the intake cam, using the exhaust cam as reference.