Single Cylinder Opposed 2 Piston Engine

[Rdean33422]

The final picture of the engine with it's black cap on.


Thanks to everyone that followed along and commented.

Ray

 

[Rdean33422]

The engine now has a home.




I had an old kitchen cabinet that I mounted on the shop wall but hadn't decided what to put in it yet.
I cut out the center of the door and put in a piece of plexiglass.
I still have room above for something else but it will have to be small.

Ray

 

[petertha]

Way to go Ray. Congrats. You build a unique, running engine in about the same amount of time it takes me to draw the head!

 

[GreenTwin]

I really like seeing engines come together and run well.
I have had a number of false starts on engine builds, where things never came together, and the build failed.
I have only succeeded with on engine (so far), and so I really appreciate those who make it look so easy.

Great work, and a nice sounding/looking engine !
.

 

[Steamchick]

Just excellent work!
Despite the ""Unconventional balancing strategy" you have overcome all that and made it work well. - That is Engineering!
And usually, a "model" is an example for us to understand your ideas. So you have truly made an Engineering Model!
K2

 

[Longboy]

Not only can you claim museum qualities in your builds but bringing an obscure design to life is an exception to standard I/C engines. Does the forum still have Model of the Month recognition?

 

[Rdean33422]

Longboy thank you, that is very nice of you to say but there are many other builders on this forum that put me to shame.

Ray

 

[Tom-AMS]

I own a high performance engine shop - since 1963, we have dynamically balances engines, from small 1 cyl to large V16's.
Couple comments/tips:
- With "unconventional" engine lay-outs, start by drawing a simple a force vector diagram of the reciprocating parts. In this case, the diagram will look similar to a 2 cyl boxer engine, only without the couple forces created by off-set cylinders on a boxer (or horizontally opposed) engine.
- To balance this engine, with all crank throws having the same off-set, the mass of the lower con rod's "big end" (include associated bolts, brgs, etc) needs to match the sum of the mass of both long con rods' "big ends" (with each of those being equal with one another). I've included a pic showing how this is done in automotive shops.
- Next the mass of the "small end" of the lower rod is matched to the sum of the mass of long rods' small ends, again both of theses long rods being equal. This is done by reversing the way the rod hangs on the fixture in the pic.
- Then match the mass of the reciprocating parts: lower piston, rings, wrist pin = upper piston, cross head, pin, and adjustable connecting "bolt".
- The crank/flywheels, only, need to be rotationally balanced - however, like a boxer engine, if the rod throws are dimensionally the same diameter / width, they do not need bob-weights attached. (Bob-weighrts are used to simulate the rotating portion of the rods mass, and a percentage of the recip mass. This percentage is known as the "balance factor"... as Ken briefly mentioned in an earlier post. (BTW, in most V engines the most common BF is 50%; some V6 use 38%; motorcycles often use from 50% to as much as 72%. On high performance engine, if we use a bF greater than 50%, it's called "over balance"; less than 50% is "under balance". Changing the Balance Factor affects the peak force acting on the main brgs / engine block, from each piston and rod in both +/- directions. Some engine builders claim a slight increase or decrease in BF% will compensate for inertia forces. The theory is, for high rpm engines, greater inertia forces generated by very high rpm are "dampened" by adding increasing the BF%, thus requiring additional mass be added to the crank (or flywh) counterweight - it helps absorb the "shock" from the inertia of extremely high piston velocity, and helps maintain adequate hydrodynamic rod brg lubrication. Over balance comes at the expense of low rpm vibration. balancing. At the other end, "under balance" is sometimes used on engines with high numerical stroke-to-rod ratios, because a longer rod's delayed moment of inertia in relation to crankshaft angle lets us lighten the counterweight and gain faster rpm accel. My experience has been that a neutral or 50% BF works best. Whenever one deviates from a 50 % BF reciprocating-mass value, compromise is inevitable. It will create an unbalance condition at low rpm, or higher rpm why. More recent engineering data with racing cranks does not support the over/under theories.
Fortunately, Ray's opposed piston engine does not require any BF calculations / bob-weights.
- Tip: When we spin balance a crank or crank rotating assembly, and have any reason to question the balancer software's suggested correction amount and/or location, we simply weigh & place a lump of modeling clay at the location on the crank (or flywh) and spin it again - if the imbalance is corrected, we know we can trust the solution.
- for home shop built model engines, one could likely get away with "static, knife edge" balancing of the crank and flywh. There is, however, a method called whip-staff balancing, used to dynamically balance small parts like model engine flywheels and cranks on a lathe. I think this link still works: It was used back in the late 1800's early 1900's, being phase out by more efficient, easier to use, "dash-pot" potentiometer, strain gauge, and now, load cell equipped, dedicated balancers. Our balancer only spins a crank for 3 to 5 secs, then shows us the location and amount of imbalance, suggests drill sizes & depth, or amount to mill off, or size of Mallory metal to add, etc.

 

[Steamchick]

What a good guide to balancing! Thanks, Tom!
With cast flywheels, after machining only the necessary surfaces, and clean-up of casting defects on the surface, I have used a bit of masking tape or whatever to fix a flywheel onto the shaft temporarily, then run the engine to see how much it wobbles. Then rotate the flywheel, about 45dgerees, try again, then figure out the best position by iteration... Only having found the best "balance" for the rough casting do I consider drilling or adding weight to improve the balance further. Usually, the flywheel's "cast imperfection" is adequate to balance the engines well, and on one small steam engine this considerably reduced the "idle" speed from over 120rpm to nearer 45 rpm. - Really impresses people at shows because it looks like the speed of the full sized engine. Not buzzing away like an electric motor!
Balancing has lots of benefits.
K2

 

[Tom-AMS]

What a good guide to balancing! Thanks, Tom!
With cast flywheels, after machining only the necessary surfaces, and clean-up of casting defects on the surface, I have used a bit of masking tape or whatever to fix a flywheel onto the shaft temporarily, then run the engine to see how much it wobbles. Then rotate the flywheel, about 45dgerees, try again, then figure out the best position by iteration... Only having found the best "balance" for the rough casting do I consider drilling or adding weight to improve the balance further. Usually, the flywheel's "cast imperfection" is adequate to balance the engines well, and on one small steam engine this considerably reduced the "idle" speed from over 120rpm to nearer 45 rpm. - Really impresses people at shows because it looks like the speed of the full sized engine. Not buzzing away like an electric motor!
Balancing has lots of benefits.
K2

in a 'round about' manner, your method of balancing the flywheel on the crank is similar to the whip-staff lathe method. good job! Cheers / Merry Christmas

 

[Steamchick]

During my apprenticeship I remember the "grinder" (because he did most of the crankshaft grinding) doing a job where he stuck a thin wooden stick on the machine (a small grinder), ran it up, measured the whip with a 6 in rule, added a bit of lead to the rotating mass, and after a bit of iteration had virtually no whip on the stick. But I have never actually done it myself with a whip staff. Only worked on this particular machine because the mount wasn't seriously stiff.
The 20 foot bed of the lathe (that I used) was so massive you could never feel vibrations, and turning 10 in diameters of 50 kg crosshead castings, was only around 30-40 rpm (or whatever?) from memory...
Likewise the cylinder boring machines I used were too slow. But I clearly remember the distinctive smell and sound of the cast iron being cut, which has worked well in my model turning!
Memories! What we were...
K2

 

[Lloyd-ss]

During my apprenticeship I remember the "grinder" (because he did most of the crankshaft grinding) doing a job where he stuck a thin wooden stick on the machine (a small grinder), ran it up, measured the whip with a 6 in rule, added a bit of lead to the rotating mass, and after a bit of iteration had virtually no whip on the stick. But I have never actually done it myself with a whip staff. Only worked on this particular machine because the mount wasn't seriously stiff.
The 20 foot bed of the lathe (that I used) was so massive you could never feel vibrations, and turning 10 in diameters of 50 kg crosshead castings, was only around 30-40 rpm (or whatever?) from memory...
Likewise the cylinder boring machines I used were too slow. But I clearly remember the distinctive smell and sound of the cast iron being cut, which has worked well in my model turning!
Memories! What we were...
K2

Ken, "what we were?" Naw, we are definitely still there in spirit. Maybe not as strong or agile, but still there.
A 20 foot bed with 50 kg castings. I bet that was a sight.

I have heard of using a whip wire on an operating engine, particularly a single cylinder. You clamp a stiff wire (like a bicycle spoke) to the engine and observe how the tip moves as you vary the rpm. You can also change the orientation of the wire to x-y- or z. It can differentiate between reciprocating, centrifugal, and rocking couple imbalances. But of course you have to figure out how to fix it, LOL.

I worked for a place that made marine navigation equipment and it all had to go thru shock and vibe qualification testing. It seems like everything built to go on a ship vibrates at 400Hz. We had a 6 foot square vibration table for the testing. The equipment being tested looked like it was wired for heart surgery. Running thru the frequency spectrum it sounded like a propeller plane getting ready for take-off. I never will forget looking with a strobe light at one critical area during the vibe testing and seeing the amount of excursion of a spring-suspended critical item in the assembly. OMG, it scared me to death. It will survive that short of vibration movement???

Lloyd