MadModder

What could go wrong?   

Hopefully nothing, but then again Murphy shows up uninvited WAY too often.

Hey nickle!

I'm reading up on balancing now. Lots of theories -- mostly similar for singles -- a certain percentage of the reciprocating weights plus the rotating weights added to a flywheel. What they don't say is how big is the flywheel and how far out the weights -- in other words, no mention of the arm.

I have a 600 pound Listeroid diesel single with two 24" flywheels powering a generator for emergency outages. Believe me, that is vibration! Yet I balanced it to the point where I don't think it is going to tear down the shed it is housed in any more. It seems quite tame actually. No math involved.

To balance, I set it on railroad ties atop a 2" rubber horse stall mat, then filled in around the ties up to level with gravel. That's like a spring and shock absorber in a car sort of. That's not balancing, but it allowed me to begin after steadying it that way so it wasn't walking around. How I balanced it was just holding a piece of chalk close to one of the flywheels near the top so that it just contacted the chalk during a major excursion. This marked the flywheel at the point of major unbalanced thrust in that direction.

Then while the engine was stopped, I picked a point 180 degrees opposite on the flywheel and added modeling clay there. I started the engine again and checked with chalk again. Less movement, but still some. It was marked in the same place, so I added more clay opposite. Eventually the excursion was nearly gone, and I called it done. I checked the other flywheel the same way. I epoxy glued on equivalent weights to the clay for a more permanent solution.

 

Done! Third time's the charm. Everything fits and no stroke interference. I gave it a brief run-up tonight and it hit 1296 RPM at 100 watts using the electric heater. For this I was running with the thicker flange displacer cylinder.

The engine is much quieter and smoother. It starts running with the new lighter flywheel after 4 minutes of warmup (the electric heater at 100 watts is somewhat slower than Sterno was, I believe) and starts at about 700 rpm, gradually increasing as the furnace heats up.

There seem to be stages of steady rpm, then increases to higher levels, where again it stays relatively consistent for a time before increasing. Maybe its some set of resonance levels. There's a fair amount of vibration (for a small engine) and I notice that if I place my hand on it to steady, I can sometimes get an increase in RPM.

I think balancing the crankshaft might help top speed, but not sure how to do that with an inline twin with a 90 degree phase difference.

Anyway, here it is with new flywheel, new power piston conrod (ball bearing big end), and new crank arm:

 

What could go wrong?   

I actually didn't want to re-pin the flywheel, because I'd like to be able to revert the engine to its original running condition. Also it's good to be able to go back when comparing tests while experimenting. So I took the opportunity to make a new aluminum flywheel. Something I'd already planned as an experiment.

 


The old flywheel was steel, and possibly heavier than needed. I did like the way it looked, though, so rather then making a smaller flywheel, I switched materials to aluminum. That should reduce the weight by two thirds, yet still look the part. I hope this new wheel will have enough inertia.

Guess we'll find out!