do the rotary engines produce any type of harmonic vibrations like a piston engine does?

 

I don't have any rock-solid info, but generally I think the issues that are present on piston engines with long, thin, highly eccentric crankshafts are not much of an issue on rotaries. I don't know of any rotaries with harmonic dampers or anything. Light pulleys and flywheels don't seem to lead to any main shaft failures, etc. The fat, stubby eccentric shaft holds up pretty weill until you really start spinning super-high RPMs from all accounts.

-Max

 

I thought that the counterweight was a sort of harmonic balancer for the motor,but I not sure

 

You definitely need the counterweights that match your rotors to keep the engine balanced. But there are reports of light pulleys causing problems on piston engines because they screw up the harmonic balancing. Crankshafts can snap or distort and cause other problems. But light pulleys and flywheels don't seem to cause any problems with the eccentric shaft on rotaries. I am sure that rotaries produce some harmonic vibrations, but they are no so destructive that you need to keep heavy pulleys or dampers on the engine like you do on some piston engines.

-Max

 

max; the reasons the pullies cause such damage on piston engines is that the race, or underdrive, or what ever they are dont have anything to dampen the vibration at all. The completely get rid of the stock rubber material, or what ever is used.

No i was really wondering about engine harmonics because from what i understand and what i have read it can be determental to making power also.

I really dont see how any type of determental harmonics would be produced in a rotary engine, unlike a piston engine where each revolution the piston must stop for a split secound and change direction.

I was just wondering if any one has dove that far into it for the quest of power.

 

Part of the damping is simply having the mass, so even if the stock part you are replacing on a piston engine has no rubber or other soft parts, it can still cause trouble.

Perhaps there are some harmonics issues to worry about on a three rotor, but I think two rotors generally don't have much opportunity for optimization in the harmonics area.

-Max

 

thanks max

 

The reason harmonic balancers are required on piston engines is they have long ropy crankshafts with many pistons twisting on it from various forces. You get a harmonic *twisting* motion in the crank, and just like touching a guitar string with your rubbery fingertip will stop it from vibrating, so does attaching a rubberily-attached mass to the end of the crank.

Rotaries have short, squat shafts, with no heavy duty deviation from centerline such as what exists with a crank throw. There are only two rotors. Rotational vibration is not much of a problem, so we don't need harmonic balancers.

Notice that flat fours generally don't have harmonic balancers either...

Harmonic "balancer" is a misnomer, the proper term is harmonic "damper". But everyone calls them harmonic balancers, because on externally balanced engines, the front imbalance is generally built into the harmonic damper/"balancer".

 

Oh Okay

 

So what about on all the 4- 5- and 6- rotors that people are putting together these days? Is there more issue with those?

(Sorry, saw this thread while searching for the topic on pulleys, and had to ask!)

 

How many people do you know, personally, that are driving around on a 4, 5, or 6 rotor rx7? Honestly...

Friggin' 17 year bump for that? Lol

 

I wonder what the longest thread necro is in the history of the forums so far.

 

Is that a challenge? 🤣😂🤣

 

I imagine it would have been a problem on that (PPRE?) 6 rotor from a few years back.

 

Pulley that's built into the hub itself, with HTD drive for oil pump and 3 rib section for alternator, no damper, worked fine on my 4 rotor to 9500 still running strong

 

unless your circumstances absolutely dictate it, don’t be cheap; have the rotating assembly dynamically balanced

and for the record; rotors don’t simply spin the way some people present it, they “orbit” about a centerline. Which makes the dynamic balancing even more important. The credit goes to Daryl Drummond for bringing me to this realization … Rob Dahm’s opinion be dahmed.
.

 

Good point. I never thought about it that way.

 

None of that has to do with harmonic vibrations, though, which is more related to crankshaft stiffness, engine output, and firing order.

Exceed about 300hp in a turbocharged Mazda BP engine, and you will start breaking oil pumps if you do not upgrade the harmonic damper, for example.

 

Once either type is truly balanced well wrt components there can be other rotational harmonics at play that have to be addressed in a different manner, but to say it has nothing to do with it not accurate imo, particularly wrt rpm and also my comment being rotary specific. I’m admittedly a bit confused by you using a reciprocating engine example to address my post though.