Jump to content

Recommended Posts

Here is a picture of an engine that is a couple of years old that was supposed to be a breakthrough in balancing

and smoothness for a single cylinder.   But I cannot remember the manufacturer.

The engine basically has two crankshafts which have gears at the end which both intertwine with a main transmission power shaft.

From what I remember nearly all of the vibration is canceled out in a remarkable way.

 

  

 

% MotorCycle single_cyl-engine.jpg

Share this post


Link to post
Share on other sites

Believe the engine was a race engine developed by BMR - Germany.
Originally started life as a Suzuki Dr800 Single
From what I can gather, the twin crankshaft configuration was initially intended to prevent the massive piston from "Cocking over" in the bore.
 

Share this post


Link to post
Share on other sites

The bmw 800 is a pretty weird motor too, a twin with a 3rd dummy rod to a counter weight. 

 

BMW_F800_balance_5.jpg

  • Like 1

Share this post


Link to post
Share on other sites

Recently I have seen some new single cylinder models featuring "double balancers"  what ever that means.

I am glad mfgrs are working so hard to smooth the engines with all the latest technology.  

I wish we could get more technically accurate info from the cycle reviewers and mfgrs themselves about the

vibration in the models they sell.

Share this post


Link to post
Share on other sites
1 hour ago, preventec47 said:

Recently I have seen some new single cylinder models featuring "double balancers"  what ever that means.

I am glad mfgrs are working so hard to smooth the engines with all the latest technology.  

I wish we could get more technically accurate info from the cycle reviewers and mfgrs themselves about the

vibration in the models they sell.

Double balancers means two counter balancers, usually located one fwd. of the crank and one aft. It would be easy to attach an accelerometer to an engine to quantify the frequency and amplitude of engine vibrations. Not sure if this would be of any value to the rider. Maybe they could strap a rider to a bike on a dyno and run it at various rpms for an hour and then ask them "On a scale of 1 to 10 how numb do your bum and hands feel"?

 

  • Like 1
  • Haha 2

Share this post


Link to post
Share on other sites

I guess im just old....but I have had many singles devoid of any counter balance.. yes some were noticeable shakers and others not so much. none of them shook apart or failed prematurely.  but most were low RPM torque monsters compared with todays high RPM zinger dingers....

I bet in 5 to 10 years some manufacture will make a new motor and brag that the engineering is so good that they didn't even need a balancer....it all goes full circle...

  • Like 2

Share this post


Link to post
Share on other sites
On ‎1‎/‎8‎/‎2019 at 10:48 PM, highmarker said:

The bmw 800 is a pretty weird motor too, a twin with a 3rd dummy rod to a counter weight. 

 

BMW_F800_balance_5.jpg

Engine is not made by BMW. It's a Rotax series 804 and it's parent company is BRP. 

Share this post


Link to post
Share on other sites
50 minutes ago, willie said:

Engine is not made by BMW. It's a Rotax series 804 and it's parent company is BRP. 

true, but sold by bmw, do they use them anywhere else? 

Share this post


Link to post
Share on other sites

the deal here is this,

A single cant really be balanced.

Balance factor, the weight of the lower half or (rotating weight of the rod) +% of the reciprocating (upper half of the rod, and piston assembly)

with low % balance factors, say 0, The thing shakes with full force inline with the piston.

with high% balance factors, say 100, forces inline with the piston are cancelled, but now picture our vertically mounted engines, as the counterweight passes through tdc and bdc it is throwing the engine fore and aft just as much as the 0% was throwing the engine up and down.

so 50% is routinely chosen, so that the amplitude of of perpendicular and inline are balanced, or spread between the two.

But when you throw the actual piston motion into the mix the way the piston moves at tdc and bdc are different,  so depending on rod ratio an engine may actually like something closer to 60-65 to actually evenly distribute inline and perpendicular forces and reduce the peak to its lowest.   This part is best demonstrated by downloading tony foales free balance program, and clicking the box "include secondaries"

the point of the balance is as that counterweight swings "forward" the counterbalance counters it by swinging back.  This does make them smoother, and can allow a higher balance factor.

those twin cranks, oppose the piston to reduce inline forces, and oppose each other to reduce perpendicular forces.  From a balance perspective that thing is bad ass.  From a racer perspective, I don't want to have to change the direction of those two gyroscopes.  Would be great for generators and air compressors.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×