Kawi2strokes.com Forum

Good afternoon Mr Tuner. You didnt read what I said, did you? Reciprocating mass to crank counterweight... yes. I agree with you there. Cylinder weight to cylinder weight... no. There is no point having equal rod and piston weights on a triple for each cylinder. It will make NO DIFFERENCE to the vibes.

_________________
http://3cyl.com/mraxl/starfire/starfire.htm

Rotational vibration happens because of the forces on the crankshaft from accelerating the pistons. Boxers and inline fours are worst case examples, since they start and stop all pistons at the same time. Inline three cylinder engines are naturally balanced in the rotational sense, provided the pistons and rods are all the same weight.

As Dayle points out, other modes of vibration are not so ideal for a triple.

_________________
If it surges, that's normal, upshift.

I did read the drivel, and I didn't agree with what yu said.

I've been doing this kind of stuff most all of my 63 years of life, and, I KNOW better than to believe what I know isn't accurate and correct. That goes for balancing, porting, head configure, and, even ignition systems.

Sorry, it DOES matter that all weights relevant to each other are correctly balanced.

But, please, keep that thought pattern going, nobody is forcing anyone to do it right.

Insert popcorn eating emoticon here.........!! (I said it was HARD to balance a triple properly, not un-necessary!!

_________________
"One day, your life will flash before your eyes. Make sure it's worth watching." : anon.

One more try before the popcorn runs out. Two pistons at 180 degrees stopping and changing direction in opposite directions, MUST be the SAME weight to cancel. If the phase is not 180 degrees, as in a triple, there is NO OPPOSING piston to cancel the one changing direction. Any balancing on a 120 degree triple can only be as in a single.... reciprocating weight and crank counterbalance weight..... there is nothing else. Each cylinder can only be balanced to its own part of the crank, and cannot rely on any other cylinder to cancel its vibration. If three individually balanced engines are coupled at 120 degrees, and each engine has been balanced in isolation, irrespective of piston weights per engine, it will run smoother than the single alone... more firing strokes.... but the vibes remain of similar amplitude. IF two different weight engines are coupled at 180 degrees, the interaction will cause secondary vibes, as the heavy end will not cancel the lighter end.... a seesaw effect. It does no harm to make the reciprocating masses roughly the same over the three cylinders in a triple, but if each individual "engine" is balanced to its own counterweights, there is little point getting manic. Thats my "drivel" for the day.

_________________
http://3cyl.com/mraxl/starfire/starfire.htm

First off, who of you balancing experts actually have a machine to balance anything on and have actually done it?

Don

_________________
Don

Seeing as how this may???? end up into an argument, Ill try to short circuit this now. Here are a few excellent links to explain what I have said. This guy keeps things simple, knows what he is talking about, and heaps of maths is not appropriate here anyway.
http://modelenginenews.org/etw/etw_bal/p3.html
You will find the triple reference part way down.
The triple balance issues can be explained mathematically fairly easily using vector diagrams similar to what is used in the electrical trades. To those interested, work your way through this lot.
http://books.google.co.nz/books?id=hpmA ... ry&f=false

Heres how I balance a Titan crank. Yes, I have done this often, and yes, I do have the machine.

Measure the weight of each connecting rod big end and the big end bearing, the small end supported on a hook.Measure the complete weight of each connecting rod small end and the total weight of the piston and rings, piston pin, small end bearing and clips ... ie reciprocating mass, and multiply by your desired balance factor.... this is a variable determined by rpm and other factors, but generally works out at around 50 percent. Add the total weight of reciprocating mass to the balance factor, and select the required bob weight to balance the crankshaft to that figure. Temporarily assemble the crankshaft and place the trued crankshaft ends or shafts on parallel knife edged surface, hang the selected bob weights off the crankshaft pin and make sure the crank will remain set in any position. Once the crankshaft has been balanced, take it apart and install the big end bearings etc , and press the crankshaft together and true the crankshaft. This is static balance.
To dynamically balance, do this.... yes, I do this sometimes too.
For Titan cranks, I have 2 rubber mounted vee blocks to accept the crank end bearings, this is spun up with a small variable speed sewing machine motor. Each conrod is held in a cantilever arrangment , rare earth magnets hold bob weights to each end of the cantilever that count for the missing pistons, rings and gudgeons. Weight is added/subtracted to each crank, opposite the crankpins to remove the rocking (for and aft) moment as much as possible. This balances the crank in two planes, but, like all engines, it will only be be accurate only at one range of RPMs, as reciprocating mass increases faster with revs than the centripedal to counteract it, and it is not the simple sine function as with simple crank rotation. Thats why boxers truly cancel reciprocating with reciprocating... and inlines to a point, With a triple, this does not happen.
OK, thats me done with this.

_________________
http://3cyl.com/mraxl/starfire/starfire.htm

Thankyou, Starfire, we look forward to your next contribution......!!

_________________
"One day, your life will flash before your eyes. Make sure it's worth watching." : anon.

Cheers cobber..... sarcastic sod. Hey, just looking at that site, take a look at this.... the ultimate triple.
http://modelenginenews.org/etw/deltec.html. I vaguely remember these used on trains.

_________________
http://3cyl.com/mraxl/starfire/starfire.htm

No sarcasm intended, an interesting thread!!

_________________
"One day, your life will flash before your eyes. Make sure it's worth watching." : anon.