I'm having real difficulty finding the answer to what seems a simple
question; I need to know the bob weight formula [balance factor] for an
inline twin [both pistons run in parallel].
Top rpm is 8500, usually runs at about 4-5000. Street use.

I'm in India, and my old 1977 Kawasaki kz400 has a stripped balancer
driving sprocket. This is basically not repairable, but I've had
correspondence with an American who has had good results by removing
the balancer shafts and having the crank balanced.
An old friend of mine is now managing a hi tech machine shop [turbocam
India] not too far away that is about to buy a balancing machine, and
he wants to help.
I need to do the preliminary work at a local shop first, including
making the bob weights; but are they 1;1 in this case [equal to
piston/rod assembly] or does reciprocating weight have to be worked out
separately like on a V8?
I'm a good mechanic and not bad with engineering. There are some local
guys who are good as well, but as I said, no one has ever done this
here.
I'm sure there's a machinist out there in usenet land who knows the
answer!

I bought the old KZ in the US in 1978, and brought it to India in 1982.
It's respected like an old Ferrari would be in the west.
It's getting hard to keep it going now, and it looks pretty rough, but
it still kills any bike in current production in India.
Thanks for your time, I've been mailing and posting this question all
over but have had no replies.
Mark Holden

wrote:
I'm having real difficulty finding the answer to what seems a simple
question; I need to know the bob weight formula [balance factor] for an
inline twin [both pistons run in parallel].
Top rpm is 8500, usually runs at about 4-5000. Street use.

This might help:

http://lodestone.dynodns.net/new/balancer/balance.html

wrote:

An old friend of mine is now managing a hi tech machine shop [turbocam
India] not too far away that is about to buy a balancing machine, and
he wants to help.

I need to do the preliminary work at a local shop first, including
making the bob weights; but are they 1;1 in this case [equal to
piston/rod assembly] or does reciprocating weight have to be worked out
separately like on a V8?

The principle is very easy:
Compensate all rotating masses fully
Compensate translating masses partial (50%, depending on application)

Rotating masses a
Masses on the crank shaft that are out of center. - crank + crank pin
rotating part of connection rod

Translating parts:
translating part of rod
piston, piston pin, piston rings

How to get the rotating mass of the rod:
It is very easy. put the top end of the rod (right where the pin is
going through) on a knife, the other end on a balance. What you read is
the rotating wheight. Reverse the setup (top end on balance) to get the
translating wheight.


Every mass that is out of center of rotation has to be compensated with
a mass that has the same distance*mass product. Say the crank pin
weights 0.1kg and is 25mm off center. The product is 2.5mmkg. You can
compensate it with a mass that is 50mm (CG) off center and weights
0.05kg Do that with all rotatning masses.
The translating masses are calculated with a distance half the stroke
and 50% of their mass.

The 50% can be varied. It depends on how the cylinders are arranged
(horizontal/vertical) and if you prefer vibrations to be horizontal or
vertical. Bikes normaly have vertical vibrations. Compensation is going
up to 70%.
Assuming translational masses are 0.3kg, stroke is 50mm and you want a
60% compensation, you get:
0.3kg * 50mm/2 * 0.6 = 9mmkg.

Now if you add all compensation masses you have to select a mass who's
CG offset and whos mass is the same product. Counterweights normaly do
have a D-shape. It takes some math to find the CG. Better to use a CAD
for that.


HTH. If I was to confusing, feel free to ask.
Nick

--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige

It depends on whether you have a 180 or 360 degree engine.
A 360 has the pistons going up & down together, and you treat it like a
single, only add up both sides' reciprocating weights and make BF around
66% of that if the cylinders are vertical.
If 180, both sides cancel each other so BF isn't so critical.
Actual figure is found by the factory by trial & error, so you're alone
there.
Add a head-steady if it doesn't already have one.

Jordan

wrote:
I need to know the bob weight formula [balance factor] for an
inline twin [both pistons run in parallel].

On 27 Nov 2005 22:09:31 -0800, wrote:

I'm having real difficulty finding the answer to what seems a simple
question; I need to know the bob weight formula [balance factor] for an
inline twin [both pistons run in parallel].
Top rpm is 8500, usually runs at about 4-5000. Street use.

I'm in India, and my old 1977 Kawasaki kz400 has a stripped balancer
driving sprocket. This is basically not repairable, but I've had
correspondence with an American who has had good results by removing
the balancer shafts and having the crank balanced.
An old friend of mine is now managing a hi tech machine shop [turbocam
India] not too far away that is about to buy a balancing machine, and
he wants to help.
I need to do the preliminary work at a local shop first, including
making the bob weights; but are they 1;1 in this case [equal to
piston/rod assembly] or does reciprocating weight have to be worked out
separately like on a V8?
I'm a good mechanic and not bad with engineering. There are some local
guys who are good as well, but as I said, no one has ever done this
here.
I'm sure there's a machinist out there in usenet land who knows the
answer!

I bought the old KZ in the US in 1978, and brought it to India in 1982.
It's respected like an old Ferrari would be in the west.
It's getting hard to keep it going now, and it looks pretty rough, but
it still kills any bike in current production in India.
Thanks for your time, I've been mailing and posting this question all
over but have had no replies.
Mark Holden

A parallel twin cannot be fully balanced because there
is no way that a single rotating mass can fully cancel the pure
up and down mass of the two pistons.

The best compromise is to balance out all the rotating
mass plus half the up and down mass - a similar trick to the Vee8
balancing. Balance the crankshaft with an added weight on the big
end equal all the weight of the big ends of the con rods plus
half the weight of the two pistons plus rings plus half the
weight of the little end of the conrods.

Because its's a compromise balance it's not particularly
critical. All that a small error does is to slightly shift the
direction of maximum vibration with little change in amplitude.

Jim

In article ,
says...

A parallel twin cannot be fully balanced because there
is no way that a single rotating mass can fully cancel the pure
up and down mass of the two pistons.

Best bet then is to cut off the two cylinders and weld them on the
sides of the motor. This makes an engine with perfect primary balance.

:^)

Actually the best bet is to contact a bike salvage yard and
get the part that's busted.....

Cheapest and simplest in the long run. Anything else is going
to result in an investement in time and money that *won't* get
paid back. If Kaw could have built 'em that way, they would
have.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Doesn't sound, from the original post, that he's likely to find another
part in a salvage yard in India.
Kawasaki have built parallel twins with no balance shafts, so don't
understand the last remark?

Jordan

jim rozen wrote:

Actually the best bet is to contact a bike salvage yard and
get the part that's busted.....

Cheapest and simplest in the long run. Anything else is going
to result in an investement in time and money that *won't* get
paid back. If Kaw could have built 'em that way, they would
have.

In article , Jordan says...

Doesn't sound, from the original post, that he's likely to find another
part in a salvage yard in India.

A lot of those salvage yards are on the internet, and one can
search their stock online. I suspect he could find one to ship
him the part easier than modifying the original design.

Just a guess.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Since this is what I call an inline engine {not a V} and the engine is a 4
stroke means both pistons come up at the same time. Almost impossible to
balance perfectly, the counter balance method would be the best for
drivability. That being said, you'll have to balance it as if it were a
single cylinder. Probably have to add a lot of weight to the counterweights
I am sure. Will make for a rough idle I am sure if you balance it for higher
RPMs. Will free up a little HP maybe.

On 28 Nov 2005 14:53:11 -0800, jim rozen
wrote:

In article , Jordan says...

Doesn't sound, from the original post, that he's likely to find another
part in a salvage yard in India.

A lot of those salvage yards are on the internet, and one can
search their stock online. I suspect he could find one to ship
him the part easier than modifying the original design.

And just exactly what kind of fun is that Jim? I mean no matter which
methodology th' gent chooses to balance it, there will always be
vibratory feedback. No such thing as a perfectly balanced
reciprocating mass. Well, besides that buttered toast strapped onto a
cats ass theory.

Now *where* that happens in his rpm's range is where th' fun begins.
Preferably not in th' sweet spot, which I'm guessing is 5-6k rpm.
That leaves a bunch of room for hitting it correctly... or adequately
anyway.

Just a guess.

Yeah, me too g.

Snarl

I was curious about this specifically, for different types of IC motorcycle
engines.
I bought a copy of Fundamentals of Internal Combustion Engine Design, i
think by Heywood?

anyhoo, it is an engineering text that covers all aspects of engine design,
not too deep for a layman, I recommend it.


wrote in message
ups.com...
I'm having real difficulty finding the answer to what seems a simple
question; I need to know the bob weight formula [balance factor] for an
inline twin [both pistons run in parallel].
Top rpm is 8500, usually runs at about 4-5000. Street use.

I'm in India, and my old 1977 Kawasaki kz400 has a stripped balancer
driving sprocket. This is basically not repairable, but I've had
correspondence with an American who has had good results by removing
the balancer shafts and having the crank balanced.
An old friend of mine is now managing a hi tech machine shop [turbocam
India] not too far away that is about to buy a balancing machine, and
he wants to help.
I need to do the preliminary work at a local shop first, including
making the bob weights; but are they 1;1 in this case [equal to
piston/rod assembly] or does reciprocating weight have to be worked out
separately like on a V8?
I'm a good mechanic and not bad with engineering. There are some local
guys who are good as well, but as I said, no one has ever done this
here.
I'm sure there's a machinist out there in usenet land who knows the
answer!

I bought the old KZ in the US in 1978, and brought it to India in 1982.
It's respected like an old Ferrari would be in the west.
It's getting hard to keep it going now, and it looks pretty rough, but
it still kills any bike in current production in India.
Thanks for your time, I've been mailing and posting this question all
over but have had no replies.
Mark Holden

Not necessarily Mike.
There've been lots of non-360 degree twin 4 strokes.
Recently Yamaha made parallel, in-line twins with 90 degree offset,
mostly to make the engines sound like Ducatis I think!

Jordan

Mike wrote:
Since this is what I call an inline engine {not a V} and the engine is a 4
stroke means both pistons come up at the same time.

On Mon, 28 Nov 2005 19:04:45 -0800, wrote:

On 28 Nov 2005 14:53:11 -0800, jim rozen
wrote:

In article , Jordan says...

Doesn't sound, from the original post, that he's likely to find another
part in a salvage yard in India.

A lot of those salvage yards are on the internet, and one can
search their stock online. I suspect he could find one to ship
him the part easier than modifying the original design.

And just exactly what kind of fun is that Jim? I mean no matter which
methodology th' gent chooses to balance it, there will always be
vibratory feedback. No such thing as a perfectly balanced
reciprocating mass. Well, besides that buttered toast strapped onto a
cats ass theory.
Snarl,
You've got it wrong about describing the cat/toast theory. If the
toast is strapped to the cat's ass the cat will end up sitting down
with all four feet on the ground. For perfect balance and levitation
the toast must be strapped to the cat's back. Don't make the mistake
of strapping the buttered side against the cat. This will accelerate
the cat towards the floor and may hurt the cat.
ERS

On Tue, 29 Nov 2005 08:12:37 -0800, Eric R Snow
wrote:

On Mon, 28 Nov 2005 19:04:45 -0800, wrote:

On 28 Nov 2005 14:53:11 -0800, jim rozen
wrote:

In article , Jordan says...

Doesn't sound, from the original post, that he's likely to find another
part in a salvage yard in India.

A lot of those salvage yards are on the internet, and one can
search their stock online. I suspect he could find one to ship
him the part easier than modifying the original design.

And just exactly what kind of fun is that Jim? I mean no matter which
methodology th' gent chooses to balance it, there will always be
vibratory feedback. No such thing as a perfectly balanced
reciprocating mass. Well, besides that buttered toast strapped onto a
cats ass theory.

Snarl,

You've got it wrong about describing the cat/toast theory. If the
toast is strapped to the cat's ass the cat will end up sitting down
with all four feet on the ground. For perfect balance and levitation
the toast must be strapped to the cat's back. Don't make the mistake
of strapping the buttered side against the cat. This will accelerate
the cat towards the floor and may hurt the cat.

Of course you are correct Eric, and I thank you for clarifying, as
this is a very important procedural distinction. I was in an
anti-kitty mood last evening when I posted that g.

And on a totally different note; not sure if it really matters much in
th' scheme of life, but there's likely more than a few of us who're
sending good thoughts in yer general direction. I don't have th'
T-shirt, but what you and your family are going through has to be a
sumbitch. Good on ya's for being there!

Snarl

No such thing as a perfectly balanced reciprocating mass.
Well, besides that buttered toast strapped onto a
cats ass theory.

You've got it wrong about describing the cat/toast theory. If the
toast is strapped to the cat's ass the cat will end up sitting down
with all four feet on the ground. For perfect balance and levitation
the toast must be strapped to the cat's back. Don't make the mistake
of strapping the buttered side against the cat.

All of this theorizing is complete bunk, and you all know it.
Any and all cats are surrounded by an aura of loose cat hair,
just waiting for something, preferably food, to stick to. And
once there's cat hair on the buttered toast, all it's floor seeking
properties are cancelled as redundant. So you've doomed the
experiment as soon as you've gotten the toast anywhere near
the cat...nevermind strapped it down.
--Glenn Lyford

Not necessarily Mike.
There've been lots of non-360 degree twin 4 strokes.

This particular engine has both pistons going up and down at the same time.
I am pretty lame in motorcycle knowledge. What well known parallel 4-stroke
engine type use the opposite, one up and one down? Sound must be quite
distinct.

O=={o] Hot Rod

"Mike" wrote in
:


Not necessarily Mike.
There've been lots of non-360 degree twin 4 strokes.

This particular engine has both pistons going up and down at the same
time. I am pretty lame in motorcycle knowledge. What well known
parallel 4-stroke engine type use the opposite, one up and one down?
Sound must be quite distinct.

O=={o] Hot Rod


Early triumphs had both 180 ( pin 180 apart ) and 360 (pins together
alternate firing). Some laverda 500 racers had 180 cranks. Yamaha 850 twin
and Triumph Bonneville america have 270 cranks where the crank pins are 90
degrees apart..... they sounf like a V twin

"mike" wrote in message
...
"Mike" wrote in
:


Not necessarily Mike.
There've been lots of non-360 degree twin 4 strokes.

This particular engine has both pistons going up and down at the same
time. I am pretty lame in motorcycle knowledge. What well known
parallel 4-stroke engine type use the opposite, one up and one down?
Sound must be quite distinct.

O=={o] Hot Rod


Early triumphs had both 180 ( pin 180 apart ) and 360 (pins together
alternate firing). Some laverda 500 racers had 180 cranks. Yamaha 850 twin
and Triumph Bonneville america have 270 cranks where the crank pins are 90
degrees apart..... they sounf like a V twin

Are you sure about the early Triumphs? My '56 pre-unit had a 360 crank.
I've never heard of any Triumph with a 180 crank, but I've never heard of a
lot of things. You're absolutely right about the Laverdas though. I seem
to remember a model test done by a bike magazine on a street model parallel
twin Laverda back in the '70's that stated that it also had a 180 crank.

Garrett Fulton

Garrett Fulton

Don't know of any currently made like this, but during the '60s most
Honda twins (all 4 strokes) were 180 degree layout.
e.g. CB72/77, CB175, CB250/350, CB450.
The exhaust sound was the norm - V twins were the rarity then.

Jordan

Mike wrote:
What well known parallel 4-stroke
engine type use the opposite, one up and one down? Sound must be quite
distinct.

O=={o] Hot Rod

Two words
ebay

thanks for all the info, guys. so the answer seems to be 50% to 70%;
quite a spread.
Just to be clear; crank is 360 degrees, that's what I meant when I said
both pistons run in paralel.
Jim;
The Bike is 27 years old; used parts will be the same age.
shipping costs to India will cost more than the entire job, machining
and all.
you can't put a different crankshaft in without new undersized bearings
and a crank grind. finding new undersized bearings will be as much work
as getting the crank ballanced,
aside from that, techincal items will get stuck in customs for months;
if I ever get them at all. you don't mail things like this to countries
like this, you make do with what's available. A full days wages here is
about $3.US, 5 for a skilled machinist. that's why we do these things
instead of just throwing the bike away; and because there is no new
bike like it to replace it with anyway.
Daniel; ebay is not two words; when you're in this part of the world,
it isn't even 1. few vendors will even ship out of the US.
information flows cheap and good though!
regards, Mark

In article .com,
says...

like this, you make do with what's available. A full days wages here is
about $3.US, 5 for a skilled machinist. that's why we do these things
instead of just throwing the bike away; ...

If the skills are there, and labor is inexpensive, maybe they could
simply fabricate a new sprocket and braze it on to the end of
the crank?

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

50% will give smallest all-round vibes, but may not be the best, because
who cares how small the vibes are in the direction you can't feel?
Most factories went for more like 65% if vertical cylinders like yours,
so that the up/down vibes you can feel are less, forward/reverse vibes
that aren't so obvious are more.
Resonant frequency of frames will be different in each direction, so BF
is sometimes adjusted to steer the vibes away from problematic resonance.
Note that Norton 360 degree twins were originally around 65%, then when
they started to rubber-mount the engines they went to 50%.
There were exceptions, some Velocettes reportedly 85%, so good luck!

Jordan

wrote:
thanks for all the info, guys. so the answer seems to be 50% to 70%;
quite a spread.

gfulton wrote:

Are you sure about the early Triumphs? My '56 pre-unit had a 360 crank.
I've never heard of any Triumph with a 180 crank, but I've never heard of a
lot of things.

For me, British Motorcycles (note: respectfully I didn't say "brit
bikes") were the classical parallel twins (360°).
But I would't bet more than a beer or two. Or ten ale. But we were
talking about beer.


Nick
--
Motor Modelle // Engine Models
http://www.motor-manufaktur.de
DIY-DRO - YADRO - Eigenbau-Digitalanzeige