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Connecting rod/bolt balancing questions
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Hopperdhh(at)aol.com
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PostPosted: Sat Mar 18, 2006 3:18 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

I am in the middle of overhauling a Lycoming IO-360-A1A for my RV-7A. It
has come to my attention that there are 2 different rod bolts that will work in
the LW10646 connecting rods. One has a small head and a later bolt has a
larger head.

First question -- Is there anything wrong with using the small headed bolt
(these are the ones I bought from Aircraft Specialties about a year ago)
PN75060?

Second question -- What is the weight difference between the two bolts?

I have weighed the rods (big ends and small ends), and could possibly use
the heavier bolts to get a better matching set to improve the engine balance.

Speaking of engine balance, what is considered good enough? Is 6 grams at
the big end of the rods really bad, or good, or what? It looks like I have
about 3 grams worst case on the recip end. The crank is good (under 1 gram),
and the piston/pins are only a couple of tenths apart.

Thanks,

Dan Hopper
Walton, IN
RV-7A N766DH Flying 144 hours.


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archie97(at)earthlink.net
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PostPosted: Sat Mar 18, 2006 4:27 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Balance criteria on any component is dependent on application parameters.
I personally maintain 1/5 of a gram on statics, and .01 in/oz on dynamics
(or better), for aircraft. Racing engines better than that.
Why not? If you are there working anyway, why not do the best, or close to
it?
(a dollar bill weighs one gram)
Archie
--


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PostPosted: Sat Mar 18, 2006 6:39 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Archie,

I took the rods to a shop to be weighed. I didn't want them to remove any
metal until I had a chance to analyze the weights. Actually, I didn't want to
risk the damage they could do! I don't have the equipment or facilities to
do the job myself, or I would do as you say. Since they were much, much
worse than the values you gave, I wonder if there is really anything to be gained
by getting so "perfect." I overhauled a Continental O-200 a few years ago
and got a very smooth running engine by putting the heavier parts opposite
each other, and matching heavy rods with lighter pistons, etc. The final
assembly was not near as close as you would have done. The Continental Overhaul
Manual states that pistons opposite each other should be within 1/2 ounce --
that's about 14 grams.

I know that you will say to send the rods out to be balanced, but I still
want an answer to my original question from those who know from experience. I
once read that "good enough is perfect." Being a perfectionist myself, I
often have to use that philosophy to move projects along.

Thanks,
Dan



In a message dated 3/18/2006 7:28:24 A.M. Eastern Standard Time, arc
hie97(at)earthlink.net writes:



Balance criteria on any component is dependent on application parameters.
I personally maintain 1/5 of a gram on statics, and .01 in/oz on dynamics
(or better), for aircraft. Racing engines better than that.
Why not? If you are there working anyway, why not do the best, or close to
it?
(a dollar bill weighs one gram)
Archie


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archie97(at)earthlink.net
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PostPosted: Sat Mar 18, 2006 7:25 pm    Post subject: Connecting rod/bolt balancing questions Reply with quote

As you indicate, it is better to spend a little time and money now,
than to wish you had.
There is no substitute for perfection........... None!

The factory recommends 1/2 ounce?
Well, keep in mind these are the same people that give us oil burners,
AD's on an engine that has not changed for over 60 years, 1/2 hp per cu. in.
And they still do not have it right.
They essentially have a captive following that buys this.
If they did not have that, they would have folded long ago.

How would you like to be buying a new car and the salesperson told you
you must run plug gaps of .016 because magnetos will not support more,
It will burn oil, Is subject to AD's which you will forever pay for,
Has poor fuel economy, Blow-by, and 1/2 hp per cu in?
Would you find these attractive? Would you buy this car?

If a small hole in the wall shop like mine can correct most of these,
why can't they? Why do they have engineering if the most basic of problems
have not been corrected? Bean counters tend to run these companies, and
quality, plus R&D have fallen dormant.
I have somewhat evaded a succinct reply to your last post, but am thoroughly
miffed with the beaurocratic ineptitude, greed, and propagandists that seem
to be the root culprit hampering any progress.
Sorry about the long wind, but I have only started, and will quit now
to cool off.

==================================================
Quote:
I took the rods to a shop to be weighed. I didn't want them to remove
any
metal until I had a chance to analyze the weights. Actually, I didn't
want to
risk the damage they could do! I don't have the equipment or facilities
to
do the job myself, or I would do as you say. Since they were much, much
worse than the values you gave, I wonder if there is really anything to
be gained
by getting so "perfect." I overhauled a Continental O-200 a few years
ago
and got a very smooth running engine by putting the heavier parts
opposite
each other, and matching heavy rods with lighter pistons, etc. The final
assembly was not near as close as you would have done. The Continental
Overhaul
Manual states that pistons opposite each other should be within 1/2
ounce --
that's about 14 grams.

I know that you will say to send the rods out to be balanced, but I still
want an answer to my original question from those who know from
experience. I
once read that "good enough is perfect." Being a perfectionist myself, I
often have to use that philosophy to move projects along.

Thanks,
Dan

In a message dated 3/18/2006 7:28:24 A.M. Eastern Standard Time, arc
hie97(at)earthlink.net writes:



Balance criteria on any component is dependent on application parameters.
I personally maintain 1/5 of a gram on statics, and .01 in/oz on dynamics
(or better), for aircraft. Racing engines better than that.
Why not? If you are there working anyway, why not do the best, or close
to
it?
(a dollar bill weighs one gram)
Archie



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glcasey(at)adelphia.net
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PostPosted: Sun Mar 19, 2006 5:20 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

I'll cautiously take what is probably the unpopular side of the
discussion..
I don't understand the emphasis that gets placed on engine
balancing. These engines run relatively slowly and the perceived
vibration in airframe is usually dominated by the propeller. The
propeller imparts vibration from a number of sources - one is its
balance - the blades are at such a large radius that the slightest
variation will result in more vibration than can be expected by the
rotating parts of the engine. Second is the pitch variation from
blade to blade. Again, the slightest pitch error operating at such a
long lever arm will have a big effect on airframe vibration.
finally, the airflow into the prop is not uniform around the
circumference since it is affected by the airframe behind it as well
as the mounting angle of the engine.

The balance of either the reciprocating or rotating parts will have
essentially no effect on the durability or output of the engine -
combustion loads overwhelm any possible mismatch in weights. A
couple of anecdotes that add evidence, but of course don't prove the
point - a friend used to win drag races by building "dual
displacement" engines - the inspectors would always check the
displacement of the #1 cylinder so he would make the first crank
throw a shorter stroke than the other three - engines ran great. I
while back I helped one of my teenagers rebuild his turbo Chrysler 4-
banger. He didn't have any money so we scrounged the parts and
picked the best of the bunch to build the engine. Some cylinders had
different connecting rods than others (a LOT different), others had
different compression ratios. Ran smooth with good power for a long
time after that. Another anecdote (urban legend?) - when Continental
was trying to beef up their engines they introduced pistons with iron
top ring glands, certainly heavier than the all-aluminum pistons they
replaced. They approved servicing a single cylinder with the new
pistons even though it would upset the balance - at least they didn't
think the balance issue was a big one. Using what Continental does
as the guideline is, of course, a risky thing.

Certainly no one can argue that poor balance is a good thing, but I
just don't think the emphasis that seems to be put on balancing is
justified. What would I do? Certainly pick the rod bolts that are
supposed to be the most reliable (whichever one that is) regardless
of weight. I would match up the other parts the best I could with
the tools I had and then I would bolt it together and go fly.

Just another irreverent comment - a "good" aircraft engine will put
out about 200 hp from 360 cu. in. displacement, or 1.08 ft-lb per cu.
in. torque, and they are rated at the minimum power, not the average
of the population. That is very good and very close to what a good
automotive engine will produce. It is compromised because of the
compromises necessary to meet all the other requirements: The idea
is to build an engine that weighs the least, burns the least fuel, is
the most reliable and lasts the longest while being built for the
least cost. If I were starting from scratch there would be some
things I would change, but it wouldn't deviate a lot from the norm.

Gary Casey
Quote:

I am in the middle of overhauling a Lycoming IO-360-A1A for my
RV-7A. It
has come to my attention that there are 2 different rod bolts that
will work in
....
Speaking of engine balance, what is considered good enough? Is 6
grams at
the big end of the rods really bad, or good, or what? It looks
like I have
about 3 grams worst case on the recip end. The crank is good
(under 1 gram),

and the piston/pins are only a couple of tenths apart.

Thanks,

Dan Hopper
Walton, IN
RV-7A N766DH Flying 144 hours.


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gary.stiffler(at)kroger.c
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PostPosted: Sun Mar 19, 2006 8:51 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Quote:
The factory recommends 1/2 ounce?

Quote:
Well, keep in mind these are the same people that give us oil burners,

Quote:
AD's on an engine that has not changed for over 60 years, 1/2 hp per cu.
in.


Quote:
And they still do not have it right.

Quote:
They essentially have a captive following that buys this.

Quote:
If they did not have that, they would have folded long ago.



They have the same design and a captive following because the FAA along
with our legal system makes competition unprofitable.



Gary AA1B 160

Cincinnati OH


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Hopperdhh(at)aol.com
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PostPosted: Sun Mar 19, 2006 10:18 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Good points Gary,

You got me to thinking! I'm an engineer, I ought to be able to figure this
out! (Never mind that I'm an electrical engineer!)

I calculated the imbalance force due to 3 grams at 2.177 inches (1/2 the
stroke of an IO-360) at 2700 RPM to be 2.98 pounds. This is the centrifugal
force which would cause the engine to vibrate. This comes from P=mv
2/r (from
my college physics book) after making all the conversions to metric and back.

Now, if I'm cruising at 2300 rpm at 60 percent of 200 HP, the average force
which must be exerted on the crank throw at 2.177 inches is 1510 pounds. (In
a 4 cylinder there is a power stroke every 180 degrees.) Actually the
pulses probably go to 2 or 3 times this number. This pulsing is what makes the
engine vibrate, or shake.

Your point is well taken.

Dan Hopper
RV-7A


In a message dated 3/19/2006 8:21:19 A.M. Eastern Standard Time,
glcasey(at)adelphia.net writes:



I'll cautiously take what is probably the unpopular side of the
discussion..
I don't understand the emphasis that gets placed on engine
balancing. These engines run relatively slowly and the perceived
vibration in airframe is usually dominated by the propeller. The
propeller imparts vibration from a number of sources - one is its
balance - the blades are at such a large radius that the slightest
variation will result in more vibration than can be expected by the
rotating parts of the engine. Second is the pitch variation from
blade to blade. Again, the slightest pitch error operating at such a
long lever arm will have a big effect on airframe vibration.
finally, the airflow into the prop is not uniform around the
circumference since it is affected by the airframe behind it as well
as the mounting angle of the engine.

The balance of either the reciprocating or rotating parts will have
essentially no effect on the durability or output of the engine -
combustion loads overwhelm any possible mismatch in weights. A
couple of anecdotes that add evidence, but of course don't prove the
point - a friend used to win drag races by building "dual
displacement" engines - the inspectors would always check the
displacement of the #1 cylinder so he would make the first crank
throw a shorter stroke than the other three - engines ran great. I
while back I helped one of my teenagers rebuild his turbo Chrysler 4-
banger. He didn't have any money so we scrounged the parts and
picked the best of the bunch to build the engine. Some cylinders had
different connecting rods than others (a LOT different), others had
different compression ratios. Ran smooth with good power for a long
time after that. Another anecdote (urban legend?) - when Continental
was trying to beef up their engines they introduced pistons with iron
top ring glands, certainly heavier than the all-aluminum pistons they
replaced. They approved servicing a single cylinder with the new
pistons even though it would upset the balance - at least they didn't
think the balance issue was a big one. Using what Continental does
as the guideline is, of course, a risky thing.

Certainly no one can argue that poor balance is a good thing, but I
just don't think the emphasis that seems to be put on balancing is
justified. What would I do? Certainly pick the rod bolts that are
supposed to be the most reliable (whichever one that is) regardless
of weight. I would match up the other parts the best I could with
the tools I had and then I would bolt it together and go fly.

Just another irreverent comment - a "good" aircraft engine will put
out about 200 hp from 360 cu. in. displacement, or 1.08 ft-lb per cu.
in. torque, and they are rated at the minimum power, not the average
of the population. That is very good and very close to what a good
automotive engine will produce. It is compromised because of the
compromises necessary to meet all the other requirements: The idea
is to build an engine that weighs the least, burns the least fuel, is
the most reliable and lasts the longest while being built for the
least cost. If I were starting from scratch there would be some
things I would change, but it wouldn't deviate a lot from the norm.

Gary Casey
Quote:

I am in the middle of overhauling a Lycoming IO-360-A1A for my
RV-7A. It
has come to my attention that there are 2 different rod bolts that
will work in
....
Speaking of engine balance, what is considered good enough? Is 6
grams at
the big end of the rods really bad, or good, or what? It looks
like I have
about 3 grams worst case on the recip end. The crank is good
(under 1 gram),

and the piston/pins are only a couple of tenths apart.

Thanks,

Dan Hopper
Walton, IN
RV-7A N766DH Flying 144 hours.


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Hopperdhh(at)aol.com
Guest





PostPosted: Sun Mar 19, 2006 11:45 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

When I read my listing as it came over the internet, I see that the carat
symbol was deleted making it seem that I got the formula for centrifugal force
wrong.

I'll spell it out: centrifugal force equals mass times velocity squared
divided by radius.

Dan


In a message dated 3/19/2006 1:19:22 P.M. Eastern Standard Time,
Hopperdhh(at)aol.com writes:


Good points Gary,

You got me to thinking! I'm an engineer, I ought to be able to figure this
out! (Never mind that I'm an electrical engineer!)

I calculated the imbalance force due to 3 grams at 2.177 inches (1/2 the
stroke of an IO-360) at 2700 RPM to be 2.98 pounds. This is the
centrifugal
force which would cause the engine to vibrate. This comes from P=mv
2/r (from
my college physics book) after making all the conversions to metric and
back.

Now, if I'm cruising at 2300 rpm at 60 percent of 200 HP, the average force
which must be exerted on the crank throw at 2.177 inches is 1510 pounds.
(In
a 4 cylinder there is a power stroke every 180 degrees.) Actually the
pulses probably go to 2 or 3 times this number. This pulsing is what makes
the
engine vibrate, or shake.

Your point is well taken.

Dan Hopper
RV-7A
In a message dated 3/19/2006 8:21:19 A.M. Eastern Standard Time,
glcasey(at)adelphia.net writes:



I'll cautiously take what is probably the unpopular side of the
discussion..
I don't understand the emphasis that gets placed on engine
balancing. These engines run relatively slowly and the perceived
vibration in airframe is usually dominated by the propeller. The
propeller imparts vibration from a number of sources - one is its
balance - the blades are at such a large radius that the slightest
variation will result in more vibration than can be expected by the
rotating parts of the engine. Second is the pitch variation from
blade to blade. Again, the slightest pitch error operating at such a
long lever arm will have a big effect on airframe vibration.
finally, the airflow into the prop is not uniform around the
circumference since it is affected by the airframe behind it as well
as the mounting angle of the engine.

The balance of either the reciprocating or rotating parts will have
essentially no effect on the durability or output of the engine -
combustion loads overwhelm any possible mismatch in weights. A
couple of anecdotes that add evidence, but of course don't prove the
point - a friend used to win drag races by building "dual
displacement" engines - the inspectors would always check the
displacement of the #1 cylinder so he would make the first crank
throw a shorter stroke than the other three - engines ran great. I
while back I helped one of my teenagers rebuild his turbo Chrysler 4-
banger. He didn't have any money so we scrounged the parts and
picked the best of the bunch to build the engine. Some cylinders had
different connecting rods than others (a LOT different), others had
different compression ratios. Ran smooth with good power for a long
time after that. Another anecdote (urban legend?) - when Continental
was trying to beef up their engines they introduced pistons with iron
top ring glands, certainly heavier than the all-aluminum pistons they
replaced. They approved servicing a single cylinder with the new
pistons even though it would upset the balance - at least they didn't
think the balance issue was a big one. Using what Continental does
as the guideline is, of course, a risky thing.

Certainly no one can argue that poor balance is a good thing, but I
just don't think the emphasis that seems to be put on balancing is
justified. What would I do? Certainly pick the rod bolts that are
supposed to be the most reliable (whichever one that is) regardless
of weight. I would match up the other parts the best I could with
the tools I had and then I would bolt it together and go fly.

Just another irreverent comment - a "good" aircraft engine will put
out about 200 hp from 360 cu. in. displacement, or 1.08 ft-lb per cu.
in. torque, and they are rated at the minimum power, not the average
of the population. That is very good and very close to what a good
automotive engine will produce. It is compromised because of the
compromises necessary to meet all the other requirements: The idea
is to build an engine that weighs the least, burns the least fuel, is
the most reliable and lasts the longest while being built for the
least cost. If I were starting from scratch there would be some
things I would change, but it wouldn't deviate a lot from the norm.

Gary Casey
Quote:

I am in the middle of overhauling a Lycoming IO-360-A1A for my
RV-7A. It
has come to my attention that there are 2 different rod bolts that
will work in
....
Speaking of engine balance, what is considered good enough? Is 6
grams at
the big end of the rods really bad, or good, or what? It looks
like I have
about 3 grams worst case on the recip end. The crank is good
(under 1 gram),

and the piston/pins are only a couple of tenths apart.

Thanks,

Dan Hopper
Walton, IN
RV-7A N766DH Flying 144 hours.


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archie97(at)earthlink.net
Guest





PostPosted: Sun Mar 19, 2006 12:06 pm    Post subject: Connecting rod/bolt balancing questions Reply with quote

Gentlemen;
This topic is far more complex than you believe.
I will not go into the finer details, but you are superficially bouncing
numbers
and quotes but not doing any correcting.
"good enough" is not good enough, "perfect" is.
Although not analogous, would you want a heart surgeon telling you:
"while I am in there, will do the least required"

When teaching machinery dynamics as part of my physics course, the text
was Machinery Dynamics by Holowenko.Check it out, and be surprised.
As far as durability is concerned, how long do you think an electric motor's
bearings will last if it was not in balance, or your aircraft gyro.
Forget RPM, it is either right or wrong, although geometrically progressive.

Vibration was mentioned. That is only a resultant indicator.
A number of factors can cause vibration, such as compression imbalance.
(just pull a spark plug lead while an engine is running)
Many other causes are culprits also, but too involved to discuss here.
If you are not going to do a perfect dynamic and kinematic balance to your
engine, why seek a way to avoid it?
No more from here.......
Archie


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Hopperdhh(at)aol.com
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PostPosted: Sun Mar 19, 2006 12:29 pm    Post subject: Connecting rod/bolt balancing questions Reply with quote

Archie,

Is this subject so complex that only you can understand it? You asked
several questions in your post, but you are not interested in the answers.

First of all, what is your definition of perfect? It must be the accuracy
or resolution of your equipment. Apparently your scales only weigh to .01
grams. What if I needed my rods balanced to .001 grams, isn't that closer to
perfect than what you could handle?

Good enough is not perfect and neither is your work. You are very naive if
you think anything in this world is perfect. There is a very good reason why
Lycoming has built thousands of engines which were terribly out of balance
yet give perfectly (ha) satisfactory service in the field. That reason is
that they don't need to be perfect, only good enough.

Dan



In a message dated 3/19/2006 3:06:47 P.M. Eastern Standard Time,
archie97(at)earthlink.net writes:



Gentlemen;
This topic is far more complex than you believe.
I will not go into the finer details, but you are superficially bouncing
numbers
and quotes but not doing any correcting.
"good enough" is not good enough, "perfect" is.
Although not analogous, would you want a heart surgeon telling you:
"while I am in there, will do the least required"

When teaching machinery dynamics as part of my physics course, the text
was Machinery Dynamics by Holowenko.Check it out, and be surprised.
As far as durability is concerned, how long do you think an electric motor's
bearings will last if it was not in balance, or your aircraft gyro.
Forget RPM, it is either right or wrong, although geometrically progressive.

Vibration was mentioned. That is only a resultant indicator.
A number of factors can cause vibration, such as compression imbalance.
(just pull a spark plug lead while an engine is running)
Many other causes are culprits also, but too involved to discuss here.
If you are not going to do a perfect dynamic and kinematic balance to your
engine, why seek a way to avoid it?
No more from here.......
Archie


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edchmiel(at)mindspring.co
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PostPosted: Sun Mar 19, 2006 4:31 pm    Post subject: Connecting rod/bolt balancing questions Reply with quote

Hmm, this should be good . Think I'll grab a beer and watch...

Ed in JXN


---


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glcasey(at)adelphia.net
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PostPosted: Mon Mar 20, 2006 5:44 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Okay, just for the fun of it let's keep this thread going. I think
there is no substantial argument that can prove that improved balance
can help durability. The combustion pressure pushing on a 5.25 dia.
piston results in a force of about 17,000 pounds, certainly orders of
magnitude more than any likely unbalance. However, the engine
balance can have an affect on accessories - notably alternator
mounting brackets.

How good does the balance have to be? Is perfection the only logical
goal? I don't think so - it should be good enough so that engine
imbalance doesn't add noticeable vibration to the airframe. Even if
it were perfect to imply that rotating imbalance will go to zero is
incorrect. A 4-cylinder opposed engine has a quite high secondary
yaw couple that can't be balanced. Even the 6-cylinder engines are
only balanced in first and second order modes - higher orders may not
be balanced (I don't know as most people stop analyzing after the 2nd
order). It's all a matter of priorities and I would put my efforts
somewhere else. Getting a dynamic prop balance after the engine is
running always seems like a good idea, although my last Cessna was
very smooth without it, so I never bothered. On the Cessna before
that I had dynamic balancing done whenever we had anything done that
could affect balance and even then it was never very smooth.

Gary Casey


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Wes Bunker



Joined: 10 Jan 2006
Posts: 5
Location: Lincoln, CA

PostPosted: Mon Mar 20, 2006 8:33 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Archie, I have to point out that pulling a plug wire will not change
compression of that cylinder. It will certainly change the combustion
pressure, which does increase the amount of vibration. A few months back my
O-320 swallowed the #4 exhaust valve head. Whole lotta shakin' goin' on, I
can tell you! Careful balancing of reciprocating parts in any piece of
machinery contributes to longevity of the bearings as well as any
fatigue-sensitive parts. Engineers may be able to tell us the specific
numbers related to this, but any old backyard shade-tree race car bulder can
tell you the facts of reality.

Wes


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Wes
N7337G
C172K
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gary.stiffler(at)kroger.c
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PostPosted: Mon Mar 20, 2006 9:35 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Quote:
Hmm, this should be good . Think I'll grab a beer and watch...



Quote:
Ed in JXN



Wow! I agree, this is interesting.



Quote:
First of all, what is your definition of perfect? It must be the
accuracy or resolution of >your equipment. Apparently your scales only

weigh to .01 grams. What if I needed my rods >balanced to .001 grams,
isn't that closer to



Quote:
perfect than what you could handle?



I have a few questions and I mean no disrespect I am just curious. If what
was necessary was .001 and you only had equipment that measured .01,
wouldn't you get different equipment?

I think in one of the original posts the balance question was brought up
because the shop that was doing the work was not trusted to remove metal
from the parts. I have not seen that in today's comments so my next
question assumes that it is not an issue. If you were balancing anything
on something that rotates what would be the reason to not balance it as
well as your equipment will allow? The result may not be perceived by your
senses but it could not have a negative effect on wear. You may not
achieve "perfection" but why set out to half-ass it?







Gary AA1B 160 N952GS


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Hopperdhh(at)aol.com
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PostPosted: Mon Mar 20, 2006 11:08 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Gary,

I have done business with this shop before! I only wanted the weights of
the rods -- big end and small end, I didn't want to risk having them grind
strength away in the wrong place or otherwise ruin the rods. Search some on the
web and you'll see that several sites advise against removing weight from
Lycoming rods. My thinking was that I could match up the rods opposite each
other in the best pairs and not have to risk ruining them.

In my first post, I wanted to know what is considered good enough.

clip ---
Speaking of engine balance, what is considered good enough? Is 6 grams at
the big end of the rods really bad, or good, or what? It looks like I have
about 3 grams worst case on the recip end. The crank is good (under 1 gram),
and the piston/pins are only a couple of tenths apart.
---

Archie says that nothing less than perfect is acceptable. I know that
perfect is impossible to achieve, so I still want to know what is considered "good
enough."

Dan Hopper
RV-7A Flying (working on 2nd engine)


In a message dated 3/20/2006 12:36:42 P.M. Eastern Standard Time,
gary.stiffler(at)kroger.com writes:
I think in one of the original posts the balance question was brought up
because the shop that was doing the work was not trusted to remove metal
from the parts. I have not seen that in today's comments so my next
question assumes that it is not an issue. If you were balancing anything
on something that rotates what would be the reason to not balance it as
well as your equipment will allow? The result may not be perceived by your
senses but it could not have a negative effect on wear. You may not
achieve "perfection" but why set out to half-ass it?

Gary AA1B 160 N952GS


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archie97(at)earthlink.net
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PostPosted: Mon Mar 20, 2006 2:40 pm    Post subject: Connecting rod/bolt balancing questions Reply with quote

Am still reading the thread, but will not comment any further regarding
this.
I will say that I own three balancing machines capable of weights of 1500lbs
to several ounces. I also have two analytical systems for checking and
locating
imbalance of rotating parts.
You are correct in bracket cracking, (also exhaust cracking), where proper
balancing of all rotating parts, (including alternator) contributes to
reduction
of such. Also, the propeller, correctly indicated earlier, is a major
culprit.
An interesting fact many may not be aware of, is that once everything is
perfect,
a simple removal and replacement of the prop will show a slight imbalance,
which would not be noticeable, but the instruments have picked it up.
BTW, I do not believe I mentioned that pulling a wire changes static
compression.
Obviously that is fixed. It will change resultant pressure due to lack of
combustion.
I cover all these aspects in my presentations to race shops, and EAA
chapters.
BTW, I am also a retired industrial engineer, college professor, currently
building racing engines.(with three world records), and have raced for over
thirty years.
Nuff said, no need to turn this into a novella.
Happy flying...
Archie
---


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archie97(at)earthlink.net
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PostPosted: Mon Mar 20, 2006 2:57 pm    Post subject: Connecting rod/bolt balancing questions Reply with quote

One last one:
Yes, one of my static scales has the ability to read .001

On a V-type engine the weight of oil in the crank throw
passages is incorporated in the bob weight formula.
Then there are certain instances when an engine will be overbalanced,
but that is another application...................
End of semantics...........


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s_korney(at)hotmail.com
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PostPosted: Mon Mar 20, 2006 3:06 pm    Post subject: Connecting rod/bolt balancing questions Reply with quote

Snip

" BTW, I am also a retired industrial engineer, college professor, currently
building racing engines.(with three world records), and have raced for over
thirty years."---------------------------------------
Just out of curiosity Archie.... What World Records do you personally
own...?

Best... Steve

----Original Message Follows----
From: "Archie" <archie97(at)earthlink.net>
Reply-To: engines-list(at)matronics.com
To: <engines-list(at)matronics.com>
Subject: Re: Re: Connecting rod/bolt balancing questions
Date: Mon, 20 Mar 2006 17:37:19 -0500



Am still reading the thread, but will not comment any further regarding
this.
I will say that I own three balancing machines capable of weights of 1500lbs
to several ounces. I also have two analytical systems for checking and
locating
imbalance of rotating parts.
You are correct in bracket cracking, (also exhaust cracking), where proper
balancing of all rotating parts, (including alternator) contributes to
reduction
of such. Also, the propeller, correctly indicated earlier, is a major
culprit.
An interesting fact many may not be aware of, is that once everything is
perfect,
a simple removal and replacement of the prop will show a slight imbalance,
which would not be noticeable, but the instruments have picked it up.
BTW, I do not believe I mentioned that pulling a wire changes static
compression.
Obviously that is fixed. It will change resultant pressure due to lack of
combustion.
I cover all these aspects in my presentations to race shops, and EAA
chapters.
BTW, I am also a retired industrial engineer, college professor, currently
building racing engines.(with three world records), and have raced for over
thirty years.
Nuff said, no need to turn this into a novella.
Happy flying...
Archie
---


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glcasey(at)adelphia.net
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PostPosted: Tue Mar 21, 2006 5:39 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Dan,
In all the fun we all ignored your original question - "how good is
good enough?" - for which there is probably no answer. At one
extreme you could just bolt the parts together and get what you get.
At the other extreme is perfection, which you won't get. I'm
certainly not an expert as to where you can remove material from
connecting rods, but I would suggest not removing material unless you
are sure there is no stress at that location. Regardless of what you
do, I propose that the difference between putting the engine together
with existing parts just matched as best you can (two heaviest rods
opposite each other, etc) and going for perfection will be
imperceptible. And it will have no effect whatsoever on power,
reliability or durability. Search for perfection someplace else.
Just my opinion.
Gary

Quote:

In my first post, I wanted to know what is considered good enough.

clip ---
Speaking of engine balance, what is considered good enough? Is 6
grams at
the big end of the rods really bad, or good, or what? It looks
like I have
about 3 grams worst case on the recip end. The crank is good
(under 1 gram),

and the piston/pins are only a couple of tenths apart.
---

Archie says that nothing less than perfect is acceptable. I know that
perfect is impossible to achieve, so I still want to know what is
considered "good

enough."

Dan Hopper
RV-7A Flying (working on 2nd engine)


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jlbaker(at)telepath.com
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PostPosted: Tue Mar 21, 2006 8:08 am    Post subject: Connecting rod/bolt balancing questions Reply with quote

Quote:
In all the fun we all ignored your original question - "how good is
good enough?"


Not to be the puryevor of doom and gloom, how about...
Crankcase cylinder deck height variations
between banks
Crankcase cylinder deck height variations
between cylinders
Crankshaft stroke variations between
journals
Connecting rod rotating weight (already
discussed)
Connecting rod reciprocating weight
Connecting rod length (pin CL to CL)
Piston weight
Piston dome volume
Piston wrist pin height
Wrist pin weight
Cylinder head volume
Cylinder intake and exhaust port airflow
Cylinder - installed height of intake and
exhaust valves

Courtesy of the Mattituck site (too lazy to type it myself). There's just a lot
more than rod weights to consider. Of course, all this may be overkill.
Shoot, give 'em a call at 800.624.6680 and see what tolerances they
use. May be enlightening....or discouraging. Your pick.
Jim Baker
580.788.2779
'71 SV, 492TC
Elmore City, OK


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