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Balancing Connecting Rods

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Hopperdhh(at)aol.com
Guest

Posted: Sat Mar 04, 2006 4:44 am Post subject: Balancing Connecting Rods

I made a search in the archives and couldn't find anything on this  subject.

 

Is is safe to remove metal from a Lycoming rod to match up a set of  4?  The 

worst one is 9 grams heavier on the big end.  That  is quite a volume of 

metal, and the rods don't look like they have that much to  spare.  One option is 

to do it on the crank.  Is it safe to remove  metal from the crank.

 

I'm concerned about the nitride coating layer, mostly.  Is there any  advice 

that anyone can give me about what to do or not do.

 

The engine is an IO-360-A1A.  The rods are LW10646.

 

Thanks, Dan Hopper RV-7A Flying 144 hours

archie97(at)earthlink.net
Guest

Posted: Sat Mar 04, 2006 5:36 am Post subject: Balancing Connecting Rods

If you attend Oshkosh, I conduct seminars on engine balancing.

Briefly, Aircraft manufacturers balance rods in total weight.

While this is satisfactory, for horizontally opposed engines,

an improvement is to separate Reciprocating from Rotating weights.

9 Grams is doable with care and stress knowledge.

On Lyc rods, there is an area by the rod bolt that is unfinished.

This area can be taken down and polished.

Do not use a grinding wheel. Metal must be removed with a high speed

belt sander so as not to allow the rod to overheat. If this happens, the 

bore will distort.

Prior to starting, you may want to check the bore accuracy. Most aircraft 

shops merely

replace the pin bushings and rod bolts. I have found that most rod bores

are "not on the money", but people use them as is anyhow. (no comment on 

that)



Same with crank balancing. For the most part, they are not usually too bad.

Grinding and polishing is my preference. The factory balancing is with a 

fairly

coarse finish.

Also, do not forget the starter gear. It becomes part of the crank 

rotational force

when attached. (as do the bolts).

Archie



 	  Quote: 	
		   



 I made a search in the archives and couldn't find anything on this 

 subject.



 Is is safe to remove metal from a Lycoming rod to match up a set of  4? 

 The

 worst one is 9 grams heavier on the big end.  That  is quite a volume of

 metal, and the rods don't look like they have that much to  spare.  One 

 option is

 to do it on the crank.  Is it safe to remove  metal from the crank.



 I'm concerned about the nitride coating layer, mostly.  Is there any 

 advice

 that anyone can give me about what to do or not do.



 The engine is an IO-360-A1A.  The rods are LW10646.



 Thanks, Dan Hopper RV-7A Flying 144 hours

Hopperdhh(at)aol.com
Guest

Posted: Sat Mar 04, 2006 4:52 pm Post subject: Balancing Connecting Rods

Archie,

 

Thanks for your reply.  I understand about the whole rod vs. big end  and 

small end weights.  The rods are actually at a local shop which  specializes in 

race car engines.  I think they are pretty knowledgeable,  but not experienced 

in Lycomings.   Could you be a little more  specific about where to remove 

metal.  The rods have quite a lot of metal  already removed along side the bolts. 

 I say that because it looks like  rough machining there.  There is an area 

near the nut on the rod proper  (not the cap) with some to spare possibly.  Or 

are you talking about on the  cap?  Knowing what 9 grams of steel looks like, 

I am worried about trying  to take that much off.

 

I will attend your seminar at OSH this summer, but that will be too late  for 

this job.  I have attended a balancing seminar already,  there.   But, they 

were just trying to sell prop "dynamic" balancing  equipment.  Don't get me 

wrong.  I am a believer in doing a final  balance job on the prop end of the 

engine, but I think it is a good idea to  match up the internal parts first.  The 

pistons were within a few tenths of  a gram, and the crank was also very good. 

 But the rods were by far  the worst.  If there is not enough "meat" on the 

rods, how do you feel  about taking some off the crank?  I know that its like 

two wrongs making a  right, but its all rotating weight, so theoretically it 

should be in  balance.

 

Thanks again,

 

Dan Hopper RV-7A

 

 

In a message dated 3/4/2006 8:37:44 A.M. Eastern Standard Time,  

archie97(at)earthlink.net writes:

If  you attend Oshkosh, I conduct seminars on engine balancing.

Briefly,  Aircraft manufacturers balance rods in total weight.

While this is  satisfactory, for horizontally opposed engines,

an improvement is to  separate Reciprocating from Rotating weights.

9 Grams is doable with care  and stress knowledge.

On Lyc rods, there is an area by the rod bolt that is  unfinished.

This area can be taken down and  polished.

grosseair(at)comcast.net
Guest

Posted: Sat Mar 04, 2006 6:00 pm Post subject: Balancing Connecting Rods

Why don't you try swapping rods with someone if that's a possibility. Or 

do you have access to a shop with inventory that might let you had pick 

a new rod to replace the 9 g heavy one you have?



John Grosse



Hopperdhh(at)aol.com wrote:



 	  Quote: 	
		  



 

Archie,

 

Thanks for your reply.  I understand about the whole rod vs. big end  and 

small end weights.  The rods are actually at a local shop which  specializes in 

race car engines.  I think they are pretty knowledgeable,  but not experienced 

in Lycomings.   Could you be a little more  specific about where to remove 

metal.  The rods have quite a lot of metal  already removed along side the bolts. 

 I say that because it looks like  rough machining there.  There is an area 

near the nut on the rod proper  (not the cap) with some to spare possibly.  Or 

are you talking about on the  cap?  Knowing what 9 grams of steel looks like, 

I am worried about trying  to take that much off.

 

I will attend your seminar at OSH this summer, but that will be too late  for 

this job.  I have attended a balancing seminar already,  there.   But, they 

were just trying to sell prop "dynamic" balancing  equipment.  Don't get me 

wrong.  I am a believer in doing a final  balance job on the prop end of the 

engine, but I think it is a good idea to  match up the internal parts first.  The 

pistons were within a few tenths of  a gram, and the crank was also very good. 

 But the rods were by far  the worst.  If there is not enough "meat" on the 

rods, how do you feel  about taking some off the crank?  I know that its like 

two wrongs making a  right, but its all rotating weight, so theoretically it 

should be in  balance.

 

Thanks again,

 

Dan Hopper RV-7A

 

 

In a message dated 3/4/2006 8:37:44 A.M. Eastern Standard Time,  

archie97(at)earthlink.net writes:

If  you attend Oshkosh, I conduct seminars on engine balancing.

Briefly,  Aircraft manufacturers balance rods in total weight.

While this is  satisfactory, for horizontally opposed engines,

an improvement is to  separate Reciprocating from Rotating weights.

9 Grams is doable with care  and stress knowledge.

On Lyc rods, there is an area by the rod bolt that is  unfinished.

This area can be taken down and  polished.

archie97(at)earthlink.net
Guest

Posted: Sat Mar 04, 2006 6:59 pm Post subject: Balancing Connecting Rods

The area on the main rod just above the nuts is unfinished on the factory 

rods.

The obvious forging mark is there, and can be taken down maintaining the

same arc curve. This area is usually good for about five grams.

I cannot go into details here, but will tell you not to try and remove too 

much

from any given area.

In certain instances, have turned a couple of grams off on a lathe.(nuff 

said here).

Do not remove any metal from the periphery of the bolt holes.

(Superior rods are completely finished.)



Do not try to correct a rod weight by working the crank.

Adding bob weights is not the answer.

It is either right or wrong. If necessary, and you are not comfortable

with rod correction, either obtain closer rods, leave it alone, or just

use total rod weight..

There is much more to machinery dynamics than wheel balancing,

and not worth the risk of part failure if not experienced in this area.

Archie

 	  Quote: 	
		   Archie,



 Thanks for your reply.  I understand about the whole rod vs. big end  and

 small end weights.  The rods are actually at a local shop which 

 specializes in

 race car engines.  I think they are pretty knowledgeable,  but not 

 experienced

 in Lycomings.   Could you be a little more  specific about where to remove

 metal.  The rods have quite a lot of metal  already removed along side the 

 bolts.

 I say that because it looks like  rough machining there.  There is an area

 near the nut on the rod proper  (not the cap) with some to spare possibly. 

 Or

 are you talking about on the  cap?  Knowing what 9 grams of steel looks 

 like,

 I am worried about trying  to take that much off.



 I will attend your seminar at OSH this summer, but that will be too late 

 for

 this job.  I have attended a balancing seminar already,  there.   But, 

 they

 were just trying to sell prop "dynamic" balancing  equipment.  Don't get 

 me

 wrong.  I am a believer in doing a final  balance job on the prop end of 

 the

 engine, but I think it is a good idea to  match up the internal parts 

 first.  The

 pistons were within a few tenths of  a gram, and the crank was also very 

 good.

 But the rods were by far  the worst.  If there is not enough "meat" on the

 rods, how do you feel  about taking some off the crank?  I know that its 

 like

 two wrongs making a  right, but its all rotating weight, so theoretically 

 it

 should be in  balance.



 Thanks again,



 Dan Hopper RV-7A

 In a message dated 3/4/2006 8:37:44 A.M. Eastern Standard Time,

 archie97(at)earthlink.net writes:

 If  you attend Oshkosh, I conduct seminars on engine balancing.

 Briefly,  Aircraft manufacturers balance rods in total weight.

 While this is  satisfactory, for horizontally opposed engines,

 an improvement is to  separate Reciprocating from Rotating weights.

 9 Grams is doable with care  and stress knowledge.

 On Lyc rods, there is an area by the rod bolt that is  unfinished.

 This area can be taken down and  polished.

redswing(at)mcn.org
Guest

Posted: Sun Mar 05, 2006 7:30 pm Post subject: Balancing Connecting Rods

---

Hopperdhh(at)aol.com
Guest

Posted: Mon Mar 06, 2006 4:00 am Post subject: Balancing Connecting Rods

In a message dated 3/5/2006 10:31:21 P.M. Eastern Standard Time,  

redswing(at)mcn.org writes:



Prior to starting, you may want to check the bore accuracy.

This is  a great suggestion. Aircraft rods are sometimes returned to service 

in  unserviceable condition because many of the shops do not edven check the 

big  end bores. If your heavy rod(s) also need to have the big end bore 

resized,  that could fix both problems at the same time.

Red  Hamilton



I almost missed this comment embedded in Archie's text.  That is a  great 

suggestion, Red.  I'll bring it up as a possibility with the shop  doing the 

balancing.  Also, see my other post on why it may not even be  necessary to 

balance the big ends.

 

Dan Hopper

Walton, IN

RV-7A  Flying since July 2004 -- Building up another engine for a  spare, or 

something!

Hopperdhh(at)aol.com
Guest

Posted: Mon Mar 06, 2006 4:00 am Post subject: Balancing Connecting Rods

Archie,

 

I have been giving this balancing problem a lot of thought.  I am used  to 

thinking race car engines -- V8s with a 4 plane crank.  In that case it  is of 

course necessary to match up all the rods and counterweight the crank  while 

balancing it.  It occurs to me that if all the unbalance (imbalance?)  is in a 

single plane -- say the small ends of the rods match but the big ends  don't, 

then a 4 cylinder engine CAN be brought into balance by just  adding weight at 

the front end.  That is, that balancing the prop does  correct for imbalance 

even at the back of the shaft.  Therefore it is not  necessary to balance the 

big ends of the rods if you do a dynamic balance of the  prop after the engine 

is installed on the airplane.

 

What do you think?

 

Dan Hopper

RV-7A Flying -- working on another engine

Hopperdhh(at)aol.com
Guest

Posted: Mon Mar 06, 2006 5:22 am Post subject: Balancing Connecting Rods

Archie and listers,

 

Sorry to reply to my own post!  Please disregard the attached earlier  post.  

I didn't have my brain fully engaged yet this morning!

 

Even when balancing a wheel (with width), you have to be able to get to  both 

ends in order to bring it into dynamic balance.  A crankshaft is no  

different in this regard.  So therefore it is important to match up all the  rod big 

ends.

 

Dan

 

 

In a message dated 3/6/2006 7:02:51 A.M. Eastern Standard Time,  

Hopperdhh(at)aol.com writes:






Archie,



I have  been giving this balancing problem a lot of thought.  I am used  to  

thinking race car engines -- V8s with a 4 plane crank.  In that case  it  is 

of 

course necessary to match up all the rods and counterweight  the crank  while 

balancing it.  It occurs to me that if all the  unbalance (imbalance?)  is in 

a 

single plane -- say the small ends of  the rods match but the big ends  

don't, 

then a 4 cylinder engine CAN  be brought into balance by just  adding weight 

at 

the front  end.  That is, that balancing the prop does  correct for imbalance 

 

even at the back of the shaft.  Therefore it is not  necessary  to balance 

the 

big ends of the rods if you do a dynamic balance of  the  prop after the 

engine 

is installed on the airplane.



What  do you think?



Dan Hopper

RV-7A Flying -- working on another  engine

archie97(at)earthlink.net
Guest

Posted: Mon Mar 06, 2006 6:06 am Post subject: Balancing Connecting Rods

On V-8 engines, the total weight of the rotating end is incorporated

in the formula for bob weight setup, and only 50% of reciprocating weight.

(which also includes, Piston, Pin, and Rings.

This basic formula can be modified for over or under balance,

but is beyond the scope of conversation here.

When a crankshaft is being corrected, it is not only balanced rotationally,

but also end to end. AKA "COUPLE".

BTW, most of my work is in racing engines.

Archie





 	  Quote: 	
		   



 Archie,



 I have been giving this balancing problem a lot of thought.  I am used  to

 thinking race car engines -- V8s with a 4 plane crank.  In that case it 

 is of

 course necessary to match up all the rods and counterweight the crank 

 while

 balancing it.  It occurs to me that if all the unbalance (imbalance?)  is 

 in a

 single plane -- say the small ends of the rods match but the big ends 

 don't,

 then a 4 cylinder engine CAN be brought into balance by just  adding 

 weight at

 the front end.  That is, that balancing the prop does  correct for 

 imbalance

 even at the back of the shaft.  Therefore it is not  necessary to balance 

 the

 big ends of the rods if you do a dynamic balance of the  prop after the 

 engine

 is installed on the airplane.



 What do you think?



 Dan Hopper

 RV-7A Flying -- working on another engine

Hopperdhh(at)aol.com
Guest

Posted: Mon Mar 06, 2006 11:21 am Post subject: Balancing Connecting Rods

Archie,

 

You're preaching to the choir here!  I have built quite a few V8 race  

engines in my day.  My racing days are over, though.  I have made  engine balance a 

hobby and have studied it quite a bit.  I once decided to  become an expert on 

vibration and balancing, but found that it was a much more  complicated field 

than I had imagined.  Fortunately, most engine work we do  does not require 

exact knowledge, and the 100 percent rotating and 50 percent  reciprocating 

formula is as close as we need to be.  Well, again that was  back in my day.  

That was the late 60's and early 70's.  I don't know  about the latest engines.  

I built many engines that way back then.   Yes, I understand that symmetrical 

cranks like 4 cyl and 6 cyl don't need bob  weights during balancing.

 

I called Aircraft Specialties Service this morning, and I think that they  

are going to work with me on getting a closer set of rods than I have now.

 

Thanks again for the advice,

 

do not archive

 

Dan Hopper

RV-7A

Walton IN

 

 

 

In a message dated 3/6/2006 9:07:20 A.M. Eastern Standard Time,  

archie97(at)earthlink.net writes:






On V-8 engines, the total weight of the  rotating end is incorporated

in the formula for bob weight setup, and only  50% of reciprocating weight.

(which also includes, Piston, Pin, and  Rings.

This basic formula can be modified for over or under balance,

but  is beyond the scope of conversation here.

When a crankshaft is being  corrected, it is not only balanced rotationally,

but also end to end. AKA  "COUPLE".

BTW, most of my work is in racing  engines.

Archie

redswing(at)mcn.org
Guest

Posted: Mon Mar 06, 2006 6:40 pm Post subject: Balancing Connecting Rods

Sorry, I had it in a contrasting color--that got stripped.

Red

  ---

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