|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

10-27-2006, 10:53 AM
|
|
|
|
Join Date: Nov 2005
Location: tulsa, Oklahoma
Posts: 178
|
|
0-320- balancing
There sure is a lot of BAD information in these posts. That includes Lycoming.
First: Lycoming's engineer is correct PROVIDED that the technicians actually balanced the crank per the print, the machine was in compliance with ARP 586 and the crankshaft has not been reground.
Lycoming is also correct when they say that harm can be done. If material is removed in a section of the crankshaft that is subjected to bending or twisting loads harm can be done. Also the method of material removal is a specific process and the nitride case cannot be penetrated without re-nitride.
BUT! crankshafts often leave the factory with severe imbalance, as much as
80 gram-inches per end. I have measured that much. I have also seen sets of pistons that had as much as 15 grams difference in spite of Lycoming service information whichs says up to 14 grams difference in the pistons is acceptable. So they don't follow their own rules. For reference purposes
1 ounce = 28.35 grams.
Shops who regrind crankshafts will often "offset" the crankshaft slightly to regrind the crank removing runout from the central main journals. This technique WILL put the crank out of balance.
Some crankshafts are dampened with dynamic counterweights. These are for
TORSIONAL dampening and have nothing whatsoever to do with the 1 per rev
which is what balancing the crankshaft is all about.
Balancing does not increase the power, but it DOES make the engine smoother. You, the pilot, may not be able to feel the difference but the rivets, avionics, instruments and sheet metal do.
As to whether is is worth it or not it is automatic at our shop and is included in the cost. But I would not disassemble an engine to balance it unless it shook badly enough that I could feel it in the floor or not read the instruments. But it is such a low cost improvement why not do it at overhaul? Any shop that does it should have a FAA approved process specification to cover this repair, and it should be listed on their Operations Specification. Do not use an automotive shop. The ones that will take the work in do not have a clue about nitrided crankshafts. Static balancing a long crankshaft is pure B.S.
Connecting rods have 2 parts: a rotating part and a reciprocating part. The sum of these 2 weights is the total weight of the rod.
A horizontal engine with 180 Degree crank throws provides a balanced condition BETWEEN MAIN BEARINGS provided the reciprocating weights, rotating weights are equal or within a reasonable tolerance. 5 grams is close enough. Marketing and competition between shops drives the tight tolerance.
If a rotating assembly is out of balance on the anti-drive end there is nothing you can do with the drive end ( propeller ) to correct the rotating assembly. All you can do is balance the propeller.
In reality, what drives the dynamic balancing tolerance is the weight of the rotating assembly and its service speed. There are accepted standards contained in A.N.S.I. tables that define the MINIMUM acceptance standards.
Thanks for the opportunity.
Monty Barrett
Barrett Precision Engines, Inc.
Tulsa, OK
|

10-27-2006, 11:12 AM
|
 |
|
|
Join Date: Sep 2006
Location: Beaver, OK
Posts: 447
|
|
YES Balance It
Jim, spend the money and get the crank balanced. If you have your starter /ring gear, have that checked as well. Balance the crank, get it within limits / grams, them bolt the starter/ring gear that you are going to use onto the crank and check the balance again, make corrections if not right, etc.. Money well spent in my opinion. Get the pistons and rods balanced as well along with the prop after you get it running. If you don't spend this small amount of money now,,,,,, you'll probably later say to yourself "I wished I'd had it balanced". My 2cent. AJ
__________________
Alan (AJ) Judy
Beaver, OK in NO MANS LAND
RV-6 IO360A1B6 C/S Hartz 200HP ?
Also Fly North American NAVIONs
Race car engine builder/Machinist/Fabricator 1982--present.
Last edited by rv969wf : 10-28-2006 at 12:28 AM.
|

10-27-2006, 11:52 AM
|
 |
|
|
Join Date: Jan 2005
Posts: 4,285
|
|
Ahaaa yes
Hey RV7AAAAAAA:
Look I suggest you also get a book by Sacramento Skyranch, Lyc & Continental Engineering manual. It has lots of great info. especially about vibration. Here is some info on their web site: http://www.sacskyranch.com/vibm.htm (specifics are for 6-cyl but the general info applies to 4-cyl)
Here is ECI's notes on balancing: http://www.eci2fly.com/pdf/DynamicBalancing.pdf (good info with minimal hype)
I am not going to get into a debate, but you are doing the right thing asking questions. I suggest you call Lycoming and ask them. Hopefully you will get one of the senior guys. E-mail may be better since you will get a more through answer. Tell them what the shop said.
The fact is a 4-bangers are going to vibrate. There are all kinds vibration modes or 1st, 2nd, 3rd....6th order. Its GREAT balance the crank to within a gram. Guess what, the crank flexes, torques, bends and is not perfectly ridged. So balance away it may help a little, but there is some other vibration balance can't help, especially 2nd order vibrations.
"BUT! crankshafts often leave the factory with severe imbalance"
I was not aware of such poor new crankshaft imbalance or poor machine work Monty Barrett mentioned, but he knows better than I do, he's a machinist and does it for a living. Something does not sound right or it should not happen. Don't know what to say.
Rods? They don't move in perfect reciprocating motion. The small end of the rod does move with the piston and can be considered to "translate" or move in a reciprocating motion. However the big end of the rod has angular motion. Shops balance the big end, total weight and centroid. To quote Lycoming:
"There are occasions when dynamic balance of the prop/engine combination can provide reduced first order vibration, but additional internal balancing of Lycoming engines is not required nor recommended. The rotating and reciprocating masses of the six and eight cylinder opposed engines are inherently balanced. The rotating masses of the four cylinder opposed design are balanced. The reciprocating masses of the four cylinder engine are not balanced as a vibratory inertia moment at second order exists in the plane of the cylinder center lines. Matching the weights of components closer will not reduce the second order moment. A redesign incorporating counter rotating layshafts rotating at twice engine speed could be implemented."
Note: Keep in mind "order" number if cycles per revolution of crank. So 1p or first order vibration at 2,700 rpm is 45 Hertz or cycles per second. 2nd order at 2,700 rpm is 90 cycles/second.
The above Lycoming comment about a rotating layshaft rotating twice engine speed (2nd order) is interesting. BMW air-cooled motorcycles just updated their 1150cc air-cooled horz opposed twin in 2006 with a 1200 cc version using a layshaft rotating twice the engine speed. Its a separate shaft from the crank and is used to dampen the 2nd order vibrations. Do you think BMW balanced their engine well? Sure they did but there is only so much static and and dynamic balance can do for "vibratory inertia moment at second order in the plane of the cylinder center lines." BMW made this major change for a reason (shaft below crank).
Lycoming is saying super tight balance will not be felt, that's all. That's the nature of a horizontally opposed 4-cylinder engine with a 1-3-2-4 firing order. Again I agree with Monty Barrett if the crank is out of specs than balance is needed, of course. I talked to Lycoming and they denied new cranks leave the factory with 80 gram imbalance. They say they tolerance on cranks and pistons, rods is much tighter than you comments. Sorry, I'm just the messenger.
All I know is when I sent my crank and rods out to ECI, they came back yellow tagged and the #1/2 rods and #3/4 rods where matched with new piston pair assemblies. The engine is as smooth it was before. I hope they held reasonable tolerances. I did not pay extra.
PS Monty, sorry for my BAD post; I'm not a machinist. Every machinist I ever meet told me they are smarter than engineer's. Apparently that's true. Thanks for your GOOD post, we could not do it with out you. 
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767
2020 Dues Paid
Last edited by gmcjetpilot : 10-27-2006 at 02:57 PM.
|

10-27-2006, 04:28 PM
|
|
|
|
Join Date: Aug 2006
Location: Coppell, Texas
Posts: 11
|
|
Balance it!
Lycoming engines have historically vibrated to some degree or other because the factory specs allow for a large amount of variation and still fall within their standards. Anyone who has had an engine balanced, crankshaft, rods, and then match pistons, notices a very large difference. In addition, your airframe, instruments, and pilot comfort benefit greatly from the reduced vibration. This isn't an ad for our Vantage engine, but the test pilot for American Champion told us "it's the smoothest engine he's ever flown behind." Crankshaft is balanced to .25 oz inch, rods are matched and balanced to 2 grams or less, and the pistons are matched to 2 grams or less for the full set. These things do make a difference, and the money spent is well worth it. Aircraft Specialties is one of the best companies in the country to do this kind of work as well.
|

10-27-2006, 11:35 PM
|
 |
|
|
Join Date: Jan 2005
Posts: 4,285
|
|
Yes Balance is good
Quote:
|
Originally Posted by Superior-Sales
Lycoming engines have historically vibrated to some degree or other because the factory specs allow for a large amount of variation and still fall within their standards. Anyone who has had an engine balanced, crankshaft, rods, and then match pistons, notices a very large difference. In addition, your airframe, instruments, and pilot comfort benefit greatly from the reduced vibration. This isn't an ad for our Vantage engine, but the test pilot for American Champion told us "it's the smoothest engine he's ever flown behind." Crankshaft is balanced to .25 oz inch, rods are matched and balanced to 2 grams or less, and the pistons are matched to 2 grams or less for the full set. These things do make a difference, and the money spent is well worth it. Aircraft Specialties is one of the best companies in the country to do this kind of work as well.
|
I don't think anyone said balance does not help or Aircraft Specialties is not a good company.
However it would be good of Aircraft Specialties to specify WHAT you actually get for the premium charge, other than to say stock cranks are out 28 grams. You state that your cranks are within 7.08 gram inch. What if they get some parts in that are already well balanced, say Superior parts? They should check it for the standard fee, right? However there $162 is cheap, most just include it as standard.
It would also be super if someone put accelerometers on their "balanced 2 gram engine" and another engine, a stock one that's just within Lycs balance allowable. I called Lycoming today and they claim that their tolerances are much tighter. Just saying.
It seems that some people says Lycoming is inferior, not just Monty but the ECI refrence link in my previous post echos that. I do believe 100% perfect balance is better, I would just like to "quantify" how perfect. If its cheap, 1-2 hours of labor, than what the heck do it. I have had nothing but good service and smooth operation with my stock Lycoming's?
Shouldn't all shops should do the best balance possible as standard procedure and not charge extra. If a premium is charged, I would like to know what level of balance they accept. [b]For example if I had new superior parts, already balanced, than it would be a waste of money to balance them. I expect any shop worth a darn will always check. Than they could call and say your crank is out say 25 grams we can get it to 1 gram, do you want to do that for $X amount. I guess when you are spending $1000's a few hundred is nothing and these shops need to eat, so give them Mo money.
Lycoming is incapable of manufacturing parts consistently within ever their own specs? That blows me away and bothers me. Lycoming say no, that's not the case? My crankshaft went through a complete overhaul at ECI, which is also a good company, so it must be OK. I never heard it was bent or out of balance. I hope they balanced it to better than stock specs, but I don't know what those specs are? They are not widely published.
As Monty said this is a Bone of Competition between shops and engine makers, 2 grams, no 1 gram, no 0.01 grams. ECI says it balances to a 1/4 th of what the stock limit is. Another company (Performance engines) says 1 gram. If they price is right and they actually balance to a hair, all the better. I think it will be hard to know what 1 or 5 grams feels like.
As a consumer you really don't know unless you see the actual balance data. The crankshaft balance equip may be automated with printout, but I think rod, piston checks are manual on a test jig and scales. I suppose they write it down. I have never seen it written down on my paper work, but they very well may keep the info at the repair station.
Thanks for the good to know info, the SPECS on the Vantage (Superior) engine are held within a few grams and Aircraft Specialties is a good company. I believe I used them to overhaul an engine accessory 10-15 years ago and was happy. Cheers
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767
2020 Dues Paid
Last edited by gmcjetpilot : 10-28-2006 at 12:24 AM.
|

10-28-2006, 01:00 AM
|
|
|
|
Join Date: Oct 2006
Location: San Antonio, TX
Posts: 1
|
|
Hmmmm
GMCjetpilot, I see you have changed / edited your second to last thread posting at least 4 or 5 different times within 8 hours! Make up your mind ???? If you have good solid facts post them, if not don't. Your trying to tell Barrett Performance Engines 'BPA' that they are wrong is outcast and just not right. They know what they are doing. Have you ever built an aircraft / any kind of engine?? Have you ever operated a machine that balances crankshaft? Do you know what bob weights are??? Lycoming 4 cyl engines don't need bobweights to balance so there is no need to tell you if you don't know. Balancing engine parts of any sort is a must if you want it done right!! Your last response is more presentable and yes your coming around by editing your responses every hour or so. But I did read your first response and it was way out of line and rude. Thanks for editing your thread several times to correct your mistakes and to appologize to Monty Barrett for the bad post. At first you were talking about Allen Barrett, then later changed to Monty, do you even know who you responded back too ???? My suggestion,,,, don't post anything until your 100% sure and never hammer on someone that has been there and done it. Books, degrees, etc. are great, but actually being hands on, seeing and working with the parts is what will teach someone more than anything.
GMC, I do have the original post that you wrote, pasted and copied that I could put back on here, but did I??? NO. I will not do that. Think before writing. FG
__________________
Frank Gomez II
Engineer Aerospace Industry
NASA Tech Specs
EV-1 /F-1 Rocket 75%undefined
Lancair
Citation
Eagle
Last edited by RV2007 : 10-28-2006 at 01:49 AM.
|

10-28-2006, 05:34 AM
|
 |
|
|
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
|
|
Look
Jim,
Just balance the d*** engine. Monty and Allen know what they're talking about and we don't need any more long-winded BS.
Look at this: If your airplane comes in at $65,000 or so, the $162 balance cost is only a miniscule .25% !!!
'Nuff said,
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga
It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132
Dues gladly paid!
|

10-28-2006, 08:04 AM
|
|
|
|
Join Date: Oct 2006
Location: Melbourne, Australia
Posts: 427
|
|
know what you're buying?
George M,
You seem quite vociferous in your defence of Lycoming etc. You state that people should know what they are paying money for, yet you yourself cannot say exactly what ECI did to 'overhaul' your crankshaft? Did they even check the balance? What about the rods/pistons?
Were you given any reports that outlined what any measurements were, or were you just told that everything was 'in-spec' just like a Lycoming crank should be?
You are an engineer, as you keep telling us all, but have you ever done any slider-crank mechanism simulations? If so, you'll already know that some surprising things can happen when you jiggle the design parameters about, in terms of bearing loads, thrust forces etc. It's not as plain and obvious as it first appears.
If it were my engine in for assembly/overhaul, I'd at least want to know what the balance data was and keep it for my own peace of mind. You don't get that from Lycoming so definitely worth $165 if they give you a copy of the data.
A
|

10-28-2006, 09:46 AM
|
|
|
|
Join Date: Nov 2005
Location: Farmington NM
Posts: 57
|
|
Quote:
|
Originally Posted by pierre smith
Jim,
Just balance the d*** engine. Monty and Allen know what they're talking about and we don't need any more long-winded BS.
Look at this: If your airplane comes in at $65,000 or so, the $162 balance cost is only a miniscule .25% !!!
'Nuff said,
|
Ooooookayyyy... yes...sir!!!
Don't know anyone here, but I have heard that both Monty and Allen have forgotten more about engines than most people will ever know (sorry this may get worse with age).
I asked a question and a ton of talented people - top engine builders, machinists, and engineers giving me advice. (How cool is that). If anyone ever posts another question about Lyc. cranks I would refer them to this thread. everything you want to know about crank balancing is here. George posted the crank balance buelltin from Lyc. and all you guys shed the light on it. Good yob.
Thanks again I know what to do
Jim
|

10-29-2006, 07:09 AM
|
 |
|
|
Join Date: Jan 2005
Location: Palm Bay, FL
Posts: 420
|
|
Balancing act!
I had recently visited Penn Yan Aero Service (Penn Yan, NY) to see how my ECI Titan O-320 engine was assembled and tested. The tour of the shop started with crankshaft balancing, matching the weight of pistons, rods, etc. The more I saw, the better I felt about my initial choice of engine and Penn Yan Aero as the vendor. After 210 hours on the airplane since June 9, 2005 - - yeah, I'm satisfied!
Jerry K. Thorne
East Ridge, TN
RV-9A N2PZ
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 12:27 AM.
|