[RV7AAAAAAA]

Got an email today from A/C Specialties asking if I would like my crankshaft and rods balanced. This kind of seems like a no brainer to me, because it's relatively cheap in the aircraft engine world. $125.00 crank balance, $37.00 for rods. Total $162.00, as posted on their website. Any reason not to? Will I notice a difference? Will my engine vibration be smoother than the subies or rotaries?

Just kidding

Jim
RV7A - under construction
Engine apart

 

[Low Pass]

I balanced (statically) my crank and rods when I "overhauled" it originally. Not sure how much this helped. But after I got the plane flying I had the engine/prop assy field balanced. The guy who balanced it said it was one of the smoothest (4 cyl Lyc) he'd seen, before beginning the balance. I'd definitely do it again, or have it done, on any future projects.

 

[cytoxin]

thaaaaats right

This kind of seems like a no brainer to me, Engine apart

you said it ....money well spent

 

[pierre smith]

Lotsa value

Hi Jim,
You can't go wrong having the parts balanced. I've realized that with a couple of big blocks, a 427 Ford and a 455 Olds in a jet boat.........smooth, smooth! Where you'll benefit is from less exhaust cracking, alternator life extended and a myriad of other vibration affected accessories lasting much longer, notwithstanding the added horsepower when you include balancing the prop/spinner later,
Regards,

 

[gmcjetpilot]

What do you get? Really

Will my engine vibration be smoother than the subies or rotaries? Jim RV7A - under construction

I'd call and ask them what you get for the money and exactly what they do and on what equipment/.

Is their regular balancing not good enough?

Here is a quote from the manufacture:

"Additional internal balancing contributes little to engine smoothness, and it may even be harmful when material is removed from highly stressed parts of the engine."


I would say the price is right but what do you get?

The factory dynamically balances the starter ring gear and crank. This is not new or special. The other reciprocating parts are statically balanced and weight matched 100%. This is all standard and expected, not special. So they want to charge you extra to do their job? Confused.

Sure, the better rotating assemblies are balanced and reciprocating parts (rods, pistons) are matched to each other, the smoother it should be. However we are talking about a 2,700 rpm engine. What is Lycoming talking about? Well they say it contributes "little"; they don't say it does nothing. Read the Ref. article below. You will read it's standard or expected to balance all the parts. It's pretty extensive. May be they are offering tighter tolerances? Really it makes me wounder what you are getting.

So where does vibration come from?

Power pulse is a big player in vibration, not imbalance in parts. Let's put it this way, if you pulled the spark plugs out and could spun the engine up to speed with no power it would be fairly smooth. It is the hammer every 90 degrees of crank rotation that makes the vibrations or thump.

Sine a prop gets bolted direct to the crank it becomes an extension and prat of the engine. The prop needs to be balanced with engine as an assembly in the aircraft mount. The whole vibratory SYSTEM needs to be balanced. Getting one part in the engine balanced to a Nano-gram is not going to make a lot of difference. Some may be? $162 worth?

Lycoming mandates and has standard balance limits which are good enough and fairly exacting in their opinion. Any FAA Approved Repair station should be already balancing the parts. Again what does the overhaul shop do for the extra bucks?

So is it worth it? At least know what you are getting.

Not trying to talk you out of it, but if they don't always do their best to balance I wounder why? Do they just spend more time? Use tighter than standard limits? I would ask them.

I have a feeling its like buying a new car where they want to sell you some extra..............under spray, warranty, special blaa blaa blaa, or they tell you that item is there special prep service fee? (BTW don't get the under-spray since all cars today should be well protected from the factory.)

Here's the article from Lycoming.

http://www.lycoming.textron.com/mai...ations/keyReprints/general/engineBalance.html

You may want to save your money for a good prop balance? Or how about this you tell them you expect them to balance to the $162 level and not charge $162 or you'll go somewhere else. Unless they are at your back door I would send it to Mattituck. You may want to check with the FAA regional maintenance and inspection branch, Better Business Bureau and some of their customers. Not saying they are suspicious or not top notch, but if you are going to use them I would do your home work, since you will be spending way more than $162, more like several thousands (+$10,000?), so $162 is peanut and may be that is what you will think? Your going to be flying behind the engine as well. Call other engine shops and ask what they charge or if they have ala-cart fees. Some might say they balance all engines to near 100% to the best of their ability for one cost.

IF THEY ASK if you want undercoat and special floor mats with your engine RUN, don't walk from that ovehaul shop.

 

[mgomez]

It is the hammer every 90 degrees of crank rotation that makes the vibrations or thump.

I thought the power pulses were 180 deg apart. Each cylinder fires every two crank rotations, and they're evenly spaced, so it's one 4 pulses in 720 deg, or one every 180 deg.

The fundamental point is valid, though: the power pulses are a huge contributor, and it's one of the reasons that six and eight cylinder engines are smoother. It's also the reason that the counterweighted crankshaft Lycomings are smoother: the counterweights are tuned to reduce some of the frequency components and make the crankshaft "look" heavier.

Cheers,
Martin

 

[gmcjetpilot]

Doha Math is hard.

I thought the power pulses were 180 deg apart. Each cylinder fires every two crank rotations, and they're evenly spaced, so it's one 4 pulses in 720 deg, or one every 180 deg.

The fundamental point is valid, though: the power pulses are a huge contributor, and it's one of the reasons that six and eight cylinder engines are smoother. It's also the reason that the counter-weighted crankshaft Lycomings are smoother: the counterweights are tuned to reduce some of the frequency components and make the crankshaft "look" heavier.

Cheers,
Martin

My head is spinning, One + One = Chair? ha ha When Johnny can't do math and a mind is a terriable thing to waste.

720 deg / 4 cyl = 180 deg. Thanks you are right. I need to send my engineering degree back.

Counter weight cranks are very interesting and are "tuned" for torsional vibration at spacific frequencies. Although no doubt it makes the engine smoother, they really are there to reduce crankshaft stress from the 6th order pulses, which causes crankshaft torsional flexing. The out of plane vibrations are still there, even with counter weighted (pendulum) weights. The weights work on a inertia and energy and are pretty ingenious. However they can get "De-tuned" and cause problems. Abrupt throttle movements a good way to "de-tune" the weights.

It's just a fact of life, a big bore 4-banger Horz opposed low rpm engine, where the left bank fires both cylinders, front than back, than the right bank, front than back fires, is going to sake a little. Also the low RPM and large pistons 5.125" dia, you are going to make vibrations.

 

[mgomez]

Just needs an overhaul!

I need to send my engineering degree back.

No need to send it back. From what I've read recently on this forum, you can just overhaul it yourself. Just takes a coupla oddball wrenches and a few new parts.

 

[RV7AAAAAAA]

No brainer no more

"Additional internal balancing contributes little to engine smoothness, and it may even be harmful when material is removed from highly stressed parts of the engine."
Here's the article from Lycoming.

http://www.lycoming.textron.com/mai...ations/keyReprints/general/engineBalance.html

I really thought this crank balance question would be a no brainer. But you helped change that. Wow from Lycoming themselves. Took your advice and called A/C Spec. regarding crankshaft balance. Told the salesman (name withheld) what I have learned from my forum buddies and the 'notice from Lycoming.' He asked me to speak with his machinist and send him a copy of the Lycoming text. After telling machinist what I read he laughed and said he's not surprised. "Lycoming don't want people to know how bad their crankshafts are". and it's routine to balance even brand new Lycoming crankshafts. He also said it was not uncommon to find cranks 28 grams out. (I guess that's bad). BTW so far these guys at A/C Spec. have been great. Don't get the feeling they are trying to sell me the "underspray, warranty special". I might still balance crank, but on hold for now. Late for work
Think I might just have them check the balance and advise.
Thanks again
Jim

 

[Allen Barrett]

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:

 

[Allen Barrett]

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

 

[rv969wf]

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

 

[gmcjetpilot]

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.

 

[Superior-Sales]

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.

 

[gmcjetpilot]

Yes Balance is good

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. 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

 

[RV2007]

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

 

[pierre smith]

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,

 

[Andy_RR]

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

 

[RV7AAAAAAA]

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

 

[n2prise]

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

 

[WilliamDCat]

It's all personal prefference and $. The average Lycoming customer would rather pay less for an engine and live with a slight increase in vibration. Where do most 4 cly Lycs go, flight schools? Will students notice the difference? Do the instructors buy the engines? Add in how well the installed assembly can be balanced, even with loose tollerances for engine and prop, and you end with a limited market for tight tollerance balancing. Is it worth ~$150? That's up to you, but have you thought about a 6 cyl Conti instead of a Lyc? If you want an apple, why buy an orange and try to make it look like an apple?

Just my $.02

 

[pierre smith]

There is one

Hi William,
There is one on Barnstormers going for under $40,000 and they can't seem to give it away. Who would want one anyway? Butcher up a neat Lyc engined design?

We have a three bladed Catto prop on ours and it is very smooth. I'd never give up my "peach" for an orange....

 

[glenmthompson]

My A/c S. experience.

I purchased a NEW Superior crank for my rebuild from A/C Spec. I negotiated that they balance the crank in their shop, and they said it was balanced to within 2 grams. I have a neighbor that is totally anal, and has a shop that balances cranks for the racing community. The crank when I got, it was almost 12 grams out! My friend Juan, balances dynamically and takes the weight off the shoulders instead of drilling holes in the counterbalances. He also balanced my friends 540 in his (much faster than Vans) RV10.
My bottom line IMHO...Balancing to the Gnats a?? is a no brainer.
Also, I LOVE A/C Spec., Bob is a GREAT and knowledgable guy. I mean nothing bad to them, just that an anal knowledgable machinist can get that little extra that most of us are looking for.
.
PS, Juan will balance a 4 cyl crank for $150 plus shipping.. He will also balance the rods for this price if they are not that out much out of balance. Per hour shop time for way out rods. This is cheap insurance Ladies and gentlemen, and my friends RV 10 is jet like in smoothness.
Glen