0-320 crankshaft balance?

[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]

Originally Posted by RV7AAAAAAA

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

you said it ....money well spent

[pierre smith]

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]

Originally Posted by RV7AAAAAAA

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/main...neBalance.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]

Originally Posted by gmcjetpilot

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]

Originally Posted by mgomez

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]

Originally Posted by gmcjetpilot

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]

Originally Posted by gmcjetpilot

"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/main...neBalance.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]

there sure is a lot of BAD information in these posts. That includes Lycoming.

First: Lycoming's engineer is correct PROVIDED that: