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Author Topic: Balancing a new flywheel?  (Read 1264 times)
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sdroadster
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« on: August 02, 2017, 10:32:43 PM »

If I buy a new Hays billet steel SFI Flywheel and a new pressure plate do I need to have them balanced as an assembly, or can I just install them?  SBC runs about 7500 rpm. Thanks
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MRK
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« Reply #1 on: August 03, 2017, 10:02:35 AM »

Take no chances and don't cut a corner. Balance them as an assembly. My .02  cheers
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jdincau
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« Reply #2 on: August 03, 2017, 10:40:41 AM »

Ask Hays.
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Ron Gibson
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« Reply #3 on: August 03, 2017, 01:53:23 PM »

I always heard the flywheel needs to be balanced on the crankshaft it is to run on and be marked for repeatability.
That being said, if the engine is not apart, I would just run it as is.
For me it would be saying Hayes doesn't know what they are doing about balancing but this guy down the street that I don't know does.

YMMV
Ron
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kiwi belly tank
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« Reply #4 on: August 03, 2017, 03:16:38 PM »

Assuming you engine is internally balanced  rolleyes, then get the assembly zero'd.
  Sid.
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« Reply #5 on: August 03, 2017, 04:18:48 PM »

If you feel compelled to even ask this question, then you'd better check.

Never, never EVER assume the parts supplier did it right. 

It's your responsibility - particularly with racing engines - do determine the suitability of any component you put into your build.

What if there is a problem?

Is Hayes going to replace the snapped crank, or the bellhousing, or offer to repair your damaged block?

At the end of the day, you are the engine builder.  Your end results will be dependent upon many, many little decisions precisely like this one.

And let's say you go ahead and have the whole assembly balanced, which is what I would do, including the crank and clutch.

When it doesn't scatter, and you bring it home in one piece, that extra $250.00 you sacrificed today will not gnaw at your guts.

But if you simply bolt it on and go, and something goes wrong - something that may or may not be associated with the flywheel balance - you'll be turning it over in your mind for the rest of your life that you should have checked it for balance.

Eliminate the variables - CHECK EVERYTHING.
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sdroadster
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« Reply #6 on: August 03, 2017, 04:49:02 PM »

Yup, I know in my gut you guys are right. Oh, I attempted to ask Hays (Holley) and was on hold until I gave up. The problem is the variables at the engine builder down the street. He has been recommended, but if it's possible to get someone on a bad day it always happens to me. I have been chasing this vibration since October at El Mirage. Thanks for the advice. Coe Family Racing...
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Ron Gibson
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« Reply #7 on: August 03, 2017, 05:15:16 PM »

You didn't say in your post that you had a vibration. Balance the entire asembly, something is wrong somwhere.

Ron
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« Reply #8 on: August 03, 2017, 05:55:26 PM »

Crank, rods, pistons, flywheel, damper and clutch!.
That's how we do it in Africa.

Hope your balancing guy is good if you have a Crower crank???.
Hard to drill if required. wink
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JimL
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« Reply #9 on: August 03, 2017, 06:48:28 PM »

During development of an FFT based NVH course (wow...over 20 years ago), we did experiment with flywheels that were artificially made unbalanced.  We learned a couple interesting things.  It seemed that the flywheel must be balanced to itself because the crankshaft does not rotate at even speed, especially under power.  The flywheel does its best to maintain its own inertia and the imbalance effect didn't do what we hoped. 

In the process of taking stuff apart and putting it back together, we found (by accident) more vibration from a flywheel that is running out of plane, than one that is out of balance.

We were trying to create training conditions that the students could physically notice, while seeing an obvious result on the FFT.  We actually got pretty far out there with added weight, but it just wasn't enough to make the engine shake like we thought it would. 

We actually couldn't feel the out-of-plane vibration until we put a trans and clutch back into the vehicle.  That  spooked us because we thought we were done and were going to send the SUV back the fleet.  It was one of those moments when you go, "uh oh....what the heck did we do?!"

Our problem was an un-noticed gouge on the bolt circle face of the crankshaft. 

We never bothered to put those tables in the FFT program, and decided not to train techs to find primary crank vibration.  You can fix a lot of cars that aren't broken if you have expensive tools to find things that aren't even there. embarassed

The one lesson, that was most useful, was that vibration you can feel MUST be working against something.  Sometimes the transmission path is more of a problem than the vibration itself.  I have seen engine vibration that was caused by poor bracing below the crankshaft centerline (back of the block) and the bottom of the bell housing.  This is often a strange one, because the actual frequency is a rocking couple effect that does NOT match firing frequency events or crankshaft/flywheel rotation frequency (I have seen some that vibrate at 1/3rd of crankshaft RPM).  Some engines need diagonal bracing of the lower circle of bell housing from a point forward of the rear block face (along sides of the block).

You can get a $15 app on an iPad or smartphone that will let you measure the actual frequency of your vibration.  Find the actual vibration frequency at whatever RPM and then do the math to figure out what it really is.  The sound frequency picked up by the mic, is the same as what your feel/hear.  I don't think you need to invest in an expensive accelerometer and signal conditioning device.

One last note:  We did teach the technicians a trick to change engine vibration amplitude by putting a paperclip in the OX1 terminal of the underhood check connector.  When they held the paper clip with one hand, and put a finger of their other hand on the battery Positive post, the engine vibration diminished on the FFT.  The test process was driving the fuel injection into a lean condition (using your body as a resistor from the 12 volt battery).  The lean condition fires softer, which makes less vibration.  This was really useful for identifying problems such as hardened radiator hoses (which shake the radiator in its mounts, which shakes the forward body baffle, which shakes the tail of the car, and makes the spare tire well boom).

One or two cylinders that fire harder (richer, higher compression, ignition issue...whatever) can have a pretty good shake going on.

Hope this helps somebody.

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Stan Back
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« Reply #10 on: August 03, 2017, 07:55:00 PM »

I've always been an admirer of your postings.  I'm a friend of a friend of yours, so I know you are real.  I understand a small percentage of what you say -- that's enuf for me.  All I know is that you know what you're talking about -- and I have a great respect for that.  Your OEM experience has taken you down paths that most of us "hot rodders" never journey.  But don't quit posting -- I learn something every time.

Stan
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JimL
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« Reply #11 on: August 03, 2017, 08:27:32 PM »

Thx for the kind words, but the only stuff I learned was from mistakes.  I don't post much these days because it is harder to put the words together to make sense.  Most stuff I write and look at and dump.

I do remember another car I screwed up.  It was a Chevy V8 in a Land Cruiser conversion I was handed the RO to put in a new clutch (back in my days as a dealer tech).  I didn't have the driver to put in the new pilot bushing (Toyota rwd models always had ball bearing pilot).  I drove it in with a hand ground down brass drift.

If you reached for the floor shifter knob with that Chevy wound up to about 5000 rpm, you pulled your hand back with bloody knuckles.  I had smashed that bushing off center (and the Toyota input shaft taper let me pull it home with trans bolts).  It was a really dumb mistake and an unbelievably violent result.  My service manager wouldn't let it go until I figured it out.  That hard black shift knob looked about the size of a grapefruit when you reached for it!

Sometimes it is not what's wrong that gets you....it is what's not perfect.  I hope this helps find or eliminate suspicion of whatever is happening.

It really is best to get the FFT app, learn to use it, and do the simple math.
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sdroadster
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« Reply #12 on: August 05, 2017, 04:05:03 PM »

I ran out the flywheel today, it's about .002 on the OD (just in back of the starter ring) and .006 on the face where the clutch engages. The vibration starts about 6600 RPM, and kicks the Autogear (Muncie) transmission out of gear.  I was hoping to find a huge problem, but so far I haven't. I'm going to run out the crankshaft flange, and pilot bushing hole next.
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wobblywalrus
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« Reply #13 on: August 05, 2017, 06:53:45 PM »

You could have a harmonic vibration when the frequency of the vibrator matches the natural resonant frequency of the vibratee.  Braces or other long and unsupported members can do this.
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« Reply #14 on: August 06, 2017, 08:11:32 AM »

the crankshaft does not rotate at even speed, especially under power
X2
Variables include: total inertia (crank + big ends + flywheel), rod geo, cranking pressure, CR, number of cylinders, more? Even changing the cam phasing will have some effect. Easier to visualize: a Gold Star will almost stall @ TDC, a V12 (almost) doesn't need a flywheel.
Which flywheel doesn't need dynamic (3-D) balancing? The one with only 2 dimensions. Don't be surprised if your newly-balanced 'wheel has holes on both sides.
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