Balancing factor of the 3.0 12v?

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Post by MR2 Zig » Sat Mar 15, 2008 3:17 pm

Just to add .... on aircraft reciprocating engines.... there is a balance procedure where the engine and propeller are balanced as a unit while on the aircraft.

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Re: Balancing factor of the 3.0 12v?

Post by ChrisS » Wed Nov 11, 2009 4:14 am

Bit of a thread resurection, but I took my V6 project to Vibration Free for balancing recently. Final figure for the entire assembly was 0.28gmm. Don't know what it was to start with as the process begins with component matching, but one of the rods needed a lot taking off it at the big-end. The new Venolia pistons/pins where pretty good (not good enough though, so the pins got tweaked), but one was a fair bit heavy, about 5g I think.

I took along 2 flywheels - the original 164 3l one, plus a 155 V5 2.5l one and had both balanced. Just hedging my bets really - I'll put the lighter one on to start with.

The boss there has a 164 V6 in his boat, a tiny tea-tray of a thing, but does it shift and it soudns amazing on open exhausts!!
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Re: Balancing factor of the 3.0 12v?

Post by bcal » Fri Nov 13, 2009 12:49 pm

Brett
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Re: Balancing factor of the 3.0 12v?

Post by ChrisS » Sat Nov 14, 2009 1:21 am

Hi Brett,

Yep, that's the one. Didn't realise it was on YouTube. Sounds sweet doesn't it.
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Post by kterkkila » Tue Jan 26, 2010 12:10 pm

rossogtv wrote:The reason for this added imbalance lies in the construction type of the crankhaft. The v6 is basicaly a 2x 3 zylinder straight construction and because when cyl 1 is up, on the opposite side no. 2 and 3 are down and vice versa(3 up, 2 and 1 down). This would cause a strong vibration when running( the crank would like to go up and down in front and back. This is no rotational vibration, but fore and aft. Against this vibration the imbalance on the pulley and flywheel acts like a balance shaft on some 4zyl engines.
This is also the reason, why the weights are on the external flywheel and pulley, if they were on the crankshaft, you couldnt balance the crank at all.
From this its easy to see, that before lightening a flywheel and pulley, it should get zero balanced by their own and brought back to this balance after lightening. Very important is also the position of this imbalance in relation to the middle of the crank lenghtwise. Look at the imbalance position of the 3.0 Alfa 75 pulley and the 3.0 164 pulley, the weight is on the 75 pulley way more in the front - this affects amount and position of the weight of the flywheel imbalance ! This same counts for the longitudinal position of the flywheel imbalance on a 2.5 and 3.0 flywheel.
This explains also why you must heavy modify the 75 3.0 flywheel in combination with the original 24v 3.0 pulley when using a 24v engine in a 75 car.
Hope the given info makes sense for you all and im not far away from truth.

I hope to get some comments on this posting especially from you hardcore guys, who have allready done some balancing ( your bob-weight % ???? ) by themselves.
Is there any information available about this "fore and aft", or rocking imbalance?

As Jim told later on this conversation, there's a method to convert externally balanced engines to internally balanced using added mass on counterweights. This is common especially with V8 engines. Jim also mentioned that the lack of space inside the engine is the reason for using external weight in some engines. This is what I've found also, but I'm getting a little more curious about what's the idea in Alfa V6 balancing really. The needed extra room for internal counterweights isn't that big actually. Why Alfa decided to use external weight in original 2.5 liter configuration in the first place? If rossogtv is right, the external weights would act like lever arms to resist V6 rocking motion. Is there any confirmation for that theory? I've been planning to convert my engine to internally balanced, but this question gives some more to think before starting the process.
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Re: Balancing factor of the 3.0 12v?

Post by kterkkila » Sat Mar 06, 2010 10:19 am

When you have had engines balanced to 50%, how deep and wide holes have you got on cranks, and on what counterweights?

Just came from balancing shop and mine was at 60%! And it was good running vibration free and strong engine. Balancing it to 50% would been meant three 12mm diameter and 20mm deep holes on first and last counterweights on crank. Those should have been drilled exactly opposite to external balance mass. This is weird I would say..
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Re: Balancing factor of the 3.0 12v?

Post by xrad » Tue Mar 09, 2010 8:48 am

Much talk about balancing but answers are not easily found.

Here is my situation. 3.0l 12 v from 164S (front drive going into rear drive GTV6). Some builders have just put the 2.5 front pulley and flywheel on the engine and say they have no issues.....

What do I need to do?

I have 3.0 164 front pulley, a 2.5 front pully, and a 2.5 flywheel. Stock pistons, rings, rods. Nothing else special....

This is for street use. not going over 7000 rpms....

I don;t have any specialty machine shops nearby either...

Can I make this work?

Anyone...

Anyone....

Anyone...??? is this discussed in JG's book???
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Re: Balancing factor of the 3.0 12v?

Post by slyalfa » Mon Mar 15, 2010 3:14 pm

I used my 3L pulley, crank, flywheel out of the old block. as I could not get any good info ether. when I put in a 'S' motor.
but if you can have the old matched to the 164 parts I would think it would be fine.

use the 164 pulley, zero it or of-set weight it to zero. then mount the 2.5 part and grind it until you are back to zero. do the same with the flywheel.

I think that is the cheapest way. right now. I think the magic numbers might be in the new JK book to do it right. but until then I think this is the next best thing.
unless you have a shop that can spin the whole motor put together and do the job.
like that vibrationfree place.
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Re: Balancing factor of the 3.0 12v?

Post by kterkkila » Mon Mar 15, 2010 10:47 pm

I've found that at least some Alfa 12V engines have been balanced originally to 47%. Then it's quite common to balance these among many other V6 engines to 50%, and think it will work fine. Some are suggesting using even higher 52-54% if engine lives on higher rpm.

The 47% came from two balance machine manufacturer and similar numbers have been mentioned on this thread too. But not sure if there have been minor adjusting during the years and engine generations. I also have discussed with pro level V6 engine (Nissan) builder who have used 50% on those high revving engines. Besides of those, I also contacted Vibration Free. It's easy to understand that they don't want to share their numbers.

After this all, I would be almost ready to make mine to 52%, but then... When I checked the original percentage of my 24V by adding more bob-weights of balancing machine, I found that it was at 60%! That caused more confusion again. Balancing machine manufacturer said that engine factory might know something, or they have sense of humor :lol:

Nissan VQ-engines are quite similar on their layout. Experiences on those engines might be relevant with Alfa engines too.

Some should explain the theory behind 60%, and then we are done with this. I do understand how the forces are working and what 50% would mean on loads on crank, but 60%??
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Re: Balancing factor of the 3.0 12v?

Post by xrad » Thu Mar 18, 2010 8:02 am

Thanks for replies!
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Re: Balancing factor of the 3.0 12v?

Post by gran turismo » Thu Mar 18, 2010 11:39 am

kterkkila,

60% blance factor is suprisingly high. High balance factor is good for high rpm but too high may cause vibration at low rpm. But if in doubt I wouldn't change anything if it was running vibration free in the first place.

My 3.0 12V was also balanced to 47% but hasn't run yet. My memory is two 1/2" holes on the rear counterweight and 3 on the front. The front ones were deeper. But it was also balanced with a lightened flywheel with the balance holes removed. I might post a pic and measure when I get home.

Is your engine a 24V out of a front drive car with original flywheel and pulley?

Or is it a 24V from a front drive transplanted into a transaxle car with 12V flywheel and pulley (which could result in a different balance factor)?

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Re: Balancing factor of the 3.0 12v?

Post by kterkkila » Fri Mar 19, 2010 1:35 pm

Jeff,

The complete assembly was from 24V 164. It was running great, but now I must change both wheels for rwd use, so balancing must be done with new parts. The wheels are going to be custom parts. Here's some pics about the job.
Image
Image

Did you use standard weight pistons and rods? Removing much from front and rear counterweights will lower balancing factor, if reciprocating parts remain the same. It would be interesting to see the pics, before and after balancing if possible.
Kimmo / alfatune.fi
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Re: Balancing factor of the 3.0 12v?

Post by Jim K » Sat Mar 20, 2010 1:15 pm

Some balancing shop guys in the US say that anything under 50% is disastrous. 50 is for everyday engines and 53 can be considered max for high rpm use only (not a realistic or practical situation). You may have heard of numbers like 58 or 60% but these are only used in some inherently unbalanced situations like Harley bikes etc, where there are specific problems. Use 51-52 for an Alfa seeing street and trackdays. The trick is to be patient enough to arrive at the maximum machine sensitivity and 'zero' all imbalance; many shops let it go before that. Its very important to make sure bobweights have the exact same orientation on every journal and exactly the same weight; strive for 0.0gr difference and don't forget to add some grams for the oil being dragged around on both rotating and reciprocating assemblies.
This subject has been popping up for years, so I figured it was time to get it over with and that's that!
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Re: Balancing factor of the 3.0 12v?

Post by kterkkila » Sat Mar 20, 2010 1:33 pm

Jim,

That's the same information what I've found too. That's because I have also been discussing with US V8 guys and balancing shops just as you and even with balancing machine manufacturers. The balancing shop I'm using might be the most accurate in Finland, and they spoke long about the accuracy demands on balancing job and on setting bob-weights.. Also oils are added on masses, just as should be.

But maybe we should discuss more with japan V6 builder, or with Alfa factory teams?
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Re: Balancing factor of the 3.0 12v?

Post by Jim K » Sat Mar 20, 2010 11:28 pm

So far, using my bobweights adjusted for different piston/rod weights, I've had three 3.0 12V cranks balanced with the expected outcome. Needless to say, I attended the entire procedure and made sure we arrived at max machine sensitivity with the bright dots in the center of the crosshairs on both ends of the assembly (in this machine; others may have different means of indication). The result was no engine vibration at all, and smooth sailing to ~7400, so I won't look any further. One was with the std flywheel weight and two with lightened flywheels to ~8.5kg.
It would be nice though to hear from someone doing GTR cranks!
Jim K.
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