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Giuliettaevo2
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Post by Giuliettaevo2 »

So you cannot mix and match cranks, pulleys and flywheels?

The reason i'm asking is I have a 164 3.0 24v engine in which i would like to put a Sei crank with the Sei flywheel and the 24v pulley... Balancing is going to be a problem this way if i understand it right.

Might just have to take another route then. :(
Drive it like you stole it...
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Post by Jim K »

Sometimes you can put a 75 or gtv6-type pulley and flywheel on a 164 crank and get away with no problem. I have had two cases happen: one where only a single 6mm wide and 5mm deep hole was required to properly balance such an assembly and one where a great number of larger, deeper holes was required for anoher similar crank (see pic below, the fact that the flywheel was lightened outside the balance cut area is irrelevant). You can never tell how close you are or how far. Taking the att. pic as a reference, the other flywheel I described used a single hole, like the one in the far left of the series of holes shown here.
Jim K.
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Zamani
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Post by Zamani »

Is there a way we can get the balance factor info ? The book is still a while a way. Maybe a plate or two of schnitzels at the Ring? :lol:
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Post by Greg Gordon »

Good idea Zamani,

I think Jim should set up a secret page with a few of these critical specs. When someone emails him proof that they have pre ordered the book, they get access to the page. Otherwise you would have to delay building that engine until the book comes out if you want perfect ballancing.

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rossogtv
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Post by rossogtv »

to Jim> thanks a lot !!! your info is of priceless value !

regarding the book> i think that there is nobody here, who will NOT buy Jims book anyway. I have a lot of specific engineering literature, where some books cost 5-10 times more like the availlable 4zyl book from Jim. I personally will buy 3-5 books, because i often had to sell my 4zyl book to alfa friends localy who came by and didnt know that such book exist. Other reason is, i get it much cheaper from the publisher then in the bookstore and postage is lower for more pieces.

Anyway the book is still not out and i needed the engine to balance now !

I have lightened substantially the pistons, piston pins and the rods, flywheel and pulley too. A lightened engine is far more sensitive to the correct balancing, so i needed an exact number !

On a stock 24v engine, the rods were between 566 and 569 gramms the pistons between 430 - 438 gramms, simmilar differences i have found on 12v and 4zyls too. Probably the 10kg mass of the stock flywheel will catch the small vibrations away, before the driver will sense them, but with a 4 kg flywheel the balancing has to be precise as possible.

My practice on 12v engines before was, always to use the crank/flywheel combo as it was originally in the engine and i have used lightened, matched piston/rod sets. Lightening them without rebalancing the crank was like using a higher balancing factor. This always caused vibrations low down ( between 2-3000), which was ok, because way up it was vibration free.
The pulley on the front is luckily easy removable and on the long 3.0 75 pulley i played around with attached weight, until i got a satisfactory running, then removed weight from the opposite side of the attached weigt.
I have allready seen 2 broken cranks - on stock 24v engines, they broke on the end of 1. main bearing, one engine had exept that no other damaged parts, the broken off front part caused some degrees valve and ignition timing shift, which stopped the engine. The engine was still able to go round, but didnt start. Because it was hard to move, the engine was disassembled and the failure was found. Only the crank and the first main bearing was damaged. This looked for me to be a perfect case of vibration failure, the cranks are otherwise a very good construction, good material and dimensions. But no matter how big and strong your parts are, vibration destroys anything.

Greg: When the alfa engine runs into vibrations between 2-3000 with 50%
balance ( factor from the GMv6es), but runs way up vibration free, that would be for my race engine good enough, i run between 4-7000, never under 3000.That means however, that the factory setup will be close to this number, probably a few % less.
I think that the factory setting will be somewhere between 45 - 50 %
As all engines use the same rod lenght, the factors for the 2.5, 3.0 and 3.2 crank will be different, say if the 2.5 has 48%, 3.0 could have 48,5 or 49% and the 3.2 even more.
I believe that this range is more practical, then the 30-50% stated before and nobody should be stranded with a dead - balanced engine.
As i will balance my crank anyway ( actually i will do 3 cranks), i will make my bobweights so, that adding weight will be easy to do and i will see, if we can find out the %, which was used at factory. I will let you know then.
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Post by Jim K »

Ok Zamani,
You got a deal! You show up at the Ring and I'll tell you all about BF, big-bore headers, new cams and pistons (over dinner...of course!) :wink:
Jim K.
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Post by fedezyl »

JimGreek wrote:Ok Zamani,
You got a deal! You show up at the Ring and I'll tell you all about BF, big-bore headers, new cams and pistons (over dinner...of course!) :wink:
Jim K.
May I join?? i'd love schnitzels too.... :D
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Barry
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Post by Barry »

Schnitzels !! Did someone say schnitzels ????

:wink: :wink:

z man,send me a blank mail will ya ?
French cars are shit and shit expensive to service and bloody awful and unreliable and expensive and friends don't let friends drive french cars and you wait years for parts.
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Post by Jim K »

Yeah, yeah, Barry, we'll send you a pic of a big f. schnitzel !! Thats as close as you'll get to one from the looks of it! :roll: C'mon Scroodge, take some diamonds out of that jar and cash them in for a good time! Be nice to have you around...a bunch of greeks, vikings, some dutch, germans and a Nigerian...hmmm, you can play Cofee Anan!! :lol:
Sure Fed, Z can buy you a schnitzel too!! :lol:
Jim K.
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Post by Greg Gordon »

rossogtv,

Your last post indicates you think I said a 50% bobweight factor causes a vibration between 2k and 3k rpm and is otherwise smooth. I DID NOT SAY THAT. You are combining what I did say with some information from another source about a G.M. V6, perhaps a different V6.

What I did say is that the bobweight numbers from A G.M. V6 will result in a minor vibration between 2 and 3k rpm. Not all G.M. V6s are the same.


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rossogtv
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Post by rossogtv »

greg: v60 from GM i know of are using 50%, of course there are v90 with numbers from 35,2%, 36,6%, 46% and also 50%. I didnt knew that there are more types of v60 from GM, so i assumed you mean that ones...
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Post by Zamani »

OK this may sound silly, but spoke to someone who told me that it is possible that you use the stock crank, flywheel, pulley, rods, rod bolts, rod bearings, pistons, put them on the balancing machine and get some sort of reference balance factor.

Then you get all the new parts, balance the rods, pistons, bolts, individually so they're all within a few milligrams , put them on the balancing machine again to get it back to the reference balance factor?
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Post by Jim K »

What do you mean "put them on the balancing machine"?? What is the exact procedure? The machanics of the process elude me as by 'reverse engineering' you will not arrive at a balance factor number.
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Post by Zamani »

JK,

I have no clue. I've seen cranks with bob weights on such a machine, but not sure what is meant by putting "them all" on the machine. Sounds like that will create a lot of noise and may kill someone in the process. :o

In theory wouldn't you just balance the crank, flywheel and pulley? The pistons and rods can be balanced separately.

I think the key to this all is the bob weights and the balance factor .
Dr. Alban
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Post by Jim K »

The theory you propose is valid only for inline engines. V engines are always balanced with bobweights on the rod journals. As a general eyeopener, here are some lines from what I'm still trying to finish....
One last but thought provoking point on the balancing discussion: when I was researching the subject I contacted Vibration Free, a very serious company in the UK specializing in all kinds of vibration analysis and balancing problems ranging from little ball-bearings, through F1 engines all the way to huge power generating turbine wheels. Their Steve Smith was very definite regarding balancing of our V6 engine: the only proper way to do it is to balance the assembled short block! The engine (minus heads) is secured on the machine and a motor spins the crank with rods and pistons on but no rings, the equivalent weight of which is glued on top of the piston crowns. This way, vibration is measured and corrective actions applied in situ. No bobweight simulation, this is as real as you can get, everything else being a compromise.
You can see from the above that the entire high-performance industry is at best only approximating good engine balance, no matter which factor they use! However, it has been 'found' that some factors are very close to optimum and that's where all the bickering starts! You may be surprised to hear that Steve Smith was very interested in the actual V6 BF as he was curious himself, not having utilized the common bobweight method in his kind of process.
Jim K.
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