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to balance or not to balance that is the question

 
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Fri Oct 15, 2010 2:26 pm    Post subject: to balance or not to balance that is the question Reply with quote

i have a bunch of sbc shortblock crap in my garage
and im thinking to assemble and sell

when should i balance if i get different weight 30 over pistons
or should i get "close enough" weight pistons???

cast cranks,stock rods, and stock replacement pistons


if i do anything beyond stock i will always balance, this is all i have ever done to date

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jeep_406
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1972 Chevrolet Nova

PostPosted: Fri Oct 15, 2010 7:06 pm    Post subject: Reply with quote

When we were kids, back in the 50's, we used to mix and match engine parts all the time without incident. As we matured and learned the correct way to assemble engines we always balance assemblies.
I suppose how the engines will be used could best determine whether to balance or not.
How deep will the rebuilds go?

I put together a 327 with mismatched pieces that were laying around. Used it in my Nova so we could move the car around the shop. I ball honed a bore that wasn't all that good and threw a set of rings & bearings at it. Really low budget. Never planned to use it for anything, then a friend needed an engine for his Street Eliminator car. He's run the engine for 3 seasons, about 325 - 350 passes without incident. He shifts it at 6200 rpm. Car ran a best of 12.20's. He's finished 5th in points the past 2 seasons at New England Dragway.
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clay
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1972 Chevrolet Nova

PostPosted: Sat Oct 16, 2010 12:28 am    Post subject: Reply with quote

I'll look in one of Vizard's book's tomorrow. In it he covered balacing and he gave the bobweight the factory used and then said if it was between "X" and "Y" it would be fine. I'll have to look up "X" and "Y" of course and I'll let you know. Clay
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clay
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1972 Chevrolet Nova

PostPosted: Sat Oct 16, 2010 12:05 pm    Post subject: Reply with quote

Here is the paragraph from his book. "First balance the rods, pins and pistons then check the weight of the rod little end. When this is done, measure the overall weight of a rod and subtract the little end weight. Add toghether the weight of the piston assembly, little end and twice the weight of the big end, including bearings and 2 grams for oil. If this is not more than 1900 grams and at least 1850 grams, then, if the crank is balanced to the stock weight of 1870 - 1900 grams, it will not be essential to rebalance the crank." Clay
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Sat Oct 16, 2010 12:40 pm    Post subject: Reply with quote

clay wrote:
Here is the paragraph from his book. "First balance the rods, pins and pistons then check the weight of the rod little end. When this is done, measure the overall weight of a rod and subtract the little end weight. Add toghether the weight of the piston assembly, little end and twice the weight of the big end, including bearings and 2 grams for oil. If this is not more than 1900 grams and at least 1850 grams, then, if the crank is balanced to the stock weight of 1870 - 1900 grams, it will not be essential to rebalance the crank." Clay








out of curiosity does he state anything about rpm ,going about it this way?

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clay
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1972 Chevrolet Nova

PostPosted: Sun Oct 17, 2010 1:52 am    Post subject: Reply with quote

Not specifically in that paragraph. However this is the feeling I get from reading the rest of his book (How to build max performance small blocks on a budget). He mentions the levels that stock reworked rods can reliably handle as being 7000 rpm and 400 horsepower for street / drag use. Most of this book is sorta of leaning toward using stock parts - hence the budget part. Depending on heads and cam of course I would expect a true street engine to be closer to the 6000 rpm max range. He did mention that in an endurance race situation stock rods will fail sooner - makes perfect sense. Hope I didn't make you more confused with my ramble. Clay
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Big Dave
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PostPosted: Sun Oct 17, 2010 2:12 am    Post subject: Reply with quote

Balance is required on all builds. The factory used ten different colored paints to determine the range of balance for all of the different parts that went intoi an engine. Soo all of the pnk rods and pistons went into the engine together, all of the lime grteen rods and pistons went into the next, etc. Slap then together and use an air gun that was preset for the correct torque for every screw and bolt in the engine which I am sure where also color coded once but they had been used so long that every biyt of identifying color was long gone.

The guy assembling the motor was talking to the guy next top him about his kid in little league and not even watching what he was doing. But the motor was flying together and was finished from bare block to short block in less than two minutes, heads on it and intake in another minute, carb and distributor spark plugs and wires inside of 15 minutes it was bolted to a test cell (a dyno basically), and a hat stuck on top of the carb that fed in an explosive mixture of propane and air held in place by an over center hose clamp.

Motor fired, timing adjusted and oil presure checked all before it started to heat up. Disconected and out of the cell and back on a hook to be painted and wraped in plastic before it had even cooled off it was sitting in a rail car.

That is the care to which the factory motor was assembled. But you only see the assembly line techs, not the machinists and other personel behind the seens making sure all of those parts were properly weighed and painted and sorted in bins to be pulled and assembled by some who had built so many motors (well his part of the motor any way as the block keeps moving down the line) that he can do it in his sleep.

I love reading about people who obsess over he exact shade of black the factory used or the significance of a pink rod. As an industrial engineer whose specialty was efficiency in production I spent a large part of my life watching other people work and striving to make the process so simple that some one could assemble a motor in their sleep. Training them was difficult but once they learned the routine a monkey could do the task assigned to them. Which is why the techs on the line could spend most of their thought process on talking with their neighbors.

Big Dave
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Sun Oct 17, 2010 3:29 pm    Post subject: Reply with quote

everything was fine till dave showed up Laughing

thanx for the info guys
ive never replaced a stock, for a stock replacement .030 piston without a rebalance
im just wondering what the outcome may be
so im going to go with the cheapest way about it here ,for a stock type rebuild

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Big Dave
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PostPosted: Sun Oct 17, 2010 11:29 pm    Post subject: Reply with quote

I'm hurt.

Anyway all of the "stock" parts are built to meet a specification outlined by the factory. The only variance will be in production tollerances that has a two standard deviationn QC interval to weed out bad parts so you are assured that 97.5% of the time it will work.

Big Dave
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Mon Oct 18, 2010 1:36 pm    Post subject: Reply with quote

thank you too Dave .....ya big lug Very Happy
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Thu Oct 21, 2010 7:47 pm    Post subject: Reply with quote

ive lost interest!!!!!
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af2
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1933 Willys Coupe

PostPosted: Thu Oct 21, 2010 9:28 pm    Post subject: Reply with quote

squeeezer wrote:
ive lost interest!!!!!


Why????????????????

Using a whole bunch of (missedmatched)parts been able too run many 331 to 433 engines.

My 431 still has missed/mached rods. I haven't run it since 86 but is still good! HMMM Never shook!? Shifted at 7500 with the Isky flat cam. Shocked
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Thu Oct 21, 2010 9:33 pm    Post subject: Reply with quote

only lost interest in selling them
i will still keep em if something comes up

i did not lose interest in building engines

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af2
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1933 Willys Coupe

PostPosted: Thu Oct 21, 2010 10:15 pm    Post subject: Reply with quote

squeeezer wrote:
only lost interest in selling them
i will still keep em if something comes up

i did not lose interest in building engines


I see! Good parts and the internet guru that says you must weigh every part! Shocked
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