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Re: V8 Pistons
#31
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PackardV8
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"There is one Ford truck piston close to the right height, but it is heavy-duty monster 125 grams heavier "

If it's too tall and that heavy then maybe some can be faced off of the top as long as it stays close to thickness of Packard piston. Thickness of skirt??

Posted on: 2008/8/24 22:31
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Re: V8 Pistons
#32
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Eric Boyle
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Making a Packard V8 piston is more difficult than it seems at first glance, eh?


Makes me very happy I gave up the V8s!

Posted on: 2008/8/24 23:14
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Re: V8 Pistons
#33
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Jack Vines
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"There is one Ford truck piston close to the right height, but it is heavy-duty monster 125 grams heavier " If it's too tall and that heavy then maybe some can be faced off of the top as long as it stays close to thickness of Packard piston. Thickness of skirt??


Lot more to it than that:

1. .050" off the top to match Packard compression height
2. .1875" off each inside of the pin boss
3. Press the bushing out of the rod and bore to Ford 1.040"
4. Rebalance entire engine - Use Mallory metal in the counterweights or add external balance weights to the flywheel/flexplate and front damper.

At retail, all this will cost about as much as custom forged pistons which are a drop-in. BTW, I just did all of the above last week because I'm building a Packard truck engine. Stand by for news.

thnx, jack vines

Posted on: 2008/8/25 0:19
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Re: V8 Pistons
#34
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PackardV8
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Jack. Sounds like an excellent solution. Interested in hearing more about your engine.

Have u tried to build any of these Packard V8's (assuming a STOCK crank) withOUT rebalancing?????

OR, to ask in a different way: Do the engines run any less smooth before rebalancing than after rebalancing????

Posted on: 2008/8/25 7:28
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Re: V8 Pistons
#35
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Jack Vines
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FWIW, I no longer build a Packard V8 without balancing it. Since we don't have good technical data, who knows what should be where.

Here are some questions for which I still don't have answers after many years and many engines. Do any of you have thoughts or references for:

1. Why do the 352" and 374" cranks have the same P/N when the balance factor is 38 grams different?
2. What is the design weight for 374" pistons? I have 352" 24.763oz - 702 g, but no published weights for 374" pistons and no pin weight. BTW, oversize pins are heavier.
3. Why were there two or three different rod manufacturers? Why did Packard mix them in the same engine when the weights are definitely different? The "Atlas" rods seem to be heavier than the no-name rods with the sort-of-pentagon-logo them.d Anyone identified any other markings besides the P/N and batch pour number?

Bottom line - yes, any rebuilt engine should be balanced. The vibration can be noticeable, especially if the pistons are changed.

thnx, jack vines

Posted on: 2008/8/25 12:44
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Re: V8 Pistons
#36
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PackardV8
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"I no longer build a Packard V8 without balancing it."

ok. That means that at one time u DID build them withOUT balancing. So u have done it BOTH ways.

What SPECIFIC advantages have u experienced with balanced vs UNbalanced???? Are they so much smoother?? quieter???? Better longenvity??? fuel mileage???? significant HP increase??? What????


OR, let me pose the question in a different way:

Why did u start balancing after having built so many with success as UNbalanced???


The first pic is a Jag V12 crank. It behaves the same as the Packard V8 crank on the knife edges.
Ignore wooden block. It is only a safety when left unattended.

Attach file:



jpg  (41.12 KB)
35_48b32f78bde10.jpg 640X480 px

jpg  (48.53 KB)
35_48b32faf29a87.jpg 640X480 px

Posted on: 2008/8/25 16:28
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Re: V8 Pistons
#37
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PackardV8
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"1. Why do the 352" and 374" cranks have the same P/N when the balance factor is 38 grams different?"

Piston is RECIPROCATING weight. NOT rotating weight. Piston weight has NO influence on crank balance whatsoever.

NOTE the lack of counterweights on many engines usualy near center journals. NOTE that he crank is balanced BY ITSELF as can be witnessed if u set up some knife edges. DISCLAIMER, crankshaft balance on kife edges does not apply to most (but not all) 2wo cylinder engines. Only to engines of 4 or more cylinders of any configuration tho i'm not sure about odd-cylinder radials.

Posted on: 2008/8/25 17:37
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Re: V8 Pistons
#38
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PackardV8
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"Bottom line - yes, any rebuilt engine should be balanced. The vibration can be noticeable, especially if the pistons are changed."

Need to get with some 40's - 50's streight 8 Buick people for the scoop on CI pistons from the factory vs Al replacements in service. That's about as wide a weight variance as it comes.

Posted on: 2008/8/25 17:45
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Re: V8 Pistons
#39
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Eric Boyle
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Piston is RECIPROCATING weight. NOT rotating weight. Piston weight has NO influence on crank balance whatsoever.


If that's true, then why is it that when you balance a crank, they take the weight of the piston and the rod and bolt it onto the crank for balancing?

Posted on: 2008/8/25 18:21
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Re: V8 Pistons
#40
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gone1951
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Very good discussion. Keep it coming.

BTW I thought the rod journals on a V8 crank were evenly distributed around the crank 90 degrees from one another. That would mean as far as ballance is concerned the weight at the jurnals would not be relative to the over all ballance. I believe they weigh the rods and match the weight of them. They may bolt weights on the journals equal the the rod weight at the crank shaft end just to get the rotating mass up to what it will be when the engine is assembled. I agree that the piston weight doesn't have anything to do with balance.

Posted on: 2008/8/25 18:51
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