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TerroRx7 03-24-2005 01:52 AM

rotating assy. balancing + mixing parts
hello all

I have a 95 LT1 and I want to add 6" rods with forged pistons on the stock crankshaft ( the engine won't exceed 6500 rpm )

but unfortunately I live in a place where we don't have any machine shop that have balancing facility

what can I do to minimize the vibrations or harmonics in this setup ?
what is your suggestion ?


strikingthematch 03-24-2005 11:40 AM

Im willing to bet that forged pistons and 6 inch rods are going to throw your balance job way out. Either find a place to do it there has to be something around there it may be a drive but something. OR if that is out of the question then maybe having new crank that is balanced for your Assembly is the best bet. There are different places that you can buy rotating form that will internally balance the entire rotating assembly for you and then ship it to your door ready to go. Spending extra is better then having your engine shake its self to death. Sure the engine may stay together unbalanced but for how long? Spending all that time and money in an engine and not balancing it is just a waste. IMO


tm454 03-25-2005 11:49 AM

old school balancing job....
First and formost a VERY GOOD scale...weight all 8 pistons...grind material off the skirt on each piston heaver than the lighest one to match the lightest piston's weight then do the same thing to the rods..weigh all 8 rods and find the lightest then grind off material on the 7 heaver rods. Taking a small amount off the skirt and off the rod's will balance the parts to each that what your talking about?? Its a lot easier to do with motorcycles.....I have done it on my drag works! Then you should balance the rotating assembly...only a engine shop can do that for you.


Rat Rods Rule!

Rob (chuck) Berry 03-29-2005 07:17 PM

Balancing the old way
Tazz is right; quite often you can get within 10 grams by selecting a heavy rod with a light piston and vice versa then find scale and grind away; although I'd tend to remove material only from the boss on the conrod, when I did fuel quality control for the Aussie airforce I used Sartorious scales accurate to 1/100 of a mg perhaps a local airport can help out, worth a try.
Dynamic balance for race conditions on your rotating mass is a speciality that most shops will not be equipped to handle so may I suggest you put up a new post asking if there is a reliable race engine machinist within coo ee (Aussie term for local-ish) of you the mail service should be able to deliver such a parcel. BTW your engine is basically an air pump so you may need more cam. fuel. different manifolding etc, piston dwell is a good place to start though.

Cheers from Aus

Rob :welcome:

Docs91RS 04-03-2005 12:48 PM

Most aftermarket pistons and connecting rods come in match wieght sets, but thats not the issue here. Your changing from the stock hyperutectic cast pistions and powdered metal 5.7 rods to a forged piston and a 6 inch forged afetr market rod. The issue isn't that they match eachother its the counter balancing on the crank that needs to be addressed. Anytime you make a change in rotating mass you need to have the crank balanced for the new parts. Wieght has to be added or removed accordingly from the cranks counterwieghts in order to maintain a balanced assembly. For the extra $150-200 it cost for balancing its the smart thing to do.


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