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 Post subject: Re: DIY Engine Balance
PostPosted: Wed Aug 05, 2009 11:57 am 
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Sad but True...

Joined: Fri Jul 27, 2007 8:20 pm
Posts: 2973
Location: Saskatchewan
and I must say I feel more comfortable spinning mine 2000rpm passed the stock limit because of this and the machine shop balance

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1991 Swift GT Build G10 +25 psi + other goodies
1996 Metro Build QR25de swap, still undecided where to take it
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 Post subject: Re: DIY Engine Balance
PostPosted: Sat Sep 04, 2010 4:32 pm 
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Joined: Sat Sep 04, 2010 4:12 pm
Posts: 1
Location: Tustin
This works fairly well with an 8 cylinder V motor too with a few exceptions. The jig involved in measuring the big and little end is not an exact science unless you have it hanging from a chain and you use a wooden center to hang the rod on, and youll still not get accuracy beyond .5g but that is plenty close. EZ way to do this is to balance all the caps to the lightest, and then balance all the rods to the lightest, now you got almost equalized rod assy's. Remember that 7-10g of oil is on each rod/piston when its running so that is about your precision when you static balance your assy. read up on this and a Lambo motor from the factory was found to be 70g out of balance and still run very well. There is a formuls you must adhere to an a V8 too, as in 1/2 of reciprocal mass + rotational mass= bobweight of crank. If you know your bobweight (eg. 2250g +- 5% for an Eagle cast Mopar 360 stroker crank) you can measure and adjust your balancing to match this and come out with a motor that is pretty well internally balanced. remember that everything attached needs to be neutral balanced too like balancer, flywheel and or torque convertor. 4 bangers are EZ to balance, just equalize all the piston/rods as the crank is a natural balance, 3 is weird, so is a 5 but a V6 is very strange. I had 2 cyl Hondas as a young man in cars, an AN600 sedan and AZ600 coupe, I could have sworn that the motor had a common throw for the 2 rods, but I think it used a "lost spark" timing scheme that in a 4 stroke, one cylinder would be on the fire while the twin was on the intake, but both would get a common coil spark? After a muffler change to an Anza style glass pack tip, it was a bit of a "thumper" but I attributed that to the 2 cylinders. I always like the Swift, maybe Ill get one one day as I drive 44 miles each day to and from work. BTW, I used a Harbor freight digital scale I got for 8 bucks and it measures up to 1kg down to .1g and is suprisingly repeatable as long as you measure on a stable surface, not your running clothes dryer ;-)


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