LiftBars, removing big fat parts, and the Center of Gravity - Page 2 - Rennlist

05-29-2015, 12:41 PM

#16

UpFixenDerPorsche

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Join Date: Mar 2009

Location: Brisbane, Australia.

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Quote:

Originally Posted by Daniel5691

1981 928S Euro 5 speed

So I am the proud owner of a set of brand-new LiftBars!

At some point, my 928 will be up on these LiftBars and the transmission will be removed for a trip to Greg Brown.

Probably before that, however, my engine will be coming out to repair a cam tower oil leak.

I will more than likely only be jacking up the front of the 928 for the motor pull,
and therefore not use my LiftBars,
it did make me wonder about any changes to the center of gravity for the LiftBars when bigger chunks of the 928 are removed.

Do you have to change the central "jack point" either fore or aft when these larger parts are removed? For example, would my 928 "tip" nose-downward toward the engine
after the transmission is removed
and the LiftBar is back and balanced only
by the centrally-placed jack (and not 2 jack stands)
in the process of returning the 928 to the ground ?

Just wondering. I welcome your comments, laughs, and mild insults.

LOL.

Since the F/R weight distribution is approx. 52%-48% (give or take), the CoG (in the vertical plane) will lie approx half way (50%) between front and rear wheels. To be specific, if I give the wheelbase a scale of 0-100 units starting from the front axle, the CoG will lie at (50-(48/52)) units from the front axle, ie at 49 and a bit. ('bit' is a precise unit of measurement).

In essence, your liftbar jacking point should be halfway between the axles, ie 1,250 mm from either, since the wheelbase is 2,500 mm. If the car teeters a bit one way or 'tother then shift the jacking points to compensate.

Or tether your labrador to front/rear as needed.

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