Jacking up the 911

[Jim Garfield]

Originally posted by klaucke
knowing a bit about VW bugs and that they are notorious for crumpling right above the jack slot in the rocker (and the same jack pad is used for bugs and 911's, the slot is the same) especially when a bit rusty, I am extremely skeptical about jacking a unibody car (namely my 911) from a point like this.

John, I wasn't suggesting jacking at the rocker but rather the 4 spots under the car recommended by the factory.

[Formerly Steve Wilkinson]

If you are going to jack on the engine, wouldn't the best place be not the sump plate but the spot basically under the lifting pad on top of the engine, which is way up near the front of the block? That's where the engine/transmission unit balances, in terms of weight distribution.

Stephan

[vash]

sherwood, i think klaucke is correct. your numbers are good with the car flat on the ground. to keep the math simple, if the car was 10 feet long, and the wheels are at the extreme ends, once the car is jacked up from the back to a 30 degree incline, the front wheels will see the 1500 and the rear would see 1000. gravity still pulls straight down, but now you have resultant forces acting. hope i just didnt give my statics professor a heart attack, cuz i am wrong

back on topic, i jack from the motor all the time, to protect things i use my folded haynes book as a cushion. no probs so far.

[911pcars]

Vash,
Would you care to plot the weight supported by the engine as you lift from 1-30 degrees?

The point is, at the point where the rear wheels no longer touch the ground, the jack is supporting the rear end of the car and the lift point is an area under the crankcase. The fact one can't see any effect this has on an engine isn't material unless one is looking for observable bending. If the weight momentarily distorts the crankcase structure 0.010" or 0.030", you're not going to see that. Are those amounts cause for concern? As far as I know, Porsche did not design the crankcase to be a stressed member of the drivetrain, otherwise we could hang suspension pieces off of it.

As in my previous post, I said, "Any harmful side effects? Who knows. I'd rather not risk it."

I also said, "Do what you think is right."

Just wanted to get the numbers right.

Sherwood

[Zeke]

Originally posted by vash
...........to protect things i use my folded haynes book as a cushion.

You think that much of it, eh?

[vash]

yea, sherwood. i hear you. i just couldnt resist getting physics-acle on ya .

too bad i am only a civil engineer and not a mechanical. i only know about things that dont move, unless it is an earthquake. but without doubt, your theory is on the safer side.

cliff

p.s. dont tempt me on plotting the load on the motor as the angle increases. haha, that is only a simple excel worksheet away. haha. thanks sherwood.

[dfink]

Because I just love seeing how far a simple post can be taken may I ask which end of the car should be raised first the front or the rear. My problem is if I jack up the rear first I can't get the jack under the front. If I jack up the front can't get under the rear. Damn maybe that is why they put jack points on the side.