Jacking Up a 993 - fell off jackstand!
07-14-2012, 03:49 PM
#46
Rennlist Member
I understand that a lot of people use the engine to lift the rear. It is convenient but I'm concerned about deforming or cracking the case. It is just aluminum after all. The magnesium cases on earlier models are much worse.
Where do you put your jack on a 993 engine? One side of the case has a lip that protrudes about an inch. It just doesn't seem strong enough to lift the car. And you would only lift one side of the case. Talk about twisting your case. Where else would you put your jack?
There is just no way that the case would not deform at least temporarily under the concentrated stress of lifting the car. Maybe that is a contribution to the frequent engine leaks on our cars. Maybe it is the cause of some of the fretting of main bearing supports that some people have observed at tear down.
Where do you put your jack on a 993 engine? One side of the case has a lip that protrudes about an inch. It just doesn't seem strong enough to lift the car. And you would only lift one side of the case. Talk about twisting your case. Where else would you put your jack?
There is just no way that the case would not deform at least temporarily under the concentrated stress of lifting the car. Maybe that is a contribution to the frequent engine leaks on our cars. Maybe it is the cause of some of the fretting of main bearing supports that some people have observed at tear down.
Huh?
07-14-2012, 04:10 PM
#47
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He's saying the mounts were designed to have weight hanging from them in tension, not holding up the weight of the car in compression. However the reality is that's only true when the car is static. While driving they are under stress in all three axises from engine torquing, cornering forces, positive and negative G's; they're gettin' action from every angle imaginable. I say, jack away..if a mount fails, it was probably on its way out anyway. The shock/impact forces of any of those are more than likely to exceed anything a floor jack being used in a reasonable manner would exert on them (think a nice 1-2 shift at redline with a dual mass flywheel and sticky tires!).
As for the front, I have successfully used the 2x8 under the trunk pan method with no signs of deformation. If you REALLY are worried about that, drive the front on to some ramps, jack up the rear and put stands under the rear of the car, and then you'll have all the weight aft of the stands acting like a cantilever. With an empty-ish tank I'd bet two guys could comfortably lift the front of the car by the wheel openings that way.
Last edited by TravisB; 07-14-2012 at 05:00 PM.
07-14-2012, 04:34 PM
#48
Rennlist Member
I know. Its what happens to them in the other direction that I was thinking about...maybe nothing. Also, you're not just lifting an engine but 2000 pounds at that point.
07-14-2012, 04:54 PM
#49
Keep in mind, when you lift the engine by the case, the mounts are no longer bearing any of the engine's weight in either direction. The jack is bearing the total engine weight. If anything is stressing the mount at that point would be the weight of the shell compressing the mounts. Also, the weight of the shell is being suspended by the four bolts that hold the motor mounts to the frame. But in reality, what is the weight of the shell? If I were to guess it's not 2000 lbs but more like 1200lbs maybe.
07-14-2012, 05:05 PM
#50
Rennlist Member
The actual weight on the jack where it is in contact with the engine is about 65% (the weight bias of our 993s) of whatever the empty weight of our 993s is.
I wonder why our owner's manuals provide specific lifting instructions...and specifically (as already mentioned prior in this thread ages ago) instructs not to use the engine as a lift point. In the end, owners can lift their cars where they please; its their car.
07-14-2012, 06:48 PM
#51
Rennlist Member
Actually, I don't think he did understand how the mounts work. But, as usual, puts forth an opinion, based on that "knowledge".
He's saying the mounts were designed to have weight hanging from them in tension, not holding up the weight of the car in compression. However the reality is that's only true when the car is static. While driving they are under stress in all three axises from engine torquing, cornering forces, positive and negative G's; they're gettin' action from every angle imaginable. I say, jack away..if a mount fails, it was probably on its way out anyway. The shock/impact forces of any of those are more than likely to exceed anything a floor jack being used in a reasonable manner would exert on them (think a nice 1-2 shift at redline with a dual mass flywheel and sticky tires!).
As for the front, I have successfully used the 2x8 under the trunk pan method with no signs of deformation. If you REALLY are worried about that, drive the front on to some ramps, jack up the rear and put stands under the rear of the car, and then you'll have all the weight aft of the stands acting like a cantilever. With an empty-ish tank I'd bet two guys could comfortably lift the front of the car by the wheel openings that way.
As for the front, I have successfully used the 2x8 under the trunk pan method with no signs of deformation. If you REALLY are worried about that, drive the front on to some ramps, jack up the rear and put stands under the rear of the car, and then you'll have all the weight aft of the stands acting like a cantilever. With an empty-ish tank I'd bet two guys could comfortably lift the front of the car by the wheel openings that way.
07-14-2012, 06:50 PM
#52
Rennlist Member
I know.
The actual weight on the jack where it is in contact with the engine is about 65% (the weight bias of our 993s) of whatever the empty weight of our 993s is.
I wonder why our owner's manuals provide specific lifting instructions...and specifically (as already mentioned prior in this thread ages ago) instructs not to use the engine as a lift point. In the end, owners can lift their cars where they please; its their car.
The actual weight on the jack where it is in contact with the engine is about 65% (the weight bias of our 993s) of whatever the empty weight of our 993s is.
I wonder why our owner's manuals provide specific lifting instructions...and specifically (as already mentioned prior in this thread ages ago) instructs not to use the engine as a lift point. In the end, owners can lift their cars where they please; its their car.
07-14-2012, 07:03 PM
#53
Rennlist Member
BTW, what do you make of 285,000 miles with an engine tray on and no top end rebuild. Sort of throws a lot of RL theories out. I noticed you didn't jump on that one.
07-14-2012, 07:10 PM
#54
Rennlist Member
I've got no dog in any hunt on longevity with or without the engine tray. It does stand to reason an engine will run cooler without. So, mine sits on ashelf. It also stands to reason much of the purpose of the tray was to aid Porsche in meeting ever-stringent noise regs.
07-14-2012, 07:41 PM
#55
Rennlist Member
How do you know? A guess? Maybe, maybe not. I'll let you know one day.
I really do not care either way, but when I join a forum and someone makes a statement to which I ask a question, "how much cooler does it run" with no response (simply because they do not have any data), I loose a lot of respect for the so-called "knowledge".
Warped valve covers! By how much? Run a feeler gauge between it and a plate glass. Never did get a reply. We really know what the solution is, but that would hinder sales.
Anyway, back to the other question. What do you make of that 285,000 mile, one owner 993 with the engine tray on all its life. We've been lead to believe that an engine tray accelerates valve guide wear. Maybe, maybe not. That must be one special 993.
Maybe you should go work for Porsche. That way we can change that engine lifting advice.
I really do not care either way, but when I join a forum and someone makes a statement to which I ask a question, "how much cooler does it run" with no response (simply because they do not have any data), I loose a lot of respect for the so-called "knowledge".
Warped valve covers! By how much? Run a feeler gauge between it and a plate glass. Never did get a reply. We really know what the solution is, but that would hinder sales.
Anyway, back to the other question. What do you make of that 285,000 mile, one owner 993 with the engine tray on all its life. We've been lead to believe that an engine tray accelerates valve guide wear. Maybe, maybe not. That must be one special 993.
Maybe you should go work for Porsche. That way we can change that engine lifting advice.
07-14-2012, 07:55 PM
#56
Rennlist Member
Well, you can't believe everything you read on the internet. Like when someone talks about the motor mounts supporting the weight of the car, when the engine is used as a jacking point.
Last time I checked, plastic was a good insulator, so I do buy into an engine running cooler without a tray. I personally don't ever recall posting anything about a correlation to valve guide wear, however. When were valve covers brought in here? I've never posted anything about valve covers on a 993 either. So why is this directed at me? Do you have some kind of complex?
285k out of a motor is remarkable, but I've always considered Porsche air-cooled sixes robust.
Funny, I'm going to get 20 PM's about you now, again.
Last time I checked, plastic was a good insulator, so I do buy into an engine running cooler without a tray. I personally don't ever recall posting anything about a correlation to valve guide wear, however. When were valve covers brought in here? I've never posted anything about valve covers on a 993 either. So why is this directed at me? Do you have some kind of complex?
285k out of a motor is remarkable, but I've always considered Porsche air-cooled sixes robust.
Funny, I'm going to get 20 PM's about you now, again.
How do you know? A guess? Maybe, maybe not. I'll let you know one day.
I really do not care either way, but when I join a forum and someone makes a statement to which I ask a question, "how much cooler does it run" with no response (simply because they do not have any data), I loose a lot of respect for the so-called "knowledge".
Warped valve covers! By how much? Run a feeler gauge between it and a plate glass. Never did get a reply. We really know what the solution is, but that would hinder sales.
Anyway, back to the other question. What do you make of that 285,000 mile, one owner 993 with the engine tray on all its life. We've been lead to believe that an engine tray accelerates valve guide wear. Maybe, maybe not. That must be one special 993.
Maybe you should go work for Porsche. That way we can change that engine lifting advice.
I really do not care either way, but when I join a forum and someone makes a statement to which I ask a question, "how much cooler does it run" with no response (simply because they do not have any data), I loose a lot of respect for the so-called "knowledge".
Warped valve covers! By how much? Run a feeler gauge between it and a plate glass. Never did get a reply. We really know what the solution is, but that would hinder sales.
Anyway, back to the other question. What do you make of that 285,000 mile, one owner 993 with the engine tray on all its life. We've been lead to believe that an engine tray accelerates valve guide wear. Maybe, maybe not. That must be one special 993.
Maybe you should go work for Porsche. That way we can change that engine lifting advice.
07-14-2012, 07:59 PM
#57
Rennlist Member
By the way, if you go through the rest of this thread, you'll notice others have mentioned what I have. Maybe you should respond to them as well.
