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How do you know when your engine mounts is bad?

How do you know when your engine mounts is bad?
Actually how many engine mounts do we have? I saw 2 on the back, near rear bumper. And 2 on the tranny cross bar. Any other?
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Old 06-13-2007, 05:28 PM
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Four. Two in the back, two holding the tranny. Dunno how to really tell, other than looking for worn, cracked rubber.

Dave
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Old 06-13-2007, 05:33 PM
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regarding the 2 on the back, near the rear bumper, so the only way is to take them out to look at them?
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Old 06-13-2007, 05:41 PM
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Place a jack under the engine and lift until you relieve the weight of it from the mounts. Then, just remove the big bolt that runs through the center of the mount, along with the cup washer. You should be able to assess the rubber in the mount at that point. No need to actually remove the entire mount...those two bolts that hold the mount in place can be a real pain.

You may have to soak the big bolt with some PB Blaster if it's corroded.

Randy
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Old 06-13-2007, 05:59 PM
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BTW,

My mounts were 22 years old when they came out. I broke both sides of the cross bar.

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Old 06-13-2007, 07:19 PM
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Dave,

Did you use PB Blaster before you attempted to remove those bolts?

Randy
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Old 06-13-2007, 07:22 PM
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Quote:
Originally posted by rcecale
Dave,

Did you use PB Blaster before you attempted to remove those bolts?

Randy
I sure did! A couple of times and gave it time (I'm sure it was over night). It was a combination of rust in the threads that the PB never got to and rust at the weld joints on the cross bar. I may have only sprayed the top side.

Hit both sides of the bolt with PB!

Dave
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Old 06-13-2007, 07:46 PM
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rcecale,
Thanks for info.

slodave,
Think that you are lucky it broke when you are working on it, instead of when you are driving it.
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Old 06-13-2007, 08:06 PM
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If you're talking about the rubber mounts, the good ol' fashioned way is to rev the engine and watch to see if the motor rocks excessively. How much is excessive? Dunno.

Another idea I've heard is to jack under the sump/engine case and watch the engine rise. The engine should only rise about 1/4" before the back of the car starts to move. If there's more, the mounts are sagging a bit.

If you remove them, cracks in the rubber are the giveaway.
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Old 06-13-2007, 08:07 PM
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Dentist,
I have not tried that but let me tell you what I feel to see if you know if that is the problem or it's normal.
On normal driving, I don't see any thing but on hard braking, I feel like my drive drain is moving slightly bit. Let me expand it a bit. On hard braking, if I let my hand (fingers) barely touch the shift knob, in front of it. Hand is resting on the armrest for firm (I have the middle armrest). at the end of the braking, I feel the knob is leaning toward my fingers. It can not be seen but enought to feel.
I think the engine/tranny must be moving forward a bit in order for the shift rod/knob to lean that way.
Is it waht I think or is it normal?
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Old 06-13-2007, 09:04 PM
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If feels loose, it may be. The nut on the bolt is on the bottom of the rear mounts, and it may be coming loose or more than likely already fell out. Put a jack under the motor and jack up you can tell if it is loose. Also attempt to tighten the tranny mount bolts.

If loose, look for other problems that may have resulted, e.g you sway bar brackets.

Goodluck.

Regards,
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Old 06-13-2007, 09:13 PM
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Quote:
Originally posted by dentist90
If you're talking about the rubber mounts, the good ol' fashioned way is to rev the engine and watch to see if the motor rocks excessively. How much is excessive? Dunno.

Another idea I've heard is to jack under the sump/engine case and watch the engine rise. The engine should only rise about 1/4" before the back of the car starts to move. If there's more, the mounts are sagging a bit.

If you remove them, cracks in the rubber are the giveaway.
Friend and I were hashing this over the other day. I guess we have too much time on our hands. He's got an early 911 at 2100 lbs. Mine is say 2400+. He's got a 901; I've got a 915. So, same basic cars with different weights, different motor mount brackets. How does one compare the mount condition with these two cars?

Lifting a heavier car puts more strain on the mounts; lifting a Carrera will strain the motor mounts more than a lightweight early 911. Can't compare accurately or consistently enough to justify trashing a $50 mount. In addition, the mounts normally flex in a rotational motion due to engine torque. Putting stress in a direct upward motion isn't really the same as rotational torque but probably close enough for this purpose.

This is what I came up with without removing the mount. You need a lift device with a weight scale on it. Lift the vehicle from the trans. mount (or engine if you're of that persuasion) an amount equal to the average weight of that particular drivetrain (e.g. 2.0 liter w/901, 2.7 w/915, 3.2 w/915, 3.6 w/G50, etc.).

Let's say my 2.7 w/915-5speed drivetrain weighs 500 lbs. Lift the drivetrain so 500 shows on the scale, then lift an add'l 50 lbs. past the drivetrain weight to preload the chassis. Measure the relative movement between engine and chassis with a dial indicator. If it moves X amount, that's one reference point to compare with other like drivetrains. Vehicle weight is then removed from the variables because we're just lifting and comparing numbers from the same type drivetrain. If you're the first to submit data, it's just that, a data point until similar examples are retrieved (btw, I'm not the data collector).

If a new motor mount produces 10mm flex from lifting a particular sample drivetrain, and my similar drivetrain produces 14mm movement, then I know it's worn more. Whether Xmm of play requires replacement, that's for the experts to answer.

However, the above is all theoretical. The old tech trick of prying the drivetrain in one direction with a 6 foot pry bar to observe deflection is what shops probably do.

Sherwood

Last edited by 911pcars; 06-13-2007 at 09:52 PM..
Old 06-13-2007, 09:46 PM
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Quote:
Originally posted by rnln

I think the engine/tranny must be moving forward a bit in order for the shift rod/knob to lean that way.
Is it waht I think or is it normal?
Not exactly sure how much your shifter is moving, but some movement of the shift knob on accel and decel is normal as there is some flex with the rubber mounts. It's tougher to determine when it's "excessive".

I thought my tranny mounts were too soft because when I installed the tranny and removed the jack the tranny/engine assembly would sag down about 1/4". When I got the replacement mounts I was a bit disappointed to see that they were no firmer than the old ones and it still hangs down 1/4". I imagine solid mounts would remove all doubt as to wear, but for street use you are going to have a lot more noise and vibration in your cabin.

PS: it's not hard at all to get a tranny mount off (on a newer style X-member) and look it over. Engine mount is also easy as long as the bolt is not seized, as per Slodave's experience.
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Last edited by dentist90; 06-14-2007 at 05:24 PM..
Old 06-14-2007, 05:21 PM
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again, thanks guys,

BReyes,
I ahve not have a chance to retorque them but I looked and touch and found that on each side of the engine, the 2 smaller bolts have nuts on the bottom. The bigger bolt in the middle doesn't have the nut. It's flush to the mount bar on the bottom (it doesn't extend through the bar), so it doesn't look like there should be a nut down there.
What is the torque on these bolts?
Thanks.

edit:
I just found an diagram/pic of this area on a 72 911 and there is a nut/washer on the bottom of the big bolt. Does anyone know if there is one on my 87/88?
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Last edited by rnln; 06-14-2007 at 11:01 PM..
Old 06-14-2007, 10:57 PM
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There is no nut on the bottom of the large bolt, on your car. The bolt screws right into the engine cross bar.

This is why you want to use the PB Blaster and break it lose real slow. It's common for the bolt to corrode itself into the cross bar, and when you go to break it loose, the end-piece of the cross bar turns with it and snaps off. (See Dave's pic above)

The only nut/washer you should have on your mounts are the small ones. Two for each mount, as shown in the diagram below.



Randy
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Old 06-15-2007, 02:23 AM
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[QUOTE]Originally posted by rnln
[B]again, thanks guys,

BReyes,
I ahve not have a chance to retorque them but I looked and touch and found that on each side of the engine, the 2 smaller bolts have nuts on the bottom. The bigger bolt in the middle doesn't have the nut. It's flush to the mount bar on the bottom (it doesn't extend through the bar), so it doesn't look like there should be a nut down there.
What is the torque on these bolts?
Thanks.

Make sure you spray release oil from the bottom into the threaded hole to reach the large bolt. (Use the long Nylon nozzle)
Crack them loose, then torque to 58 ft-lb if they are M12 x 1.5 like on the SC's.
As for wear:
Climb under there.
You can see and feel how much wear there is in the mounts by checking the space between the large convex washers and rubber insert.
Some space (about 1/4") is normal.
Mounts are important to keep the engine/transmission unit on the correct plane to assist proper shifting and keep the rotational movement of the unit to a minimum.
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Old 06-15-2007, 06:50 AM
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Many have experienced stuck bolts on the threaded engine bar, and attempts to remove them may result in overstressing and breaking the threaded end(s).

I would suggest modifying to the earlier-type engine cross mount that uses a nut and bolt arrangement. Remove the threads and use the proper size fasteners. In any case, use anti-seize to allow easier removal at a later date.

Sherwood
Old 06-15-2007, 08:02 AM
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I first noticed that my mounts were bad when I had shifting problems. The shifting linkage was all rebuilt so I knew that the actual ****er and transmission weren't the problem.

I used two of the Porsche mounts and two of the Wevo mounts. That totally cured my shifting problems. There was a slight increase in noise but nothing objectionable.

Richard
Old 06-15-2007, 08:09 AM
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Quote:
Originally posted by slodave
BTW,

My mounts were 22 years old when they came out. I broke both sides of the cross bar.

Unfortunately a common occurance. Next time try whacking the bolt heads a couple of times with a big a$$ hammer to break some of the corrosion free. Preferably after a good soaking in PBB.
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Old 06-15-2007, 10:39 AM
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So if you see the bolt in there, tightening from the top may just do it, and when you put a jack under the bottom center of the motor it will just lift the car.
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