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Engine vibration at 3000rpm

Dear fellow 911 owners. My 87 G50-911 with 96k kilometer has recently developed a problem.
I can feel a vibration at around 3000rpm and it seems to occur under load on every gear except the 1st. 2nd is the most pronounced. I can hear the vibration as it causes the gear box/shift to hum. The engine accelerates smoothly from 1000-5000rpm but seem to go through a rough spot at 3000rpm.

I don't know if the clutch has been replaced, but it seem to drive fine with no slippage.

Can someone please help me narrow down or diagnose the problem?
Old 11-21-2007, 11:44 PM
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HI Anthonycanada
you could try this,



taken for educational purposes

is there any noise at idle, from the transmission?

regards mike
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Old 11-22-2007, 05:11 AM
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I had a recurring vibration around 3k rpm, too in my g50/3.4
It seemed inconsistent, but was regularly appearing.

In the end, I ran two cans of Redline fuel cleaner through it (S4, I think).

That cleared it up for me. I think it was possibly a sticking injector.
I was amazed how well the stuff worked...better than Techron for me.
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Old 11-22-2007, 05:33 AM
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Thanks Mike and s5uewf.

There is no noise or vibration at idle. It happens at around 3000rpm only. The engine seems to be rougher at that revolution. It comes and goes but if I hold it at 3000rpm up a hill, I usually hear the hum through the gear box.

These are simple fixes and I will try them out this weekend.

Cheers,

Anthony
Old 11-22-2007, 07:34 AM
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possilbe your rubber chutch dics is broken
Old 11-22-2007, 07:41 AM
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NO... not the clutch I hope porsche man. Don't want to drop the engine.
Old 11-22-2007, 05:15 PM
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Checked it out with the mechanic. The vibration is coming from the air conditioning compressor. Removed the belt and the vibration was gone.

I wonder how many 911s are running without a/c? I am thinking of taking it all out.
Old 12-04-2007, 11:10 PM
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I read this thread earlier this week, and Mike's comment rang bells.
Of corse! ..... with the cross brace being first tightened to the rear engine bracket and then installing the engine to the vehicle, this would most likely lead to an uneven loading on the engine mounts.

After the reinstallation of my engine (3.2L with 915 box) earlier this year, the car felt like it had solid engine mounts. This was more noticable at a stationary idle, and around the 3000RPM area - 5 gear cruising. I could even hear a slight noise resonance at the 3000 RPM area.

So this morning I slackened off the 4 bolts securing the engine bracket to the cross brace. While doing so there were a couple of "creak-creaks" as the weight distribution trued up on the brace and rear engine mounts.
Then tightened up the four bolts. Now the test drive to find if this made any difference, YEP !! .... the vibration of the vehicle at idle has gone as has the vibration and resonance previously experienced at 3000 RPM cruising.

What reference is made in various manuals as to a proceedure when re-installing engine?

Thanks to Mike (again), and to Anthony who kicked of this thread.

Paul
Old 12-07-2007, 07:52 PM
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Quote:
Originally Posted by CruiseControl View Post
I read this thread earlier this week, and Mike's comment rang bells.
Of corse! ..... with the cross brace being first tightened to the rear engine bracket and then installing the engine to the vehicle, this would most likely lead to an uneven loading on the engine mounts.

After the reinstallation of my engine (3.2L with 915 box) earlier this year, the car felt like it had solid engine mounts. This was more noticable at a stationary idle, and around the 3000RPM area - 5 gear cruising. I could even hear a slight noise resonance at the 3000 RPM area.

So this morning I slackened off the 4 bolts securing the engine bracket to the cross brace. While doing so there were a couple of "creak-creaks" as the weight distribution trued up on the brace and rear engine mounts.
Then tightened up the four bolts. Now the test drive to find if this made any difference, YEP !! .... the vibration of the vehicle at idle has gone as has the vibration and resonance previously experienced at 3000 RPM cruising.

What reference is made in various manuals as to a proceedure when re-installing engine?

Thanks to Mike (again), and to Anthony who kicked of this thread.

Paul
Just wanted to add that I had to do this also. Horrible vibration at 3000-3400. Loosened the bolts on the engine crossbar and the engine settled slightly, tightened them back up and no more vibration.
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Old 11-15-2010, 03:45 PM
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Quote:
Originally Posted by Anthonycanada View Post
Checked it out with the mechanic. The vibration is coming from the air conditioning compressor. Removed the belt and the vibration was gone.

I wonder how many 911s are running without a/c? I am thinking of taking it all out.
i wouldnt. wait another summer before you do. besides, someday you will sell the car, if it is original, you may get more for it.
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Old 11-16-2010, 04:49 AM
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"Deviation in parallelism could cause tension between the transmission carrier and the engine carrier--this in turn could cause transmission of noise to the body"
I have the same issue on my `87 911
engine rebuilt--vibration at 3000 RPM started after rebuild
I replaced all 4 mounts--no joy
back to the rebuilder 2X--no joy
I finally replicated vibration when a/c turned on/off--no vibration difference in different gears, but direct correlation to RPM, specifically ~3000 rpm--that puts it right in the interstate cruising speed in high gear.
back to rebuilder--showed to him--"I'll replace compressor for you"
compressor leaking around clutch, but still cooling
to mechanic #2, showed him all the issues--
he installed new compressor, long shot re:vibration, but it was on the way out anyway--no joy, still vibrating when new a/c compressor turned on
Later, at home, 6 hrs into checking for engine parts touching body, I found this forum.
am trying to access bolts holding engine to carrier
on my car, it's 3 17mm bolts--got the top (easiest) loose.
can't get to the other 2 bolts with the tools I have without doing a half engine drop--that negates the whole "let the engine settle on its mounts" thing.
mechanic #2 willing to help access and loosen, re-tighten carrier bolts...on a Saturday...
everybody to knock on wood....been chasing this bi*ch for at least 2 yrs.

Last edited by Brorag; 07-19-2019 at 03:48 PM..
Old 07-19-2019, 03:10 PM
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update--tried it--didn't work.
It might for others....
next.....

to:'info@pelicanparts.com'

Car:
’87 911 cab
Engine recently rebuilt

Problem:
Some vibration at ~3000RPM
Heavy vibration at ~3000RPM when the A/C compressor on

Done
New engine/transmission mounts ~1 year ago
Replaced compressor
Under car looking for frame contact prior to correlating to A/C—no luck
I tried this—no luck:
https://forums.pelicanparts.com/porsche-911-technical-forum/378680-engine-vibration-3000rpm.html

Result:
No difference—still have:
Some vibration at ~3000RPM
Heavy vibration at ~3000RPM when the A/C compressor on


I’ve not driven this thing for 1-2 years--sure would like to but it back on road…..

John Dellinger,
a.k.a. Brorag on forums

Last edited by Brorag; 08-19-2019 at 11:46 AM..
Old 08-19-2019, 11:42 AM
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follow the oil line from the engine to the oil line to front cooler.Where it meets with the muffler is an area with possible contact...right in front of the right chain housing.
Ivan
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Old 08-19-2019, 11:36 PM
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I had a similar problem a few years ago with my ‘87. There is a thread on it as well (see below). There was a slight vibration inherent in the system, but it was being amplified by a loose spare time mount and loose battery tie down. Check those and any other possible (heavy) loose items. When I tightened everything up, the vibration essentially disappeared.

Drive train vibration at 3300 RPM
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Old 08-20-2019, 04:31 AM
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