Engine Vibration at 3100 RPM

jayweitekamp · 01-29-2012, 09:39 AM

I just recently replaced my clutch on my 02 Boxster. Everything went perfect thanks to Wayne's outstanding DIY writeup. Now I'm pretty sure that prior to this clutch replacement I didn't have a vibration at 3100 rpm but I sure do notice it now after the clutch replacement.

I double checked the transmission mounts to ensure that everything was torqued properly and still have this vibration... Does anybody think this could be bad motor mounts and completely coincidental or should I dig deeper into my clutch replacement job?

Thanks and much appreciated

harryrcb · harryrcb's Garage

Quote:

Originally Posted by jayweitekamp

I just recently replaced my clutch on my 02 Boxster. Everything went perfect thanks to Wayne's outstanding DIY writeup. Now I'm pretty sure that prior to this clutch replacement I didn't have a vibration at 3100 rpm but I sure do notice it now after the clutch replacement.

I double checked the transmission mounts to ensure that everything was torqued properly and still have this vibration... Does anybody think this could be bad motor mounts and completely coincidental or should I dig deeper into my clutch replacement job?

Thanks and much appreciated

did you remove the flywheel? did you torque the pressure plate evenly? did you check your dual mass flywheel if it is worn ?

jayweitekamp · 01-29-2012, 10:08 AM

harrytrcb.

No I didn't replace the flywheel since it was still within the spring back specs. I also torqued the pressure plate evenly (snugged each one up in a cross pattern, then torqued in a cross pattern)

thanks

jayweitekamp · 01-29-2012, 10:10 AM

also more clarification on the vibration. It is slight but noticeable only at 3100 rpm. by the time I get to 3200 it evens out. Feels like a harmonic vibration very similar to my sons jetta MK4 before we replace the motor mounts. Hence why I'm leaning in that direction. Just don't want to start throwing $$ at a problem before I know what the problem is.

thanks

The Radium King · 01-29-2012, 10:40 AM

a search at 986forum (and probably here) will show lots of talk about the 3k vibration. i have it too. some say it is drone from their exhaust, some say it is deterioration of the dual mass flywheel, some say it is a failing motor mount. depending on what you read, folks have either successfully or unsuccessfully addressed the drone by fixing one of the above. the official porsche position is that the car is supposed to do it, so no help there. you may have distrupted any one of the above with your clutch job, so those are the places i would start to look. if would suck great bowls of suckiness if it was your flywheel what with you just having been in at your clutch ...

BerneseMtnDog · 01-29-2012, 11:14 AM

I believe your '02 will have the earlier designed motor mount which is very prone to failure. Mine was in bad shape at 84k miles and also created the 3k vibration. I'd start there since the upgraded part is fairly cheap and job is not too difficult to do.

Steve

WVBlackbear · WVBlackbear's Garage

Do you get a (Clunk) when shifting hard, or accelerating/decelerating?
I just finished a clutch job on my 05 and don't have a bad vibration at 3K but am now noticing the clunk. (I don't think I could have felt it before due to the clutch slipping so bad)
Since I checked my transmission mounts, I am going for my motor mount.
Good luck!

WhipE350 · 01-31-2012, 05:04 PM

It might be that your front engine mount was starting to crack and with all the engine wiggling doing your transmission it cracked some to the point you now feel a vibration. Donno just a thought.
Also how many miles do you have on he new clutch. I just did mine and have a couple hundred miles on it and now it is so smooth. Not sure if there is a break in period but mine at least now feels great.

Auf los! · 02-01-2012, 03:39 AM

In a bid to improve my shift action, last year I replaced my 01-design motor mount with the latest design mount. The shifter action didn't improve any, but my 3000rpm vibration vanished, like magic!

EBS_Don · 02-01-2012, 10:07 AM

The motor mount is the likely culprit but I have seen some funny stuff with the rear catalytic converters as well. I have installed bypasses on these cars and that vibration magically went away.

jayweitekamp · 02-06-2012, 09:15 AM

Thanks everybody for the comments. I have decided to replace the motor mounts. I agree that with the movement/jacking/supporting the engine to remove the transmission that is has probably cracked/messed up these mounts.

I'll post a status after I have done this replacement in a couple of week.s

jayweitekamp · 02-06-2012, 09:17 AM

also I have about 200 miles on the new clutch now and the vibration still exists. There isn't any clunking or weird sounds when shifting. Everything is as smooth as the day I bought it (now after the clutch change). Pedal feel as well as travel truly exhibits a new clutch feel.

Fly911 · Fly911's Garage

I used to have the same 3100 rpm vibration, especially on coasting and part throttle. Never under acceleration or WOT. About 6 months ago i bought a $250 aftermarket muffler (Chineese, but OK), not only did the vibration disapear, but I also gained 100HP on my butt dyno (at least it sounds like 100HP more, like a GT3!). So the vibration is a sound resonance around 3k rpm.

spongebob · 02-10-2012, 10:11 AM

When I experienced this long time ago on my 2000 base tried a few different ways to get rid of this. First step was of course the motor mount but it didn't help.
Next step was the flywheel, no change here either.
But once when I changed to a S muffler I noticed a change in the amplitude of the vibrations. So I tried to mount it on different heights an with pretension in the pipes with the help of a hydraulic jack and depending on this pre-tension it became better or worse but not perfect.
Then I bought bypass pipes and voila, the vibration came at 3500 rpm instead.
Guess it was the lower weight that made the vibration to show up at a higher frequency.
Finally I bought the most recent motormount from the 987, really soft. It cured the last vibrations but instead I do get a feeling of the engine moving around, probably just imagination.

jayweitekamp · 02-11-2012, 11:39 AM

Well today I got around to installing the new motor mount. After some jiggling around and lowing the engine to the right distance I was able to remove the mount/bracket.

Upon removal it was quite easy to see where this vibration was coming from. The old mount was completely cracked all the way around and was quite loose in the bracket.

Installed the new one and once everything was put back together, I started the car and revved the engine up to 3100 and whoa-la no vibration. Took it for a spin and shifting was definitely smoother as well as zero vibration ~3100 rpm.

Thanks to everybody for all of your input.

Rossman · 09-15-2021, 03:55 PM

Today I changed the engine mount on my 2001 986, I was getting a vibration between 3000 & 3300 rpm ‘s up or down, when I removed the existing one I could see the mounting rubber has cracks and was split in a few places. Good news after replacing it the vibration is gone..

jluetjen · jluetjen's Garage

I'm with Rossman on this. I'm not sure which year/model you have, but be aware that the front motor mounts have been updated over the years. I have a 2002 986 2.7, and when I pulled out the front motor mount, it was cracked through. I discovered that the 986 motor mounts (986-375-023-05 and -07 -- which includes the brackets) are obsolete, and you now get the 987 motor mount (987-375-023-05, which just is the bushing insert itself), which is a direct replacement for the original insert.

Great!

I looked at the arrangement of the design of the motor mount, aligned the new one like the old one (which I had been careful not to remove yet) and swapped it out.

It made a noticeable improvement, but yet there was still the harmonic vibration at 3000 RPM, especially on overrun. I'm pretty sure that this harmonic is just a feature of the flat-6 engine with the bore, stroke, etc. of these cars.

Doing further research, I discovered that there is a notch in the bracket (visible at 5:00 in jayweitekamp's picture). You will also notice that there is a notch, bump or arrow on the mount insert. It may not be obvious until you look for it. These are the alignment marks which need to be aligned. Unfortunately I can't see it in this picture, but it's there.

Long story - short, I currently have the motor mount upside down in my car. I don't know if Porsche flipped it as part of the redesign or not. It may have been mis-installed by the previous owner -- I don't know. This is not as strange of an idea as you might think since we're dealing with wave function vibrations. Whether the engine is resting on the bulk of the rubber or "hanging" from it can make a difference in how the motor mount reacts at certain frequencies.

So fixing this is now back on my to-do list the next time that I've got the car up. The good news is that it's not a night-or-day difference. It's not going to make your engine blow up. But it will have an impact on that annoying vibration.

In the next 6 months or so when I fix the installation in my car, I'll post the results.