Engine vibration around 2K RPM

[CellerDweller]

Hello everyone!

I've been putting this question off long enough. I've spent a good deal of time searching and there are a butt load of posts relating to engine vibration, but none that closely resemble my problem.

My profile is up to date - basically stock automatic TSI AWD with a re-built engine with approximately 1000 miles since the rebuild. I have had this vibration since the re-build and I did install the BSE "kit". There is an aggressive vibration that starts at 1850 RPM and stops when I pass 2000 RPM. It's not a problem if I accelerate through that RPM band, but if I sit there (usually happens at 30mph as I'm driving through town) it rattles the exhaust. It doesn't matter if I'm driving or sitting in the driveway in park.

The timing marks were all aligned properly and the timing components were replaced at the time of the re-build.

Hopefully someone out there has dealt with this problem.

Thanks!

 

[Cdc1221]

My personal opinion, that vibration is probably caused because of the bse kit . These engines are designed to run with a balance shaft, and if you eliminate it and dont have the engine balanced then it will vibrate. Maybe bryanwheat will chime in on this one though as im not 100% on this

 

[CellerDweller]

The only reason I didn't think it was due to removing the balance shafts was that other posts relating to engine vibration state that it can be felt at 3000 to 4000 rpm.

BTW - car idles smooth to 1850ish and once past 2K runs good as well.

 

[FeaR-GSX]

Your setup is the same as me and i have the same thing. most naotably is my sunroof vibrating around that rpm range but its not like the engine is shaking, at least in my case so im not worried about it. Is your engine shaking? that could be something different

 

[CellerDweller]

The vibration is defiantly from the engine because it causes my entire exhaust system to vibrate. My engine mounts are original and in need of replacement, but since the exhaust is bolted to the engine the mounts won't help. My main concern is that the vibration will eventually rattle the bolts and engine apart.

 

[dsmcurse]

for some reason i dont think its because of the bse kit. ive done this mod to eclipse's that were stock engine and just bolt ons and never experienced this. ive done the balance shaft eliminator mod on a engine that was still in the car. had like 140k on it. engine never vibrated like that. and those shafts dont truly absorb vibration they soak up engine noise. you can kill those shafts out of there and if done properly there should be no negative effects. your car is automatic. how about the ringgear? how did it look? (automatic version of flywheel) thats all hunky dunky? tourqe converter?

 

[FeaR-GSX]

Your sure the exhaust pipe itself isnt loose further down the car?, 1800-2000 rpms could be point of resonance for the exhaust pipe and thats why it only vibrates at that rpm range

 

[dsmcurse]

i agree with the above post. plus you mentioned that your motor-mounts are half way dead and shot. i would look to either replace or repair those. you can repair the rubber inserts homemade syle. they turn out damn good if you know the trick. save's a guy some coin from havin to buy replacement motor mounts. the two side mounts are way more critical then the two that are front and rear

 

[CellerDweller]

Alright, some good info here. If it's not crappy out tomorrow I'll get under the car and check out the exhaust system. The ring gear and torque converter looked good when I had it apart.

I also borrowed a data acquisition system and a couple of accelerometers - one for the engine and one for the exhaust to see where the vibration originates and what the natural frequency is. I'll post the findings. Strange that I'm running the ebay SR-S 3" catback and a Punishment racing 3" down pipe, with cat delete, and nobody else has complained about this...I's a pretty common setup.

 

[CellerDweller]

I finally had a chance to look into this further. There's a pretty cool app available for around $5 called "Vibration" for the iPhone (not sure about android). It uses the tri-axis accelerometer in the phone and can sample at 100 samples/sec Max. I used a dab of hot glue, which is easily removable from plastic, and glued my phone to the valve cover and rev'ed the engine from idle through 2200 RPM (in park). The phone collected the data and displayed it on two charts - time vs amplitude (g's) and RPM vs amplitude (in g's). The maximum amplitude was .22 g's. I then put the phone on my exhaust near the muffler (exhaust was not hot enough to melt my phone at this point) and again rev'ed the engine from idle to around 2200 RPM. The max amplitude was .64 g's at 225.47 RPM, which is definitely a different RPM than the engine.

Long post, but it looks like FeaR-GSX is correct - the exhaust system is resonating at a frequency relating to 225.47 RPM (graph was set to RPM instead of frequency). Best $5 spent IMO! Now I need to find out how to dampen this vibration.

Thanks for the input guys!

 

[H@xtGSX]

Heavier/more hangers... I have a complete stainless 3" exhaust that is pretty heavy, and I had to weld in 3 extra hangers to get it to stay put and quiet. If they are crusty and falling apart, they aren't preventing or absorbing much vibration. That said, fix your mounts. Either get news ones, fill them full of window weld, or get the solid inserts. It makes a fairly large difference in how the vibration is transferred, which with the solid mounts is more to the chassis, but if the chassis is braced also, it basically eliminates most of the vibration... Except for right around 2500 rpm. That is one of the points where the harmonics of the engine are just right to shake everything in the car.

 

[FeaR-GSX]

Glad i could help man.
Checking the little things,Take your Time and be Patient is what ive learned with these cars