Vibration accelerating between 30-40mph - K20A.org .:. The K Series Source . Honda / Acura K20a k24a Engine Forum
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Old 01-24-2017, 06:52 AM   #1
ryboto
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Default Vibration accelerating between 30-40mph

As the title states, I am getting vibration, which feels like it's across both the drivers side and passenger side of the car, coming from the front, when I accelerate between 30-40mph. It's also present if the car is at constant velocity, between those speeds and it's under load(going uphill). Recently, I just replaced the transmission internals with what's listed below.

My car:
2004 EP3
K24A2
K24Z7 trans internals with 06si LSD in EP3 case
New wheel bearings
New hardrace compliance bushings
Innovative/avid racing engine mounts
New Moog ball joints/end links/tie rods
New brake pads and rotors
New axles and half shaft
New Comp Clutch and Lightweight Flywheel

The vibration was very bad initially. I replaced the axles, and it's reduced quite a bit, but it's definitely there. Excluding the transmission and axles, all the components above were new within the last year, and I never felt vibrations when driving(car is a daily). It wasn't until after installing the new transmission that the car vibrates at these speeds. Any ideas?

Already done:
balanced wheels twice
new axles/half shaft
checked trans fluid
inspected motor mounts, no damage.
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Old 02-16-2017, 05:27 AM   #2
ryboto
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Default Re: Vibration accelerating between 30-40mph

Motor mounts could cause this even if they aren't clunking?
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Old 03-03-2017, 10:32 PM   #3
Dc5stunnin
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Default Re: Vibration accelerating between 30-40mph

If you got aftermarket mounts, yea cabin vibration is to be expected I reccomend the lowest durometer if it's a daily. I had 70a and my panels rattled so bad it annoyed the crap out me made my car feel like a beater. I swapped out my engine and tranny mount with I think it was 60a and kept the rear mount 70 as reccomended by hasport and its way more tolerable.
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Old 03-03-2017, 11:14 PM   #4
LotusElise
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Default Re: Vibration accelerating between 30-40mph

Quote:
Originally Posted by Dc5stunnin View Post
...yea cabin vibration is to be expected I reccomend the lowest durometer if it's a daily. I had 70a and my panels rattled so bad it annoyed the crap out me made my car feel like a beater. I swapped out my engine and tranny mount with I think it was 60a and kept the rear mount 70 as reccomended by hasport and its way more tolerable.
Yes, less stiff durometer of the motor mounts shift the resonance to lower engine or driveshaft speeds (depending what is the cause).

@ryboto
A inline 4 engine has free 2nd order forces, you can either delete them in the dead centers or in between those with the counterweight, but you can't delete them for the complete rotation. Consequently the engine mounts play a big role, as they can help to compensate these vibrations or even increase. If you e.g. have very stiff mounts and hard durometer the resonance will shift to higher speeds of engine or driveshaft. But also softer durometer are able to increase the amplitude at just a lower resonance frequency. The system counts, so I guess you just need to test what helps.

My K-series mounts are pretty stiff and the elastomere or durometer are very hard, there is no resonance dedectable in any kind of engine speed or driveshaft speed.

With our customer engines for genset drives we do a lot of vibration measurement to ensure the endurance capabillity of parts on the engine. Those system are complex, sometimes weakening of areas help, sometimes stiffening, but there is no general rule which always lead to success. Just test it.

Markus
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Old 03-03-2017, 11:19 PM   #5
LotusElise
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Default Re: Vibration accelerating between 30-40mph

Quote:
Originally Posted by ryboto View Post
Motor mounts could cause this even if they aren't clunking?
I wonder why you report only vehicle speed, maybe the cause isn't the enigne speed alone, maybe the driveshaft is unbalanced and lead to resonate there?

You can prove it easily if you run that speed with your car in a corner, where through the angled postion of the joints the systems get more damped, and lead to a reduction in the vibration amplitude...would be interesting to read about your test result to that. The angle has to be significant: 20 or more (big empty parking place?)

Markus
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Old 03-04-2017, 12:45 AM   #6
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Default Re: Vibration accelerating between 30-40mph

Quote:
Originally Posted by ryboto View Post
Any ideas?
Just got a idea to separate the vibration sources in more detail:
  • idle the engine at the engine speed where you find it from 30-40 mph and see what is happening with the cockpit vibration: 1st continious speed in 200 rpm steps for 20 s, 2nd with transient load through a short WOT tip but still in idle (= zero load on the flywheel) to rise the engine speed through that engine speed bandwidth of 30-40 mph on street
  • go to a steeper mountain street and go into decelleration mode while driving downhill with 50 mph, while going through the 40 to 30 mph window you observe the vibration level
The idea behind is to separate the vibration source into drivetrain and engine. The point, you reported that under load it is observeable, could indicate it has something to do with the crankshaft balancing or the engine tuning in some way (e.g. a wrong ignition timing on only one cylinder due to a strange offset or ECU failure).

It also can come from e.g. the LSD, maybe a bolt is missing...just brain storming .

Markus
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Old 03-11-2017, 03:45 AM   #7
LotusElise
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Default Re: Vibration accelerating between 30-40mph

Any further recognitions/experiences/results on that?
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