engine vibration...where to look ?

[chargerdon]

Ok..   with my 360 LA bored stroked to 408 Internally balanced, I  have picked up what im fairly certain is an engine RPM related vibration.   

I thought after a high speed run that i had a driveline vibration, and pretty sure i did...but reworking the transmission (A518) to higher in the tunnel and adding a 2 1/2 degree shim to the rear axle i'm fairly sure i've corrected that.  Last week with the entire car up on jack stands the rear supported under the axle, and using my cell phone camera to take movies of both the front and rear u-joints at speeds up to 75 (yeah...i was real nervous doing that) they both appear to be rock solid.   So, fairly certain that's corrected.   

But i still have a vibration.   Driving the car at about 55 you can feel it in the seat of your pants and in the steering wheel...   Not a sawing like would occur with tire out of balance but a buzzing feeling.   So, began to notice that it is RPM related more than speed.   .i.e at 55 when i engage the overdrive and then the locking torque converter dropping RPM to about 1700 the "buzzing type of vibration definitely is reduced to almost normal release both putting RPM back to around 2400 and you can definitely feel it !!   

I thought what the heck and replaced the spark plugs with new ones, but that made no difference.   Today i started to simply rev the engine slowly while parked and in neutral and starting at about 2400 RPM you can feel the vibration and at about 3500 its darn noticable...again...its almost like a vibrator that you can feel in the steering wheel and in seat of your pants.   

Again, think maybe ignition i want to check each cylinder...   so i used my infrared gun on each of the headers at full operating temperature i shot all 8.   Here are the results...all farenheit  cyl 1 about 480, 3 about 600-630, 5 510-530, 7 480-540
passenger bank... 2 380-410, 4 409-440, 6 455-570, 8 425-440      I think this proves all cyl are firing and the middle two on each bank definitely the hottest.   While this was going on the outside temp here in NC was around 55 and the temp gauge in the car was showing low normal.   I shot the thermostat neck and it was a solid 185 (180 thermostat in her). 

Last time i checked the timing the static was at about 15-17 BTDC  and the total was at 38 BTDC.    I was going to check it again, but discovered that my timing marks on the Damper (SCAT unweighted) were missing.   I guess their on with tape and it must have come off.   Wonder if the damper is the problem??? 

Any suggestions what to check next ??   

[Scooter]

I had similar vibration issues, 360LA. I had checked the u-joints as they sat and they seemed fine. Chased my tail for a few weeks. Finally dropped the shaft and both seemed fine on the workbench as well. Lube was fine and no slop I could detect. I swapped them out anyway... vibration gone. Prolly the best $50 I spent last year other than the new house... lol.

GL!
-scoot

[chargerdon]

Thanks Scooter...but in this case pretty sure its the engine itself, as i can feel the vibration sitting still just by revving the engine in neutral. 

[Scooter]

^^^ In that case.. I'd double check timing, advance and retard it and see if there is any change to the frequency. If no, check that dampner.

My2c

[73_Cuda_4_Me]

I had a similar bad vibration on my 340/727 combo, and finally isolated it to the torque converter. This was on a 70 340, internally balanced. This was not an overdrive/lockup TC, though. Correct style torque converter and flex plate, but was 'generic' store brand from a popular on line parts store. I ended up installing a good name brand TC (that cost twice as much), and that cleared right it right up.

[MoparLeo]

OK, lets back up a little. Has this vibration been there since the engine was new ? Diagnosis is a step by step process. Always start at the beginning and eliminate one thing at a time. Never assume that anything is ok just because it is new. Plenty of defective parts out there.
More detailed history would be good.

[chargerdon]

OK, lets back up a little. Has this vibration been there since the engine was new ? Diagnosis is a step by step process. Always start at the beginning and eliminate one thing at a time. Never assume that anything is ok just because it is new. Plenty of defective parts out there.
More detailed history would be good.

NO, when i first had this engine built, by a reputable close engine shop it was fine.   It was built and INTERNALLY balanced using  SCAT brand stroker crank.  And a new SCAT brand damper for internal balance.  Very smooth.    At that time i was using a 904 transmission with a new torque converter for internal balance.   It ran good but was worried the new horsepower was too much for the 904 plus i wanted overdrive.

Then i changed out the transmission putting in an A518 and a new Lock UP Torque converter for internal balance.    It seemed to run pretty well for about 6 months, but, the first time i had a chance to drive the car on a fast highway I noticed a bouncing type of vibration at higher speeds.  Starting at about 65 and taking it up to 80 it was a really bad bouncing type of vibration.   SO i decided to check the drive line angles.  Found them way off...   Did a lot of work to get the A518 higher at the rear..which is difficult as not a lot of clearance, and then put in a shim at rear axle...   

Still thought i had a drive line issue, so that is when i used my cell phone camera to record both U-joints with car on stands and running it up to 75.   Locks rock solid..plus that vibration is way different then when the driveline was off.   

Began to really pay attention to when it occurs and realized that it is RPM sensitive not speed.   I.e at 55 it runs around 2200 rpm and that is when it starts, but, turn on the overdrive and LU dropping the RPMS to about 1500 and it is way less.  Then noticed that just sitting in neutral and revving the engine slowly the vibration begins around 2400 and by 3500 RPM its i strong buzzing kind of vibration.  So no longer thinking driveline. 

After that is when i was going to check the timing and noticed the timing marks gone from the damper.   I guess they had used a timing tape and it came off.   

Ill try advancing and retarding it after i find the TDC mark and see if it makes any difference.   I am also really thinking maybe all of the work to raise the transmission tail has "damaged" one of the engine mounts.   I have the type of mount on drivers side that has the safety bolt thru it. 

[Scooter]

I've found solid, pinned and poly lock mounts do transfer a lot more engine vibration... good for troubleshooting if you are in tune with how your engine optimally runs.

If you are getting it sitting in neutral and revving the motor you can probably eliminate everything rearward of the flywheel.

That it ran fine before but just started notes something definitely changed or is failing.

Let us know what you come up with on the timing.

[MoparLeo]

Obviously the vibration was not engine related if it changed only after the transmission/torque convertor was changed. That is why you don't just start to change several things at once and go back to what was changed or removed and replaced. What about the driveshaft ? Flex plate, torque converter ? Properly check the driveshaft angles ? Home made trans crossmember or professionally assembled unit ?  Details matter.
https://www.therangerstation.com/tech_library/pinionangles.shtml

[Burdar]

You didn't say how long you've been chasing this issue.  I assume you've run multiple tanks of gas through the car since the issue first popped up?  I had a very similar issue after the car sat over the winter.(with Sta-Bil in the gas) Engine vibration starting at around 2000rpm.  It turned out to be bad gas.

[chargerdon]

Obviously the vibration was not engine related if it changed only after the transmission/torque convertor was changed. That is why you don't just start to change several things at once and go back to what was changed or removed and replaced. What about the driveshaft ? Flex plate, torque converter ? Properly check the driveshaft angles ? Home made trans crossmember or professionally assembled unit ?  Details matter.
https://www.therangerstation.com/tech_library/pinionangles.shtml

Yes, the vibration probably started about the time i changed the 904 out and A518 in.    However, you have NO CHOICE but to change several things when you go from 904 to A518.   First the torque converter has to change as the 904 and 518 have different splines at the front.   Yes, the transmission crossmember has to change as the A518 is a much bigger around unit, and NO there is no A518 in a Challenger off the shelf crossmember.   So, i fabricated it myself.   The yoke had to change because the spline count is different.   The Driveshaft had to be shortened.   I had that done at a professional shop and BALANCED...they also replaced the two U-joints with new ones.   SO unfortunately that all has to be done at the same time as a system!!!     No changing one at a time and going back !!

HOWEVER, i do believe that the vibration i felt at that time WAS driveline vibration as i didn't get the tail of the transmission high enough...a518 fit in the tunnel but lower do to its much larger diameter in the tail section.    That is why i reworked the crossmember and the transmission mount to get it higher.   Originally, i had about a 6 degree down angle.   Now i have a 3 1/2 down angle (measured at the front crankshaft pully after the rework.  The pinion with a shim about 2 1/2 degree up angle.   That makes the front u-joint angle about 2 1/2 degrees and the rear about 1 1/2 up...   So that the difference between the two is only 1 degree.   This falls in line with the guide you listed. 

BUT, i think i've had two DIFFERENT vibrations.   The first was almost guaranteed to be driveline angle related and was speed related.
  I.e the faster i went the worse it got and it was a "bouncing" type of vibration.  That is why i did all of the work to raise the back of the transmission higher.   

Now, the vibration i get is NOT speed related, but is RPM related and occurs with car sitting still and simply revving the engine...it gets pretty BUZZY at about 3000 and up.   Thus i think along with the camera shots of the u-joints that it is no longer driveline but instead engine.    So, what changed?   Again, i'm thinking that the work i did with the A518 to raise its tail, either damaged the flexplate, or the engine mounts.   Or maybe the engine vibration has been there for a while and i didnt notice it due to the driveline vibration.    Hard to remember for sure. 

[dodj]

Hmmmm. Everything smooth before 518 swap. Wasn't evident at lower speeds.
Driveline angles can certainly give you high speed vibration.
Have you shifted into neutral at highway speed just to 100% eliminate tires bearings etc?
You have ensured your driveline angles are correct? centre section pinion not loosened off a bit? (happened to me). Maybe output yoke of trans have some bearing play?

If all those other items are good...... Based on what you have entered as evidence, I'm thinking you may have a flex plate or torque converter crack/failure/out of balance issue.

Good luck. Vibration issues can be a bear to eliminate.

[ek3]

engine vibration in neutral means it is not drive line related.  you have most likely got a bad converter/ broken flywheel or balancer /pulley issue.

[dodj]

 

[Chryco Psycho]

What do you know about the build ?
Was everything properly balanced inside ?
if you use a lighter piston without balancing for example the rotating assy inside could be the issue.
A customer bought a crate 360 years ago  , I checked everything before installing it , there were numerous issues , cam was out 1 tooth for 1 .
I can't recall all the other issues but it was poorly built . after fixing obvious problems we installed it & the dash would bounce 2" at 2500-4000 rpm .
We had to pull hte engine tear it down completely & have it all balanced to fix it .
Not saying this is or is not the issue with yours . It could be just a bad converter / flex plate / damper problem , all external issues , but it will not be easy to eliminate those if it is the issue .