Engine/Cabin Vibration

[2seater]

For context, this is a 1989 replacement engine in the 1988 Reatta. The balancer is apparently not original but it is unknown if other items were replaced inside the front cover. Is it possible the balance shaft is out of phase if a mistake was made doing a timing set? Unknown.

 

This was a little snippet I found for the reason for the strobe or timing light.  

 

Strobe Light Applications for Machinery Problem Solving (automation.com)

[2seater]

Just for interest and loosely related to this thread: I found a strobe tach app and a video tach app in the iPhone app store. The strobe tach uses the flashlight and while I found it did work in a darker environment, the brightness of my flashlight varied a lot. It may just be my low level iPhone. If the light level remained steady it could be useful for zero money. The video tach adjusts the camera frame rate to pretty much do the same thing and seems to work better for me. Again, a free app.

[TripleC321]

So I took my car to the third mechanic to try and have them diagnose this issue. (For context I’ve replaced the engine in it with another LN3)

 

I was told the following from the mechanic:

 

“We think the engine vibration you are having is due to it being out of balance. Specifically, the flywheel is balanced to each engine on engines of that era. Because you used the old engine flywheel on this different engine, they are no longer balanced”

 

this seems like a load of nonsense?

[DAVES89]

That is true on some engines but not ours. I swapped a rebuilt 3.8 into my Red and I'm sure we kept the Red's original flywheel with the new engine.

 2seater would know for sure.

[2seater]

Dang, I wish I had a good answer on that. There are definitely weights on the flexplate but I am also pretty certain it can only bolt on one way. Even though the six bolts are in a circle, there is a subtle difference in the spacing between them so it should only align one way. The engine that is in the car now was made from parts of different engines and both the balancer and flexplate were new pieces. The difference is, the whole assembly was balanced before assembly. I remember the owner of the shop mentioning I should rotate the flexplate to the right when assembling, meaning after the bolts were all started, I was to hold in the direction of an arrow he had drawn before tightening. He had to remove a fair amount from the crank to balance but I thought it was because I chose the wrong balancer? Lots of people have replaced their balancers without incident and I would think the flexplate should be no different as long as for an LN3 and it wasn't fudged into place.

[2seater]

The video tachometer appears to work pretty well. I used it on my s/c and alternator while idling and the numbers calculate pretty close to what they should based on the pulley ratio. It is a free app unless you want the ability to change by one rpm which costs $2.99 one time. The free app adjusts down to five rpm increments.

[TripleC321]

The flywheel only went in 1 direction to my recollection. Was very easy to bolt in. 
 

I guess it could have come off in a certain orientation that I missed, but if as you said I would have encountered resistance lining up the holes if that’s the case. 
 

I do recall it only fitting on one way due to bolt hole location. 
 

So what the mechanic describes is a thing? If so, then my amateur replacement engine job I did myself is gonna come back to haunt me. 

[TripleC321]

17 minutes ago, 2seater said:

The video tachometer appears to work pretty well. I used it on my s/c and alternator while idling and the numbers calculate pretty close to what they should based on the pulley ratio. It is a free app unless you want the ability to change by one rpm which costs $2.99 one time. The free app adjusts down to five rpm increments.

Should I do this at idle? Or at the RPM the vibration is biggest?

[Ronnie]

2 hours ago, TripleC321 said:

So what the mechanic describes is a thing?

I wouldn't think it would be "a thing" on a 3800 when using parts from the similar years. But on other engines, for example, a 350 smallblock Chevy engine is internally balanced. Meaning all rotating parts in the engine are balanced so that any other 350 harmonic balancers or flywheels and flexplates from the same or similar year could be used and the engine would still be in balance. On the other hand, a 400 smallblock Chevy engine was externally balanced and needed to have a flywheel (flexplate) and harmonic balancer for a 400 smallblock for the engine to be in balance. Some of the big block Chevy engines were like that too but I don't remember which ones. I owned a '77 Monte Carlo with a 400 smallblock is the reason I remember it being externally balanced.

[2seater]

I wouldn't think it should be an issue, but I have no way of knowing for certain. To isolate a vibration visually I would think you want to look at it where it is most pronounced, 

[TripleC321]

1 hour ago, 2seater said:

I wouldn't think it should be an issue, but I have no way of knowing for certain. To isolate a vibration visually I would think you want to look at it where it is most pronounced, 

I have can’t seem to tell where it is most pronounced. 
 

I know the dash shakes really really good at 1200 RPM. I could start there and at the pulleys with the video tach tomorrow morning and see. 

[TripleC321]

3 hours ago, Ronnie said:

I wouldn't think it would be "a thing" on a 3800 when using parts from the similar years. But on other engines, for example, a 350 smallblock Chevy engine is internally balanced. Meaning all rotating parts in the engine are balanced so that any other 350 harmonic balancers or flywheels and flexplates from the same or similar year could be used and the engine would still be in balance. On the other hand, a 400 smallblock Chevy engine was externally balanced and needed to have a flywheel (flexplate) and harmonic balancer for a 400 smallblock for the engine to be in balance. Some of the big block Chevy engines were like that too but I don't remember which ones. I owned a '77 Monte Carlo with a 400 smallblock is the reason I remember it being externally balanced.

then this mechanic is spouting hogwash at me. I figured they were. Guess it’s time to add another mechanic to my “do not use” list XD

[Ronnie]

11 hours ago, TripleC321 said:

I know the dash shakes really really good at 1200 RPM.

Are you certain the engine is running on all cylinders when that occurs? A dead cylinder can cause the engine to feel like it's vibrating. Here is something I usually do if I suspect an engine is missing.

 

Park in a safe location. Put the transmission in drive and hold the brake really tight so the car can't move. Then start pressing the accelerator down slowly with increasing force to put a load on the engine. See if at some point the engine changes tone and starts missing or a cylinder goes dead. If that happens you might have found your vibration.

[TripleC321]

3 hours ago, Ronnie said:

Are you certain the engine is running on all cylinders when that occurs? A dead cylinder can cause the engine to feel like it's vibrating. Here is something I usually do if I suspect an engine is missing.

 

Park in a safe location. Put the transmission in drive and hold the brake really tight so the car can't move. Then start pressing the accelerator down slowly with increasing force to put a load on the engine. See if at some point the engine changes tone and starts missing or a cylinder goes dead. If that happens you might have found your vibration.

Here’s a link to the video of that test. https://share.icloud.com/photos/07fr9jJZ5XIkhKHfhl5n_gD5g
 

I heard the “drone” change but that’s normal as far as I’m aware?

 

you should be able to tell better than I. If I need to redo the test with the phone hanging over the engine bay to better capture sound I can. 

[TripleC321]

I also applied the video tachometer suggested. I didn’t really get anything useful from pointing it at the engine bay. But I did measure the vibration of the IPC cluster somewhere around 120 RPM or 2 Hz. This is a rough measurement as it because harder to measure the closer I got. The vibration my body was experiencing sitting in the car affecting my ability to measure accurately. 
 

this was with the engine at 1200RPM

[Ronnie]

Until today I couldn't get the video to play. It might just be the video but it doesn't sound like my car. It has a deeper thud. Do you have a loud muffler on it?

[TripleC321]

17 minutes ago, Ronnie said:

Until today I couldn't get the video to play. It might just be the video but it doesn't sound like my car. It has a deeper thud. Do you have a loud muffler on it?

Which video are you referring to? The videos can sometimes take an hour to upload on my end and be accessible at the shared link. 
 

the exhaust on my car is stock, minus a replaced catalytic converter in 2017. 

[Ronnie]

2 hours ago, TripleC321 said:

Here’s a link to the video of that test. https://share.icloud.com/photos/07fr9jJZ5XIkhKHfhl5n_gD5g

This is the video I looked at.

[TripleC321]

13 minutes ago, Ronnie said:

This is the video I looked at.

Gotcha. Well that’s a video of the Rev while braking test you told me to do. 
 

do I need to redo it with the microphone closer to the engine?

[Ronnie]

No, it just doesn't sound right to me in the video. Does it accelerate and run smooth on the highway?