340 Engine Shake

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plumkrazee70

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I am moving over to this forum from the 4 speed forum as I have determined that my issue is not transmission related.

I have a 70 Dart 340/4 speed. The motor was out last winter for the 4 speed install and while.it was out I installed Edelbrock aluminum heads and a lunati -10200703 cam.

I broke in the cam fine, but it has an intermittent shake at idle. It shakes so bad that shifter moves all over, but it will smooth out above 1100+ rpm. I first noticed it when I had it in jack stands to verify the clutch engagement and the driveline was rattling like crazy (intermittent).

I removed the driveline installed a slip yoke and the shake is still there.

340 .040 over
Edelbrock aluminum heads
Lunati cam (number above)
Air gap
Fitech EFI

I've verified timing, played with the idle tune, double checked firing order, swapped plug wires and nothing changes.

I'm at a road block as I don't know where to go from here. I need some help.
 
Ok Plumcrazee70,

A few questions:

Forged or cast crank?

What harmonic balancer are you using?

Is the car an original 340 4-speed car?

Did you have the EFI on it previously?

What motor mounts are you using?
 
Sounds like a classic balance vibration from mismatched parts such as harmonic balancer, flywheel and such.
 
Ok Plumcrazee70,

A few questions:

Forged or cast crank?

What harmonic balancer are you using?

Is the car an original 340 4-speed car?

Did you have the EFI on it previously?

What motor mounts are you using?

Forged crank
No. /6 auto car. Has 68-72 K member now
Neutral balancer (brand unknown)
New build never had anything but EFI
Rubber biscuit mounts that are new.
 
The motor was put together quite a few years ago, so going by memory, but here are some pictures.

IMG_20130202_162447_939.jpg


IMG_20130202_162453_682.jpg


IMG_20130204_193539_335.jpg


IMG_20130204_193545_629.jpg
 
In the fitech dashboard, do you see anything change when the shake happens?
Does afr suddenly drop, or rise? What about map?

What about exhaust LEAKS? I was convinced I had none, but I did and the symptoms were similar to this. Of course any issue with the fitech and the idle would do something similar..
Do you have a vacuum line hooked to your fuel pressure regulator?
 
In the fitech dashboard, do you see anything change when the shake happens?
Does afr suddenly drop, or rise? What about map?

What about exhaust LEAKS? I was convinced I had none, but I did and the symptoms were similar to this. Of course any issue with the fitech and the idle would do something similar..
Do you have a vacuum line hooked to your fuel pressure regulator?

That's the thing, there are no visible signs. I did a data log and nothing changes. No dips in vacuum, AFR, rpm, nothing. I also used the large Guages feature to monitor that while it happens and no changes. I don't think I have any exhaust leaks. I used remflex gaskets on headers and collectors, everything else is welded. What is a way to check check for exhaust leaks?
 
That's the thing, there are no visible signs. I did a data log and nothing changes. No dips in vacuum, AFR, rpm, nothing. I also used the large Guages feature to monitor that while it happens and no changes. I don't think I have any exhaust leaks. I used remflex gaskets on headers and collectors, everything else is welded. What is a way to check check for exhaust leaks?

Have a friend hold large cloths/rags/plugs of some sort, and close off the tailpipes, you move around listening for leaks, they will be quite aparent.
Caution, be quick, those cloths get hot fairly fast.
 
Have a friend hold large cloths/rags/plugs of some sort, and close off the tailpipes, you move around listening for leaks, they will be quite aparent.
Caution, be quick, those cloths get hot fairly fast.
Damn! Kinda old school there! Dig that!
 
That's the thing, there are no visible signs. I did a data log and nothing changes. No dips in vacuum, AFR, rpm, nothing. I also used the large Guages feature to monitor that while it happens and no changes. I don't think I have any exhaust leaks. I used remflex gaskets on headers and collectors, everything else is welded. What is a way to check check for exhaust leaks?

With the car cold, and you key on the system. What does afr read? Don't start it, just key on.
Should start at 14.7 then climb to 20.1 and stay there..
A bad sensor will just stay at 14.7

I'd do as inertia suggested to check for leaks.
 
Would a mis balanced engine smooth out beyond idle?


I'm with RustyRatRod on this one.

First , start the engine. go under the hood and rev the engine and look at the harmonic balancer. rev the motor to the rpm where you notice the shake. Is the balancer rotating smoothly or is there a wobble? Even a slight wobble and the balancer may be toast. Are you certain you have a correct flywheel for an internally balanced engine? How tight was the pilot bearing when you installed it in the crank? I'm guessing there were no issues with the drivetrain before you put in the 4-speed so the vibration is related to the crank, harmonic balancer or the flywheel balance.
 
I'm with RustyRatRod on this one.

First , start the engine. go under the hood and rev the engine and look at the harmonic balancer. rev the motor to the rpm where you notice the shake. Is the balancer rotating smoothly or is there a wobble? Even a slight wobble and the balancer may be toast. Are you certain you have a correct flywheel for an internally balanced engine? How tight was the pilot bearing when you installed it in the crank? I'm guessing there were no issues with the drivetrain before you put in the 4-speed so the vibration is related to the crank, harmonic balancer or the flywheel balance.
Definitely, if no prior issues, anything Switched out After the Swap would be Highly Suspect.
 
I'm with RustyRatRod on this one.

First , start the engine. go under the hood and rev the engine and look at the harmonic balancer. rev the motor to the rpm where you notice the shake. Is the balancer rotating smoothly or is there a wobble? Even a slight wobble and the balancer may be toast. Are you certain you have a correct flywheel for an internally balanced engine? How tight was the pilot bearing when you installed it in the crank? I'm guessing there were no issues with the drivetrain before you put in the 4-speed so the vibration is related to the crank, harmonic balancer or the flywheel balance.

Here's the thing. It shakes at idle raising the rpm just off idle, and the shake goes away. I'll take some videos of the balancer. I am certain everything is for a neutral balance crank.

What I'm not 100% sure of is:

Did the machine shop balance my rotating assembly. It's been so long. The a roller bushing was used in lieu of the pilot bushing. This is a new build so now way to know really anything before.
 
Get a closer shot of the crankshaft parting line on the crank throw, please. It appears to be a forged crank, but lets be certain.

Yes, that's the way an out of balance engine will respond. Shake at low rpm, then get much better or disappear, then probably reappear somewhere higher up. That's sure what it sounds like. Another possibility is a broken valve spring. That could cause a skip down low and when rpm increases, compression can blow the valve back shut and make the skip disappear. I've seen it several times.
 
Get a closer shot of the crankshaft parting line on the crank throw, please. It appears to be a forged crank, but lets be certain.

Yes, that's the way an out of balance engine will respond. Shake at low rpm, then get much better or disappear, then probably reappear somewhere higher up. That's sure what it sounds like. Another possibility is a broken valve spring. That could cause a skip down low and when rpm increases, compression can blow the valve back shut and make the skip disappear. I've seen it several times.

I took the valve covers off yesterday and didn't notice anything broken as I thought the same thing. Is there something I can do besides a visual? Here is all my crank pictures that I have.

IMG_20130202_162441_317.jpg


IMG_20130202_162447_939.jpg


IMG_20130202_162453_682.jpg


IMG_20130204_193539_335.jpg


IMG_20130204_193545_629.jpg
 
I dont think its balance related as you look to have the stock rods and forged crank. Stock flat balancer? Get it shaking at idle and start pulling plug wires one at a time. See of anything changes. You could be losing a cylinder due to a wonky distributor bushing or something. Your O2 sensor will tell you if you lose a cylinder as it will go rich without combustion. Are you absolutely sure you got 5 and 7 plug wires correct? Bit me twice!
 
I dont think its balance related as you look to have the stock rods and forged crank. Stock flat balancer? Get it shaking at idle and start pulling plug wires one at a time. See of anything changes. You could be losing a cylinder due to a wonky distributor bushing or something. Your O2 sensor will tell you if you lose a cylinder as it will go rich without combustion. Are you absolutely sure you got 5 and 7 plug wires correct? Bit me twice!
The Spark Drop is a damn good idea. If it's there, Your gonna know!
 
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