Appears to be original motor, 87K miles, so I would assume 187K,
Original Duraspark ing,
The timing is good, so I will assume the damper is good. And I believe the counterweight are mounted to the center part of the balancer, the outer ring slipping would only impact the timing.
Plugs and wires are acceptable,
The vibration is not on any particular cylinder firing,
The vibration is 100% of the time, just idling and as it revs up.
As you are driving, once up to 50 plus, it becomes more harmonic,
The Carb performs really well (Autolite  2100)
There is a tinny sound under acceleration 85 % of the time which made me think cracked flex plate, but it doesn't do it when torquing the motor by holding the brake.

I don't think it is anything like ignition, miss-fire, because it runs well and has good power.

I don't think it related to a bad cam loab as the motor is really quiet, and the times I have had a worn loab on a cam, I also has rocker noise.

When cranking the motor, it sounds like there's an alignment issue, sounds like a Chevy that need the starter shimmed.
 

Get a squirt bottle and fill with water.
When the engine is hot....give each exhaust port on the manifold a squirt.
IF one does NOT sizzle ....that's the weak cylinder...or bad plug.
Sometimes on a V-8 it is REALLY hard to diagnose if there is a miss or just a vib.
It's free.......and don't take much time....and will eliminate bad plugs(or wires)
6sal6

Mounts are good,

I'll try the water; I have an infra-Red heat gun as well.

All the cylinder compression readings were 140-150 (Cylinders 4 & 8 were 150, all others were 140.

All the plugs looked decent, if anything a little on the Hot side, just a little whiter than I would have liked.

We all like Photos, so here is what I'm working on. The frustrating thing about this, is this is the third one of these that I have had in the last 10 years and both of the others were short beds that I got talked out of, or into selling, and regretting it. I picked this one up because it is extremely clean with almost ZERO rust which is rare in our area. But now I am going to cut this on down to a short bed (why didn't I just keep the others)

For a brief moment ai thought about keeping it mainly stock, but the plan is convert to SWB, Crown vic front chassis, T-Bird independent rear.

'One of the coolest Ford trucks' I ever saw was...
a long bed (about that year)....slammed really low...with a really nasty sounding FE engine.... nice wheels and fat tarz !
That dude was  RIGHTEOUS !
6sally6

Nice truck.

PM sent.

Yea, there is a block plate between the block and flex plate, I agree on the firing order and mixed-up wire, that was one of the first things I checked. I know it's hard to describe and can be easily confused, but it doesn't feel like a miss fire or dead cylinder. It feels like a vibration in the rotating assembly.

The flex plate and starter need replaced, so I will pull it apart to that point and inspect everything and make sure all of the parts are correct dia, balance, and depth. Based on the cost of a stock replacement torque converter, I may change that as well. 

I have a 97 model 351 roller motor, standard bore in great condition that is my bucket list motor I want to build, but I would like to get this motor figured out and run it for a couple years while doing all the frame, chassis, and body work. 

I have done a manual 5-speed swap in everything I've built but would like to do a 4r70w (I want a nice comfortable cruiser). But with that I would like to do the drive line as well as the suspension and brakes in steps. I know it will take more time and probably cost more, but it's frustrating when you change everything from one end to the other and then you have an odd noise, vibration, issue, and you're scratching your head at where to start at which new upgrade bit you in the butt.

Plus, I like a challenge, so if this motor cost me a few hundred bucks and it's running smooth I will feel like I won.

Speaking of..........starters.
It almost looks like the teeth woulda engaged better withOUT a block plate!
Since ya gotta have that maybe....a starter that throws INTO the flex plate further.(like mentioned above 3/4" vs 3/8".)
Just a WAG on my part.
Once you've eliminated a mis-firing cylinder.....maybe swap out the balancer for a new on or a known good one.
Insure the RIGHT flex plate was put on the last time the PO had it apart. (ck to see if a weight may have come off the flexplate)
S'all I got........
6s6

Have you counted the teeth on flexplate?
Perhaps wrong balance as mentioned.

Last edited by Nos681 (1/25/2023 12:31 PM)

I would also check to see if engine thrust bearing is about gone. Had a 302 with C6 in a Bronco that got real noisy while braking. Timing chain was cutting into timing cover

I don't have much to offer on the vibration.  I too would love to build a short bed.  I've been following a couple of different ford truck FB groups.  The lack of space to work on projects is my biggest hold up.

kardad wrote:

We all like Photos, so here is what I'm working on. The frustrating thing about this, is this is the third one of these that I have had in the last 10 years and both of the others were short beds that I got talked out of, or into selling, and regretting it. I picked this one up because it is extremely clean with almost ZERO rust which is rare in our area. But now I am going to cut this on down to a short bed (why didn't I just keep the others)

For a brief moment ai thought about keeping it mainly stock, but the plan is convert to SWB, Crown vic front chassis, T-Bird independent rear.