The 1993 302 in my 66 coupe has a vibration. From about 1700 to 2400 RPM. Go above 2400 and it smooths out. Feels worse when driving but is noticable when in Park. Not a bone jarring shake but it is annoying & can be felt in the steering wheel.
I'm pretty sure the flexplate is a B & M 50oz (a receipt for it was in the paperwork I got). It is tight & I don't see any cracks.
I don't know what the HD is.I looked at it on the car & it looks fine and pretty new.
I've had the car 5 months. The 5.0 was installed 1 year before I bought the car.
If the HD was a 28oz wouldn't it have killed the bearings by now?
Also I don't recall feeling this vibration when I bought the car.
If it's not the HD, flexplate oraccesories is there anything else I can check besides the rotating assembly?

 

Look at my post about rpm related vibration. I have been tracking down a vibration in my Cleveland that hits about 2500 and stops about 4000. The main culprits are the wrong flywheel and harmonic balancer for your crank. I replaced both and it did not fix my problem. Another cause can be a bent crank. That cannot be determined until you have it miced. Accessories and accessory pulleys can also cause a vibration. Driveline can also be the problem if it only does it while in gear rolling down the highway, but it sounds like your's is isolated to the engine. Wish I could help more, but I cannot find mine either. At some point you just have to live with it or replace the engine.

 

We've been working on Urban Cowboy's problem for quite awhile now. His next test is to take off the fan belts one at a time to see if one of the accessories is causing it. Most likely it's an internal rotating assembly porblem, but we just can't figure what it would be without tearing the 351 apart.

 

I have a question about the same thing.
I took out a 6 and dropped in a good running 302. I used the 6cyl torque converter and the car has a very outof balance feeling vibration. Could it be the converter?

 

Someone correct me if I am wrong, but I think TC and Pressure Plates/Clutches are neutral balanced (not balanced for a particular engine); however, the flywheel and I think the flexplate are balanced for a particular engine. Almost all engines are balanced differently and sometimes different years of engines are balanced differently, so it is almost an art to know what parts are interchangable when it comes to correct balancing. To confuse the issue even further, some engines are interanaly balanced, so they require a neutral or 0 balance flywheel and HB.

 

I've been working on the car today & have a little more info.
I hooked up a vacuum gauge and watched it while revving the motor.
At idle the needle bounces a little but that may be normal.
At about 1700 the vibration is there and I noticed the vac gauge needle was not steady. Around 22 hg and moving about 2-3 hg. Increased RPMs to 2000, smoothed out some, vacuum steadier. Increased to 2500, no vibration, vacuum gauge steady as a rock. Have a smaller vibration at around 3400 RPM.
I'm not sure if I have a harmonic vibration or a vibration caused by motor missing a little.
What would cause a slight miss at 1700 RPM but rut run great at higher RPMs?
Would a bad HD or whatever cause the vacuum to vary?
I have a new dist. cap & rotor, new Pertronix Ignitor & coil (and I ran a 12V wire for the Pertronix), new wires & sparkplugs gapped at .045.
I have a Holley 1850 and I have adjusted the floats & air/fuel per Holleys instructions.
I ran some Sea Foam through it.
I have about 18 hg vac at idle. I have the timing set at 12 degrees.
Any thoughts?

 

Good idea about the vacuum gauge. I have to try that to see if I have the same problem.

Sorry, no idea why your vacuum would fluctuate with the vibration. I would not think the HB would affect the vacuum in the least. The only thing I can think of that might do that would be some variation in the cam timing possibly at those rpms. All timing chains have some play, so maybe the timing wonders a few degrees at thoserpms thus creating a vibration? I am really guessing.

Anyone know what would cause vacuum variation at a steady rpm? How can you check timing slack or wonder?

 

You have those plugs gapped just about as far as the pertronix will allow. My suggestion is to re gap them to about 0.040, and set your timing at 10 or less.

 

Update.
I've been checking her out again today. After trying some other stuff I decided to remove the V-belt & try it. The evibration was 90-95% gone to my surprise. Maybewe areclose to solving this problem. I think I can rule out the alternator as the cause since that is the 2nd alternator & it vibrated with both. The water pump spins nice & has no play so it seems OK. But I found 2 possibilities.
First I noticed the HD (which I think is a new aftermarket one) was running smooth & true, but when I watched the pulley it has a very slight amount of wobble. Not much but I can see it. It looks like the one from the original 289. I can't see it's bent anywhere but it is covered in thick globby paint and maybe that made it not be mounted flush all the way around??. I'm taking it to work tonight and I will sand blast it & try to put it on a lathe so I can spin it and see if it is wobbling.
Also it has the old fan blade from the 289. One fin is bent slightly and another is bent about 1/4".
Do you think that might make the vibration? I was thinking about getting a flex fan or going electric one day anyway, so I might be getting one now.
Which do you think is the more likely culprit?

 

That is a deffinite issue,,,, no doubt an I-6 balancer will cause a vibration on your V-8,,, change it or you will suffer engine damage...