I have been chasing this vibration for months. Vibration starts at about 3300 RPM and runs all the way to redline. It does NOT matter which gear, how fast the car is traveling, clutch in, clutch out, or stationary. The vibration FEELS like what you would experience with an unbalanced drive shaft...but, it isn't driveline related.

I have changed the alternator due to slight shaft wobble - no change
I have changed the water pump to a correct '69 pump to ensure the fan is perfectly centered - no change
Correct, unbent, unbroken 5 blade fan
New, internal balance harmonic balancer (8") - no change
Replaced the previously installed resurfaced and balanced flywheel and pressure plate with a new RAM units - no change
New pilot bushing
No bent or wobbling pulleys
New engine mounts - no change
New trans mount - no change
Ignition wise, new, correct gapped plugs. New wires. Distributor is a stock unit with new points and condenser set up per specs. Car doesn't pop, or seem to miss. No hesitations no stumbles. Nothing.
Under 3300 RPM, its smooth as butter.

The block is the numbers matching that was rebuilt in the late 1980/early 1990's. It is .030 over. Flat top pistons, stock rods, stock crank, stock intake, carb, exhaust. Otherwise, the build is unknown.

I have a horrible feeling that there is something internally wrong and I am going to have to rebuild the engine...but, perhaps somebody out there has experienced this before and has a solution.

Thanks for any input.

Sammy

 

If those .030 pistons were heavier than the originals and the engine wasn't balanced..............well your going to be building a new engine.

 

Did it ever run smoothly over 3300 during the time you have owned it?

 

I do recall one time in particular that it ran to redline smoothly. I only remember that because I told my wife how amazing it was. I think after that is when we started going after things like the clutch package, shimming the distributor, changing the rear trans bushing. My first thought was the original flywheel wasn't surfaced and balanced correctly. But, after installing a new clutch package, the issue remains. Not sure if a bent distributor shaft could cause such a vibration...Didn't notice any issue with it besides the end free play which was shimmed to Lars spec.

 

Check your exhaust and exhaust hangers. Also check your exhaust clearances. You want around an inch of clearance all around (if you can get it).

 

It is a great thought...I checked them yesterday. At the trans all is secure and plenty of space as they pass through the frame. The rear...well, maybe .75 inch between the bottom of the spring and and the top of the pipe. I also run full chambered so tons of clearance elsewhere.

I may throw it back up on the Quick Jacks and just check again. You never know.

 

After all those changes, I'd be pulling the engine before it turns into a handgranade. I forsee a rebuild in your future.

 

When did the vibration start? Has it always been there since you bought it? If it is a new problem after your purchase you need to look at what you did to the car before the vibration started. I recall you had some carburetor and maybe ignition quirks. Or it's possibly a new valve train problem like a broken valve spring.

 

carb is sorted out. Valves...well, it was there with the original heads and remains with the new heads. Doesn’t mean there isn’t a broken spring now...easy enough to to take a look. Barring that, it leaves just the ignition...I keep coming back to that as a possibility but can’t seem to make the leap that a bad ignition would cause this issue at the exact same RPM every time. Might be my own ignorance on the subject.

 

Not always. The engine in my vette has been running fine for 6 years without any vibrations. also .030 flat tops I bought the freshly machined shortblock the shop owner told me had a ring break within a couple thousand miles with the rotating assembly. But upon pulling apart for inspection I found the bearings full of metal and it grooved up the crank. I ended up cleaning up, rehoning and replacing the crank with a scat crank and never rebalanced the rotating assembly. In hindsight it would have been a good idea to have it balanced but...

 

Long shot but stick a boroscope in the pan or take the pan off and look for a slug of Mallory metal........years ago, slugs of Mallory that are used to balance assemblies with heavy pistons and rods were installed in the crank radially, as opposed to horizontally though the crank counter weight as everyone does now. If a slug was not welded in properly......the crank could fling it out and instant vibration. This is rare, but I have seen it before.
I would pull the pan personally and see if that has happened or a piece of piston skirt broke off.....if a piece of skirt breaks off on the non-thrust side, it could run for years before anyone ever knew but be 30-40+ grams out of balance.......rule of thumb is 50 grams heavy or 25 grams light is acceptable for street engines at the crank on the crank bobweight, so if the crank was on the the heavy side and a skirt breaks off then it is a definite maybe.
The fact that it happens at 3300 and higher says to me rotation related, not exhaust or ancillary components.
Also, do a compression check to see if you if you have one that is way off.......

Jebby

 

I've never seen mallory added in a 350 originally with cast dished pistons then rebuilt with a flattop piston which is heavier than the dish piston. What I have seen and done is weld the factory balance holes on the end counter weights to add weight to the counter weight side of the crank to balance the assembly. I know when I balance a engine which I do often, I would never leave the throw side of the crank heavy, not even a gram, I always leave the counter weight side heavy by 2 grams.

 

I guess I should have cleared up that the "acceptable" tolerances are 25/50 from a purely mass rebuilder standpoint......and yes the +2 on the counter weight is always what you shoot for in a precision shop. I balanced over cranks for World and my other employer years ago and 2 grams was the number. Even the program on the balancer wanted 2 grams to show a "good part" on the screen.
The Mallory suggestion is a long shot I know......just a flight of ideas......

Jebby

 

Got it neighbor.

 

In my opinion, a unbalanced rotating assembly should vibrate at all RPMs. Not just the upper end.

You installed a resurfaced flywheel and a new clutch. Both will vibrate engaged or not engaged. I would suspect something inside that pressure plate. Perhaps a broken spring, or the fingers, throw-out bearing area, weights, etc.

With the vehicle up on ramps, I think I would remove the inspection cover and have someone bump the IGN key while you do a visual inspection. In neutral, both clutch out, clutch in. You can always by-pass the neutral safety switch if you have to.

In another post was a question on flywheel alignment. Was a dowel used?

 

I had a similar issue years ago and chased a few things. I ended up finding a motor mount was beginning to fail and the fan was touching the shroud at higher rpms. Might be worth a look as you only see this when the motor torques over.

 

Would a poorly functioning ignition cause this issue? The engine does have new plugs, wires, cap, rotor, condenser and properly shimmed. Coil is also new.

I have not performed a compression check.

 

Ill check the shroud and fan edges but the motor mounts are new Moroso solid mounts.

 

There was no dowel to begin with and upon further research it seems to not have ever been used in the Gen 1 350. Even with a zero balance crank and flywheel, would the orientation matter?

 

Pan has been off recently to repair a leaking seal. Nothing in the pan.