390 shakes at 1000 rpm – 1500 rpm – 2000 rpm, runs smoothly at 3000-3500 rpm.

[SReist]

I had a vibration/drone in my 428CJ for years. I had the stock pistons replaced with forged TRW's on the rebuild. The machine shop that did the work said I didn't need it balanced although I wanted it done. The machinist was an old bastard set in his ways and no one knew anything but him. Well the engine shook but I never drove it much and it used oil from day one. It finally shook the
damper loose and just about screwed up the key way. Took one of my spare CJ blocks up to Barry and had him put in a new Scat stroker rotating assembly. That was the best money ever spent
on that car. Smooth as silk and never used oil, ever. The number matching motor is now on a stand out of harms way. The stroker is just a joy to drive. The moral of this story is always have
them balanced. That's one thing you can rule out when chasing problems. Good machinists/ engine builders like we have on this forum are a huge advantage. Steve

[Clark Coe]

Clark, my mistake, sold in KS, made in Mexico.  I have used a few of these and they are nice.  I don't pick them for strokers, only because most of them live up near 6000, but wouldn't think twice on a street GT.

Regardless, there are a ton of quality big balancers out there for a stock-ish 390 that work real well, I wouldn't spend more than 100 unless you are planning a high rpm engine or stroker later

https://aacincdirect-com.3dcartstores.com/1968--1976-Ford-360-390-428-Damper_p_61.html

The ones I had all came out right for TDC, and have graduated timing marks and were balanced correctly when stuck on the crank during balance

Ross, thanks for the referral. To check on availability of a 390 balancer. I called Advanced Automotive Componets, Saturday afternoon and someone actually answered the phone and confirmed in-stock availability....I was impressed. Got one ordered on their web site.

I had a vibration/drone in my 428CJ for years. I had the stock pistons replaced with forged TRW's on the rebuild. The machine shop that did the work said I didn't need it balanced although I wanted it done. The machinist was an old bastard set in his ways and no one knew anything but him. Well the engine shook but I never drove it much and it used oil from day one. It finally shook the
damper loose and just about screwed up the key way. Took one of my spare CJ blocks up to Barry and had him put in a new Scat stroker rotating assembly. That was the best money ever spent
on that car. Smooth as silk and never used oil, ever. The number matching motor is now on a stand out of harms way. The stroker is just a joy to drive. The moral of this story is always have
them balanced. That's one thing you can rule out when chasing problems. Good machinists/ engine builders like we have on this forum are a huge advantage. Steve

Hello SReist. I do wish I had the money in 1980 to balance this engine. I am really hoping a new balancer fix in my engines 2000 rpm shake.
I do plan to follow your path to a 428 stroker. I have three 428 industrial motors in storage that need to be disassembled and inspected for a usable block. There is 462 stroker in my future.

[Clark Coe]

No joy!  Installed new balancer, but the 390 motor in my Mustang still shakes at 2000-2400 rpm! 

Last night I installed a new stock balancer from Advanced Automotive Components in McPherson, Kansas. Then today, with the Nebraska outside temperature at 8 degrees Fahrenheit, I opened the garage door and started and warmed up the motor at idle, only to confirm the 2000-2400 rpm vibration remains the same. Engine continues to be much smoother at 3000-3500 rpm.

Next, I plugged all vacuum hoses (power brake booster, PVC valve and tilt wheel vacuum storage canister) attached to the Streetmaster intake. Disappointingly, the 2000 rpm shake remained. Vacuum at 550 rpm idle remains a very steady 17 inches.

The new balancer came with deep stamped timing marks to 30 degrees. Top Dead Center precisely aligned with the timing pointer. For $69.50, this was a well-made balancer. Like Ross said the original 53 year old balancer was junk, I had to remove the crank pulley to be able to see the rotten rubber ring. It was bomb just ready to destroy the radiator, fan and pulleys.


I wish I had spent the extra dough to have this engine balanced when I built it in 1980. I was short of funds at that time to spend more than I did. Given that it was a 9.5 compression, mild cam street build, not balancing seemed like a reasonable gamble…guess not. Do not want to disassemble this engine, has even compression, does not smoke or does leak oil.

Is there anything more to check?

Thanks for everyone’s input.

Clark

[gregaba]

I would remove the clutch etc and run it again. I know what a pain it is to do especially when it is 9 degrees outside but I suspect you have an unbalanced clutch assembly.
With the tranny pulled back and no clutch assembly on the engine then it is in the engine.
These problems are a real pain to figure out.
Greg

[My427stang]

Clark, I am buried this week but may have some time next Sunday if you want another set of eyes on it.

[GerryP]

Just to rule it out, unplug the vacuum advance and see if that makes any difference.  I think you're looking at a mechanical imbalance but you for sure want to make sure you've snatched the low hanging fruit.

[Clark Coe]

I would remove the clutch etc and run it again. I know what a pain it is to do especially when it is 9 degrees outside but I suspect you have an unbalanced clutch assembly.
With the tranny pulled back and no clutch assembly on the engine then it is in the engine.
These problems are a real pain to figure out.
Greg

Greg, thank you for the suggestion. I have had two different, complete flywheel/pressure plate/clutch disc assemblies in my Mustang. The all Ford component flywheel assembly installed in 1980 was dynamically balanced by a reputable shop and the new, last year McLeod flywheel and 26 spline diaphragm plate/clutch assembly from Modern Driveline. This vibration has deviled me with both assemblies. I suspect either hard parts imbalance in the engine or a fuel distribution/calibration problem with the carburetor.

Just to rule it out, unplug the vacuum advance and see if that makes any difference.  I think you're looking at a mechanical imbalance but you for sure want to make sure you've snatched the low hanging fruit.

Gerry, I did not mention it, but I did try disconnecting the ported vacuum advance line and it made no difference. I have been thinking about pulling all of the plugs and to read on their condition and color.

Clark, I am buried this week but may have some time next Sunday if you want another set of eyes on it.

Ross, that would be great if you could spare some time. My Mustang is in an insulated and heated garage. It is a balmy 45-50 degrees F out there...lots better than 48 years ago when I wrenched on this car on my father's farm, in a converted chicken shed with a Knipco kerosene heater. That garage had holes in the foundation that a possum could climb through. It was drafty enough that there was no chance to be overcome by combustion flumes from the kerosene heater.

Thanks all.   Clark

[chris401]

.

[machoneman]

Beg, borrow or steal an known good carb just for giggles?

[My427stang]

Clark,

I got your message and will shoot you an email.  Good advice here on the forum.  I would start this week by looking close at the distributor cap and rotor for tracking, potentially the coil for arcing to the intake, maybe check resistance of the plug wires and separate them, ugly if required, to ensure no cross fire

I do have both an operable 1850 and 3310 if it comes to that, but the vibration at that high of an RPM seems more of a crossfire, scatter, or dropped spark to me, at least without hearing it

I would also be very surprised if it was a balance issue, assuming it's a 390 crank.  It takes a bunch of weight to make them shake when everything is zero from the start, unless you have a broken skirt, etc.  Although, if nothing else found, you could check crank end play in the car to see if at an early time in the rebuild, you took out a thrust bearing.  Not generally a shake, but if things can move around, sometimes they can do funny things

[Joe-JDC]

Any unbalance would get worse as the rpm increase, and would not go away at a high rpm and come back in.  Balance does not come and go in rpm changes, it magnifies itself with rpm.  Joe-JDC

[Tom Gahman]

Have you checked for a sacked out mount, or a line or hose or anything fouling the body?

[wayne]

I know its a 390 but if you still have the 428 weight and can bolt it on not sure if can get to it with bell on. See if shakes more or less it will cost nothing just to see.

[Blueoval77]

Just for reference I swapped a 300 inline 6 for a 351 W many many years ago and being young used the 6 banger flywheel and clutch and the whole thing. What could go wrong ?
It has a vibration exactly like he is talking about here and yes Joe , I know it makes no sense but it did go away with more rpm.... It was an old 4x4 truck and I was in my 20s so how much it went away is up for grabs but it certainly lessened to the point that the guy that owned the truck didnt want to spend the money on the right wheel and swap it.

[Joe-JDC]

Did you check your pilot bushing/bearing?  Worn or missing needles can let the trans input shaft wobble/run out of round and chatter/or cause imbalance.  Joe-JDC