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I am planning to put a T-5 transmission in my 68 stang with a 289. I thought it was 28 oz. externaly balanced eng. Then I was told by the machine shop that a 289 is internally balanced and the flywheel is netural balanced. I have not been able to find that info any where else. Does anyone else have any info on this?
The small block fords are external balanced at 28 oz for the early years and 50 oz for the later years. Check out Tom Monroe's book on engine building.
Then I was told by the machine shop that a 289 is internally balanced and the flywheel is netural balanced.
Find a new machine shop...run away...quickly!!! Never call on these guys again! Sounds like they don't do much Ford work, I'd really find another shop that has Ford experience I wouldn't let these guys touch my stuff....ever.
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1966 Fastback
1966 Coupe
1998 GT
"Government is not the answer to our problems, government is the problem."
The 271hp/289 was internaly balanced. It had no harmonic balancer on the front, just a steel pulley. Is that what you have?
Actually the Hi-po had an external balancer as well and it was heavier than the run of the mill balancer. There is not enough room in the crankcase to balance a small block. All Ford small blocks to include the Cleveland family are externally balanced.
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1966 Fastback
1966 Coupe
1998 GT
"Government is not the answer to our problems, government is the problem."
Found this on another site. I mentions a heavier balancer, but it was inside the timing cover. My brother-in-law had a 1954 Merc with a 289hp and 4-speed and I remember it looking odd with just a cast pulley out front.
"In 1963 Ford released the 289 High Performance which produced 271 BHP @ 6000 RPM. Somewhat stronger connecting rods with 3/8" bolts, thicker main bearing caps, solid lifter cam, screw-in rocker arm studs, machined valve spring seats, forged steel exhaust valves, a dual point mechanical advance distributor, and better flowing exhaust manifolds round out the package. Those fitted to Shebly GT 350 cars rated at 306 HP also featured a high rise aluminum intake manifold and Tri-Y headers.
The 289 HP features a high nodularity cast iron crankshaft, Brinell hardness tested to ensure quality. To prevent 4th-order harmonic vibrations from destroying the crankshaft at higher RPM, the engine uses a different vibration damper and an add-on counterweight. A portion of the 28.2 oz.in. imbalance found in the normal small block damper is moved to the additional counterweight. Moving the mass in towards the front main bearing reduces bending loads on the crankshaft. The special damper also has a larger more massive inertial ring. The add-on counterweight is 0.150" thick. As a result a special crank sprocket is used, C3OZ-6306-A, itself being 0.150" thinner than the normal 289 sprocket. The counterweight is both keyed to the crankshaft and indexed to the sprocket with a 1/8" roll pin. The images below show the counterweight and sprocket with its roll pin hole, as well as a comparison of the the normal and thin sprocket. "
It depends on what the amchine shop meant. Were they going to turn and balance your crank and rotating assembly and externally balance it on top of that. That is how my 302 is setup
The HiPo cranks were of a slightly different metal but were cast in the same molds as the normal 289 cranks so were the same shape and therefore balance. As a result of being the 'small block' there wasn't room to completely balance them internally; they all had external balance hardware. The HiPo damper was much thicker but when combined with the extra internal counterweight at the timing chain I don't know that the overall imbalance was any different. My understanding is that the added mass changed the resonant characteristics of the crank assembly to allow sustainted higher RPMs. The internal weight also had to be used with narrower timing sprockets and therefore narrower timing chain.
I don't see why you couldn't use the HiPo balancing hardware on a standard engine but since the standard engine won't run at 7k I don't know what you would gain for the extra cost and effort. Better to have the machine shop balance the engine with the parts you are going to use (including flywheel and clutch, etc) which would cost less and probably give a better balance.
This is all very intersting to me. I have a 66 289 that when we bought it, was rebuilt with about 10k miles on it. Driving it at speeds of arounf 50pmh or higher, produces a harmonic vibtration. I first suspected the wheels - 4 lug-slotted for universal fit, and swapped with no change. Then, I had new gears put in the rear end, and a new drive shaft put in, still no luck. Then I changed the motor mounts and hamonic balancer (28.2oz). Still no luck. Someone here said change the tranny mount, but I haven't done that yet, and know I'm wondering if it a result of the rebuild?
289 engine balance internal or external? 
