using a late 60s 302 , out of a boat that had 400 hours ,trans is a c4 . when we start the motor , there is a bad vibration , so bad it tears the trans apart when driven ,, two trans have been ruined . must be a balance problem , owner thinks the motor is internally balance .I told him to check harmonic pulley to see if it has spun , any ideals ?

 

Harmonic balancer or flywheel/flex-plate. Unless something is bent in the engine.

Did you use the same torque converter in both transmissions?

 

Not internally balanced. There are also early and late balances.

 

Must make sure both harmonic balancer and flex plate match the engine .
You will need to work out if it's early 28oz or later 50oz balance .

 

same flex plate and converter

 

What sort of damage is happening to the trans ?

 

The 28 and 50 oz flex plates are definitely not the same. I think 50 oz are late 70's and newer, so if you are sure it's a 60's engine you should be in the clear with a 28 oz. But there are a bejillion combinations of balance, ring gear tooth count, converter bolt pattern, etc. Thanks, Ford!
https://www.summitracing.com/parts/s...view/make/ford

 

how do I find when the motor was built , numbers on block , where to find what they mean?

 

These letters are above the starter

More info on what the characters mean: https://www.enginelabs.com/engine-te...ers-1952-1996/

 

Casting codes on early 302's are located behind the starter on the right side of the block. You need to find the cast identifier/engineering number, and the date code that looks like a little tag screwed onto the side. The info in the "it still runs" link above isn't entirely accurate.



In the above photo, the engineering number starting with C5 shows the engineering was done in 1965, but the date code 7A25 shows the block was cast in 1967 January 25.

 

Is it far enough off I should delete it?

 

You could. There's certainly other websites with more correct info. The worst part was where they said the engineering number was the manufacturing date, which is totally wrong. I hate seeing that kind of misinformation propagated.

 

Was it rebuilt (or otherwise worked on) after being pulled out of the boat, and before you put it back into use? The change from 28oz balance to 50 oz occured in 1981. The first thing I'd check is to make sure no one swapped flywheels or balancers on you with later parts. The next thing is to find out if there's any odd marine specific stuff on it or in it that we wouldn't know about, being car guys. Was it originally reverse rotation or anything crazy like that? Beyond that, all I can think of it open it up, tear it down for inspection and see if anything's bent.