Hello

i am rebuilding my first engine it is a 390 out of a 76 f150
i took it to the machine shop and he told me it was cracked at the rear freeze plug. he said he may be able to fix but wanted another opinion. so my question is if it is worth fixing a cracked block or if you are better of getting a new one. And if you don fix it could there be future problems.

Thanks
Green

 

I'd consider another block, pickyourpart special is 120 carb to pan so.. whats he want to "try to fix it" ?

 

Keep in mind the 360 block is the same as a 390 block. There's plenty of 360's waiting to grow up and become 390's with the right crank/rods/pistons

 

new block, unless machinest is top notch and has all the equipment to weld cast iron.
BTW where are you located, someone may ne able to point you in the right direction on getting another block.

 

i did my research when choosing a machinest and i think he is pretty good. i was told that it was a small crack on the exterior of the block next to a frost plug and he would only charge 85 for the fix. i think i will try it. i was wondering if i just make the antifreeze mixture like 75/25 if that would stop the possibility of it freezing and cracking again

 

repairing the block is no better nor worse than the welder doing the work. It is quite capable of being repaired and lasting forever.

 

75/25 might help in keeping the coolant from freezing, but not necessarily keep it from cracking again. A bare block from the junkyard is less than $50, and if he is boring out your existing block already, it wont cost much more to have another used block cleaned and mag'd. If the block checks out OK, I think you would be ahead a bit, but if it comes up bad, you loose on the gamble. In the factory repair manual ('74) there is a brief section on cracks. The fix, epoxy in the block. The repair is only doable if its in the water jacket, it has an illustration on where the repair is applicable. I am not sure I would have trusted epoxy from 30 years ago.

 

Listen to your machinist.

The outer water jacket is not structural and can be repaired by a competant welder.

The next question is wether or not there are any other cracks, will the machinist warranty his work?

 

Not all machinists are worthy of listening to. I have drive 3 hours to get a machinist that is worth two cents that don't do botchery and call it an engine.

 

i just got it back there were no other problems and the cracke sealed up perfect. thanks for all your opinions guys

 

How was it repaired?

 

it was welded im not quite sure what technique was used though