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Ive got a 76 cutlass with a small block 350 and BOP turbo 350, all stock, i found alisting on craigslist of a 425 olds, did aome digging its actually a 1974 455, with 74 smog heads, but the guy swears up and down its a 425, how can i tell for a fact that its a 425, and how can i tell if the previous owner did it right and swapped crank, rods, and pistons?
Look at the deck above the water pump for block ID. Also l ID the heads, look at the head casting letters and numbers. Sounds like you may have done this already? Post the numbers here.
To answer the last part youd need to disassemble it.
Ask to hear it run. Take a compression check.
Last edited by droldsmorland; Sep 14, 2018 at 10:09 AM.
Ive got a 76 cutlass with a small block 350 and BOP turbo 350, all stock, i found alisting on craigslist of a 425 olds, did aome digging its actually a 1974 455, with 74 smog heads, but the guy swears up and down its a 425, how can i tell for a fact that its a 425, and how can i tell if the previous owner did it right and swapped crank, rods, and pistons?
The only way to tell if this is a 425 reciprocating assembly inside a 455 block is to measure the stroke. You SHOULD be able to do this through the spark plug hole. A 425 crank has a 3.98" stroke. A 455 crank has a 4.25" stroke. If this motor was assembled with 425 crank and rods and 455 pistons, the pistons would hit the head due to the taller compression height on the 455 pistons.
Are there casting numbers on the end of rhe 425 cranks and what are they? And if i happen to determine it is a 425 crank is it pretty safe to say whoever swapped it did rods and pistons because otherwise they just plain wouldnt work or the head would get smacked etc.
Sorry i guess i worded my first post funny the guy selling it knows its a 1974 455 block and heads but he says the previous owner swapped the internals with 425 internals.
Are there casting numbers on the end of rhe 425 cranks
If only it were that easy. The FORGING number (since all 425 cranks are forged, not cast) is on a counterweight. You'd have to drop the pan to see it. Again, the ONLY way to check this without tearing the motor apart is to measure the stroke through a spark plug hole.
Actually, there is one other thing you can try. If you have access to an inspection camera that can fit between the flexplate and the block, you might be able to see the notch in the crankshaft output flange. Cast 455 cranks have a "U" shaped notch like this:
425 cranks have a sharp-corner "L" shaped notch like this:
And for completeness, the extremely rare forged 455 cranks (don't hold your breath) have a rounded "L" shaped notch like this:
this engine was run in another vehicle so wouldnt that make sense to swap it right with the rods?
You realize that we've already spent waaaay more time talking about this than it takes to just slip a dowel in the spark plug hole and check the stroke, right?
You realize that we've already spent waaaay more time talking about this than it takes to just slip a dowel in the spark plug hole and check the stroke, right?
Well lets examine the situation shall we, i am trying to get as much info as i possibly can, the engine is currently 2 hours away from me ntm it will not turnover, so, i was trying to gather as much information as possible as to not get screwed over on this, thank you
Well lets examine the situation shall we, i am trying to get as much info as i possibly can, the engine is currently 2 hours away from me ntm it will not turnover, so, i was trying to gather as much information as possible as to not get screwed over on this, thank you
If it runs at all, the crank, rods, and pistons have to be matching. My comments in your other thread were because all you mentioned was a 455 block and 425 crank and rods. It sounded like a pile of parts, not a complete motor. Sorry, but the mind reading thing still isn't working. As for the quality of assembly in this frankenmotor, no way to tell without tearing it apart. You've now been warned.
