I just pulled the oil pan off of my 318 to install an oil pump and noticed that the front and rear rod journals were drilled like the early 340s.It is definately a forged crank.The block was cast in ?/14/72 the month casting was omitted.Front of block JM 318R 40773161.This eng was in a 68 Dart Post project car that I bought..The engine came out of a 72 or 73 Scamp. The K frame from the Scamp was LBP with disc brakes.It also had a front sway bar. I know that Mopar sometimes cleaned the parts shelves from the previous years. Any input?

Sounds to me like the engine has had major surgery at some point. Been many 340/318 shaft transfusions over the years.
and some definitely came with a steel shaft.

Some 318's came with a steel crank!

ive owne to date 2 68 318 with steel cranks ,
and bushed rods,,!!
right out of fact

318's of that era were cast crank in a Scamp. Nice find, but not stock.

I did just the opposite. I put a truck 318 steel crank in place of the cast crank in a 340 i had.

Were any 318s drilled or is it a 340 crank?

Might be 273

Randy

I've never had 318 and 340 cranks side by side. What is the difference exactly between a 340 steel crank and a 318 steel crank? Are the harmonic balancers similar?

biggest difference is balance, 340 rod and piston combo is more than the 318's in weight.

Aren't the balancers and rods the same between steel crank 318s and 340s? I,ve never seen a diff. ozz

Early teens had lighter rods, later on they commonized to the heavier rods. Piston wieght is different too, 318 is lighter.

As for balancer, not 100% what, if any, difference there is. I don't have a parts book handy to see if they are the same number or not.

No one has answered my main question:Were 340 cranks the only SB cranks that were drilled?

Stop yelling .... francis I can here you just fine

looks like something to sell on ebay , must be a 340 crank

I believe he is refering to the through drill on the front and back crank throws (1+"). The 273 and 340 steel cranks were drilled. The 318 steel crank was not.

Randy

Its been a few years(20+) since i had the two cranks side by side , but I seem to recall something about the 340 cranks being radiused and the 318 not or very little . Been a while so I could be wrong.