Machine shop called to tell me my 312 block has a sizable crack in the water jacket. I just pulled the engine out of my 56 merc parts car to find it has a 292. This will be a high performance build and crank offset ground to increase stroke. Now the question, am I better off cutting the crank down to 292, or align boring the block to the larger main size? I'm more concerned with doing it the best way rather than the cheap way.

I believe you find it's a better idea to turn the 312 crank mains down to 292 size ,bearings and the rear seal are easier to git and block is stronger . Make sure the machine shop turns the rear seal area correctly.

hoppys1956

Make sure also they turn the oil slinger down to 292 crank size also.

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

I'm in the minority here, but I prefer to bore the block to 312 main size.  That way I don't reduce the overlap between the throws and the main journals on the crank.  I don't bore the rear seal area, and turn the 312 crank's seal area to 292 size, and use 292 neoprene seals.  Which ever you choose, if the crank gets reground, make sure the machinist dresses a radius on his grinding wheel so that the original radii on the journals remain.  The two cranks that I have broken were regrinds with the radius gone.  The cracks started in the areas where the radii used to be.

John - "The Hoosier Hurricane"

John Thats one of the reasons I said about turning the crank down I kinda remember us talking about turning the cranks and you talking about trouble gitting shops to dress the grinding wheel to properly radius the crank throw,and what I've seen the main bearing and seals seem to be cheaper for 292's than 312's

HOP

hoppys1956

The overlap was my concern with the offset grind and smaller mains. Has any one had a crank fail that was properly ground?

I have not had one break, but I have found a couple with cracks forming in the radii after 3-4 seasons of drag racing in my supercharged 312s.  I finally adapted a fluid damper and the cracking hasn't shown up yet.

John - "The Hoosier Hurricane"

Total agreement with John about the journal radii.  Regardless of which tack you take on using the 312 crankshaft, be sure that the radius is maintained at the journal edges.

 

My own druthers for the cast 312 crankshaft is to cut the mains down to the 292 size as this allows the main bolt threads to be spaced further from the main bearing bore itself.  Bearing speed is the other consideration as the 292 mains do free up some additional horsepower.  On the flip side of all this is the overlap that John mentions but I’ve yet to have a problem with this to date when machining the cast cranks but journal filet radii is part of the equation here.  The other part of the equation is how finely the crankshaft and the related components are balanced.  As John mentions, there are some differing opinions on this and this one’s mine.

Lorena, Texas (South of Waco)

I too prefer to make the crank fit the block.  I am very adamant about the radius though, I don't know how many times I've had to tell someone their crank is junk because a crack has started in a fillit with no radius.  I was fortunate to learn a long time ago how important the radius is, the first shop I worked for just wanted you to dress the edge of the grinding stone with a diamond "free hand" this was quick but not good enough.

   God Bless.   Tim                           http://yblockguy.com/

350ci Y-Block FED "Elwood", 301ci Y-Block Unibody LSR "Jake", 312ci Y-Block '58 F-100, 338ci Y-Block powered Model A Tudor

tim@yblockguy.com  Visalia, California    Just west of the Sequoias

Jepito

What is your location? I`m in south west Ohio . I should have what you need , either a 312 block or C2AE ''292''  or other. If interested give me a call if no answer leave message & I will call back. Thanks  Harry Hutten 513-868-3311