Assembling parts for a stree/performance build for my 55. Have 292 blocks to choose from, but thinking about using a 312 crank. What is involved in the process? do I just have the mains turned down to stock 292 specs? What about the rods?

Has anyone out there done this to their 272/292 block, and what are the added benefits?

Dan

Daniel Jessup

Lancaster, California

aka "The Hot Rod Reverend"
check out the 1955 Ford Fairlane build at www.hotrodreverend.com

Daniel,  What you're suggesting is a common swap into the 272/292 blocks.  If using pistons with the stock pin location, then you'd want to use the shorter 312 (ECZ) rods or the C1TE truck rod.  If using custom pistons, then you'd have the wrist pins placed to suit whatever length rod you ultimately end up with.

Here’s some of the reasons I prefer to use the 312 cranks in the 292 blocks besides the obvious stroke increase.  (Some of this I copied from a similar post I did on the old forum)

1. First and foremost is the abundance of 292 blocks versus usable 312 blocks. And many of the later model pickup 292 blocks are capable of being bored out to +060 312 (0.110” over) after verifying cylinder wall thickness by sonic testing.  For that matter, many of the early model 292 blocks can be bored heavily if they pass the sonic check test.

2. Reason two would be the smaller main journal of the 292 having a reduced bearing speed versus that of a 312 which is worth a little bit of horsepower due to a reduction in drag.  The 292 and the 312 share the same rod journal size so no size difference there but you'll need to pay particular attention to the connecting rod length as the 292 rods would push the pistons out of the bore.

3. The 292 block is expected to be inherently stronger in the main bearing area than the 312 due to the extra material that’s available due to not having a larger main bore size. It must be remembered that the 312 main bolt spacing across the length of the hole is the same as the 292 but the larger size main bore gets the sides of the hole dangerously close to the main bolt threads which makes the 312 block somewhat weaker in this area.  There's been reports of a large number of 312 blocks cracked in this area which has been attributed to using the 292 main bolt torque.

4. And then another reason would be the cost of the main bearings; 292 main bearing sets are considerably less expensive than the 312 sets.  And if cutting the 312 crank down in the mains for the first time, you'd have the luxury of running standard size 292 mains leaving room for future grinds providing you ultimately don't run out of grinding room on the rod journals first.

As far as the cost of turning the 312 mains down to 292, it will vary somewhat from shop to shop but all that’s being removed is 0.125” maximum to get back to a standard size 292 on the mains. It would be ideal for the shop that's grinding the mains down to leave the oil slinger in place between the rear main and the seal.  Talk to your grinding shop to see what their capabilities are on this as it takes a narrow stone to grind down the rear seal surface to the 292 size while maintaining the oil slinger; not all shops will have this narrow a grinding stone.  But having the rear main crankshaft oil slinger missing should not be considered a show stopper if the grinding shop is not capable of keeping it in place.  I'm using the 292 neoprene rear main seal on my roadster's cutdown 312 crank that doesn't have the oil slinger with zero issues.

Lorena, Texas (South of Waco)

Ted - this is exactly the kind of info I was looking for. Thanks a mil'. After hearing much of what you have said - I will be looking to go that route. Anything to look for when it comes to checking out used 312 cranks? My biggest concern was the rods to use because I will be using stock pistons. Are the 312 and 292 at the same pin heights?

I have 4 or 5 blocks to choose from, they range from a 55 272 to a block that was in a truck in the late 50's. I also have some of the other goodies like the high ratio rockers, the 57 intake, and a couple sets of C and a set of G heads.

I am building a street/performance motor that will probably be seeing its fair share of highway miles and ultimately an a/c add on. Any further suggestions would be great.

You and John need to get together and write us a new Y Block Rebuild Book! I'd pay for it double!

Thanks, Dan

Daniel Jessup

Lancaster, California

aka "The Hot Rod Reverend"
check out the 1955 Ford Fairlane build at www.hotrodreverend.com

Besides looking at the overall appearance of the crankshaft and making sure it's suitable for regrinding, check for nicks and damage where the crank has been mishandled or in an engine that broke.  If the crankshaft is overly rusted, some of these problems may not be apparent.

If looking at cranks, carry a micrometer or dial caliper along with the journal specifications so the amount of undersize or past grinding can be determined.  Although the mains may have already been ground on heavily, they are going to be cut to 292 size anyhow so this shouldn't be an issue.  But the rods journals, if already cut to 0.030, could be a show stopper.  Ideally, you'd want to look for a crankshaft that's had minimal grinding on the rod journals so you'd have room to stay with the conventional Y-Block journal undersizes.  An alternative to saving a Y crankshaft that's been turned down heavily on the rod journals is to cut it down further to the common 2.100" or 2.000" sizes and use an aftermarket rod.  But at this point you're potentially looking at some custom pistons if you can not make the stock wrist pin location work out for you.

If you've got several cranks to select from, then pick the crankshaft with the best or most centered location for the main journal oiling holes.  When grinding the crankshaft to the 292 main size, the oil hole will tend to 'creep' back towards the journal's edge.  And if that hole is already off center and closer towards the journal edge by way of manufacturing variance, then that will become more compounded when grinding another 0.050"-0.060" off of the journals side.

Unfortunately, this next step happens after you've purchased the crankshaft and that is to have the crankshaft checked for cracks.  My preferred method is to have the crank sonafluxed where the crank is immersed in a solution and then examined in the dark with an ultraviolet light.  But the other methods of crack detection should also suffice.  Y cranks are not noted for cracking but needs to be checked regardless.

The 292 and 312 pistons share the same wrist pin height.  But.... not all 292 pistons will work with a 312 crank due to some varieties of 292 piston skirts being longer and allowing them to contact the 312 crankshaft counterweights.  The shorter 312 rods brings the piston in question closer to the crankshaft thus creating this scenario.  Modifying the 292 piston in question will get you around this but definitely dry assemble the engine beforehand so you haven't balanced the assembly before finding this out.

Lorena, Texas (South of Waco)