Will std. 312 pistons work in a 292 block? A 312 crankshaft and rods are to be installed in a 292 block. The 312 crankshaft has been turned down .125 on the 312 mains including the rear main seal journal. A good friend of mine asked me this question and I told him that this would work. The machine shop was unsure if you could use 312 pistons because of the deck height. I hope Iam right.

                                                                            Andy of Mayberry

Yes, a 312 piston is .050 oversize from a 292 piston. The 312 uses shorter connecting rods to compensate for the longer stroke. The build-up that you describe requires the 312 connecting rod with stock-type pistons.



So, you could use 312 pistons as a .050 oversize 292 piston. I think the pistons are more expensive and the rings might be different. A .060 over 292 piston might be a better choice with either a 292 or 312 rebuild; cheaper pistons and rings.



See John Mummert's web site for technical details.




Best regards,



Paul Menten

Meridian, Idaho

Ditto on Paul's “Yes”.  272, 292, and 312’s all share the same wrist pin height or location.  As a general rule, you can use 312 pistons with a 272/292 crankshaft and 292 rods but you may have crankshaft counterweight clearance issues when using a 292 piston with a 312 crankshaft and 312 rods.  The distance between the wrist pin and the lower pad and/or skirt on the 292 piston is generally more than what you’ll find on the 312 pistons.  It’s that increase in pad thickness found on the oem or exact replacement 292 pistons that may prove troublesome when trying to use the shorter length 312 rod.

Lorena, Texas (South of Waco)

Thanks Ted and Paul for the 312 piston info!! Should the rear main seal be turned .125 to make it 292 specs or should the machine shop make it a couple (.002) larger than the main journals so maybe it would seal better?

  Congrats to Ted and the rest of the EMC crew for making that 375 cubic inch really perform!! 524 H.P. on pump gas and a vacumn secondary carb. What month Popular Hot Rodding has the EMC results?

                                                                                    Andy of Mayberry

Craig, the rear seal is not the diameter of the mains. I would need to check but I think the 292 seal is 2.620" and the 312 is more than .125" larger than that.

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

John, Please let me know what the rear main seal seal diameter should be if you use a 312 crank in the 292 block. Thank you.

                                                                 Craig Seyfried

Factory seal diameter for a 272/292 is 2.620”.  Although the 292 neoprene rear main seals give no problems with the seal journal being at ‘spec’, there’s no reason that the journal diameter for the seal cannot be as much as 0.005” over spec.  That only makes the seal 0.0025” higher per side which isn’t much but may give some additional latitude once wear starts setting in.  I always make the seal diameters on the turned down 312 cranks slightly on the large side as it doesn’t hurt anything doing so.  Always better being too large than too small.

 

Here’s a previous thread on the subject.

http://www.y-blocksforever.com/forums/Topic12519-3-1.aspx

Lorena, Texas (South of Waco)

Ted, thanks for the info about counterweight interference with 312 cranks and 292 pistons. I never would have guessed there would be a problem.

Best regards,



Paul Menten

Meridian, Idaho

Andy; I bought a re-built short block years ago that was re-built by "Mustang Re-builders" and was told it was a 292. The pistons had .040 on top so I thought it was the basic +.040 292. As it turned out it was a .090 over 292 with  .040 312 pistons. I checked the block numbers to be sure. I ran it for a long time and it never got hot real fast as some do that were overbored. Just a little info for thought.

________________________________________________________________________________

Old Y Block

Just fo info those 312 .040 over pistons were the largest Ford sold. In a 292 block they worked out to about 306 cu. inches.

Paul