I am in the process of removing the engine in my '55 Thunderbird to install the 345 Y and got a surprise.  When I removed the bellhousing, clutch, and flywheel, there was a little round dot on the crankshaft flange.  The heads on this engine have the freeze plugs in the front of them, and I assumed it was the stock 292 that came in the car.  I checked the part number on the block and date code since I had it up on the lift.  The block number is ECZ-6015-C, and date is 74*R.  Is this a factory replacement shortblock?  I guess I will be tearing this engine down now to see what it really is instead of putting it in the corner and leave it for the next owner.  It is tempting to install a set of ported -G heads and leave it.  Joe-JDC

JDC

Looks like somewhere along the way a 312 short block found its way into your ’55 ‘Bird.  It will be interesting to check both the bore and crankshaft and determine if they are standard sizes or if a rebuilt short block was installed in the car.  If the crankshaft is standard, then check out the dates on the bearings to determine if the engine has ever been rebuilt since new.

I recently had a standard bore 312 in the shop that had the original 1956 dated main bearings but had 1971 dated rod bearings.  From the looks of the sloppy job where the ridge was cut out of the tops of the cylinders, it could have been an in-chassis rebuild where the engine just received new rings and rod bearings.

Lorena, Texas (South of Waco)

My 55 Tbird has been in the family for 50 years. The odometer shows 83,000 miles. Since it's been in the family, it's been driven very little, spending most of its life in the garage. I discovered the block is dated 56, but I don't know if its a 292/312. My dad said it was a 292, but he never said anything about the engine not being original. I, too, wondered if the short block could have been replaced under warranty. The heads, intake, carburetor, and exhaust manifolds are correct 55. 

What's the meaning of the diagonal groove on the dot? 

64F100 57FAIRLANE500

I don’t think there is any major significance to the slot in the dot.  Looks like a screw head which may have been a quicker method to put the dot on the crankshaft flange when casting.  Maybe an internal code?  Service or replacement crankshaft?

There are currently nine 312 crankshafts here in the shop and only one had the slot in the ‘dot’.  Of those nine, one did have an extra dot along with the aspirin sized dot.  I have seen similar small dots on 292 crankshafts but no clue as to the meaning.  Here’s are pics of the 312 crankshaft with the screw slot and the other with the additional ‘dot’.
  

  

Lorena, Texas (South of Waco)

Hmmmm, thanks for the reply. Probably an unsolved mystery long gone with the foundry. These shafts were used through the 1960 model year (Mercury) so it's possible the job may have been handed over to one of thje other foundries?

64F100 57FAIRLANE500

No such luck!  Junk Yard Dog!  The 312 that I just removed from my '55 T-bird is a rebuilt mismatch of parts from at least three different engines.  There was blue paint overspray on the pushrods and timing cover, freeze plugs in the ECG-D heads('55 272), and the crankshaft is .010"/.030" with every connecting rod mismarked in all locations, but numbered as if reconditioned and balanced.  The bore is +.040", so it will need a refresh for sure.  So, it looks like the 345Y is going to find its way into the engine bay with the T-5 attached.  I am still undecided on whether to install the headers or just go with the previous exhaust system for now.  Joe-JDC

JDC

While I would initially vote for the headers, using the existing stock exhaust manifolds and pipes would have the car up and running much quicker.  If going for a stock ‘under the hood’ look, the factory manifolds would go a long way in retaining that look especially with the aluminum intake also painted the same color as the heads and block.  In the grand scheme of things, the headers and an up graded exhaust system could be done later without much issue.  And it would be interesting to see how the car performed with the stock exhaust.

Lorena, Texas (South of Waco)

Hello  Joe  Are you planning on giving details on the (345) motor you build for TB. Thanks

There is an article in the July-August 2021 Y Block Magazine covering the build fairly well. (Issue 165).   Joe-JDC  

JDC