The other side of this coin is the cam tunnel hole alignment.  While the 272 and 292 engines have a straight through bored hole, the 312 engines are bored from each end and meet somewhere close to the middle.  Some blocks are worse than others depending upon the tooling or how the block was set up in the boring fixture but many 312’s suffer some degree of cam tunnel misalignment.  Put this misalignment in combination with the occasional undersized hole and you have a worst case scenario.  The factory resolved this by using 0.010” undersize bearings in the 312 blocks and once installed, the cam tunnel was honed back to the correct size from end to end ending in a straight hole once more.  Hence all the issues with 312 cam bearing installations when new cam bearings are installed as part of a rebuild.

Lorena, Texas (South of Waco)

When I took my current engine block to the machine shop, I gave them the cam I was going to use.  I told them about my previous experience and asked them to make sure the cam rotated freely.  It did.

The cam bearing can be installed crooked or ‘cocked’ by not having the tool square when installing the bearings.  The front one can be trickier than the rest in that regard if installing all the bearings from the front of the block.   Or the cam bearing holes in the block can be undersized by a small degree and that in turn makes the cam bearing I.D. too small when installed.

Lorena, Texas (South of Waco)

Other than not aligning the oil holes or not centering the cam bearing, how can a bearing be installed wrong?

Years ago I built a 312 engine for a 1957 Victoria.   I used an Isky cam in that engine.  When I installed the cam, I could hardly get it to turn in the block.  I had to build a tool to scrape the cam bearings so the cam would turn freely.  I wasn't pretty, but I had no choice.   Since then, Ted and others have stated some machinists install YBlock cam bearings wrong.  I have learned to never assume a machine shop knows YBlocks.  It's better to assume they don't and check everything twice.

I love the beautiful cars pictured in this post, the convertible and the bird! Very nice machines men....

Did you install the cam yourself?  If no, it's been reported here & elsewhere that some blocks have misalligned Cam bearing castings. Or did you have difficulty installing the Cam into the bearings? If so, Ted or others here might have suggestions to cure the issue..


Paul

Do you have a ground strap attached from the engine to the body?   I also have a ground from the generator bracket to the frame.   A bad ground really can cause frustrations.   Hopefully you find a simple solution.

There's a very similar post over on the HAMB, which I suspect is you. You note you're trying to start the engine with a battery charger set on the "engine start" setting of 225 amps IIRC. That won't do it. When I had a fleet I had a charger that would, but it was so big it was mounted on a hand truck to move it around. You need a decent, fully charged battery that will hold the cranking amps long enough to fire the engine. I just went thru this with a bad battery (one year old, expensive Odyssey, showed 12 volts). Wouldn't crank my 312 even with the charger on start. When they tested it it was almost at the bottom of the scale for bad. Replaced it for free. Problem solved.

So get a good battery in the circuit, and if necessary jump it to a battery on a running vehicle till you see if it cranks. As stated above, don't keep going till you cook the starter.

Edit: I should have said crank rather than start the engine.

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

i put a 312 in a 56 this past summer and it turned over to slow to start.the car had sit for 10 years and the motor almost as long.in the end corrosion around the ends of the battery cables was the cause.