Can you still have sticking valves without any evidence of bent pushrods?  And can this be diagnosed with the rocker arms and shafts removed?   I removed the rocker arm and shaft assembly from each head and checked each pushrod individually.   All looked good to the naked eye by rolling each one on a level surface.   As background, I purchased this 56 Thunderbird with a 312 about a year ago.   The prior owner had health problems and the car had been sitting for about five years.  The engine had been rebuilt in the past and can't have many miles on it.   The gas tank was represented as being "cleaned and flushed" but was actually disgusting with a large amount of sediment on the bottom.  I did not try to start it after taking possession until the gas tank was replaced and other fixes taken care of first.   I was finally ready for a test start up.   It caught fire immediately but ran very rough and died shortly.  I tried it a couple more times without success.  It ran before I took delivery but I suspect the damage had been done due to the bad gas tank and varnish deposits in the valve guides.    Thoughts and recommendations appreciated!

I will suggest performing a cranking compression test on the engine.  Be sure to do that with the throttle in the wide-open position.  That test by itself will rule out a majority of the mechanical issues that can be happening with the engine.  Or on the other side of the coin, point you to what is actually going on.

Lorena, Texas (South of Waco)

Thanks Ted.   I was thinking that might be the next logical step.

Willie, be sure to pull the coil wire out of the cap before cranking it with the throttle wide open.

John - "The Hoosier Hurricane"

At risk of scope of work expansion and this turning into a saga I had to ask myself why I had a mix of 7/16 and 1/2 inch adjusting nuts on the passenger side?    But thanks to this forum and John the HH this was quickly answered.   And it gets better.   Valve covers are aluminum but valve cover studs are not 4.25”.   So the studs were not bottomed in the heads and had extra washers on top of the rocker stands to fit the aluminum valve covers (aarrrghhh!).   At a minimum I will double check the rocker shafts and arms on this side.  Stay tuned.  

From past experience pushrods will not cause sticking valves. with them out i would check to see if lifters might be sticking or possible a bent valve causing it to stick, visually 1 valve may look a little shorter or slightly different angle. While apart if you have a compression tester, remove the valve core, remove the oil fill cap, put something on intake and exhaust to let you know if air is flowing through it, make sure nothing is in the way of when the crankshaft turning and normally leakdown test are at 100psi, id recommend at least 50 psi to each cylinder, listen for where the air is coming from, with rockers removed no air should come out of the exhaust or carb, it will automatically put that cylinder to bottom dead center, if crank doesnt move you either got really lucky or have a massive leak or resistance for that cylinder to move. only the out the crankcase oil fill cap. can also compare how much is going into crankcase by sound but it will only indicate an obvious fault. If nothing, lifters look good, cam lobes look good. i would put it together and start at the basics. was fuel lines blown out and carb rebuilt after fuel tank replaced. hows your timing, did you replace your points cap, coil wires plugs etc. age can kill all of those also. good luck let us know what you find
Seth

Thanks Litshoot for your thoughtful and thorough suggestions, much appreciated.   Upon further inspection, three rocker arm adjusting nuts did not appear tight enough to remain stable.   These were replaced and the valve lash was set cold to 0.019.    A cranking compression test yielded the following results at 6,200’ in elevation with four or five crank rotations until stable:  #1 = 145,  #2 = 145,  #3 = 150,  #4 = 150,  #5 = 145,  #6 = 155,  #7 = 150,  #8 = 150.  Adjusting for altitude the numbers would be almost 30 psi higher at sea level.

Another test start was similar to the first one.   Engine fired but would not remain running and would not rev.   Traditional trouble shooting would be in order, fuel, spark, timing, etc.  My guess is the rebuilt teapot carb and bad gas from the seller’s efforts to get the car running could be the culprit.   But rather than fool around with the teapot I’m going to install the new parts I had already stockpiled a year ago:  Blue Thunder aluminum intake, CRT tach drive distributor and a Holley 4150 or similar carburetor.

As background, although this is a 56 Thunderbird, the car has large letter G heads.   So a 9.7 to 1 CR.  However, the prior owner left the intake, carb and distributor as 56 original.  I assume this was so it looked “original” for Thunderbird shows but that doesn’t matter to me.   Future upgrades will include Mummert aluminum heads (finally arrived after 14 months!) a true roller timing set and most likely Mummert’s 265S camshaft.   Hopefully next winter for that effort, I’m not getting any younger.

Unless you have popup/domed pistons and/or heavily milled heads, it's highly unlikely that your static compression ratio is 9.7. ECZ-G heads have nominal 69cc combustion chambers. Taking .006 off the deck will reduce it by approximately 1cc. I cc'd my stock ECZ-G heads that had never been surfaced after leaving the assembly line and measured 70cc. With .013 removed, the chambers are now approximately 68cc. 292 bored .075 to 3.825/w 3.46 stroke, zero-decked, flat-top pistons/w no valve reliefs, and Best head gaskets (.046 compressed thickness), Ted calculated a 9.35 for my static compression ratio.

Thanks.  The 9.7 to 1 figure is as advertised by Ford.   When I was communicating with John Mummert about his heads he advised the stock CR was really only about 9.2 to 1.  Ted Eaton assisted with some calculations on dynamic compression ratio making various assumptions as to actual bore, quench, combustion chamber volumes, etc., and camshaft options to obtain a reasonable dynamic compression ratio using pump grade premium at my altitude. I have not been into the engine and I have not cc’d the new aluminum heads so all that is TBD.

With the 60cc aluminum heads, your static compression ratio could very well be 9.7. 

Having calculated your DCR to safely run on 91 octane, you have covered all of your bases. No doubt, I'm not alone when it comes to the number of Y-block owners who owe Ted Eaton a debt of gratitude for all of his help.