All of the above are good suggestions.
I was thinking along the same line as George. Many engine rebuilds,
although within manufacturers' specs, often cause problems that didn't
exist prior to the rebuild. If the engine was put together as "tight"
as possible, i.e. at the closest limits of recommended tolerances,
this can cause a host of problems such as an engine to run
excessively hot for example or to be nearly impossible to start. Even
though everything is within specs according to the book, the compound
effect of this is a "too tight" engine.
Any machining of the block and head will affect the valve clearance. A
thicker head gasket may be necessary to return things to the proper
position.
Regarding Mark's idea to move the distributor: All cars are different,
of course, and I have no experience with Marmon straight 8's, however,
it is possible to install a distributor incorrectly without it being
180' out of time. The worm gear at the base of the distributor shaft
has to engage the drive gear in exactly the right place or the rotor
will be moved slightly one way or the other.
Set the engine itself at #1 TDC as described earlier.
Set the rotor to point exactly at #1wire.
Slip the shaft down the hole and watch the rotor.
If the rotor moves one way or the other, pull the Dist. out and rotate
the shaft in the OPPOSITE direction of the previous rotor movement
until the rotor moves the same distance in the opposite direction from
it's original starting position (#1 wire).
When reinstalling the distributor, the rotor should now move in the
same direction as it did the first time and should stop at TDC.
Even though the distributor worked before the rebuild, don't assume
anything. Check it thoroughly. The Dist. cam could be excessively
worn. Check the spring tension of the breaker points. (a special tool
is made for this) Weak spring tension can cause point chatter
(bouncing) and excessive tension will cause extreme wear of the
rubbing block, cam and points.
You don't say whether the distributor was rebuilt along with the
engine, only that it worked before the rebuild. Check the bearings at
the top and bottom of the Dist. shaft. If they are worn or the wrong
size, etc. you will get side play of the Dist. shaft. Side play causes
irregularities in timing. This can be checked with a dial indicator.
If the side play exceeds specs, the bearings and/or the shaft will
have to be replaced.
A slightly bent Dist. shaft could also cause these problems.
Double check your coil too.
Check the spark output on each plug wire. A weak or intermittent spark
at all the wires points to the coil, Dist. cap, rotor, or high tension
wire from the coil to the Dist. I know this sounds extremely basic but
sometimes it's the simple things. I once went through a whole
diagnostic rig-a-ma-role on a 1972 Monte Carlo because I took my dad's
word for it that he filled up the tank. He in fact had only put a
couple dollars in it and had run out of gas.
I hope you solve this problem. Please let us know what finally works
out. If any new information comes to light, tell us about it.
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