More problems we are hearing about !!
Broken inner valve springs, caused by using the wrong outer valve spring shim with too small of a hole in the center so the inner spring can't fit down in it's own seat. Causes coil bind and breakage.
Broken rockers.. most common causes are exhaust valve guides too tight, locking up the valves, if a intake rocker breaks most common cause is bad gas, old fuel turns to glue and locks up the intake valves in the guides.
Reproduction rocker arm failures.. some of the 1953-59 iron repros have push rod holes machined incorrectly breaking the push rod tips off! We always recommend our bronzed bushed rebuilt assemblies.
We are getting reports of cheap overseas and Mexican lifters chewing up camshafts. We sell only made in USA.
Failing water pumps! The new 53-55 264-322 water pumps (we sell rebuilt ones only) have plastic impeller vanes that spin on the shaft! stick with high quality rebuilts.
Remember to check your carburetor jetting, most performance cams require richer mixtures, don't ruin the engine running it too lean!
CAM WILL NOT FIT WITH NEW CAM BEARING....
It is very rare that camshaft will slide right in, maybe in one out of 50 engines that will happen. When these engines were new, cam bearings were undersized and line bored in the block..The machinist should always check cam fit before the block leaves the shop. The cam must be the first thing you install in a block. Scrapping the bearings with be necessary to fit the cam, someone with experience will be best and only a small amount in the correct places to make the camshaft fit. One of the reasons we grind casting flash from the lifter area when rebuilding these engines is so we don't cut our hands fitting the cam in the block. Front cam bearings can also be put in wrong.
Not installing the distributor all the way down into the block so the oil pump shaft will not engage.
Installing the intake gaskets wrong! the 1957-66 engines have ports that are offset with the bolt holes, there are flags or tags on the ends of these gaskets, they must face toward the other gasket, NOT outboard toward the valve covers. If you see the intake gaskets when you look between the intake and the valve cover they are on wrong causing a vacuum leak! This should be one of the first on the list.