Why do some Atomic Four engines have trouble with sticking valves?
Atomic Four engines had some problems with valve sticking because the original clearance specification between the valve stem and the valve guide of .002″ – .003″was a bit tight, and the exhaust valves would stick when carbon which had built up in the lower part of the valve guide jammed the valve stem in the valve guide when the guide and valve stem clearance became smaller when the engine was hot. In order to help correct his problem the factory made a modification to the valve clearance in 1970 (at serial # 176500), and increased the clearance specification to .0025″ – .0035″. This new specification is obtained when the valve guides are reamed to .315″ – .316″ (an 8 mm reamer is perfect). If non-standard bronze valve guides are installed they should have even more clearance… .004″ – .005″ because the bronze guides expand more than the standard cast iron guides. Even when valves are installed with the correct stem/guide clearance, exhaust valves sometimes stick when the valve sprin
