by jspbtown » 25 Wed Nov, 2009 6:00 pm
Before you start tearing into it I would take some measurements. Remove the rocker arms and measure the overall spring height on the ones that adjust correctly and the one that is not right. Compare those measurements.
Are they all the same?
No, the one that is out of whack is taller:
Then your stem may be stretched or you may have lost a valve seat. Either way the head needs to come off.
Yes they are the same height:
Then compare your pushrods. All the same length? If so then maybe you have a lifter hung up in a bore. Slide a pushrod into the lifter and turn the motor over while applying pressure to the pushrod. Does it go in and out? If not, then your lifter is hung up. You can try to rotate the crankshaft so that cylinder is at TDC and try to gently tap the lifter back down with an old pushrod and a hammer. Be careful! You may need to split the case to get at the lifter if you cannot free it.