671 broken rocker arm shafts

" I have an in-line 671 in a b

" I have an in-line 671 in a boat. The rocker arm shafts keep breaking. We have replaced all of the shafts, rockers, and stands. First the #6 cylinder broke, then #5,followed by # 4, and 3. Sometimes they last just a few hours, others last 30 hours. Everything is torqued correctly. All I can figure is that the remanufactured (reliabuilt) head was machined incorrectly. No one I can find has ever seen this problem, and several different mechanics are stumped. Any ideas would be great. "

" is this something that start

" is this something that started after you put a rebuilt cyl head on,if so what else was done??? "

I don't know. We bought

I don't know. We bought the boat with about 200 hours on the rebuilds. We origanally had problems with the by pass valve. we discounected that and later had the shaft problem. The engine runs great until the shaft breaks.

" Cam bearings ? Sounds like a

" Cam bearings ? Sounds like a major internal problem. Question why heads~ what lead to this problem. On going rocker arm breakage is a cause to delve deep into the engine. A lot of slop or ware somewhere to do this sort of damage . Get the specs. for cam lift, then do a loaded measurmrnt ( everything in place ) then remove all rockers etc and re do test with no pressure on camshaft. Maybe if lucky will help . Another question Oil pressure? If cam shaft brgs gone oil pressure will drop when engine loaded and oil warm.
Good luck
BJ "

head is probably warped check

head is probably warped check if cam spins free when all rockers loosened of

"Actually it does not sound li

"Actually it does not sound like a major internal problem unless the people who installed a new cam have placed a cam with too great a lift. More than likely your lifters are bottoming out on the springs, have you checked your valve adjustments and spring tensions? Chances are that your head has been shaved to the point where the cam lift is greater than the valve travel, start with spring tension, valve height specs and then you may need to shim the mount blocks on the rocker shaft. That should solve your problem."