View Full Version : Hercules MBL motor

07-10-2006, 07:31 PM
"I have 1954 chris craft sportsmen with a hercules MBL 158HP motor. The problem is a knocking problem that increases with RPM.I did a compression check all six cyl were 107 to 120PSi.The oil pressure at idle is 3-5 lb increasing to 10lb at 2,000 RPM. There is a lot of back pressure and smoke coming out of the breathers at 2,000RPM. My guess is the bearings are going. Can new bearings be installed from bottom side only leaving top end alone? Or is this wishfull thinking.

01-31-2007, 08:43 AM
"I'm not too familiar with Hercules engines, but if there is allot of back pressure make sure the crank case in venting properly. If the oil pressure is out of specification bearings are usually the cause for that. Since this motor has both of these conditions it needs to be rebuilt or at least taken out of service before more damage is done. If it were mine I would rebuild the motor and try and keep all original parts."