new motor ?

[debt finder]

hi everyone , i have a 82 sea ray sun dancer with a merc 260 in it . let me start by saying i redid the whole electrical system and fuel system ( everything but the pump ) because the motor won't go over 3400 rpms , and when i open it up full throttle i hear knock sound coming from around the #8 Cly . then when i take the throttle down to where it cruises at 3400 i don't hear it anymore not at start up or idling either . did a compression check all the cylinders were good except #5 was only 64 psi , so i plan on doing a leak down test when i get a chance .any thoughts on the knock ? and why do i only hear it when under a load ?

 

[Limited-Time]

Re: new motor ?

Welcome to iboats.
65 PSI in one cylinder sounds like a head gasket. Don't bother with the leak test. At this point just bite the bullet and pull the head, and do an inspection.

 

[debt finder]

Re: new motor ?

thanks for your input about the head gasket . i was looking down the back of the motor and saw a oil leak , thought it was comming from the oil sending unit but found out it's leaking from under the intake . just happens to be on the same side as cly #5 .

 

[debt finder]

Re: new motor ?

OK looks like I'm going to do the head gaskets so i was looking over some posts and they said if i put a set of vortec heads on it would increase hp by 20 . if this is true can anyone tell me if it matters what year they are and will stock heads raise the hp or do i need high performance heads ?