big knock in engine help

[record hunter]

I,m helping friend with mer cruiser 165 hp the 470 4 cyl I.O. He has a big knock what should be the first thing you should do take compression test and how do you tell what the knock is from. It runs but not that good. any sugestions would be great we are not rich and need to do any work ourselfs .

 

[achris]

Re: big knock in engine help

If you suspect a bigend, then pull each plug lead off in turn and if the noise goes, that's your problem...........<br /><br />Chris.........

 

[WillyBWright]

Re: big knock in engine help

You can isolate the noise in two ways.<br /><br />With a 2' - 3' piece of hose. Listen in one end and move the other end around the motor and you can narrow-down where the noise is comong from.<br /><br />A slightly more accurate method involves something long and hard. Keep your pants on! I mean something like a 2' to 3' metal rod or wooden dowel. Press one end against that little lump of flesh in front of your ear until it plugs your ear and the other end around on the motor. That can get you even closer than the hose.<br /><br />Compression test would be a good idea, but it won't isolate a noise. It'll tell you what kind of condition your piston and cylinder are in.