Newbie with an engine knock 3.0

I recently purchased a 89 Smokercraft with a 3.0. I got this boat cheap so i expected some problems. I have been able to fix almost all of them myself. Most were electrical. However, when the boat is at idle there is a knock in the engine. It doesn't sound "tinny," so i don't think it is a lifter or a valve. When the boat is above idle the knock goes away and runs like a champ, no dogging, no lagging, no roughness, it runs great. Any thought to what this may be? I am guessing it's a rod, but before I dump a new engine in it I would like some other opinions. I took it to my local boat guy and he said there is no way to be sure until the engine gets tore down and by that time you might as well buy an engine..

Any thoughts?

Re: Newbie with an engine knock 3.0

try running the engine with the drive off (supply water directly to the thermostat housing) - and while the drive is off, inspect the u-joints and gimbal bearing.

You can buy a filter cutter and next oilchange cut the filter and look in the pleats for bearing material or anything out of the ordinary.

Re: Newbie with an engine knock 3.0

How safe is this thing to run? My mechanic said if it were his he would "run her till she quits." He told me to put some sea foam in it and if it is a valve that will usually take care of it. He also said if it blows, it blows. I might last 6 minutes or it could last another 6 years with out any problems, but keep in the back of your mind that a new engine is in your future.
I plan on changing the oil in the next couple of weeks to see if there is any metal in it.

Re: Newbie with an engine knock 3.0

A boat is not something you run until it breaks, especially not when you have the chance of being stranded out in the middle of a lake.

Like mentioned above, remove the drive and start the motor to see if the noise is present.

If the noise is still present, do a compression check on each cylinder. If you find a bad cylinder, do a valve adjusment to verify its not a collapsed lifter or damaged valve/seal. If velvetrain is within spec, you have a bad cylinder and a rebuild is in the near future. Scope the bore to see if its scorched, scratched, or damaged to get an idea of what might be happening.

Regardless, I would not be running an engine that knocked at all. A short block rebuild is a lot cheaper than a long block rebuild, and if you lose a piston, you can bet your bottom dollar that your gonna be replacing EVERYTHING.

Re: Newbie with an engine knock 3.0

Any ideas on ballpark costs for taking the drive off and having everything scoped? I had my mech. price out a rebuild and said it would be 1500 for the motor 700 core charge with a 3yr warranty and 500 for the swap. If taking everything apart is going to be upwards of $1000 i might as well stick a new motor in it.

Re: Newbie with an engine knock 3.0

As said before pull the drive and start the motor....that way you will know what it is.........for sure!

Re: Newbie with an engine knock 3.0

6 bolts to pull the drive off, you can do that in your driveway by yourself and save you some money.

Re: Newbie with an engine knock 3.0

so i pulled the drive off, still made noise, i pulled the valve cover off and made sure it wasn't a loose rocker. the noise sounds like it coming from behind the roter cap in the engine. I was also told to take the boat out and get it warm and see if it does it then. Not run the **** out of it just warm it up, because it could have the wrong oil in it. Any other thoughts?

Re: Newbie with an engine knock 3.0

my next step would be to do an oil change (straight 30 weight, or 20W50 or 25W40) and cut the old filter if it doesn't go away after that.

the lifters are in the area you describe so it could be an oil issue- a lifter not pumping up as a result of foaming oil- make sure the level isn't over full - that can cause foamy oil as the crank dips and whips it up.

Re: Newbie with an engine knock 3.0

Cut the oil filter apart and there is nothing out of ordinary in there, we are in the process of changing the oil right now and so far i have take 1 gallon + of oil out of it.