Knock or tick?

[sethjon]

My sons boat. OMC, 4.3. Lift the motor cover and theres an odd sound. My son thinks it sounds like a ticking, not too loud. I think it sounds like a knock. Check the oil and its about 3/4 qt low so I add it. Its back on the trailer and about to take it out again and now the oil looks about 3/4 qt high. My first thought is water in the engine but its a perfect color and density looks right. Any ideas on noise and oil?

 

[skideck2]

Re: Knock or tick?

noise is hard less ur there..usually when she knocks, a true knock, that's gonna get you in trouble, you know it. oil could be just the angle of the boat the trailer?

 

[Bridar]

Re: Knock or tick?

Is it more of a "lifter tick" or more like a "bearing "knock"? How's your oil pressure?

 

[sethjon]

Re: Knock or tick?

Oil is good. To me it sounds like a feint knock. To my son it sounds like a tappet tick. According to his shop, the mechanic also thought it was a tappet, but I have no faith in him. I should also say tht it sounds like it coming from the top of the engine more than in the middle. Having said that maybe it is a tappet tick.

 

[Howard Sterndrive]

Re: Knock or tick?

can take the vee belts off the front and run it without alternator and w/p turning. see if it goes away. Alternators like to tick when they're going south. so do water pumps.
A mechanic's stethoscope is $10 or so at harbor freight and other discount stores. A long screwdriver or broom handle against your ear works too.

 

[sethjon]

Re: Knock or tick?

Thanks Howard. Last thing I would have thought about is the alternator. didn't think they made noise unless the bearing is going but what I'm hearing definitely is not that. Will let you know.

If it is the water pump, how much of hassle is it to replace?

 

[Howard Sterndrive]

Re: Knock or tick?

the rotor in the alternator can start to touch the stator winding if either the bearings are going, or the stator got hot/deformed. and tick tick tick
water pump is a breeze. 30 min job.

 

[HopinImFloatin]

Re: Knock or tick?

also, a cam related noise, i.e lifter or rocker noise will occur at 1/2 engine (crankshaft) speed. This difference in speed should be noticeable at idle rpm. A rod, or wrist pin or main knock are a bit more rapid? sounding. Hope this makes sense. If you think its a valvetrain related noise its usually easy to isolate by removing and running the engine with the rocker covers off and CAREFULLY putting the wooden end of a hammer on the pushrod end of the rockers one at a time. the little extra pressure on the rocker usually will quiet the effected cylinder giving you a path to further diagnosis.

 

[Idlespeedonly]

Re: Knock or tick?

If you take off the rocker covers, you had better cover your interior. Oil will splash everywhere.

 

[HopinImFloatin]

Re: Knock or tick?

ill admit, iv'e never done this on a boat engine, but on cars it works well and never really had an issue but surely the potential is there. I would assume a low idling marine engine would sling less oil, maybe not, but they do make clips that go over the rocker lube holes to prevent this while adjusting lash on hydraulic lifters with the engine running. randy is right, if you try this, be ready to kill the engine if it gets messy

 

[sethjon]

Re: Knock or tick?

Thanks again. I first thought it was a rod but its not that loud. The noise is indeed fairly rapid and with the engine cover down you can't hear it. He took it out the river last weekend and took a 20 mile trip and back at about 3ooo RPM and he said it ran fine. I hope its not the calm before the storm. I would think if its serious that after or I should say during a ride like that a bigger problem would have emerged. What do you think?

 

[HopinImFloatin]

Re: Knock or tick?

20 miles at 3k is a good stressor for a weak bearing i would think. Like sidekick2 said, noises are tough unless you can hear it yourself, tough over the internet! Could be a lifter but its not like a car when it breaks, cant just get out and walk. Really should try to isolate it in my opinion. Its easy enough to pull the covers. Do the broomhandle/stethescope deal to get a basic cylinder area with the covers on and go from there i would say. Ignoring it is probably not the best idea, hate to see a repairable problem turn really ugly.

 

[Tkdcal]

Re: Knock or tick?

Another possibility is the timing chain. Not sure if that engine comes with nylon gears, but when the nylons start to wear out, you can get slop in the chain and it slaps against the timing chain cover. I had that happen on a chevy 350 and was a bugger to figure out where the noise was coming from.