Help, Merc. 5.0 MPI "ticking" sound at idle

[Tahoe 55]

I have a Merc. 5.0 MPI with a Alfa with 62 hours on her. The boat is 2 years old. At the start of this season I notice a "ticking" sound coming fron the engine at idle. It sounds like an exhaust leak "tick". The noise changes with RPM. As you advance the throttle, it gets louder and faster until normal engine noise over comes it. Seems to be louder when the engine is cold and seems to be coming from the starboard/aft side of the engine and low. I've crawled all around looking for exhaust leaks and can't find one. I can't get back and down far enough though to inspect the area where the noise seems to be coming from. There isn't any water coming into the bilge and if the exhaust was leaking that far back, I would think water would be leaking out too. I tightened all hose clamps anyway though.

When My wife 1st pointed out the noise, I though it was normal and it had always been there, but it seems to be getting worse as the season goes on. All gauges read normal and the engine is fine on power. After I couldn't find a problem, I'd been ignoring it, but as it seems to be getting worse, I think I need to solve whatever the problem is.

Any ideas or suggestions?

 

[greg82255]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

It could be a valve, have you changed the oil recently/ are you using the correct weight oil? I had a ticking sound last year and it was because I had put in a cheap filter, valvetrain was getting starved of oil. Changed the filter and put in new oil, no more ticking.

 

[Blk-n-Blu]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Maybe the exhaust flapper in the Y pipe.

 

[Tahoe 55]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

I changed the oil while winterizing last year. I used all good Merc stuff back. I don't think the noise is coming from inside the block. I used a stethoscope on each cylinder and head. I didn't head anything abnormal.

 

[Tahoe 55]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Maybe the exhaust flapper in the Y pipe.

Thanks for the suggestion. I was thinking that, but a friend had a noisy flapper and it was a totally different sound and it didn't change in exact correlation with RPM like mine does...

 

[Tahoe 55]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

No other ideas?

 

[Blk-n-Blu]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Maybe a spark jump. Check it after dark and look at the plugs and wires and also the coil.

 

[Tahoe 55]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Hmm, I'll check that.
If that's not it, I guess I'm going to have to take it by the dealer...

 

[fossill]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Ticking noise is usually either a sticky or misadjusted lifter, exhaust leak between manifold and block or a transient spark from a loose coil or pulg wire, but that should be accompanied with an engine miss. Usually a liter of Rislone engine oil conditioner will help if its a sticky lifter.

 

[Don S]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Make sure your oil level is not overfull. If the crankshaft hits the oil, it will aerate the oil and will cause the lifters to clatter.

 

[Tahoe 55]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

The oil level is a little high. Just a hair over the full mark. I'll drain a little in the morning before we take her out. See if that helps, but the noise doesn't seem to be coming from the top of the engine. I'll probably be better off if it doesn't fix the noise...

 

[Silvertip]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

the distributor shaft turns at 1/2 crankshaft speed. Have you pulled the distributor cap and checked for evidence of wear that would cause a snap as the spark jumped the gap from the rotor to the plug terminals. If it is low on the block there is nothing external that would cause the noise. Internal it would be rod or main bearing, piston slap (possibly a broken skirt), a bad lifter, a misadjusted valve, a valve in which the rocker arm stud is pulling itself out of the head, a worn rocker arm or pivot ball, a bent push rod, or if the engine has a mechanical fuel pump, a weak return spring. I've known about engines that were rebuilt due to this issue only to find out the engine itself was not the problem. That issue by the way goes back to 1955 and the small block introduction. It could also be something in the drive.

 

[Tahoe 55]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Thanks for all the suggestions. I lowered the oil level to the mid-range on the stick. I removed about a 1/4 of a quart.... This didn't change the noise. We had the boat out all day Saturday and I swear the noise is louder when I first start it up at the ramp and I'm idling out of the no wake. After I've run for a little while, the ticking is still there but not as loud and it's not very loud to begin with. It sounds like an old car or truck with a small exhaust leak. It's more of an aggravation than a problem. Guests aboard don't even notice it until I say ?You hear that ticking noise". The say "Uhhh.... yeah, kind of... Sounds normal to me, but I don't know much about boat engines...."

I crawled all around the engine again this weekend and can't pin point the location of the noise other than its very low, starboard and aft. Almost like it's under the drive coupling, right at the transom... I could be coming from the exhaust hose itself and I?d call that normal except that it?s only coming from the starboard side. The port side is quiet? Guess I'm going to call the dealer and see if I can bring it by in the next few weeks and have him listen to it on muffs... Just sucks to have my fairly new boat sound like the Klopecks car (from the movie The Burbs). That's pretty much what it sounds like....

 

[Blk-n-Blu]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Possibly the starter bendix not re-seating after start up and ticking against the ring gear.

 

[fossill]

Re: Help, Merc. 5.0 MPI "ticking" sound at idle

Put a wrench on the exhaust maniold to block bolts to see if they are tight, or if you're up to it you can always replace the gaskets that go there. Inexpensive repair.