sleeper_dave

Well some more searching and I now know where the flappers are located. The question now is, how do i verify that those are the problem? I suppose I could unhook the exhaust and start the motor, but then i'll be dumping water in the bilge.

White Knuckles

Just let your engine idle, and listen to the sound through a long screwdriver touching the exhaust.

sleeper_dave

I went down to the boat yesterday and checked it out. Those flappers are definitely making noise. I don't quite see how that noise can manifest itself under the valve covers, but everything i've read in searching says that exhaust flapper noise is commonly misdiagnosed as lifter noise, so hopefully that's the only problem. If I can get the parts today i'm going to replace them.

tmthunder

Nice work Dave glad that you found the issue. You should have the flappers in your y pipe and also in your exhaust tips exiting your transom unless you have the rubber ones on the exterior of the tips. You should beable to look right up inside the tips from the outside and see those flappers. The ones in the Y pipe you will have to take the diverters out to see inside the y pipe.

sleeper_dave

I have the external flappers on the thru-transom exhaust.

I swapped out the flappers yesterday and it didn't fix the noise.

I'm wondering if the noise is normal or abnormal at this point. It's not loud enough to be a collapsed lifter and it doesn't sound like piston slap (according to a mechanic friend). It's coming from under the valve covers, and it's not coming from just one or two cylinders either.

How much valvetrain noise is "normal" on a stock 502?

I may just be paranoid here, trying to fix something that isn't broken. On the other hand, I may need to pull the valve covers off and check out the rocker arms. But I think it's a gen V motor, meaning non-adjustable rocker arms. So that would mean it's either normal or something wierd is wrong. Although the motor was apart before i bought the boat, so who knows what year heads are on it.

stinger390

Dave,

Did you run it with the flappers removed from the pipe and see if the noise was still there? If you just replaced them with new ones, they would still make noise, new or old. Just the fact that they are in there causes the noise.

pstorti

external rubber flappers won't cause the noise. go to this page http://www.eddiemarine.com/store/car...duct_list&c=59 and look up your exhaust and see if you have an internal flapper that looks like "non-burn flapper" shown there. If there are no internal flappers the noise is from something else.

Did you do the screwdriver test?

sleeper_dave

No, I didn't run it without the flappers. On my boat the top of the y-pipe is pretty close to, if not under, the waterline, making it difficult to do something like that. I could try that on the hose, though.

I did use a screwdriver to try to isolate the noise before changing the flappers. It did sound like there was noise coming from the flappers.

Would the exhaust flappers in the y-pipe cause a noise when the exhaust is going through the transom? I would assume that some exhaust would be still be going through the prop anyway.

Switching the silent choice to quiet doesn't seem to affect the noise.