502 making noise

[brettokok]

Hey guys, new to the forum since ive had some problems with my boat

502 Merc EFI... had 6 people in boat and a 23p prop(all i had for the weekend) so obviously it was hard to get on plane but i only had to get up a few times and thought i would be alright. When returning to dock i heard a loud knocking all of a sudden and I quickly killed the engine. Have only started for seconds to feel for knock location. It is not in the bottom end. It seems to be knocking directly under the upper intake manifold as weird as that seems. I first thought a valve, maybe pushrod snapped but you feel no hitting or weird vibration on the valve covers or anywhere except the intake manifold. I have oil pressure and it turns over/runs/fires with no problems or anything... just the very "tin" sounding knocking. Is there anything in the upper/lower intake itself or throttle body that could break loose? Any ideas are appreciated. Was going to rip the exhaust manifolds/intake manifold/valve covers off tonight but its monsooning in my driveway. Normally keep it stored inside at father-in-laws(cant work on it there)

 

[Windykid]

Re: 502 making noise

Does it sound like a Cam lobe?

You would have to pull the valve covers and check all rocker arms.

Also check for metal on dip stick.

It could also possibly be a carbon build up in a cylinder.

 

[brettokok]

Re: 502 making noise

tearing off exhaust manifolds/intake manifold(upper/maybe lower)/valve covers tonight...

No metal on dipstick...

hoping it isnt cam lobe... dont want to pull motor
The fact that it runs fine makes me think its not a cam lobe.. but i dont know what could just break off in the intake or throttle body and slap around in there...

 

[brettokok]

Re: 502 making noise

so only took throttle cables/throttle body and upper intake mani off tonight and stopped. Tomorrow will be exhaust manifolds and valve covers... hopefully i wont have to get into the fuel crap and lower manifold.

looks like so much crap to take off to get valve covers clear for take off. Wish this was like the 5.0 in my mustang and i could just take the valve covers off without removing anything else. ha

 

[brettokok]

Re: 502 making noise

So turns out the pushrod broke right through the rocker arm and must have been slapping around..... now to find one rocker arm and pushrod(pushrod just incase its weak from slapping)

....lame, but...

so glad its not lower end....

 

[brettokok]

Re: 502 making noise

if anyone cares.... notice the pushrod that went right through the rocker arm.. ha

 

[45Auto]

Re: 502 making noise

At least it's an easy fix. Did you find the broken piece of the rocker arm? Any indications of why it broke - valve bind, slipped keepers, spring bind, whatever?

 

[brettokok]

Re: 502 making noise

haven't found the broken piece going to try to get the oil pan plug out and see if its in there.

Not sure why it would have broke.. going to put new rocker($7) and pushrod($19) in and crank over by hand and see if the vavle operates correctly. Lets hope its smooth and I find the piece if I can get to the oil plug and move on with life.. ha

I also wont have 6 people in the boat again with a 23p prop trying to get on plane... I assume it broke under stress since it was taking forever to get on plane. Hopefully changing the prop if i'm taking out a bunch of friends will help this plane issue??

 

[brettokok]

Re: 502 making noise

talked to a good friend engineer from mercury... says the 454 and 502s have common problems of rocker arms(not valves or anything else) cracking and breaking after 225-250 hours.(and no i didnt ask him why they dont make better rockers, ha) Got 1 pushrod, 16 rockers, and some gaskets... hopefully back on the water this weekend

SWEEEEEET

 

[brettokok]

Re: 502 making noise

so got it all back together... no more slapping or knocking of the pushrod/rocker arm... instead i get a vibration whenever its 1100 rpm or higher... idles fine. the vibration sounds like its coming from the back part of the motor. anyone ever use the mercruiser gaskets for lower intake manifold for a 502? Did you have to cut any parts of the gasket out to make it work? I thought there was a part that was open on the stock gasket and sealed over on the new one.... maybe i should have cut it open.... any ideas on vibration?

 

[dodgeramsst2003]

Re: 502 making noise

sorry about the broken rocker arm, but I doubt it was because you had 6 people on board with the wrong prop. Any engine can only make so much HP. Say you have a 350hp engine, whether you have 2 people or 6 people on board, the engine can only make a total of 350hp. The engineers who designed it, designed all the working parts to be able to withstand that amount of power. I would chaulk it up to a bad stamping. I'm a dyno/instrumentation tech and develop engines and I've put my fair share through some abuse. If they break its because of poor engineering, or a bad manufacturing process (or my mistake, but don't tell anyone). If its poor engineering they redesign the part, if its bad manufacturing they fix the problem. I wouldn't worry about taking 6 people out again, you're problem was going to happen at some point, it was just a fluke that it happened when it did. The 502 has been around for a while and I've actually run one on a dyno, there is no breaking that engine as long as you don't over rev it. Its a good hunk of iron.