nengine be knocking but not sure

[ddaydanson]

Hi, i have a 96 bayliner trophy 2352. it has a remanded 96 5.7 in it. I have noticed my 5.7 merc sound like it has a quiet knocking at around 2500 rpms. i had the oil changed last month and the mechanic put 10w30 into it. it was loud prior to the oil change but got quiet after. although it was loud before, it didnt seem like a knocking, but im really not sure because i had loud boats before.

prior to the oil change I noticed that when i would check the oil level, the dip stick had oil all the way up. even after wiping it and reinserting it into the tube, it still showed the oil all the way up the stick. after the mechanic changed the oil, it still showed all the way up the dip stick.

after i heard this knocking sound, i checked the oil and of course it was still all the way up the stick, but it seemed to be more runny, but it was clean with s light smell of gas.

a month and a half ago i replaced the carb with a carter. the carter didn't have a vacuum inlet at the bottom for the pvc valve, so i ran it into the top of the fame respirator. the other thing was the gas pressure was around 11 psi, so i reduced it to 3.5 as recommended by the carb guy. I've had it out a few times since and it didn't act up on me.

another thing, I took it out last week an hour to my destination and and hour back. on the way back the engine would stall under 1000 rpms so i had to keep it over 1000 rpms while in no wake. i checked the inline filter and the gas appeared to be brown looking and my fuel pressure regulate was stuck at 6 psi.

I put a video up on youtube with the engine making this noise. i'd appreciate it if someone could take a listen and let me know what they think.

https://youtu.be/5pij2418kP8

 

[ddaydanson]

ni ideas? anyone?

 

[Scott Danforth]

after i heard this knocking sound, i checked the oil and of course it was still all the way up the stick, but it seemed to be more runny, but it was clean with s light smell of gas.

most likely you took out the bearings......time to pull the motor

 

[ddaydanson]

Is that what it sounds like on the video?

 

[ddaydanson]

also, what could have caused that?

 

[ddaydanson]

i dont know, it's really hard to get to them. but i was just researching a few things. I had a holley carb that had the inlet air fitting at the bottom that the pvc valve was connected to. On the carter the port for the valve was blocked off. I ran the pvc valve hose to the top of the flame resister along with the air hose from the other side where the air would go back into the engine. Do you think it's possible that there isn't enough suction to pull the air out of the pvc valve? Would that cause the oil to run up the dipstick because of pressure? And could that cause the knocking?

 

[ddaydanson]

also, forgot to mention, it looked like a little oil slick around the boat. I couldn't tell if it was from me or not, but between the boats around me i think mine was used the last.

 

[ddaydanson]

lol, it really sucks when ur having issues like this and need some sort of answer on a sunday to rest your mind.

 

[scoflaw]

You've got a few thing going on. Your motor oil should be 15-40 or something close, not 10-30.
​
​by moving your pcv hose, you have disabled the pcv. No big deal, and not your current issue. The crankcase can still breath and has nothing to do with the high oil level.

​Your oil has probably been overfilled both times, drain it, and refill with correct oil, and verify the level on the dipstick. Monitor the level after that. If it the volume increases, it's either gas or water

​The stalling has nothing to do with your knocking or overfilled condition.

 

[Bt Doctur]

You need 20 w-50 , 25W-40 ,Rotella 15-40 Diesel 10W-30 is way too thin once your at temps. There is no inline viewable filter allowed in a boat,
Brown gas is usually bad gas , so try running on a remote tank. Carb fuel pressure should never exceed 6 psi in most cases. High pressure allows gas to get into the crankcase diluting the oil and causing bearing failure nnot to mention the rings grinding on the cylinder walls.

 

[biggjimm]

I can't really hear the knocking noise in your video, too much wind & other stuff, but if your oil level keeps rising that much & smells like fuel it sounds like your carb is running way too rich & all that fuel is going past the rings & into the pan. It dilutes your oil to the point that it can't provide the protective layer for the bearings & they start knocking. It will eventually sieze. And depending on the rpm's it's running at when it siezes, it may tear up a whole lot more stuff when it does.

Unfortunately it sounds like Scott is right on the money & it's time for a rebuild or a crate motor.

Good luck.
Jim.

 

[ddaydanson]

Yeah, the engine was a reman and dropped in last season. As far as oil, I used 30wt because on this forum I thought it said it was ok:
http://forums.iboats.com/forum/engi...nd-inboards/640580-what-oil-to-use-5-7-engine

I spoke to an old timer just now and he told me before i pull the engine look at the pvc valve. He said there has to be vaccum because it will cause pressure in the crank case and he remembers some of the engine's oil pan being sucked in and out which caused the same noise. It's a really low knocking noise only at higher rpms, not a noise that stands out like a bad bearing. He also said the high oil on the stick could be from the pressure going out that way.

I appreciate your responses and will do it, but first I want to try the cheaper way first. I'm going to take off the carb and drill the hole for the vaccum port, then run the 15-40 and see what happens with that. I'll repost once I try these things.

Thanks and I appreciate the responses.

 

[Scott Danforth]

Your motor, your choice as to do as you wish, however the gas in oil took out your bearings.

Right now, if you did not score the crank, your only out gaskets and bearings and a few hours of time.

If you continue to run it, it will grenade on you at the worse possible time and cost you a new motor

 

[biggjimm]

I don't suppose I'd be drilling holes in the carb either.
My mercruiser 5.7 has the pcv valves plumbed into the flame arrestor from the factory. Almost 40yrs with no issue. Now if they get plugged up that can cause some issues but they don't have to be hooked to vacuum.
If that was your problem, for a diagnostic test you could simply pull the pcv valve out of the valve cover & let the engine vent into the air. That would correct it if the pcv valve was the issue.

Good luck.
Jim

 

[ddaydanson]

Scott, thanks for the advice but we do not know for sure that is whats wrong. did u hear the video? i'm not saying it is not whats wrong, but i'd like to do some troubleshooting before i come to that conclusion. It would be an expensive project if that's not what it is.

big, I grew up in the 70's and 80's where pvc valves where "always" connected to the vaccum under the carb. the holley i took off was connected this way as well. you have to have the valve in and connected to a vaccum to maintain positive vaccum inside the engine. if you took the pvc valve out, it would not maintain the positive pressure and will not prove anything. the pvc has a spring in it that releases when there's too much pressure and there has to be a vacuum to pull it out.

when there's too much pressure in the crank, it has to go somewhere. thus the reason the oil is creeping up the dipstick. It can also blow rings and seals and spit oil out the exhaust. I know you may be thinking about modern day engines where the pvc is basically a relief valve. but if your engine is from the 90's, you may want to do some research on the topic.

the engine is a re-manufactured engine about a year old. the bearings are updated and probably is not the issue, but not saying it's not. but after listening to it again, it does not have the typical bearing distinct sound. I went back and took a look at the oil again. It's got a slight gas smell, but so does the oil in my car. It's slight. Also, when the oil was changed, he put 5 quarts in it. It was up the distick even after the change. So it could be pressure. Plus, if it was a bearing, the oil pressure would be affected I believe.

I already drilled the hole and will be threading the vacuum tube in place tomorrow. I'll make a post tomorrow to update this.

 

[Scott Danforth]

Gas in oil will ALWAYS take out your bearings. Again, your motor, you do as you want. The rest of us say pull your motor and fix

 

[Bt Doctur]

I grew up in the 70's and 80's where pvc valves where "always" connected to the vaccum under the carb.

Except marine engines dont have any vac under high throttle positions so the vents just sit infront of the flame arrestor and get sucked in.

 

[biggjimm]

You can hook it to the vacuum port, that's fine, I'm just saying it doesn't have to.
Autos & marine engines are more different than most folks understand. For instance, look at all the years that marine engines did not have to adhere to the emissions requirements that autos did. That's one of the reasons the pcv is plumbed in to the intake vacuum on your auto, so the vented crankcase fumes can be burnt off in the combustion process.

I've seen engines with venting problems that would blow oil out the dipstick tube, heck they'd even blow the dipstick out for that matter, but it didn't cause the oil to be consistently high on the stick. I wonder if it could have the wrong tube & dipstick in it by chance??

Is the correct amount of oil being put into it? No offense, it's easy to do with every engine combination being different. My Merc 350 takes 6 qts with the big filter but my truck 350 only takes 5qts.

Also, whether this motor has trashed bearings or not, you need to figure out what's going on with your high fuel pressure because if your bearings aren't shot, they will be if it continues to dump raw fuel into the intake.

I don't recall if you said of not but does it run rich?

Anytime your pressure is that high it's more than likely going to force the needle & seat open & dump that fuel in the intake where it will end up in the pan causing the aforementioned problems.

Good luck & I hope you get it figured out.
Jim.

 

[scoflaw]

Still sounds like your overfilling your oil . You don't just drain and add 5 quarts, and then say, wow it's up high on the dipstick.

My last 5 qt. small block would only take 4 after it was sucked out.

 

[ddaydanson]

Hi,

Ok, I drilled the port into the carburetor and threaded an air tube into it. I placed it back on and routed the pvc correctly and started it. After this I was able to check the oil correctly. It was not over filled. I understand the newer fuel injected engines have the pvc routed differently, but the older engines (96) has to have vacuum, there's documentation all over the web so you can do your own research and you'll see. I would probably look into yours if it's not correctly routed, otherwise you may have an issue later.

As far as the noise, turns out it's in the drive train and not the engine. We're going to take the outdrive off and look at the gimble. I figured this out by researching and I started it and raised and lowed the outdrive and turned the steering. By doing these steps the sound changed and it wouldn't have if it were the engine.

I was really sweating it at first and that's why I asked the question on here before researching the problems. Thank you for your inputs, even though they were way off. I can understand though because when you mention knocking from an engine, that would be the first thing you'd think about if you didn't know any different. ANd if you're from the younger generation you wouldn't know how a pvc operates. Anyways, thanks and if you ever have a light bulb blow, check the light before you start changing circuit breakers, it'll save you time and money.

Goodnight