nengine be knocking but not sure

[Scott Danforth]

Marine motors do not have pvc valves. Just breather tubes to the spark arrestor.

 

[ddaydanson]

what are you talking about? do your research. this is a 96 5.7 merc and it does have a pvc. Dude, please do some research before you give this "nonsense" advice. Someone who doesn't know any better may mess their boat up listening to you. You really need to lose some stripes off your ranking here. The only thing you said that even made any sense in this whole topic was "gas in oils takes out bearings", which is true but has no relation to my case. Do yourself a favor, read these urls I provided. One even speaks about drilling a hole for the pvc, IN A BOAT MANIFOLD. matter of fact, here's some references

http://www.boatstore.com/mercury-quicksilver-21-806603-valve-pcv.html (you can buy one here)

http://www.ebay.com/itm/Mercruiser-...ash=item2eca2aa3bc:g:8pEAAOxyFPNSJ56q&vxp=mtr Top


https://www.glen-l.com/phpBB2/viewtopic.php?t=16238 (Look at this page towards the bottom)

Nova SS Posts: 2433 Joined: Sat Nov 15, 2003 10:42 pm Location: Stirling, ON [h=3]Re: Crankcase ventilation and flame arrestor questions[/h]

• Quote

Postby Nova SS ? Wed Jun 20, 2012 2:01 pm
FWIW, you have to have the crankcase vented somehow or you will end up with leaks. I would have a breather on one valve cover(to allow fresh air to enter the motor) and a PCV valve, with a hose leading to the intake manifold/carb/or flame arrestor assembly, on the other valve cover to allow gasses to escape the motor. Running without a way to vent the crankcase will, as I said already, cause leaks as the pressure builds up in the motor especially on longer runs. (fixing the leak will be a PITA once the motor is in the boat)

 

[ddaydanson]

thanks bigjim, yeah, without the regulator its about 10 - 11 psi (the fuel pressure). I bought a rebulator from autozone for about 39 bucks but am going to purchase a holley 804 because i heard good things about them. this one from autozone seems to creep up and i have to tap it to bring it down.

i preffered to stay with the pcv on this one because that's what this engine called for. once I hooked it up at the bootom of the carb like the holley carb was setup, the oild on the dipstick went back to normal and I was able to read it accurately.

We checked out the gimble bearing and it was bad. the bellow leaked water into that area. Thinking back now I remember it making a humming noise when I would bank a hard port or starboard turn and a noticeable difference in the pitch of the sound when trimming the out-drive. It never dawned on me that it was going bad, but then again the last one I replaced was over 10 years ago on the searay.

Thanks again bigjim for your input. I didn't mean to go off on the other two like i did, it's just the way they continued to insist the engine was blown. It reminded me of that know-it-all friend we all had when we were younger, the one that gets proved wrong time-and-time again but still goes on..lol

 

[TyeeMan]

I have rebuilt 5.7L, rebuilt by Mercruiser, 4 years old. Everything external is new, manifolds, water circulating pump, fuel pump,4 barrel carb, etc. Everything was assembled at Mercury Marine and shipped as complete drop in unit. Put gas and electrical to it and let er buck.

But, , wait for it, , , , there's no PVC valve!! Just a vent coming from each valve cover to the flame arrestor. Egad, clearly Mercury Marine must not know what they are doing!

Pretty sure Merc, and the guys on this board that have been around for a while know very much what they are talking about. Just sayin.. .

 

[scoflaw]

It's a PCV valve not PVC, and yes indeed Merc uses them

 

[Scott Danforth]

Other than a few ford based motors of years past, stock I/O motors do not have a PVC valve. They do not have enough ported vacuum to open the check valve. They have vents to the spark arrestor so the airflow from the motor helps remove vapour

As you get into boosted racing motors, the vents get replaced with a puke tank, then a vacuum pump and puke tank combo.

However stock I/Os only get a vent, with two $.35 plastic elbows and $0.40 worth of plastic hose.

Same for Mercruiser, volvo, indmar, ilmor, PCM and others.

However some of the EFI motors are now coming with CATs and improved aerosol recovery

 

[scoflaw]

0w345831
0l352976
0l325388

​These are my last 3 merc engines, all 3 had a pcv valve

 

[jrs_diesel]

I guess my Cummins should have all sorts of leaks by now since its crankcase vent goes nowhere near the intake. (sarcasm)

In all seriousness, it does have a crankcase vent, but it vents to the atmosphere, and not the intake for the simple reason that (most) diesel engines don't have intake vacuum. This is in a truck, but diesels in boats will usually have the crankcase vent routed near the air filter or flame arrester and before any turbo/superchargers. Same thing for gas engines.

The bulk of crankcase fumes is blowby from the piston rings. That has to go somewhere or else you risk blowing out seals (and causing an oil leak) so the block can ventilate itself. We don't want oily fumes to accumulate in the bilge so the valve covers have hoses to route the crankcase gases to the flame arrestor where they get sucked down the intake and then burned. Doing it this way ensures that the fumes will always get sucked down the intake.

Routing the tube to the base of the carb like you did does not help this process at anything other than at idle when there is vacuum in the intake manifold. What concerns me more is that you seem to have more blowby than usual and is pressurizing your block enough to move oil up your dipstick. Do you see a lot of vapors coming out of your vent tubes when the engine is running? Wondering here if you have a blowby issue, or simply a clogged vent tube.

Fuel/oil dilution is a concern too. 2% is considered bad, which works out to 4 ounces of gas in a 6 quart system. You should address this as well.

 

[ddaydanson]

The boat came from Merc with the holley 75021 you can see it at this page: http://www.allcarbs.com/detail.php?pid=1166&mfgn=1&ctgn=50&stt=10&gb=2
​This carb is a marine carb that Merc was shipping with some of their 5.7s at that time. This carb has the vaccum port at the bottom starboard side under the electric choke which goes directly to the PCV. The vent tube went to the top of the spark arrester. Everything worked great in this configuration. I was having issues with flooding and other carb problems so I went with a Cartr carb. I tested the fuel PSI and found that it was at between 10 -11 PSI, which was most likely my problem with the holley, so I regulated it down to 3.5 psi.

The Carter did not have the vaccum port but did have the spot blocked off. When I initially received the Carb and noticed no port, I called the place where I bought it from to ask about it. After I told him the year and make of the engine, he said I could drill it out and connect the pcv. He also recommended I try to connect it to the spark arrester in which I did.

​I didn't notice any issues with the performance, but one day when I was checking my oil level I saw that the oil was all the way up the stick. No matter how many times I'd wipe and reinsert, it still was the same. So after research I found that the PCV configuration was the issue and I changed it, and it worked immediately.

​I believe this year merc has to have the PCV to maintain a positive ventilation hence the name Positive Crankcase Ventilation. I think the vent tube for this year type motor wouldn't be sufficient for it.

The thing that puzzles me is you say there's no vacuum at high idle, but the vaccum at the bottom of the carb seems that it would pull more since the air/fuel mixture is pulling harder to fill the strokes of the piston. In this case the vacuum should be stronger than idle. But non the less, the vacuum on tom the spark arrester definitely wasn't strong enough and this is the same configuration other boats including mine use.

​Just for poop n giggles I think I'll contact Merc and find this out.

 

[ddaydanson]

No Title

Oh, this is the carb showing the vacuum port, and the other picture it the bad gimbal bearing that scared the crap out of me. lol

 

[Bondo]

The boat came from Merc with the holley 75021 you can see it at this page

Nope,.... Yer very, Very Wrong on that, 'n the pcv thing,....

Merc hasn't used a Holley carb in 30 years or more on standard production motors,.... None,.....

Yer motor came from Merc, in 1996, with the Merc/ Weber/ Carter AFB carb, 'n crankcase Vents to the carb cover,....
No pcv valves, Nowhere on it,....

Some of the electronic motors have a pcv, but no carbed motors used 'em,... Just open air Vents,...