Trouble after intake manifold replacement

[carrier82]

The thing is, I recently replaced the intake manifold of my old Bayliner. The engine is a generic 350 with Cobra parts. The manifold I replaced was Edelbrock Performer made of aluminum. As the boat is in salt water, the aluminum corrodes so bought a used steel manifold. The manifold I bought is from some Mercruiser engine (quadrajet). Used previous carb with an qj->edelbrock adapter. I had to drill the four center bolt holes a bit as the manifold was likely made for some earlier model of 350 with different bolt angling. Timing set to 8 degrees BTDC @ idle, same as before.
The engine worked well, until today I went for a slightly longer test drive. After approx 10 minutes i smelled burning oil and noticed that there was oil on top of the valve covers. The exhaust manifolds were very hot. One of the exhaust manifold rubber joints got damaged because of the heat. So I limped back home at very low rpm.

The main difference between the two manifolds is that the Merc manifold has two water channels blocked, but the edelbrock intake has all four water channels open. I was thinking that marine engines don't need four water channels as the Edelbrock intake is likely an automotive part. Before switching back to the aluminum intake for this season, I would like to hear your opinions, please

 

[Bondo]

Ayuh,..... Check, 'n change the raw water impeller 1st,.....

I truely doubt the intake manifold is the problem,....

If the impeeler is good, I'm guessin' clogged risers,....

 

[carrier82]

Temp gauge showed a steady 175F with engine running smoothly all the time. The water flow was good on muffs as well. Impeller was replaced last season. Btw, I also noticed a sudden rise of oil pressure before the incident. To me this feels more complex.

 

[carrier82]

After giving this a second thought, I came to suspect intake leak. If i remember correctly, only the port side exhaust was hot and oil spilled on the port side valve cover. I have AFR meter installed which showed normal readings but it's installed on the starboard exhaust manifold. Is it possible to have a leak that only affects cylinders on one side?

 

[carrier82]

Sorry for the dumb question. Of course it is...

 

[Bondo]

I had to drill the four center bolt holes a bit as the manifold was likely made for some earlier model of 350 with different bolt angling.

Ayuh,..... Did you use the special angled washers with the manifold conversion,..??

If not, that explains the oil leak,....

Those bolts need sealer too, as the go into the oil galley,....

 

[jimmbo]

Pictures of the these manifolds would be nice. You said you had to drill 4 bolt holes. Was that redrilling, or making holes where there were none before? Were these in about the center of the length of the intake?

 

[carrier82]

Bondo. No I didn't use angled washers but I did grind the manifold "bolt base" to be fit. It might be it wasn't good enough. Jimmbo I drilled the existing four holes at the center of the manifold to a different angle. Bolts 1 to 4 in the linked picture. I hope the rise of oil pressure and oil leaking is not a symptom of head gasket or piston failure...

 

[jimmbo]

As Bondo said, it is doubtful the manifold is the problem. Oil pressure sender might be leaking. Did you ever install a new water pump impeller?

 

[carrier82]

I don't change water pump impeller annually. It was replaced last year. If you mean the one on the outdrive. Engine water pump is 8 years old. Oil pressure sender is unlikely leaking and I haven't done anything to it. To me it seems the oil was leaking from the oil fill cap. As cooling water temperature was normal and the water flow was good on muffs the previous day, I find it very hard to believe that there is a cooling water issue. Next thing I'll do is check compressions / search for vacuum leaks.

 

[Idlespeedonly]

What king of outdrive do you have?

 

[carrier82]

OMC Cobra transom with SEI116.

 

[jimmbo]

You say the oil is coming from the oil filler cap. That could caused from an unvented crankcase. Are the crankcase vent hoses clean and positioned at the spark arrestor? Some marine engines retain a PCV valve, if so, is it and its hose clean?

 

[carrier82]

No Title

The breather hoses that go from top of valve covers to the carb were non-obstructed. Not sure if I have PCV valves. I do have some plastic connectors on top of the valve covers that have 90 degree angle to the breather tube. I was able to suck air through the breather tube with the oil cap removed.

Today I went to check compressions. Fortunately there seems to be no damage due to overheating except for one damaged rubber tube joint. All cylinders showed approx 170psi (cold) and held pressure. I just replaced all the spark plugs before yesterdays test drive, so they are brand new. In the picture one can see spark plugs from port side of engine (right in the picture) and from starboard side of the engine (left in the picture). I have two socket wrenches. One of them wrecks spark plugs... That I had me shipped from UK.

I still believe in my theory of lean running port side cylinder group. Don't those spark plugs (right) look like the engine has been running lean? I was going to plug the AFR meter to the port side exhaust manifold to test for lean mixture. Didn't do that after I broke the spark plug as I didn't have spare ones with me.

To sum up, this is what I know:
- Replaced intake manifold.
- AFR meter showed slightly rich mixture on starboard side exhaust (~12, as supposed).
- Coolant temperature (raw water cooled) was 175F at the time of the incident.
- Oil pressure jumped from 40 to 80 psi at the time of the incident.
- Smelled burning oil and pulled over to check. Engine compartment full of smoke from burning oil.Oil spills around port side valve cover.
- Turned off engine.
- Starboard side exhaust manifold wasn't hot to touch.
- Port side exhaust manifold seemed extremely hot and made popping sounds along with the rubber joint tube almost boiling (didn't have the courage to touch).
- Tried to start my Volvo Penta 4 hp back-up engine. Didn't start. It did start before the test drive at the harbor...
- Started main engine without problem. Back to harbour @ five knots without problems.

 

[jimmbo]

Is the hose from the thermostat housing going to the port exhaust manifold flowing water? On a V8 with a two plane intake, which the two manifolds you have are, 2 cylinders on each head are fed from one side of the carb and the other two are fed from the other side of the carb. So all the cylinders on one side can't be lean without the other side being lean too, unless you have a completely dislogded intake gasket.

 

[carrier82]

I'll check the port exhaust cooling next time I'm at the boat. As all four cylinders are fed with two tunnels from the carb, adjacent to each other, I would guess if there is leakage at the wrong spot, all cylinders on that side could be affected. It'll be next week until I can get to the boat to do some more work.

 

[jimmbo]

No Title

If you are a factory type manifold 2 cylinders on each side of the engine are fed by one side of the carb. The inner two on one side and the front and the rear cylinders on the other side of the engine.

 

[carrier82]

Jimmbo, what you said made me think that there may be other options to engine running lean. Before I proceed working on the boat, I was wondering if the square bore to spread bore adapter I use has something to do with this. I doubt it does, but still asking as I have limited knowledge on these adapters. I have an Edelbrock 1409 carb waiting to be installed to the boat, to replace the automotive Holley I currently have (don't want to do this until the intake manifold replacement turns out well though). In the Edelbrock manual it is said that one must not use "open" adapter instead of a four hole adapter. The adapter I have is open type. Could this be causing me trouble?

 

[jimmbo]

It will certainly reduce the signal the venturies receive at low speed and mess up the metering at low speed. I can't say it would make one side run lean as it is still a dual plane manifold. I can't find a picture of the adapter Mercruiser used to mate the Edelbrock/Weber/Carter carb to the spreadbore manifolds. It was phenolic resin and used large a o-ring in a grove instead of a gasket to seal. It was the best adapter I ever saw, as it did not try to isolate the primary from the secondary as some adapters do, but allowed some of the secondary's flow to the now larger primary passage while tapering the secondary side down

 

[carrier82]

Went to the boat today to do some diagnostics. I did rule out my vacuum leak theory. Tested for vacuum leaks by spraying carb cleaner around the engine and had no response. Moving the AFR sensor to port side showed that it wasn?t running lean. Removed the thermostat just in case, refilled oil level to "full" and went for a test drive. This time I had no issues except having a sensation of "do I smell burning oil?" without any smoke from the engine compartment. At the dock, I noticed that the oil level had dropped back to half full. I?m beginning to suspect I have two different issues:

A) damaged impeller or clogged riser causing manifold to overheat. Neither of the manifolds were not so hot after today?s test drive, although the sea wasn?t nearly as rough as it was the time before. The trip I did was a bit shorter than last time.
B) At the dock, the stern of the boat floats very deep. Replacig the aluminum intake with a cast iron one made the situation worse and with the full fuel tank, I can?t say the boat floats level. Now I?ve added oil at the dock with the engine tilted towards the stern. Could it be that because of this I?ve added too much oil which wants to be burned or be spilled on top of the engine, because the boat levels at cruising speed as bow dives lower (perhaps causing oil level to shift too high)?