Blow-by Oily Smoke

[RandySaint]

Last weekend, we were pushing through some silty mud at low tide and the engine started smoking. As I've investigated, I believe that the smoke is blow-by (it comes hissing out of the oil filler cap) and I will probably be buying the AT-4CVS Indigo PCV kit to prevent the smoke from entering the cabin.

My question is that it appears the blow-by problem happened kind-of all of a sudden, and I'm wondering if this could be an indication of something more serious about to happen.

Some details about my A4
Boat: Ranger 28
Prop: 2 blade
RPMs: even at full throttle, max out around 1200
Oil: full, not dirty-looking

The guy I bought the boat from says that it's 9-10 hours on the motor since an overhaul, but I'm not sure what that entailed.

Bottom line, should I be concerned?

[ndutton]

How long have you owned the boat?
Never smoked before?
Engine temperature gauge functioning? What temperature when this started?

"pushing through some silty mud at low tide" means you were sucking up silty mud into the engine and then the smoke symptom started. I'm thinking there's a connection.

[Dave Neptune]

Hmm?

Randy, first welcome tot the forum. Two things and a bit more. First you say the blow-by started all of a sudden correct? If so not good and maybe not bad. That could be as simple as sticky rings and top oil (MMO) treatments stand a good chance of working. You may want to do a compression check.
The RPM's you are turning are lugging the engine which will exagerate the blow-by. Do you know anything about the prop?
Did you get any papr=er work regarding the rebuild/overhaul?

Dave Neptune

[romantic comedy]

How bad is the smoke? DId you do a compression check after the smoke?
An extreme is that you could have a burned piston, with a hole. Did you lose power?

When my 283 v8 blew a piston, the cabin filled with smoke, and the engine kept running.

[RandySaint]

I've only owned the boat for 3 months.
I hadn't noticed the smoke before, but now it happens whenever the engine is loaded. But after thinking about it, I don't know if I ever really loaded it before. The only times i had run it before was for about 20 minutes to get out of the marina onto the lake or back. The morning it started smoking, we had run it for almost an hour. Had it off for a 1/2 hour. Then, had to push it hard.

When it happened the engine temp was normal, down in the 160 range. (not knowing the boat, I don't know the calibration of the gage, though) although it seemed the manifold was really hot. I initially suspected overheating (and a bad gage reading). It's raw water cooled. I removed the thermostat and tried running it. I still got the smoke, even though the engine was cool. That led me to the blow-by conclusion.

The prop is a 2 blade, looks like about 12". I've never had it out of the water, so don't know much more than that. I know the RPM is lower than I'd like, but was trying to solve other things first. If this is at the heart of the problem, then I may need to replace the prop sooner rather than later.

I have not yet done a compression check post-smoke. Will a finger pressure check be sufficient, or will i need instruments?

[Ball Racing]

While "finger pressure" compression test seem easy,
it is also easy if you do have alot of compression pressure to force air into your skin, and into your blood which is a bad bad thing.
Tools are best.

[Loki9]

If it's really a fresh rebuild with only 10 hours on it, then the blow-by is normal as the rings haven't seated yet. My rebuilt A4 smoked a lot initially and slowly got better and better. It has about 50 hours on it now and the blow-by is mostly gone.

[RandySaint]

Quick compression test (finger over hole) seems that all four cylinders have good compression.
So, I tried adjusting the timing as was discussed in this discussion

http://www.moyermarine.com/forums/showthread.php?t=6408

But it didn't seem to change the blow-by.

Loki9, thanks, maybe this is normal. Did yours smoke right from the start following the rebuild? Or did it come & go as things settled in?
Did you see more when the engine was under load?

Until it settles in and i get the PCV add on, can i just move a blower flexible hose over above the oil filler cap to vent the smoke out?

I saw another post that you could check for metal debris in the oil by running a magnet over the dipstick as you pull it several times while the engine is running. I tried that and found no metal debris in the oil.

So is there anything else I should be looking for that might indicate that this is a more serious problem?

Thanks for all your help on this!

[Sony2000]

I think your primary problem is 1200 rpm. It was never higher, and should be higher with a 12" prop. Call the former owner to make it go faster. The carb should be looked into.

[RandySaint]

In order to get the engine running i had to disassemble, clean and reassemble the carb. The engine will rev high without the propellor engaged. I think it's getting enough fuel.
So if I suspect the prop, I'm thinking that either the prop is too big, there's too much friction on the shaft or there's debris caught on the prop.

[Sony2000]

Some random thoughts:
1. Transmission in neutral, dive under the boat and turn the prop back and forth. (Transmission has oil)
2. Your running on 2-3 cylinders.
3. Your have a partial fuel blockage.
4. Timing is set way after TDC.

[Loki9]

Loki9, thanks, maybe this is normal. Did yours smoke right from the start following the rebuild? Or did it come & go as things settled in?
Did you see more when the engine was under load?

Mine smoked from the start and it was worse under load. I installed a PCV system, it helped but did not completely eliminate the smoke.

[Ball Racing]

If a "rebuilt" engine needs 10 - 50 hours to stop pumping smoke out the base,
something was not corrected during the rebuild.
The cylinder walls must have been out of round really bad, or there were deposits in the ring lands that were not removed.
Or the wrong size rings were used for the bore size.

[RandySaint]

Thanks for all the help!

I put some MMO in the cylinders, let it sit overnight, hand turned the engine, put some more MMO in and then started it up. Lot's of white smoke out the exhaust, but it seems the blow-by smoke in the oil filler tube is lessened.

One thing this helped uncover - while checking for the blow-by smoke, I saw little whisps of white smoke around the manifold. Looked at the back and saw that the exhaust flange gasket was leaking white smoke. I wouldn't have noticed it if I hadn't had to burn off the MMO.

[RandySaint]

RPM question

In regards to my 1200 max RPM under load, I started taking a look at the fuel system. Taking a close look, it appears that I've got both a mechanical fuel pump on the engine and an electric fuel pump upstream.

Could this setup be starving my engine under load?
Perhaps the mechanical fuel pump is unable to provide the flow and the electrical upstream is of no effect due to the mechanical one?

I'm leaning towards removing the mechanical and getting a Blank plate cover and let the electrical do the work.

Any ideas?