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  #1   IP: 76.64.226.164
Old 07-07-2018, 09:26 PM
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Exclamation Crankcase Smoke

Hi, I'm new to this forum..

I have a 1970 C&C Corvette with the venerable A4. Had it for 15 years around with no major engine issues. This year for the first time, under load the there is smoke coming out of the crank case center hole.

I've been reading that this may be caused by worn rings and 'blow by' into the crank case.

Also I see Indigo sells a Crankcase Ventilation System..

Anyone have any experience with this retrofit? Does it work?

Does Moyer have a similar kit?

Am I just delaying an inevitable engine overhaul?

Is there anything else more sinister that could be causing this? I'm reluctant to run the engine much until I'm confident it's safe to do so..

Thanks very much for your thoughts...
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  #2   IP: 76.7.110.221
Old 07-08-2018, 08:31 AM
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Marian Claire Marian Claire is offline
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Welcome to the forum. A compression test may help evaluate how each cylinder is preforming. I have never had a PCV valve but I think in general they work. The rub is that you are treating a symptom and not the problem. How you plan to use the boat is a factor. I do not think you will be doing any harm to the A-4 running the engine if it is just worn rings.
Did the smoke/blow-by begin suddenly?
Dan S/V Marian Claire
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  #3   IP: 76.64.226.164
Old 07-08-2018, 08:55 AM
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Thanks for your input..

Yes it just started suddenly this spring after launch

I am planning to run a compression test soon.
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  #4   IP: 76.7.110.221
Old 07-08-2018, 09:26 AM
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"Is there anything else more sinister that could be causing this?"
Years ago I was motoring and heard a "crunch" and instantly smoke was puffing out of the oil fill. The engine ran fine but seemed to have lost some power. She got me back home, a trip of over 1000 miles and I did a compression test. One cylinder showed about 45 psi. The others 120+- psi. I planned to make more long trips so I decided to rebuild the A-4 and found that the rings in the low compression cylinder had snapped/broken. A rare occurrence.
Dan S/V Marian Claire

Last edited by Marian Claire; 07-08-2018 at 11:02 AM. Reason: corrected compression #s
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  #5   IP: 32.211.28.40
Old 07-08-2018, 01:22 PM
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Rings do wear out, and will cause smoke in the cabin. The PCV system will work for minor cases of smoke, but the problem will soon overpower the PCV. Rings are supposed to have an end gap of about 10 mils. My first engine tear-down, I found that the lower rings had over 100 mils end gap - they were just going along for the ride! New rings (and a new transmission seal) brought the engine back like new.
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Old 07-08-2018, 01:23 PM
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I can testify that the PCV kit pulls smoke and fumes in the crankcase back into the combustion chamber, and keeps the air inside the boat cleaner. IMO this is a CO safety issue. Your rings may be worn, but the A4 will still run, if less powerfully. I change oil every 50 hours, and add 8 oz of MMO to 3 quarts of new 15w40 'diesel' oil. I also put 2 oz of MMO in 5 gal of fuel. In 2500 hours of operation I have not removed the head or the valve cover. Compression is still over 100 on three cylinders, and 95 on #1. When I remove the PCV I can see a difference in the air quality. If you don't have a PCV there should be a hose from the crankcase side to the flame arrestor at the air intake. If the opening in the side of the crankcase is closed,smoke will exit from behind the flywheel, and from the oil fill tube if the cap is off.
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  #7   IP: 76.64.226.164
Old 07-09-2018, 11:17 AM
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Thank you all..

A teardown and ring and/or valve replacment job is above my pay grade as they say.. If I bring in the marine mechanic to do this worst case, any ideas on how many hours this should take a competent machanic to do? Dont want to be ripped off, the boat is worth practically nothing on paper these days unfortunately...

The engine is having other problems as well, which I'm not sure is related to the smoking or not.. Its running very rough and surging / spluttering. Won't hold constant RPM.. Ive replaced fuel filters and spark plugs to no avail. I have eletric fuel pump, would that possibly be the culprit? I would think it would fail outright, not partially if it was bad?

Any other tips? Bad gas maybe? Should I tear apart the carburetor? Replace the ignition coil, distributor cap and/or cables?

I'm getting a bit out of my depth.... :-(
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  #8   IP: 72.194.219.196
Old 07-09-2018, 12:04 PM
JOHN COOKSON JOHN COOKSON is online now
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Quote:
Originally Posted by Frostp View Post
The engine is having other problems as well, which I'm not sure is related to the smoking or not.. Its running very rough and surging / spluttering. Won't hold constant RPM.. Ive replaced fuel filters and spark plugs to no avail. I have eletric fuel pump, would that possibly be the culprit? I would think it would fail outright, not partially if it was bad?
Any other tips? Bad gas maybe? Should I tear apart the carburetor? Replace the ignition coil, distributor cap and/or cables?
I'm getting a bit out of my depth.... :-(
Your "depth is is fine. You are aware of possible problems.
Rather than jump back and forth between systems (fuel, ignition) let's start with one system and be sure it is correct before moving on to other possible problems.
Water in the gas can cause all sort of weird running problems. So try running from an auxiliary fuel tank directly to the carburetor and see if the rough running goes away. Then we will know if the (possible) fuel problem is related to the boat's part of the fuel system or the engine's part of the fuel system.
All of the above is in IMO only. There are other valid approaches to trouble shooting.

TRUE GRIT
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Old 07-09-2018, 12:11 PM
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I have the Indigo kit and it does work. Sooner or later you'll want to fix the engine, but this is a good stopgap and every modern engine has this system.
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  #10   IP: 76.64.226.164
Old 07-09-2018, 09:28 PM
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Thanks again all...

Think I found the cause of my sputtering.. There was a loos-ish wire between the oil pressure switch and the fuel pump. Re-crimped that, and seems to be running smooth now. Although only a short test, will need to do a longer sea trial until I fully declare vicory on that ;-)

Did a compression test.. Had 100, 90, 90 and 60 psi. Re-ran the test on the 60 psi cylinder after putting some oil in it per suggestion on another thread here, and it bumped up to 110 psi.

So I guess the rings and/or valve guides are worn as suspected. I will order / install the crankcase vent kit and investigate additives to help the old-girl along here in her golden years or until I break down and have the engine rebuilt or replaced...

Cheers
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  #11   IP: 32.211.28.40
Old 07-09-2018, 11:05 PM
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Frostp,
Doing an engine overhaul when not under pressure (ie: over the winter) is an enjoyable task - perhaps even therapeutic. Yes, you'll have to find a shop to do the stuff you can't do (grind/replace valve seats) but most of the stuff is easy. Get a copy of the Moyer overhaul manual (highly recommended) and at least read through it.
You can do you present engine or find another to rebuild. My original engine was junk (cracked block) but the two others I've rebuilt, one was free and the other cost me about $300 in pieces. Fortunately I did the first overhaul before I needed it. The second is still in my garage!
Any engine you consider buying, give a good inspection to the block for cracks in the area near the valves. Also good to check the block for corrosion - see how much metal is left in the area around the head studs and the manifold studs. Pull a few studs and probe with a hooked piece of wire to check wall thickness - nice to have at least a stud diameter in wall thickness.
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  #12   IP: 76.64.226.164
Old 07-10-2018, 09:27 AM
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Thanks Al.

I'll definitely consider the options when we get closer to lift out time this fall. Major mechanical work like yanking engines and rebuilding I've never done, and am somewhat leery as I don't have that kind of expertise.. Certainly learning quickly though lol...

Afraid of breaking stuff and making matters worse...
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  #13   IP: 69.161.109.238
Old 07-10-2018, 07:55 PM
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Worn Exhaust valve stems& guides also lets pressure into the crankcase.
I replaced mine with stock- snug fit-(not reamed) guides,and noticed
less blow from the oil fill cap.
I already have great compression, but the spent gases seemed to find their way into the crankcase at 3,500 rpm
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Tyring to keep the Bay's Wooden Boat's history from dying off completely.
Daniel
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  #14   IP: 32.211.28.40
Old 07-10-2018, 09:42 PM
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Hey, at 3500 RPM you're lucky the valves don't find their way into the crankcase!
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