1976 Merc 3.0L (140) Smoke from flame arrestor

[tiku]

Hi folks!

First, a little background information. The engine has not seen too much attention before (purchased the boat this summer) and I believe that it has vacuum leaks, etc.

I got it running fine after I changed filters, did the tune up, plugs, oil changes and adjusted valves. The engine has been hard to start but worked well. Then suddenly (during the last trip this summer) after taking the boat off plane and running at low rpm's for couple of minutes the engine developed rough running and started to die. I limped back home after some serious restarting.

Back at the dock and when trying to restart, it takes about 30 attempts (even with quick start spray). It won't idle below 1000 rpm and it still is rough. The thing that bugs me is that after failed starts there's a small cloud of white or light gray smoke coming from the flame arrestor. I have adjusted the carburetor and I believe that the mixture is about right even thought there is a slight "popping" sound coming occasionally.

The engine is going to be rebuilt this winter but I'd like to have an idea what's causing this. Anyone to the rescue?

 

[getinmerry]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Could be fuel, spark, timing, valves, or almost anthing. Some more information would be a help.

 

[Windykid]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Might want to check the carb float.

 

[180shabah]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Couple of questions:

What makes you suspect a vacuum leak?
Why do you think the engine needs rebuilt?

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The mixture adjustment screw/s on the carb only affect idle mixture.
you need to do some troubleshooting before you start waisting time and money. You have new plugs, did you set dwell and timing? You said that you think you adjusted the mixture properly, how can you tell if the engine won't idle. Did you adjust the choke to spec? Is the carb in need of a rebuild? What is the condition of the gas? Do you have a water seperator? Have you done a compression test(leakdown test would be even better). What is the vacuum at idle?

 

[Haut Medoc]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Do a compression test.....​

 

[tiku]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Details, here they come (at least to some extent)

The engine has idled perfectly before, this symptom appeared couple of days before I took the boat out for winter.

I am planning on doing the carb rebuild during the winter and no, I have not checked the float yet. (had no need, it was running ok) Previous owner has disabled the choke. (butterfly valve is in vertical position, no heat pipe) Propably it has it's effect on the hard starting .

The reason why I'm opting for a rebuilding job is that previous owner had blown the exhaust valve on 4th cylinder and in addition I think that since the engine is over 30 years old and I have no idea how it has been maintained I'd like to play it safe. The spark plug in the number 4 cylinder is also concerning me. It has a rusted look on it. (water in cylinder?) The others are are fine.

When the engine was operating properly there was a metallic rattling sound at around 1200-1300 rpm's. I know that it can be anything from a loose bolt to exhaust shutters, which I'm also planning to replace. Idle rpm was set to around 500 rpm with gear forward and the engine runned smooth as silk. (except the occassional misses)

Also, there is what I believe to be excessive blowby when you open the valve cover oil fill plug. I asked my local shop what could be the reason why I have milky (mayonese like) oil in my filler cap and in the tube that goes from valve cover back to carb. They suspected blowby and moisture to do this. In their opinion this blowby is caused by normal wear and tear in a over 30 year old engine. There was no milky oil in dipstick. When I added STP's stop smoke additive it seemed to further ease the engine and reduced some noices.

Dwell and timing were set by a friend of mine, so I believe that they are correct.

My WOT rev's are 3900, far away from the recommended. This could be the prop but again I'm not sure. I havent tried any others.

I also have concerns over the appearance of the seals that previous owner has used. They are more or less gaskets that come from a tube. Effective? could be, trustworthy? Dont really know..

The reason why I'm suspecting leaks is that the smoke that comes form the flame arrestor seems to be eminating also from the head to manifold seam. There is also a hissing sound that can be heard after unsuccesfull starts.

I'm planning on doing full restoration to this boat, so therefore I want to get the engine just right. Anyway, I'll do a compression test next weekend and take it from there.

 

[tiku]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Compression test has been done.

Cylinders (about results):
1= 150 psi
2= 10
3= 10
4= 150

Adding oil did not change the results.

After removing the exhaust manifold and carb I pulled the head. The reason for low results on numbers 2 and 3 was a blown head gasket, neatly burbed through the wall between the two cylinders.

I also tried a "test" recommended by an old mechanic and mixed some gas and oil and poured it on top of the pistons and waited to see how long it takes before it drains to crankcase. This test is supposed to tell its tale on the sealing ability of the piston rings.

The results were that the oil&gas mixture was still floating on top of the pistons when I left the boat. My guess is that it took about an hour or so... So it is reasonable to believe that they are fine. There were no scratches or other marks on the cylinder walls.

Also the intake & exhaust manifold looked fine to me after 30 years of service (I'm assuming its the original one)... All it needs are new seals and some rust removal and a touch of paint.

In short, instead of doing a rebuild I'm opting for the head to be resurfaced and for a carb rebuild kit... Hope it works.. Thank you all for your help..!

 

[180shabah]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Sounds like a plan to me, good luck.

 

[Haut Medoc]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Compression test has been done.

Cylinders (about results):
1= 150 psi
2= 10
3= 10
4= 150

Adding oil did not change the results.

After removing the exhaust manifold and carb I pulled the head. The reason for low results on numbers 2 and 3 was a blown head gasket, neatly burbed through the wall between the two cylinders.

I also tried a "test" recommended by an old mechanic and mixed some gas and oil and poured it on top of the pistons and waited to see how long it takes before it drains to crankcase. This test is supposed to tell its tale on the sealing ability of the piston rings.

The results were that the oil&gas mixture was still floating on top of the pistons when I left the boat. My guess is that it took about an hour or so... So it is reasonable to believe that they are fine. There were no scratches or other marks on the cylinder walls.

Also the intake & exhaust manifold looked fine to me after 30 years of service (I'm assuming its the original one)... All it needs are new seals and some rust removal and a touch of paint.

In short, instead of doing a rebuild I'm opting for the head to be resurfaced and for a carb rebuild kit... Hope it works.. Thank you all for your help..!

I would replace the manifold & riser.......

 

[tiku]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Well folks, I decided to pull the engine from the boat and to tear it down to pieces. Eventhough it looks good I just want to be sure. So bye bye cash...

First notion was that the bolts that keep the front engine mount (stringer) attached were simple wood bolts and they really were not tight. They are bolted to plywood that has had it's share of moisture. The rear one's were nearly welded though.

So, now the block and all accessories are worked on, clening (glassbead blasting) and then off to the shop. The things I know so far are that I need a new alternator, piston rings and seals.

Are there any good rebuild kits for this engine? I am not even asking if I could crank up a few HP's from the engine.. I'm under the impression that 140 is as much you can ask for.

Would this kit be any good?
http://greenbaypartsworld.net/webstore.cfm?action=product_view&page=G181AM

Stille motre related questions, what paint should be used on the enigne, black of course but what kind? What about the sterndrive? How shoul it be painted?

 

[Bondo]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

The reason for low results on numbers 2 and 3 was a blown head gasket, neatly burbed through the wall between the two cylinders.

Ayuh,......
A Very Close Inspection of the Block in this area is advised,...... You may need to deck the block a few thousandths to properly Clean up the burn-thru......

what paint should be used on the enigne, black of course but what kind? What about the sterndrive?

Ayuh,......... My motor is covered with Rustolium,..... So's the Outdrive......

How shoul it be painted?

Clean, Sand, Clean, Prime, Paint,............. Pretty much like anything else........

 

[Don S]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Replace those rear motor mounts. They have cost many a coupler and an additional engine pull to replace them. Since it's already out, replace them. Just be sure to read the instructions carefully with the new mounts..... They mount different than your original.
I seriously think you are wasting money on the kit. You don't need pistons, cam, or lifters.
As long as the pistons, cam, and crankshaft bearing surfaces look good, just rings, bearings, and some serious head work should make it like new.

I'm with Bondo on the Rustoleum. While it's slow drying, it stands up to the marine enviornment nicely. On the drive, it really shines (Pun intended).

And make sure all the rotted wood in the transom, stringers, or mounts are repaired before you put it back together.

 

[180shabah]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

I'm with Bondo on the Rustoleum.

I'm with Bondo as well, just try to avoid any temptation you may have to use CAT yellow

 

[tiku]

Re: 1976 Merc 3.0L (140) Smoke from flame arrestor

Thanks for the advices.

Hmm.. I suspected that some care has to go into the rear engine mounts, also I'm planning to tear apart the softened wood under the stringer.

I also hope that new pistons are not required, hopefully new rings will be enough. The block itself and the head are going to be checked and properly fixed. I have a cousin that works with racing engines, so I trust him on this.

Is there any other way to remove the gimabl housing other than obtainig the hinge pin removal tool? I have those screws on the side and I'm wondering if I really need the special tool. Since the engine is already out why not dismantle the transom assembly, check and paint it as well. (The boat also leaked a little this summer, time to check gaskets)