NGC: outboard motor diagnosis

[Moto]

Here's a problem I'm having trouble diagnosing for my 2005 Mercury 4HP four-stroke outboard motor, on my sailboat. I hope some of you can help.

I overheated it after launching on a calm day and motoring toward my mooring. I didn't notice any problem until the motor began to slow down while I was going at low to moderate speed. I saw a bit of smoke from under the head unit cover. I then saw that the cooling system had failed -- no output from the weep hole, which I hadn't checked somehow. Later, with no wind available, I used the motor again after it had cooled, for a short time to get back to the harbor.

On inspection, the impeller had failed, so I replaced it and started the motor up in a bucket at my house. It started on the first pull, as usual, and ran fine at idle for about a minute. Then I relaunched my boat and hoped it would work as usual.

Instead, it started on the first pull, as usual, but died within 5 or 10 seconds. It was then impossible to restart, so I pulled the plug and observed liquid gasoline on the electrodes. I let the motor cool, and replaced the plug with a an old clean one and then a brand new one. It started two or three times after that, but never easily, and died with two or three seconds. I never saw liquid gasoline in later plug removals, though I could smell gas on the plug.

I took the boat and motor home, cleaned the carb jets with compressed air and reset the float level -- my real goal was to see if there was something suspicious with the carb, but I didn't find anything. I also drained the gas and replaced it with fresh. (I always use non-alcohol premium, btw.)

I also measured the resistance of the coil. The primary resistance is about 0.3 ohms, within spec, but the secondary seems to be 6200, outside the 2000-4000 ohm spec. (I'm not real confident in my $40 multimeter.)

So my questions to the group are:

1) Is it the coil, and was that smoke a telltale sign? (It seemed to come from under the upper unit cover.) My supposition is that the damaged coil is marginal, so that the engine can start (and sound fine) sometimes, but that the coil fails very quickly from internal warming once it does. Does this make sense? Is it diagnostic of the trouble?

2) What other explanation seems possible?

Thanks. I may delete this thread after I get some useful responses, to avoid cluttering up the forum. I'm at the point of giving up and giving it to some outboard repair shop.

As I write this I seem to understand the problem more clearly, and it does seem to be the coil. But if I get confirmation from some of you gurus, I'll feel better about ordering a new one. I'm a little iffy on the plausibility of the initial overheating due to the impeller failure having then caused the secondary circuit coil resistance to increase.

On the bright side, compression seems normal.

Moto

[Triple Jim]

A coil swap with a known good one (or good ones) seems like a worthwhile thing.

It's easy enough to check a 5,000 ohm resistor with your meter to check its calibration.

[Two Checks]

I think you are on the right track. Good compression shows the rings/cylinders arent hurt.

Curiosity...what kind of sailboat (NGC)?

[uncle]

You might look to the fuel pump.  I have seen the thin rubber membrane get messed up and pump too much gas a well as too little.  It might be that if it got too hot under the cowling that it cased a pump issue.  There are rebuild kits that are cheap,  but a new pump isn't too expensive either.

[oldbike54]

 Just curious , have you actually tested the compression ?

 Dusty

[Moto]

Just curious , have you actually tested the compression ?

 Dusty

No, you caught me! I couldn't find an adapter that would fit, in my collection. It feels like it did before, more or less, when I pull. [EDIT: There, I just ordered one, to arrive Sunday.]

Triple Jim, That's a good suggestion! I went to Radio Shack for a resistor. My gauge checked out OK.

Two Checks, It's a 1982 Slipper 17. Nothing fancy, but a money pit compared to a 1976 Guzzi T3! Thanks for asking.



Moto

[StuCorpe]

I like both the boat and the bike!

[Moto]

I like both the boat and the bike!

 

Dusty, I went back out and pulled the motor through a few more times. Now it seems like essentially no compression. Before it must have been wishful thinking. I'll do a compression test on Sunday when the gauge adapter comes, and then will have time to strip it down as needed. Sigh.

As usual, talking issues through with the group seems to have helped.

Moto

[oldbike54]

Dusty, I went back out and pulled the motor through a few more times. Now it seems like essentially no compression. Before it must have been wishful thinking. I'll do a compression test on Sunday when the gauge adapter comes, and then will have time to strip it down as needed. Sigh.

As usual, talking issues through with the group seems to have helped.

Moto

 Let's hope it is just a blown gasket . The "puff of smoke" mentioned in your OP kind of gave it away .

 Dusty

[charlie b]

On other motors I've seen with overheating issues the head gasket fails.  Problem is the source can be a warped head from the excess heat.  Not sure if the little motors react the same or not.

[Muzz]

If you are runining it in salt water now would be a good time to make sure the water intake and the galleries are not clogged with salt.

A blocked intake will lead to premature impeller failure.

[Moto]

On other motors I've seen with overheating issues the head gasket fails.  Problem is the source can be a warped head from the excess heat.  Not sure if the little motors react the same or not.

That's what I'm expecting.

[normzone]

Now you have an opportunity to port and polish it - you could tear it all the way down and do static balancing! Wait a minute, does it have more than one cylinder ?

Do we still do those things ?

[boatdetective]

I'm not sure about your access- but snake a light into the plug hole and have a look see. I am now using a thin LED light like the following:https://www.amazon.com/Streamlight-65618-Stylus-Flexible-Arctic/dp/B00008BFS6/ref=sr_1_1?ie=UTF8&qid=1470456067&sr=8-1&keywords=stylus+reach

You want to look at the cylinder walls. The greatest heat build up will be right there in the cylinder and there's a good chance you can scuff the cylinder. Once aluminum deposits on the rings, then you have aluminum to aluminum contact- and rapid galling (adhesive wear). I typically see this type of damage inside overheated outboards (and looking at failed marine engines is my bread and butter )

[Two Checks]

Nice trailer sailer, Moto. I was in the market for one a couple years ago but had to put new HVAC in the house and that put an end to a boat.

Good luck with the outboard.

[Moto]

Update: The compression tester adapter arrived.

Pulling the starter rope with somewhat more effort than usual produced readings of about 30 to 60 psi, after five pulls, throttle and choke open, cold engine. (The Clymer manual said to use "normal cranking speeds.") But when I used both arms and really hauled, I could get 125 psi after three pulls. (I confirmed that reading with two different gauges.)

The manual gives these specifications:
    8.5:1 compression ratio
    36-50 psi
    99-127 psi [normal compression measurements with decompression mechanism disabled]

I couldn't find a decompression mechanism in the parts diagrams or on the engine, though one is claimed in the sales literature as well as the manual. Evidently it was disabled (if it exists at all) when I achieved 125 psi. EDIT: I found the decompression release in a diagram. It operates like a mechanical ignition advance, with a weight that pulls a lever as speed increases, disengaging the compression release. I just pulled the cord fast enough for that disengagement to occur -- faster than usual manual starting.

I also noticed that when I pulled more vigorously I could again feel the compression, unlike my report of two days ago.

With that much compression I resolved to try again. I used another new plug and my more vigorous pulls. The motor started but barely wanted to run, needing full choke for maybe a minute -- before the overheating it had needed it for only a few seconds. After a minute or so it seemed to catch its full breath and accelerated. It ran normally in a bucket, sounding fine, for 11 minutes (with cold water refreshers).

As I now think back on the original failure (due to overheating), the slowing of the engine was almost surely a seizure. I don't know what the smoke coming out of the cowling was -- could be electrical or the gasket. I think it was blueish, for what that's worth. Maybe hot oil.

I suppose I may have damaged the rings, etc., but that they may seal up more when the motor gets warm. I'm very tempted to relaunch, and use the motor very sparingly. I only really need it when going in and out of the little launch harbor (or in dead calm, if my kid has an appointment!). I keep the boat at a mooring, so may need the motor only a couple of times if I play my cards right. Is this a bad idea?

I'll be out of town for a few days, but will buy an Android LED boroscope (~ $20) to look at the cylinder walls when I get back. Thanks to BoatDetective for the LED light recommendation, but I think the deep 12mm spark plug hole won't provide a direct line of sight.

Unlike a Guzzi, the cylinder is cast as part of the block, so complete disassembly seems to be needed to address new rings, piston, re-honing. I wonder if I'll need to go there. New power heads (motors) are $750; new complete outboards are $1350.

Thoughts and suggestions welcome.

Moto

[Moto]

You want to look at the cylinder walls. The greatest heat build up will be right there in the cylinder and there's a good chance you can scuff the cylinder. Once aluminum deposits on the rings, then you have aluminum to aluminum contact- and rapid galling (adhesive wear). I typically see this type of damage inside overheated outboards (and looking at failed marine engines is my bread and butter )

BD,

Looking again at your post, it seems that a reasonable move would be to replace the rings ASAP to avoid the progression of the galling. Could that be enough, or is a rebore, etc., always needed?

Moto

[boatdetective]

If you have severe scuffing- then you are beyond boring.

I forgot to mention- did you check the lube oil for sparkly bits? You can always cut open the oil filter and spread the paper out- it will tell the story if anything has been chewed up.

[Penderic]

Maybe room for one more ......





 

[Moto]

I just got back from a trip, and I'm back to square one with the overheated Mercury 4HP four-stroke.

The oil has no discernible metal bits in it at all, at least by my eye. I drained it from the plug at the bottom of the sump. There is no oil filter on this little engine, and not even a strainer. The measured compression is actually right in the specified range.

However, the motor is now hard to start, while before it wasn't.

I can't see it being a carburetor problem (I checked the carb and found nothing). Timing is electronic, and presumably unchanged.There isn't much else to consider, I think.

So I am again left supposing that the high resistance of the secondary coil winding, 6200 ohms versus the specified 2000-4000 ohms, could cause a weak enough spark to account for the hard-starting problem. (I bought a resistor to verify my ohmmeter is accurate, and I also pulled off the ignition wire to confirm the problem is in the coil itself.)

I saw smoke -- a waft rather than a puff -- maybe blue, when the motor overheated and seized. I no longer think this was likely to be the result of a blown head gasket, given the good compression. Could it have been the coil smoking?

I don't see an argument that high temperatures might increase the resistance of the coil winding. Can anybody offer an explanation? If so, I'll be more inclined to pay $100 for a new coil. I'd hate to waste the money if it doesn't make sense.

It's been a very good motor until now, and I'd rather keep it running than put it up on that rail with Penderic's collection! It seems to me that it is still in overall good condition, even though it had a minor seizure.

Thanks for your ideas.

Moto

[oldbike54]

 If in fact it seized up this isn't a coil problem .

 Dusty

[Sasquatch Jim]

 A boat that size could be fitted with oars or a sculling oar to get in and out of the harbor.  For that matter it should be capable of sailing into its' own slip.  Note that old sailors did not have motors, yet somehow they got into and out of their slips.  Drop the main and enter the moorage area under jib alone, as you can cast it loose as you arrive.

[Penderic]

Not very helpful but I found some old manual prop drive pics ......   







There are people that restore old outboard motors too. Wouldn't mind one of these....


Collectors! 

[Moto]

A boat that size could be fitted with oars or a sculling oar to get in and out of the harbor.  For that matter it should be capable of sailing into its' own slip.  Note that old sailors did not have motors, yet somehow they got into and out of their slips.  Drop the main and enter the moorage area under jib alone, as you can cast it loose as you arrive.

Not as easy as it seems. The passage to the launching ramp is too narrow for tacking and the boat is 1250 pounds, 8 feet wide, with high gunwales and poor rowing or sculling prospects.  For day sails from my mooring, though, no problem. I suppose I can use the other, sailable harbor, and avoid starting the motor at all the rest of the season, until I have time to deal with it.

[charlie b]

Me?  I'd replace the coil and try again.  At least get rid of that factor or solve the problem.

[Moto]

Me?  I'd replace the coil and try again.  At least get rid of that factor or solve the problem.

I think I'm coming around to that. With good compression, and no obvious reason to suspect carburetion or ignition timing, something must be wrong or else it would start as before. The wind's coming up now so I'm going to launch under sail from the other harbor.

I think when I do get the head off later on I can hope to see minor damage.

Here's an optimistic account based on past experience (http://www.smokstak.com/forum/showthread.php?t=70544):

Andrew Mackey
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Exclamation Re: Seized piston engines can run again but not for long? WHAT DO YOU THINK?
I have worked on many 2 and 4 cycle engines that have seized and ran again! Quite a few loosened up when they cooled off, Put 16:1 mix in them, and they ran good! I had a customer bring in a Sears blower. Her son ran a full tank of straight gas in it before it died. It was locked up tighter that tricky dicks hatband! I put kerosene in the cylinder, left it to sit overnight, and the next morning, gave the starter a yank for the hell of it. man was I surprised when it pulled over!. I put some SAE 30 in the carb and the cylinder, and pulled it over some more. Fresh 16:1 with SAE 30 non detergent oil, a couple of yanks, and the machine fired up and ran pretty good. It continued to run another 3 years before a second dose of straight gas did it in. This time, melted aluminum was visible in the muffler, without taking it off the machine!

A shop I used to work for when I was a kid, used to free up stuck engines all the time. If after freeing up, they didn't smoke too bad, they were returned to service! The engines were used on MOPECO heater blower units, used to blow and heat fresh air into manholes for Public Service Utility. The operators almost never checked the oil on their equipment, and every piece of equipment I worked on for them had seized at one time or another! We sold more Kohler pistons than I could count! More often than not, the heads were pulled, and kerosene was poured on top of the puston. We has a special oak block turned to fit the cylinder within .020" of the cylinder diameter. The block was placed on top of the piston, and given a sharp rap with a 2 pound maul. If the piston came loose within a couple whacks, and at bottom Dead center there was no aluminum transfer on the cylinder, the engine was flushed out with kerosene, fresh oil put in the case, and the engine would be test run. If it was quiet (no rod rap), it was returned to service. Heavy smoke, rod rap, or aluminum in the cylinder meant engine overhaul, usually a honing, new piston and con rod, and a gasket set had the engine running just fine. Occasionally, we would find the crank blued by the overheated bearing. The aluminum would be scraped off the crank, the journal polished with 1,000 grit crocus cloth, and the engine would be re-assembled, none the worse for wear!

B&S engines, seized, were an easy fix. Flush out the crankcase with kerosene to remove any debris. Remove the spark plug. Add a mix of 1 pint kerosene and 1 pint SAE 30 oil to the crankcase, turn the unit upside down and let it sit 24 hours. Next day, turn the unit upright, remove the starter cover, and put a flat jaw monkey wrench on the starter pawl, and turn the engine over. Usually the engine would turn, hard at first, but would loosen up in short order. The starter would be re-installed, the spark plug re-installed, and then the engine would be started and run for about 10 minutes with the kero-oil mix in the case! The oil/kero mix was then drained, the crankcase filled to the proper level with SAE 30, and the unit test run again for 1/2 an hour, at full load. If it ran good, and didn't smoke too bad, $75 Please, and off you go! Some B&S engines would lock up 2 or 3 times before they would blow up, usually because they were again run out of oil! If the engines smoked too bad, they were replaced.
Andrew

At 4 horsepower from 123cc, my Merc has pretty low specific output, so maybe it's less likely to blow things up at a low-throttle partial seizure. It only slowed and then died, but never literally froze up.

The wind is calling.

M.

[LaMojo]

If the spark plug has a healthy spark, I wouldn't waste money on a new coil. 

I would go ahead and pull the head and have a look see.  Won't cost more than a head and valve cover gasket to put back.  You may find that the head gasket shows some blow by when the head warped from overheating (Where the smoke came from), but I would have thought that there would have been some water in the oil.  I'd take the head to a outboard mechanic to have it checked out, that is, if the cylinder hasn't been ruined.  A crack may have developed around the valve seats.  Pull the thermostat and put it in a pan of about 150 deg. of hot water and see if it opens.  Replace the diaphragm in the fuel pump if it has one.

Simple engine should be easy to work on.  When trying to remove bolts, slowly TIGHTEN slightly before trying to remove them.  If they become stubborn to remove, alternately tighten and loosen the bolt easily until it is free.

If the spark plug didn't show any unusual deposits on the electrode, the piston and cylinder is probably O.K.  That leaves probable head problems.

[oldbike54]

 I had an old stationary engine on a generator with a small crack in the head . Would show about 110 PSI of compression when stone cold , but as it warmed up the crack expanded and things went woogity .
 

 Dusty

[charlie b]

It's hard to judge a coil by spark without compression and fuel.  What 'looks' like a healthy spark can be not enough to light the fuel mix.

Head gasket and/or warped head are still at the top of my list too.  Cracked head/cylinder is also a possibility, but, I would say less likely.

Coils are cheap, especially since this one does not seem to meet spec.  If a new one still shows problems then pull the head. (I'd probably pull the head anyway just to see if anything else is amiss).