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Old 11-10-2019, 17:41   #1
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3GM30F white smoke solved

Hello - I have a 3GM30F that started smoking white. After extensive research and troubleshooting I concluded that #3 cylinder did not have compression under load and concluded I must have a valve problem. I removed the head and visual inspection did not reveal any evident valve issue. I started rotating the engine by hand and notice #1 and 2 pistons basically flush with the top of the block at TDC but #3 was down about 100 mils. I dropped the oil pan and found a couple pieces of cast aluminum, removed the #3 piston and found the rod bent and the fragments off one side of the piston wrist pin fittings. All this can be repaired but my question is what was the cause. I was not losing glycol and the head gasket looks fine. The engine ran fine on 2 cylinders with no noise or slap, their was nothing loose on the #3 piston assembly. Here is my First Mates description of the sudden stoppage event. She started the engine and thinking it was not running re-engaged the starter and boom the engine stopped. I got on the boat and immediately started the engine normally but now there was a white smoke plum. I have the heat exchange and will test it for leaks but the engine ran a number of trouble free hours after the incident without smoke once I rerouted the #3 fuel to a jug. What happened? How did I get a one time slug of fuel or water?
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Old 11-10-2019, 18:24   #2
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Re: 3GM30F white smoke solved

I had that same issue many years ago. Yanmar can run backwards, on rare occasions. Usually if bump started when hot. Water is sucked in from exhaust.
Mack engines used to do this on occasion, but don't have wet exhaust, so just a matter of shutting down, and restarting.
After many phone calls, and finally talking to an engineer, they admitted the fault, and paid the repair, but that engine was only one year old at the time...

Cheers.
Paul.
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Old 11-10-2019, 18:36   #3
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Re: 3GM30F white smoke solved

3GM30F owner, welcome aboard CF.

How old is the engine?

There have various reports in the past about of a batch of bad pistons supplied to Yanmar that ended up breaking after many hours of service in the 3GM30 series of engines - maybe this is one of them?

By the way, when you say it's the #3 piston, you do mean the one further from the flywheel, right?

Sailorchic34 had a longish thread abut this issue some years back, maybe it would worth searching for it.
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Old 11-10-2019, 20:41   #4
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Re: 3GM30F white smoke solved

Water in the cylinder from the exhaust would be my guess. Had that happen on a Volvo that I got it started lifting the compression releases and dropping them before all the water pumped out of one of the cylinders.
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Old 11-10-2019, 23:45   #5
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Re: 3GM30F white smoke solved

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Originally Posted by 3GM30F owner View Post
Hello .......... and found the rod bent and the fragments off one side of the piston wrist pin fittings.....

What happened? How did I get a one time slug of fuel or water?
Opps, I missed the bent rod on my first reading so scrub my previous post!
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Old 12-10-2019, 03:37   #6
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Re: 3GM30F white smoke solved

Greetings and belated welcome aboard the CF, owner.
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Old 12-10-2019, 06:57   #7
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Re: 3GM30F white smoke solved

Thanks for the replies and welcomes.

Grit - The backward start explanation seems plausible. I am going with it since there doesn't appear to be any mechanical fault.

Wotname - The engine is 1995 vintage but low time, I estimate 2000 hours +/- 20%, always freshwater. Correct #3 is furthest from the flywheel. The engine looks new externally and I have never had any problems prior to this event.
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Old 12-10-2019, 09:30   #8
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Re: 3GM30F white smoke solved

Bent rod can definitely result from a water-lock, i.e., water getting to the piston via the exhaust valve. In addition to starting "backwards", this can be caused from water being pushed back into the engine from wind causing waves to slap against the exhaust at the transom, or if exhaust is out the side from excessive rolling when the engine is not running.
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Old 13-10-2019, 08:00   #9
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Re: 3GM30F white smoke solved

my 30 gm30f has run backwards. It was after a brisk downwind sail with large waves and I let water get in the exhaust. Luckily there was no damage. Lesson learned.
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Old 13-10-2019, 10:19   #10
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Re: 3GM30F white smoke solved

Quote:
Originally Posted by 3GM30F owner View Post
Hello - I have a 3GM30F that started smoking white. After extensive research and troubleshooting I concluded that #3 cylinder did not have compression under load and concluded I must have a valve problem. I removed the head and visual inspection did not reveal any evident valve issue. I started rotating the engine by hand and notice #1 and 2 pistons basically flush with the top of the block at TDC but #3 was down about 100 mils. I dropped the oil pan and found a couple pieces of cast aluminum, removed the #3 piston and found the rod bent and the fragments off one side of the piston wrist pin fittings. All this can be repaired but my question is what was the cause. I was not losing glycol and the head gasket looks fine. The engine ran fine on 2 cylinders with no noise or slap, their was nothing loose on the #3 piston assembly. Here is my First Mates description of the sudden stoppage event. She started the engine and thinking it was not running re-engaged the starter and boom the engine stopped. I got on the boat and immediately started the engine normally but now there was a white smoke plum. I have the heat exchange and will test it for leaks but the engine ran a number of trouble free hours after the incident without smoke once I rerouted the #3 fuel to a jug. What happened? How did I get a one time slug of fuel or water?
How long did she crank the engine before it started? It cranked more than 15 seconds, it is possible that seawater was cranked into the aft most cylinder via the exhaust elbow. (No exhaust to push water on through the water lift muffler.)

A 3GM30 should start virtually instantly. If not, something is wrong and the engine needs to be serviced. If the engine doesn’t start in 10 seconds, stop, and close the seawater intake valve before you crank any more. Open the valve the instant the engine “catches”. If more than a very rare occasion, or exceptionally cold, fix the problem before you wreck the engine. Same holds true for all the engines with wet exhaust.
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Old 13-10-2019, 10:37   #11
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Re: 3GM30F white smoke solved

Quote:
Originally Posted by 3GM30F owner View Post
Hello - I have a 3GM30F that started smoking white. After extensive research and troubleshooting I concluded that #3 cylinder did not have compression under load and concluded I must have a valve problem. I removed the head and visual inspection did not reveal any evident valve issue. I started rotating the engine by hand and notice #1 and 2 pistons basically flush with the top of the block at TDC but #3 was down about 100 mils. I dropped the oil pan and found a couple pieces of cast aluminum, removed the #3 piston and found the rod bent and the fragments off one side of the piston wrist pin fittings. All this can be repaired but my question is what was the cause. I was not losing glycol and the head gasket looks fine. The engine ran fine on 2 cylinders with no noise or slap, their was nothing loose on the #3 piston assembly. Here is my First Mates description of the sudden stoppage event. She started the engine and thinking it was not running re-engaged the starter and boom the engine stopped. I got on the boat and immediately started the engine normally but now there was a white smoke plum. I have the heat exchange and will test it for leaks but the engine ran a number of trouble free hours after the incident without smoke once I rerouted the #3 fuel to a jug. What happened? How did I get a one time slug of fuel or water?
The cause may be it's a design defect. Many people have had issues with piston skirts cracking in the 3GM30. They can crack and run for quite a time, but it sounds like yours came apart partially. Who knows how long it was cracked.
BUT, It IS possible, especially from your description, that you got water in the rear cylinder causing the bent rod and didn't suffer a cracked piston to start with.
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Old 13-10-2019, 15:30   #12
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Re: 3GM30F white smoke solved

Remember the OP has stated (and confirmed) the bent rod was in the forward most (#3) cylinder, not the aft one (#1).
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Old 13-10-2019, 18:48   #13
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Re: 3GM30F white smoke solved

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Remember the OP has stated (and confirmed) the bent rod was in the forward most (#3) cylinder, not the aft one (#1).
Maybe I really don't understand engines as well as I thought I did, but I've never understood why everyone thinks that water will only enter the aft most cylinder from the exhaust. It seems to me that all cylinders are connected via the exhaust manifold and therefore, whichever cylinder has the exhaust valve open at the time will get flooded if water comes into the exhaust. Can someone please enlighten me?
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Old 14-10-2019, 09:14   #14
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Re: 3GM30F white smoke solved

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Maybe I really don't understand engines as well as I thought I did, but I've never understood why everyone thinks that water will only enter the aft most cylinder from the exhaust. It seems to me that all cylinders are connected via the exhaust manifold and therefore, whichever cylinder has the exhaust valve open at the time will get flooded if water comes into the exhaust. Can someone please enlighten me?
It's mostly because many engines are angled to allow the prop shaft to angle through the hull. Therefore the aft cylinder is lower and the water gets there first. If the valves are completely shut tight and in good shape then you are correct, the water may not enter there first. But also a small bit of water may be sitting there when the first crank of the engine occurs, go in and damage the engine.
Of course I suppose with a modern drive leg type of situation (no shaft) that the engine could be level.
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