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Old 29-11-2015, 04:40   #1
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Hydrolocked Volvo Penta Gas/Petrol V8

A friend of mine has hydrolocked his 8.2 liter VP marinized General Motors V8. It's raw water cooled.

The engineer on Mallorca says an exhaust valve stuck, which caused seawater to be drawn into a cylinder. How does that work? I can't picture it.

Also - I want to bring him new con rods from the US (they cost 500 euros on Mallorca - EACH!). Can I use standard Oldsmobile rods? Best place to buy them?

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Old 29-11-2015, 05:40   #2
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

Your gonna need more info. Engine model, displacement ect. Clearly, the head will need to come off. It may need a piston (s). Likely you can get the parts but some effort and consultation to be sure they are correct.
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Old 29-11-2015, 06:06   #3
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

If it is the same block as the GM performance big block any aftermarket supplier should be able to set you up. Pretty pricy from GM Performance.
MAKE SURE OF ALL THE DIMESIONS BEFORE YOU ORDER!
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Old 29-11-2015, 08:04   #4
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

19170198, same rod for 8.2 and 7.4. Readily available, oddly enough a quick search yields GM as the most economical source: (but you might find others)


ROD | Genuine GM | 19170198
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Old 29-11-2015, 10:25   #5
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

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Originally Posted by jimbunyard View Post
19170198, same rod for 8.2 and 7.4. Readily available, oddly enough a quick search yields GM as the most economical source: (but you might find others)


ROD | Genuine GM | 19170198
Thanks, very useful!!!

I didn't realize it was a special forged performance part. Yikes. Still, $100 each doesn't sound too bad. I think we only need to replace four of them.

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The motor has Volvo-Penta product number 3869370, type 8.1 GI-H. I believe that other than the marinization parts it is a standard big block GM motor.
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Old 29-11-2015, 17:47   #6
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Hydrolocked Volvo Penta Gas/Petrol V8

Since the engine is coming out. I'd consider replacing the bearings with just new ones, not oversize and a new oil pump and new rings. Should be cheap parts and your there, why not go back with new? Known as a redneck overhaul I'm assuming you can't remove the pan with the engine in.
Now this is where it's hard to pick a point to stop, but since the heads are off anyway, shouldn't they go to a machine shop, especially since one valve stuck?


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Old 29-11-2015, 19:21   #7
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

Get to the US and buy all the recommended parts for a sudden stoppage. You can get pretty much anything for any engine at an auto parts store that has an intelligent sales person. They truly have catalogs for almost everything.
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Old 01-12-2015, 05:12   #8
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

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Originally Posted by a64pilot View Post
Since the engine is coming out. I'd consider replacing the bearings with just new ones, not oversize and a new oil pump and new rings. Should be cheap parts and your there, why not go back with new? Known as a redneck overhaul I'm assuming you can't remove the pan with the engine in.
Now this is where it's hard to pick a point to stop, but since the heads are off anyway, shouldn't they go to a machine shop, especially since one valve stuck?


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The engine is already out and apart, and the plan is to do very much as you suggest

Crank journal and big end bearings will be replaced with new standard sized ones, rings will be replaced, bores will be honed. Valves will be ground and guides will be checked. Block and heads will be checked for flatness.

Good idea about the oil pump

I marveled at how easy the engine came apart. The engineer only charged for three hours of time including pulling it out of the boat. I've never owned a vehicle with a Detroit V8; I see here some of the appeal. Taking apart a Porsche flat six is a horse of an entirely different color. I can get one of those out in less than an hour, single handed, but taking it apart is a different matter altogether.



Now how did the seawater get in there in the first place? My friend wants to know so he can argue with his insurance company. I don't understand how a stuck valve could do it; can someone enlighten?
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Old 01-12-2015, 06:12   #9
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

RE, the Detroit V8, they are very, very simple devices, and very, very durable. I believe for example a camshaft lifter for a GM motor is the same for all motors, very many of the parts are interchangeable. The venerable GM small block will live forever, the little Mighty Mouse turns 60 this year I believe and is the strongest it has ever been.
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Old 01-12-2015, 06:19   #10
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

Seawater wise, the water has to be in the exhaust manifold of course before a stuck valve can let the water in, and to be truthful, I don't buy the stuck vale theory at all. Of course no matter how it's shut down a V8 will most likely have more than one valve open, it's just not possible that they are all closed, one being open will let water in, and the water most likely is what stuck the valve, GM motors are almost immune to stuck valves, I have never even once seen a valve stick on a GM motor, many on aircraft, but not GM motors.
Of course there is never a time where water in the exhaust manifold is normal.
Now I believe if not mistaken that Marinized Big Block GM motors have a reputation for the exhaust manifold mixer not having a long life? I had one boat with dual Mercruisers that were 454's and was warned to keep an eye on the exhaust manifolds, but never had a problem, but to be truthful I didn't keep the boat long enough, wonderful Sportfisher, 36 ft., but Lord those Big motors could go through some fuel
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Old 01-12-2015, 06:54   #11
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

One place to look for the water(coolant) ingress is the intake manifold. I have a 350 cubic inch Chevy that has leaked coolant into the manifold on 3 different occasions. Cause? Warped intake manifold. Finally had it milled flat..no leaks now for 5 years. A64 is correct, depending in the cam, some valves will not be seated no matter how you shut it down. Just need to keep things tight goesinta and goesouta. Keep oil in it and the beast will chug along as long as you ever need it.
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Old 01-12-2015, 11:47   #12
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

I used to help several neighbors get their v8 powered stern drive boats going when fishing season came around.
Most of these boats were left in the driveway all year, and needless to say had dead batteries, wet iginition systems etc.
It was very common to find water in the cylinders when they called me to help get the mess sorted out.
The water came from extended cranking when trying to start an engine with a dead ignition system.
Raw water pump dumps into exhaust manifold/heat exchanger and there's no hot exhaust to blow the water back down the pipe.
Instead, it flows by gravity into the cylinders.
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Old 01-12-2015, 20:31   #13
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

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Now how did the seawater get in there in the first place? My friend wants to know so he can argue with his insurance company. I don't understand how a stuck valve could do it; can someone enlighten?
All the above are possible.

Also possible are a blown gasket between riser and exhaust manifold, cracked riser, cracked manifold, obstructed exhaust outlet, an emergency shutdown from a high rate of speed followed by a restart attempt, the stern being caught under the dock in rough weather or during an abnormally high tidal cycle, or fishing in rough water with the engine off.

Both Volvo and Mercruiser have mechanical means to keep water out of the exhaust down pipes, and to keep it from being pushed back up into the engine in adverse conditions, but neither are 100 percent effective, and I've seen both systems fail (usually because of operator error, but also because of mechanical faults).

With hydraulic lifters a stuck valve is possible, but for the engine to pull water into a cylinder while running or starting, the water would have to overcome the exhaust pressure of the other cylinders, get sucked into the cylinder with the stuck valve, and then the valve would have to unstick and the engine could go ahead and bend a rod. Seems unlikely but I guess not impossible.

Conversely, the valve could stay stuck, and the cylinder could act as a pump and pull water into the manifold on shutdown, which could then flow into the properly functioning cylinders and cause the bent rods on restart.

Obviously very hypothetical. It would be interesting to know the details of how it happened as well as the age and hours on the engine.

As for what really happened, manifolds and risers can be pressure tested for cracks, and leaking gaskets can usually be seen by careful inspection. A stuck valve is self evident (if it has remained stuck), so if nothing was seen on teardown, my bet would be something to do with operating conditions, i.e. water coming into the exhaust ports normally left open when the engine is at rest. Were the bent rods all on one side or on both? If on one side, maybe a stuck valve. If on both, more likely water intrusion from less than ideal conditions.
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Old 03-12-2015, 01:16   #14
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

Thanks; very interesting and helpful!

I can't imagine how a stuck valve would do it. A cylinder with a stuck open valve obviously can't be hydrolocked, as that cylinder will never be sealed -- the water would just come back out. And how could a cylinder with a stuck open valve act as a pump? I call BS on that theory.

All the other ones sound plausible to me, however. The classical cause of hydrolocking is overcranking, as you both suggested -- I'm kicking myself that I didn't look more carefully at the exhaust system to see how that would have happened. On my boat, I know to drain the muffler and shut off the sea cock if the main engine doesn't start immediately (which has never happened), in order to avoid this. This one doesn't have any muffler; the exhaust system is much simpler. But I guess it could happen.

I'll be sure my friend has the block, heads, and manifolds checked for flatness and cracks, before the motor goes back together.

As to age and hours -- at least 10 years, and very, very few hours. Boat is used just a couple of times a year. The engine looked quite good on the inside, no varnish or rust, very little carbon, bores in good shape with original cross-hatching still in evidence, crank journals clean, etc.
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Old 03-12-2015, 09:06   #15
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

Hello Dockhead,

A cylinder with a stuck exhaust valve will certainly act as a pump. Here's the scenario: on the normal intake stroke the piston travels down, and as the inlet valve is open, the piston pulls in fresh air and fuel from the inlet manifold. Then the piston comes up on compression stroke but instead of compressing the mixture, it forces the mixture out the stuck open exhaust valve. Next the piston starts down on what would normally be the power stroke. Normally both valves will be closed on the power stroke, however in this case the inlet valve is closed but the exhaust valve is stuck open and the dropping piston creates a vacuum in the cylinder and thus pulls in air/gases from the exhaust side. This pumping action causes all sorts of erratic gas flow patterns within the exhaust manifold, and can easily result in water in the cylinder.

Believe it or not, but for a period of time both Mercruiser and Volvo Penta had water "reversion" problems with their GM 454 engines. This problem was caused by excessive valve overlap on the cam shafts that were supplied by GM. Under certain load and RPM conditions the valve overlap caused pulsing behavior within the exhaust manifold and further down the exhaust system and the end result could be serious water penetration problems into the engine. Both manufacturers tried to counter this with flapper valves in the exhaust down pipes, crossover pipes between left and right cylinder banks to disrupt pulsing, etc. This problem, which never occurred in cars or trucks, caused serious warranty problems in the marine world, and as I recall didn't go away until the
454 production stopped.

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