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Old 03-12-2015, 09:19   #16
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

many of the v8 outdrive installations are just too far above waterline to ingress water easy. Hard to say without knowing the installation. Is this an outdrive or shaft drive?
So GM had two "modern" big blocks right? the 454 and an Oldmobile of similar displacement. Too bad it's not the small block , rebuilt long blocks go for about $1600 for those!
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Old 03-12-2015, 10:14   #17
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

Well it wouldn't be a very efficient pump, and I don't think it very likely the cause, but every other down stroke of the piston with the stuck valve would pull water into the manifold and cylinder, not all of which would be expelled by the subsequent upstroke, possibly yielding a net positive gain of water in the manifold, allowing the normally operating cylinders to be flooded on shutdown. Almost all pumps with valves operate with some level of 'leakiness' in the valves...

Overcranking with an inboard/outboard is not normally an issue; the water generally just runs out the outdrive, or in the case of some high performance applications with through-the-transom exhausts, directly out of the boat.

Generally speaking, the parts that let the cooling water out, and keep seawater from coming back in are pretty reliable, but if they get stuck closed they can let water back up into the engine, or if they get stuck open can let seawater in in adverse conditions.

In certain applications, the engine can be mounted too close to the water line, making having an issue along those lines more probable.

At 10 years, the manifolds and risers can be shot even with low hours, in my experience Volvos' cast iron manifolds are a bit worse for longevity than Mercruisers', but it's really more dependent on the operating and storage conditions...
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Old 03-12-2015, 10:48   #18
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

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Originally Posted by DougR View Post
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.

DougR
Wow, really interesting, thanks!
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Old 03-12-2015, 10:50   #19
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Re: Hydrolocked Volvo Penta Gas/Petrol V8

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Originally Posted by Cheechako View Post
many of the v8 outdrive installations are just too far above waterline to ingress water easy. Hard to say without knowing the installation. Is this an outdrive or shaft drive?
So GM had two "modern" big blocks right? the 454 and an Oldmobile of similar displacement. Too bad it's not the small block , rebuilt long blocks go for about $1600 for those!
It's an outdrive, not shaft.

And the engine is 8.2 liters or a 502, not 455, although I think it's basically the same engine (big block GM).
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