Valves Breaking
03-05-2008, 09:12 PM
#11
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Seahawk, You said it happened twice. Was it the same cylinder or a neighboring one.
I think pressure checking your exhaust is in order. Its a good idea to do it every season on HP motors no matter what exhaust you have as a regular preventative measure.
As far as no rust, it is possible the exhaust is weeping and the heat evaporates the moisture away not allowing it to rust. The pits may be the result of them getting wet when hot.
I think pressure checking your exhaust is in order. Its a good idea to do it every season on HP motors no matter what exhaust you have as a regular preventative measure.
As far as no rust, it is possible the exhaust is weeping and the heat evaporates the moisture away not allowing it to rust. The pits may be the result of them getting wet when hot.
03-05-2008, 09:45 PM
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something else to look at is if you stop fast water can backwash into the tailpipe and enter the cyl. head and hit the valve, make sure your flappers are in great shape
03-06-2008, 09:28 AM
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HP 500s come with inconel exhaust valves. Were the valves possibly replaced with standard SS during a rebuild? With it being the center cylinders it sounds like you've got water getting in from the riser, dumping on hot exhaust valves. You absolutely need to use inconel exhaust valves in a performance engine.
03-06-2008, 12:06 PM
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Seahawk, You said it happened twice. Was it the same cylinder or a neighboring one.
I think pressure checking your exhaust is in order. Its a good idea to do it every season on HP motors no matter what exhaust you have as a regular preventative measure.
As far as no rust, it is possible the exhaust is weeping and the heat evaporates the moisture away not allowing it to rust. The pits may be the result of them getting wet when hot.
I think pressure checking your exhaust is in order. Its a good idea to do it every season on HP motors no matter what exhaust you have as a regular preventative measure.
As far as no rust, it is possible the exhaust is weeping and the heat evaporates the moisture away not allowing it to rust. The pits may be the result of them getting wet when hot.
No not the same head but still one of the middle cylinders. Remember one broke at the top.
Last edited by seahawk; 03-06-2008 at 12:14 PM.
03-06-2008, 12:37 PM
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Phil, The center cylinders are most vulnerable to water. Do you still have the turbulator plates in place? The are designed to catch the condensation from the tail pieces. Definitely pressure check manifolds and tail pieces.
03-06-2008, 04:20 PM
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It is a plate that is located between the tail piece and the manifold. Often they are removed because it looks like a restrictor plate but it has an important function. It is similar to the gasket but has a smaller opening and curls up in center. On the gil its actually called a diffuser not turbulator sorry thats what its called on 496's
Last edited by MOBILEMERCMAN; 03-06-2008 at 04:22 PM.
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03-07-2008, 07:46 PM
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Dry to the transom is good- unless there's a leak in one. Could be a gasket- could be a pinhole. Some of the Gil's would erode badly at the port area if you lost water pressure. IIRC, there was a run of Merc's with CMI's on them that had exhaust issues- they lasted a couple seasons before springing leaks.
I would have the heads re-done with Manley or Ferrea stainless intakes and Inconel exhausts. Have the manifolds pressure tested to ensure you have no internal leaks.
I would have the heads re-done with Manley or Ferrea stainless intakes and Inconel exhausts. Have the manifolds pressure tested to ensure you have no internal leaks.
03-08-2008, 02:25 PM
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BT
