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Exhaust Manifold life span


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My friend pcm 351 Ford self destructed the other day. (87 supra) We pulled the exhaust manifolds off and they were clogged with rust. Our current theory is the exhaust rust caused the motor to drop a valve which then got pushed thru the cylinder wall

My questions for my Monsoon, 1999 with 525 hours on it:

at what point do I get concerned and start looking for rust problems, ?

how long do the exhaust manifolds last?

Does anyone replace them before a failure?

Thanks

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I doubt exhaust manifold rust caused the engine to drop a valve. Cast iron is going to rust but any flakes would be washed down stream not back into the engine.

A 1987 boat engine has one of two things going against it that could potentially cause a problem.

1) The engine is used a lot and succomed to fatigue.

2) The engine sat a lot and internal corrosion led to a failure.

I'm no expert though...

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martinarcher

My port side manifold on my Bu started to fail a few years ago, was patched with JB weld. I changed them both for a pair of Stainless Marine manifolds. They were 24 years old when they came off.

Search the net...everyone has a different answer. I think the water you run in has a lot to do with manifold life as well. I always store mine throughout the winter with them full of antifreeze. I would think that would help keep corrosion down in the off season.

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I doubt exhaust manifold rust caused the engine to drop a valve. Cast iron is going to rust but any flakes would be washed down stream not back into the engine. A 1987 boat engine has one of two things going against it that could potentially cause a problem.

1) The engine is used a lot and succomed to fatigue.

2) The engine sat a lot and internal corrosion led to a failure.

I'm no expert though...

I agree that's true in theory but since water can definitley work it's way "up stream", it could take pieces with it. That is the reason the gaskets in between exhaust manifold and risers need to be leak free. IF leaking water out it can be leaking watre internally into the "wrong" pathway and can work it's way up the engine causing catastrophic failure. Some people at Skidim change their manifolds regularly from what I have heard. As for life of the part, I doubt there's a concrete answer depnding on use and climate.

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I agree that's true in theory but since water can definitley work it's way "up stream", it could take pieces with it. That is the reason the gaskets in between exhaust manifold and risers need to be leak free. IF leaking water out it can be leaking watre internally into the "wrong" pathway and can work it's way up the engine causing catastrophic failure. Some people at Skidim change their manifolds regularly from what I have heard. As for life of the part, I doubt there's a concrete answer depnding on use and climate.

That's pretty interesting. If I were to change mine, I'd be calling MA to discuss the stainless marine route that he went. :rockon:

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I doubt exhaust manifold rust caused the engine to drop a valve. Cast iron is going to rust but any flakes would be washed down stream not back into the engine.

A 1987 boat engine has one of two things going against it that could potentially cause a problem.

1) The engine is used a lot and succomed to fatigue.

2) The engine sat a lot and internal corrosion led to a failure.

I'm no expert though...

The boat had the old style baffles on the exhaust tips which became plugged from the rust particles. I will take some pictures

yes, the boat sat around in an indoor garage without draining the block, less than 600 hours on an 87. Also, the gauges had stopped working.

Its seems like it is never just one thing wrong.

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I can almost cannot wait for mine to rust our so I can replace my manifolds with something from Stainless Marine. Those look nice. :rockon:

CB

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  • 3 months later...

Thanks for the link back to the stainless marine project, saw that the first time. It is interesting, but pricey.

Yes they are pricey but look at the overall cost over the years not just the upfront cost. If you run on fresh water its probably overkill but I run on salt water and now realize they are cost effective.

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After listening to the sound on Matt's videos, I am sold. It's on my list of projects, just way down the list. Its a good thing I live a long way from Western PA, because Hearing them in person would bump them to the top of my list.

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After listening to the sound on Matt's videos, I am sold. It's on my list of projects, just way down the list. Its a good thing I live a long way from Western PA, because Hearing them in person would bump them to the top of my list.

LOL.gif Feel free to fly in for a ride. Thumbup.gif

They are worth it. I am a cheapskate so I watched ebay for months. I found a guy who built a super high performance small block for a race boat and gernaded it on the dyno. He threw in the towel and sold the parts on ebay. The manifolds had 3 hours on them and I think I paid about half price. Rockon.gif Just keep your eye out.

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My friend pcm 351 Ford self destructed the other day. (87 supra) We pulled the exhaust manifolds off and they were clogged with rust. Our current theory is the exhaust rust caused the motor to drop a valve which then got pushed thru the cylinder wall

My questions for my Monsoon, 1999 with 525 hours on it:

at what point do I get concerned and start looking for rust problems, ?

how long do the exhaust manifolds last?

Does anyone replace them before a failure?

Thanks

We have boats that we are servicing with 2,500 + hours on them with no issues like that. Unless you run in salt or brackish water, i wouldn't be concerned about it at all.

Its not hard to pull and inspect your exhaust manifolds at all if you ever wanted to take a look.

-Paul

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We have boats that we are servicing with 2,500 + hours on them with no issues like that. Unless you run in salt or brackish water, i wouldn't be concerned about it at all.

Its not hard to pull and inspect your exhaust manifolds at all if you ever wanted to take a look.

-Paul

As usual, Paul is correct. Cast iron manifolds have a very long life expectancy ... espcially in fresh water. I recommend pulling the riser off every couple of years to replace the gaskets which gives you a good opportunity to take a closer look at the internal condition of the manifolds. Those gaskets are very crucial to the life of your engine and over time , through expansion and contraction of the manifolds, get "worked" and can fail.

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As usual, Paul is correct. Cast iron manifolds have a very long life expectancy ... espcially in fresh water. I recommend pulling the riser off every couple of years to replace the gaskets which gives you a good opportunity to take a closer look at the internal condition of the manifolds. Those gaskets are very crucial to the life of your engine and over time , through expansion and contraction of the manifolds, get "worked" and can fail.

i worry about busting a corroded manifold bolt.

  • any tips for removal?
  • torque spec for installation?
  • use anti-seize on the installation?

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