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1994 7.4 390CPMY Mercruiser risers

GAS engine, transmission and generator repair and maintenance discussion forum.
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tonyiiiafl
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1994 7.4 390CPMY Mercruiser risers

Postby tonyiiiafl » September 25th, 2022, 6:10 pm

Closed cooling, risers only, manifolds are anti-freeze cooled. Just completed season 6 on the risers, so it should be time for replacement. It is a Gen 5 Mercruiser, I am seeing dry joint, wet joint, 7 degree, 14 degree.........??

I looked at the past repair order and the repair mechanic just said "2 risers" no part numbers!

SO, any input to dry joint, wet? I know that they can be inspected, but to pull all 4 off, then put them back on if they look OK, just doesn't make sense to me.

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Re: 1994 7.4 390CPMY Mercruiser risers

Postby paulr » December 10th, 2022, 4:36 pm

Take them off and change now. I learned the hard way.
Why risk a 4-$5000 rerpair.
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Re: 1994 7.4 390CPMY Mercruiser risers

Postby tonyiiiafl » December 10th, 2022, 6:25 pm

Agreed. I have ordered 2 sets.
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Re: 1994 7.4 390CPMY Mercruiser risers

Postby km1125 » December 11th, 2022, 10:07 am

Yea, for the amount of work to get the old ones off, I'd just replace with new rather than risk trying to reuse them. You'd need some advanced testing to really validate the old ones anyways. You could validate that they're not already leaking, but could not really validate that they have any certain amount of "life" left in them.
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Re: 1994 7.4 390CPMY Mercruiser risers

Postby paulr » December 22nd, 2022, 4:50 pm

The company i work for does this testing on all the pipe we install that carries corrosive materials before its installed.
Period tests over time indicates the rate of ware. When it gets to 30% - 40% of original we change them out.
On a reiser or elbow there is no way to test the interior wall of the elbow that will fail.
The only thing you can do is change them or gambel. I see it everyyear at my marine in NJ

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