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Old 17-03-2021, 06:55 PM   #1
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Angry Water in cylinder bore

After a low compression test reading on my Mercruiser 4.3 V6 engines in my old Draco Sterling I pulled the heads off to find water in the middle cylinders. Iím trying to narrow down whether itís the cylinder heads being porous or the exhaust manifold/ risers. The engines are 30 years old but have only 250 hours on them. Iím hoping to fit new piston rings to the affected cylinders. Iíve had her since last year and she was always a lazy starter. Any advise would be appreciated.
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Old 17-03-2021, 09:25 PM   #2
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When was last time manifolds and risers were changed? Worth whipping them off to inspect.
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Old 19-03-2021, 12:09 PM   #3
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Thumbs down Risers and exhaust manifolds

Iíve checked with the previous owner. The Risers and manifolds were replaced about 6 years ago. The puzzle to me is why is it that only the middle cylinders are affected. The motors ran sweetly last year but Iíve taken the heads off one engine and one exhaust valve is rusted open. The port engine now also has low compression on the middle cylinders.
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Old 19-03-2021, 07:56 PM   #4
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I'd defo be checking manifolds and risers / riser gaskets and exhaust flappers. Have you taken them off and inspected? Manifolds and risers are serviceable part. Can last as little as 5 years so wouldn't discount just because they were changed 6 years ago. They rot inside. Failure will cause ingress.
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Old 19-03-2021, 08:16 PM   #5
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Aluminium risers

I see on eBay US there are aluminium manifolds and risers available for some engines. Does anybody have any experience of fitting them. Having to swap out cast ones ever four years or so seems a bit onerous.
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Old 19-03-2021, 09:21 PM   #6
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Country: UK
Location: Coventry (but from Lee on Solent)
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Boat make: Extreme 21
Engines: Merc V8
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The aftermarket ones aren't great and are so expensive in uk compared to us but the oem ones are v expensive. We did have a set of oem stainless risers but they may be gone now. I'll check. They were on v8 but think risers are same. Replaced with dry joint as manifolds cracked. Dry joint is way to go
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Old 12-06-2021, 07:00 PM   #7
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I’m about to swap out the old manifolds and risers on these 4.3 V6 Mercruiser engines. The engine numbers say they are circa 1990. Can I do a “dry joint conversion on this engine or are they too old? Any workarounds if so?
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