MOD TO CONSIDER FOR I.O MODELS 23'+

[231CALIFORNIA]

as some of you may have experienced I/O exhaust manifolds/Elbows and "flapper" valves dont last forever.   Something to consider at Manifold time.
I dont have closed cooling full or half but religioulsly flush and rinse with saltaway leaving a bit in engine after shutoff(bravo2 drive/raw water pump belt driven not in outdrive)
a symptom of recent "mild" failure is a hard start, a bit of water in cyl.
Time to replace exhasut system. mine failed brand new(flawed mercruiser casting)
and then lasted ~12 more years (exceptionally long), replaced manifolds /elbows and risers , now after just a couple  hours  misfire and roughness, back to shop.
stuck exhaust valve, bending pushrod ,requiring removal of head(s)and intake/EXh.
Now I can do most of this myself if needed, but the engines in many of our boats have limited access to exhast - head bolts and spark plugs, requiring a patient double jointed midget with a universal joint to remove and retorque exhaust and plugs.(especially on 251w/a  big blocks/231w/a  small blocks ,and larger boats with twins sandwiched in  IMO).
now I sent the heads out to machine shop and their opinion is that engine has seen regular "minor" water intrusion since new  and said they see it all the time with boats  with engine located "down low" even with flappers and risers and new manifolds.
Recomended Upgrade  3" spacers between risers and manifolds to increase protection from small backflows and intrusions when engine off/ boat in water.
figured it might help and since I was already heads off /valve job I might as well add them to an already unscheduled aprox 2.k+ engine repair and parts were available ASAP.(requires new bolts,extra gasket, downpipe adapter) adding a few hundred bucks(now and to future exh refits).
So if you have a 231 or 251  big block  or similar ,and its manifold time, you may want to consider the Modification.   4" avial as well im told .
maybe not necessary, engeneers didnt specify them, but costs keep a lot of good things out of our boats.

presented for your consideration , most will be fine without, but offshore every edge counts and boats in shop catch few fish.

just an idea im trying to make my proline a little more SALTY.

[a7ewizard]

It has been my experience that the most common source for water intrusion is at the gasket/joint between the manifold and riser. The first sign is rust on the spark plugs (inspect the middle 2 in each bank) as the water leaks between these castings. IMO, adding a spacer adds another joint which now doubles the chances for a problem! If you have access to your old mans and risers, inspect this area to look for signs of leakage and/or soft areas or breaks in the the surfaces where they mate.

I run a VP but there has to be mounting height specs available from Merc for your application. Therein should specify the minimum height of the risers above the water line at rest. If you meet this criteria, you probably don't need the spacers Unless you are sure of the back-flow thru the outdrive. I know that the flappers in my Y pipe were fully removed years ago........they had a tendancy to come loose and lodge further down the exhaust system ( I believe this was the cause of a bellows tearing?)

12 years and you are pushing the envelope!

[231CALIFORNIA]

Agree about most common leak place, also
Agree there is some added risk from gasket 2/joint 2. considered that.
old manifolds eventually got a leak in water jacket, my old elbows were stainless.
Merc. no  longer reccomends the stainless because of differentials in the thermal expansion rates causing gasket failure at the riser joint. good idea, didnt work in field. Im looking for metalurgical magic  I guess.
back to cast iron for now.
there are  New "ceramic" powder coated parts avail for a left nut$ now but no super guarantee to go with them. I have often painted manifolds and elbows inside and out   but dont know if it really helps much in hot saltwater environment
. mayeb powder coat adhears longer0
I  flush and rinse and monitor plugs at changes etc so im normally on top of manifold issues. have changed far too many over the years on my boats,  wanted to put in FWC but ther is so little service room as it is, there is clearance for the 3" spacer. that is a compromise i ahd to make with proline that almost made me buy something with better engine access.
I used to pull risers and inspect and re gasket every year. didnt do that end of last year as I had put on all new exhaust at end of season.
BTW I have a Ford /omc 351 that got a stuck valve once and bent pushrod in same way,
so I Replaced pushrod rocker and pivot, thumped top of valve with ball peen and everythign freed up and ran fine for a year, next year another valve stuck and i had to pull a head to fix as it wasnt coming loose. ran another 5 years.
manifolds(end riser) went out and manifolds were not avail at any price in about 2005. Just bought a Center riser adapter kit  and hope to put that boat back into Bay use /lake use if she isnt frozen up from sitting(i had oiled cyls) or fuel sys isnt varnised shut(have spare carb somewhere).

Somehow bronze or some other alloy exh or full fwc might be worth a grand or so extra at purchase if it saved a few sets of cast iron replacements and increased reliablility? But even the 4stoke outboards are having cooling corrosion destruction issues as they get 7-10 years old now .

my old "flappers" were gnarled a bit but no chunks loose.
But i did have to deal with a chunk of bravo 2 impeller up in my thermostat housing after a long 170 mile RT offshore run at 25knots most of the way, whne i throtled back at harbor temp went up to about 180.

[231CALIFORNIA]

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