8.1 manifolds replacement question

Discussion in 'Sport Cruisers' started by liv2ryde100, Apr 30, 2018.

  1. liv2ryde100

    liv2ryde100 Member

    329
    May 17, 2012
    long island
    05' 340 dancer
    Twin 8.1's
    hey I know I’ve been asking a lot of questions on here about manifold replacement, and thanks for all the help from everyone. Just a couple more questions about the step by step...
    When I drain the manifolds before removing, will any antifreeze be coming out or just sea water? Seems like just seawater but wanna be sure I have everything for the job before I start.
    Also is there any other step by step I should be following? Thanks
     
  2. Jimmy Buoy

    Jimmy Buoy Well-Known Member

    Dec 3, 2008
    Sarnia, Ontario, Canada
    340 Amberjack
    twin 8.1S 370 Hp + 4.5 Westerbeke Genset
    Seawater only in the 8.1 manifolds.
     
    M Prod likes this.
  3. liv2ryde100

    liv2ryde100 Member

    329
    May 17, 2012
    long island
    05' 340 dancer
    Twin 8.1's
    Is there a water rail on the manifold? I see it in a shop manual but I don’t hear anyone talk about it, I know I don’t have risers so that’s good
     
  4. LG111

    LG111 Active Member

    409
    Jan 4, 2015
    NW
    410
    8.1
    Okay here's the deal on 8.1s. 2001 to about 2003 had aluminum manifolds with aluminum water rails below them. The screwed on drain coupler to the rail was stainless. That drain point was the achelies heal the entire set up in saltwater application. Best you'd get is one year literally then the joint just blew apart from corrosion.

    Next was the manifold. Maybe two years in salt if you got lucky. The riser or elbow is stainless so no issues there.

    There is a cast iron kit that supersedes the water rail version. That manifold has a built in drain with a cast coupler drain. No issues there now.

    There is no way for raw water to get from the elbow / manifold to block. Hence dry joint via the two water hoses on both sides of the elbow. Chances of the stainless elbow to fail is near zero. However, cast manifolds get about 5 to 6 years in salt. Atlantic salt maybe slightly less and Nw pacific salt maybe slightly more.
    Between the elbow and riser is a gasket. It's called a tubilator. It's an inverted cone that catches condensation in the elbow so it won't drip into the cylinders. What does get caught gets blown out as soon as you start your engine.

    After you replace the new equipment and tourqe to spec. Re-tourqe after several hot runs. Including the elbows.

    Fyi the 496 8.1S do not have zincs in the cooling system because the manifolds drain hence there is no seawater to zinc. Example: After about an hour with the engine off, if you pull the caps off the heat exchanger or pull your cooler hoses off you'll only find drips of water. Where did the water drain.... out of the dripless around your shaft and out... ever wonder why it takes so long for water to exit the side exhaust at first start. The system has to refill all the coolers hoses and manifolds first.

    Hope this helps.

    8.1S 2001 lived it learned it.
    Mark
     
    KevinC likes this.
  5. KevinC

    KevinC Well-Known Member

    Feb 25, 2011
    Long Island, NY
    2004 340 Sundancer
    1988 Proline Center Console - 90hp Mariner/Mercury
    1969 Boston Whaler
    Twin 8.1 V-drives
    Mark:

    Excellent description!

    +1 on the Aluminum Manifolds - from my research I found that any boater going from fresh to salt needs to verify that the manifolds are not aluminum or are 100% likely to experience problems if not swapped out soon.

    -Kevin
     
  6. liv2ryde100

    liv2ryde100 Member

    329
    May 17, 2012
    long island
    05' 340 dancer
    Twin 8.1's
    Thanks guys for all the details, my parts are Salk ordered up for the job, I’m supposed to bring the boat home Saturday and start working next week on this. Just waiting for my Kroil oil to get delivered!!
     
  7. liv2ryde100

    liv2ryde100 Member

    329
    May 17, 2012
    long island
    05' 340 dancer
    Twin 8.1's
    How do I re route the water line for the shafts? Do I pull the brass plug on the new manifold? What fitting do I buy to put in there?
     
  8. LG111

    LG111 Active Member

    409
    Jan 4, 2015
    NW
    410
    8.1
    Yes pull the plug and use on new manifold.
     
  9. liv2ryde100

    liv2ryde100 Member

    329
    May 17, 2012
    long island
    05' 340 dancer
    Twin 8.1's
    So pull the brass plug out of new manifold? It’s at the other end of the motor does that matter? Also it doesn’t look like the fitting in old manifold is a direct swap. Kind of looks like a different size but I’m not totally sure yet
     
  10. rondds

    rondds Well-Known Member SILVER Sponsor

    Oct 3, 2006
    Jersey Shore
    2001 380DA
    Merc 8.1s (2008)...Hurth ZF 63 V-drives...WB 7.0 BCGD (2013), Garmin 8208 & 740 MFDs, GMR 24xHD dome
    There is no way for raw water to get from the elbow / manifold to block. Hence dry joint via the two water hoses on both sides of the elbow. Chances of the stainless elbow to fail is near zero. However, cast manifolds get about 5 to 6 years in salt. Atlantic salt maybe slightly less and Nw pacific salt maybe slightly more.

    That's what I thought, but a friend (mistercomputerman, on CSR) had this happen on both engines (ie: elbows fail). I had never ever heard of this happening, but I have now. The rest of his hardware was all new about 4 seasons ago. He boats out of Virginia Beach (very salty).
     
  11. rondds

    rondds Well-Known Member SILVER Sponsor

    Oct 3, 2006
    Jersey Shore
    2001 380DA
    Merc 8.1s (2008)...Hurth ZF 63 V-drives...WB 7.0 BCGD (2013), Garmin 8208 & 740 MFDs, GMR 24xHD dome
    One note about the dripless...I had a dripless fail b/c it melted from heat when the tiny little brass elbow that exits the exhaust manifold got crudded up with rust chips. I bought this kit from Tides, put a plug in that exhaust manifold and tapped into the hose to get water for the dripless - both engines.

    The orefice in that brass elbow that comes off the manifold is tiny, and it's a 90* turn. Way too easy to get occluded.

    https://www.tidesmarine.com/ws/index.php?route=product/category&path=22_24
     
  12. Third Edition

    Third Edition Active Member

    151
    Apr 9, 2017
    NE Florida
    360 Sundancer 2002
    T-8.1L V-drives
    We have our boat in salt water/brackish water on the Atlantic side. We bought it from the Gulf of Mexico side where the water is more salty. We just replaced a SS elbow that was corroded. It happens.
     
  13. mistercomputerman

    mistercomputerman Active Member

    Jan 6, 2008
    Virginia Beach, VA
    410 Sundancer - 2001
    Twin 8.1L Mercruisers - 2009

    Two stainless steel elbows out of 4 (one on each motor) are leaking water into the exhaust manifolds. This causes rust in the manifold, rust on any of the exhaust valves and valves seats that the sea water gets to, salt buildup on the spark plug and maybe a slight hunting of 20 - 40 rpms in the engine when running (which you will probably not see with an analog tach), and maybe some evidence of seepage around the "dry joint" turbolator gasket, provided you catch it early enough.

    Otherwise, you hydrolock the engine and at best, bend a rod, or at worst throw the rod through the block.

    Rule #1:
    A exhaust dry joint is just that...a DRY joint. If there is ANY evidence of seepage around a dry joint, do not run the motor until you figure it out. It is most likely a corroded turbolator gasket (which is in the joint to cook off excess moisture/condensation in the exhaust-it does not help with an elbow leak) or a leaking elbow.

    In order to repair this, you have the following expenses:

    4 exhaust manifold about $2500
    4 elbows about $3000
    4 heads to the machine shop about $1000
    4 sets of head bolts and gaskets about $1000
    5 or so days worth of labor about $1000
    miscellaneous whatthehellever about $1000
    two new trans and 2 new oil coolers about $800

    Anyone add all this up yet??????

    These are 2009 Merc 8.1 motors. I changed the manifolds 4 years ago, but, did not change the stainless steel elbows. That was a mistake. Spending the $3k then would have saved me the extra $8k I am spending now, because the manifolds would not have been all rusted up and the elbows would only be halfway through their useful life and not leaking.

    Live and learn... Your mileage may vary.

    PS. If something on your boat fails and you have others like it, those others are about to fail as well. Bite the bullet, pull the trigger, spend the money and replace all of the similar components....just sayin'
     
    Bodkin Creek George likes this.
  14. Bodkin Creek George

    Bodkin Creek George Member SILVER Sponsor

    550
    Sep 11, 2008
    Bodkin Creek, Chesapeake Bay Md.
    2004 340 SDA
    8.1 V-Drives
     
  15. Bodkin Creek George

    Bodkin Creek George Member SILVER Sponsor

    550
    Sep 11, 2008
    Bodkin Creek, Chesapeake Bay Md.
    2004 340 SDA
    8.1 V-Drives
    I found a leaking elbow as well and it was stainless
     
  16. liv2ryde100

    liv2ryde100 Member

    329
    May 17, 2012
    long island
    05' 340 dancer
    Twin 8.1's
    I currently have both motors in pieces, swapping 4 manifolds and 4 elbows. It’s going pretty well, I broke one bolt out of all 32 so that’s pretty good. Hopefully I’ll have the job done by the end of the week
     
  17. b_arrington

    b_arrington Active Member

    596
    Feb 21, 2007
    Setauket, NY
    270 Amberjack (2006)
    AB Ventus 9 VL RIB
    350 Mag MPI Horizon w/ BIII
    1998 Envinrude 15 HP 2-stroke
    The guy that owns my boat yard always tells me the same thing. No. 1 reason I'm happy with a single engine and have a hard time upgrading to anything larger.
     
  18. LG111

    LG111 Active Member

    409
    Jan 4, 2015
    NW
    410
    8.1
    Mistercomputerman I owe you a HUGE thank you for your post and the detailed description on the rpm hunting!!!!! About 6 weeks ago my starboard engine started hunting 10 to 20 RPM around 650 rpm. You could not hear it nor did it show on my analog gauge. But my Vessel View mobile pick it right up!! I thought it was the IAC. Or the new crank shaft sensor.

    Several weeks back I noticed a white line on the back side manifold. Figured it was condensation leaking from a failing tubilator since the humidity had been so high with the change in season. I didnt think twice since most of the moisture was gone over the past few weeks. I read your post and thought that's It! I pulled the riser today and brought it home. Filled it with water to the hoses. Sat it on a paper towel for three hours. When I checked it, the towel had a quarter size wet spot. And there it was a very fine crack on the inside rim weld.
    Ordered a new riser today. Spoke to a mechanic about the hunting. He said Yup, the hunting is due to moisture getting on the spark plug and interruting the spark. Once the few drops are burned off the hunting stops. That was mine. After a high rpm and going to 650 rpm, the tubilator over flowed until the small amount of water burned down and the pressure was low enough that the crack only weeped.
    Also the tubilator was not as bad looking as the pictures above but mine did have rust on both sides of the cone. I did a spot check on one suspicious riser on the other engine. All good on that one!

    Thank you again!!

    Mark
     
    b_arrington likes this.
  19. liv2ryde100

    liv2ryde100 Member

    329
    May 17, 2012
    long island
    05' 340 dancer
    Twin 8.1's
    i finally finished my manifold and elbow replacement last night. woof. came out good no leaks, thanks everyone for all the help
     
  20. Espos4

    Espos4 Active Member

    509
    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Good news!
    Luckily you haven't missed anything.....how many consecutive days can it rain ?!?!?!?!
     

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