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  1. #1

    Default 8.1L Riser Replacement (1st timer)

    New to this forum and Crusaders. Have been an outboard guy my whole life and always have done my own work. If I can master Yamaha HPDI's I should be able to learn about the Crusaders. The past owner was not up on the maintenance since the boat did not move much. 2002 Crusader 8.1's and the starboard engine is running hot. Checked the risers and they were very hot to the touch and I am leaving a good steam trail. So i am going to replace the risers as it appears from the looks of things (original paint still on bolt heads not disturbed) that these very well may be the originals. Seems to be pretty straight forward, drain the manifolds, soak the nuts and bolts in PB blaster, remove risers and gaskets, clean up mating surfaces, new gaskets and blocker plate, install new risers. Only question I have is, do you use gasket sealer on the gaskets between the riser and manifold? Other than that am I missing anything?

    Thanks for any input

  2. #2

    Default Re: 8.1L Riser Replacement (1st timer)

    Steam usually an indication of reduced raw water flow. Bad impeller, clogged U tube, or delam hose are also possible.

    As for changing risers:

    The first and biggest challenge is removing the old units. I would strongly recommend first cutting off the exhaust tubes attached to the outer elbows (assuming the outer tubes terminate to a 45 degree fiberglass fitting). Wireless tubes can simply be cut off with a utility knife. Wire tubes will require a Dremel tool to cut the coils to simplify removal. If the boat is in the water the exhaust outlets at the transom must be plugged or expect to be terrified when a deluge flows in as soon as the outer exhaust tube is removed. I found a rubber cap used for PVC tubing that had an OD exactly correct to plug the exhaust at the transom. To minimize water/coolant intrusion into the exhaust manifolds during removal, attempt to drain any residual raw water from the elbows by removing the brass plugs from the base of the elbows, and disconnect the coolant hose from the manifold and drain as much coolant as possible to get the level below the elbow mating surface.

    Unbolting the elbows would seem to be straight forward – eight long bolts and eight nuts on studs. My problem was one bolt that was seriously stalled due to corrosion between the bolt and the mounting bore. A sheared bolt would have been a major setback. A few minutes with the blue tip wrench on the lower boss and the bolt backed out fine. One nut was heavily rusted to the stud and sheared at the bearing surface – no big deal since I was replacing all the hardware. After removing the bolts and nuts is when it gets a little crude. It is very common for rust to form between the stud shanks and the associated mounting bores of the elbows. You cannot merely lift the elbows off the studs ! Women and kids should not be present for the next phase of the operation. The school solution is to employ a four-pound plus sledge and whack the elbows from side to side to rock the units up the studs. A heavy sledge is essential since low velocity impacts still carry much energy (KE=1/2MV**2 for the Dilbert types). The studs were heavily corroded in my case, however, numerous whacks and much Deep Creep later the old Blackfin finally yielded all four elbows.
    The studs were easily unscrewed from the manifold using a stud puller. The old gaskets were scrapped off and the surfaces on the manifold and block-off plate were cleaned with acetone. All the threads were chased and new studs were installed dry and tightened in place with the stud puller. Marine grease was smeared around the shanks of the studs in hope of avoiding the Thor routine next time. I researched the issue of sealer on the gaskets on the internet and did not find any reliable direction. Many recommended installing gaskets dry while others recommended Permatex. One troop went dry but later regretted it when leaks developed. I elected to use a light film of Permatex around all openings.
    Low profile OEM elbows are no longer available so I researched aftermarket options. The wrench-benders at my local marina were down on the elbows made offshore. Their biggest dissatisfaction was a high degree of porosity which limited longevity. I went with Barr units (CR20-98126) ordered from Boaters Plus. They appear to be perfect replacements – already painted Crusader blue, great fit, include new gaskets and a complete hardware kit, and made in the USA. I also ordered four additional gaskets since two are required per elbow (FWC manifolds). Service from Boaters Plus was excellent – ordered Sunday night and had them in hand to do the job the following Saturday.
    With the gaskets gooped and in position, I maneuvered the elbows into the exhaust tubes while slipping the elbows on to the studs. I elected to put anti-seize on the bolt threads which some do not recommend. I also greased the bolt shanks. After tightening the hardware in sequence, the job was pretty much over. The final issue was the 1.0 inch water hose fittings on the elbows (CRU97911). The only way to remove the fittings is with a pipe wrench. I managed to remove all four but cracked three of them when they collapsed slightly under the load of the wrench. OEM units are available but cost $25 plus. I went with Mercury Part Number: 22-807155 which is compatible and only cost $7. It also has a hex fitting which simplifies removal/installation.
    Hope anyone taking on this challenge finds this helpful. Every three years or so the elbows need to be changed and patience and planning will make the job just a little easier and predictable. Everything considered, it was not that bad. Not looking forward to doing it again any time soon !!

  3. #3
    Join Date
    Sep 2008
    Maryland - USA

    Default Re: 8.1L Riser Replacement (1st timer)

    welcome to ME.com!
    Mullet's discussion (I think) applies to fresh water cooled (FWC) units and it sounds like that's what you have as you mentioned "blocker plates".
    I'll add that if you are FWC and the saltwater from the heat exchanger dumps into the riser (vertical lift between the manifold and the elbow), you can relocate it to the coolant side to extend their service intervals....and make sure you change both if they've seen salt water for a while.
    When you are done, you'll have to purge the coolant side....a couple heat up, cool down cycles will do it if you have the purge bottle and the cap is working. also, once done, retorque the fasteners once the engine has cooled off (you can run a trip and get it the next time if necessary).
    Finally, if the maintenance has been poor, you might as well inspect/service the raw water pumps.....new impellers/gaskets at a minimum - maybe a major overhaul kit if necessary....

  4. #4

    Default Re: 8.1L Riser Replacement (1st timer)

    Thanks for the input guys. Yes it is FWC. I got one of the old risers off today and they were clogged up pretty good. Look like originals which means they are 15 years old. Bolts are in good shape, soaked them for 2 days in PB Blaster. Came off a little tough but not bad. Plan on using no-seize on the bolts when I put it back together tomorrow. Looks pretty straight forward. Blocker plates looked good but I am still going to use new ones when I reassemble tomorrow. There is no "riser" or "Spacer" the elbow sits right on top of the manifold and the raw water enters through the elbow. Glad I am taking this on, the existing elbows had 60-70% blockage. Certainly going to drop the temps. Impeller is also going to be changed tomorrow.

  5. #5
    Join Date
    Mar 2009
    Portland, Oregon,

    Default Re: 8.1L Riser Replacement (1st timer)

    Quote Originally Posted by matta0413 View Post

    There is no "riser" or "Spacer" ..... the elbow sits right on top of the manifold and the raw water enters through the elbow.
    I was going to say that all too often "Riser/Spacers" are confused with what is actually an "Elbow".

    Glad I am taking this on, the existing elbows had 60-70% blockage.
    Are you speaking of blockage at the seawater transfer ports..... or at the spent seawater mixing chamber?
    (the transfer ports are not used when the SS block off plate is incorporated).

    Rick ... aka Ricardo..... AQ series Volvo Penta repair
    Portland, Oregon
    28' SDN F/B w/ twin Volvo Penta 5.7L DP's

    Please... no PMs! Post your questions on the forum.

  6. #6

    Default Re: 8.1L Riser Replacement (1st timer)

    The water ports on the elbows were jammed with rust/rot. Gonna take her out tomorrow and see how much better the temp/steam situation is.

  7. #7

    Default Re: 8.1L Riser Replacement (1st timer)

    Forgot to close out this thread. After changing the elbows things did improve but still ran hot. Changed out the raw water pump as the plate was scored as was the interior of the housing and that did the trick.

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