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  1. #1

    4Tech 215 engine failure after exhaust hose came off

    Suffered an engine failure at hour 21 of an SBT replacement. Cyl 2 wrist pin failed, and am a little stumped on the root cause because of facts leading up to this.
    After perfect break in to 10 hours, ran ski last season to just under a total of 21 hours.
    First run- idled 15 minutes through no wake. Accelerated to plane, engine bogs and ultimately shuts off with no code. Noticed ski sinking, pulled seat and found exhaust hose popped off at resonator. Was taking on water, towed it back and was half full. Exhaust clamp appeared to fail from corrosion.
    That evening, pulled plugs and cold started to blow out moisture but found that cylinders were dry. Oil level was same as when I changed it this year. Put plugs in, fired right up. Installed new stainless clamp.
    Second run- same idle time and same issue. Pulled seat, found exhaust hose popped off, this time at water box outlet. Clamp failed, was shiny at fracture like it was over tightened. Put hose back on, wouldn’t start. Cold started, then started normal and fired right up. Returned to dock, installed new clamp.
    Took back out, under acceleration hesitated with poor idle. Revved engine in reverse and idle normalized. Accelerated to full speed and power, ran great and was normal for 5 min. Idled for a bit then drove normal. Seemed to run ok, but not quite full power. Ran about 15 minutes goofing around.... then got a low oil pressure alarm.
    Shut it down, checked oil level. Normal, fired up and ran for a few minutes, low oil pressure. This occurred several times, twice engine died and restarted to get to shore. At 2 points low oil pressure blipped and cleared on its own.
    Final run to shore at low throttle , engine died with no alarm... seized.
    Pulled engine and found both oil pumps in good condition. But main pump suction screen was completely plugged and deformed with aluminum. Oil passages found clean, oil level and quality found normal.

    SBT is warranting engine, calling it a forged piston failure.
    Did find bearings worn and warned me to check oil circuits, but I believe low oil pressure was due to completely plugged screen due to piston failure.

    Why would engine shut down if exhaust hose came off?
    Wondering why two clamps failed on exhaust hose like this?
    How could exhaust hose failure cause engine damage?

    Asking dumb questions hoping to learn something I need to check before reinstall. Checked oil ports, regulator, pumps. Checked intercooler for leaks, cooling system is clear, thermostat works.


  2. #2

  3. #3
    Also, cyl 2 exhaust valves bent.

  4. #4

  5. #5

    Join Date
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    Clean out the oil and water passages in your new one before installing it. Pull the heads and oil pan if you know how. We found metal shavings in SBT motors fresh out of the box. They're known for taking shortcuts when building them.

    I went through 3 SBT motors in my boat (Yamaha MR1s, same motor as the FX HO) before I gave up and bought one from an independent builder. The warranty's great but the time out of the water wasn't worth it. First set, one failed during break in, the other 6 hours later, boat was in the shop 2 months and then 3 months last year. Then one of the replaced motors seized up this year. Now I have 1 SBT motor in it and one from the indie. I'm buying a second motor from the guy to swap this winter because it runs noticeably smoother and I don't want to deal with the boat being in the shop anymore when the SBT eventually blows again.

  6. #6
    SplishSplash's Avatar
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    It shuts down with an exhaust leak because the exhause smoother the engine, no oxygen.
    As for the 2 clamps failing, worn out or cheap clamps or overtightened .
    Im suprised SBT replacing it, they would ususally say water intrusion cause the hoses came off.

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  8. #7
    Thank you. Good point on clamps and agree. Was thinking I overtightened, but hard to eliminate that for root cause since many things happened in sequence. Odd unless I assume they just failed and then a separate issue occurred with engine.( still struggling with this though)

  9. #8

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    ugh, SBT are the worse. It seems like for 5 motors you change you get 1 good one. I learned the hard way years ago on a 951 Rotax

  10. #9
    Asking this one again-
    Why would this engine stall and not restart with an exhaust hose becoming disconnected from the water box?
    I get an exhaust “valve” failure. But I’m not getting why this could happen from an exhaust hose? Loss of backpressure- does this mess with AFM and go lean possibly?

  11. #10
    Got Boost? psycho rxp's Avatar
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    Quote Originally Posted by Bondski View Post
    Asking this one again-
    Why would this engine stall and not restart with an exhaust hose becoming disconnected from the water box?
    I get an exhaust “valve” failure. But I’m not getting why this could happen from an exhaust hose? Loss of backpressure- does this mess with AFM and go lean possibly?
    With the seat on the engine was sucking its own exhaust fumes, no oxygen to burn

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