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Thread: Never underestimate the little things

  1. #21
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    Quote Originally Posted by Popa Sam View Post
    I would not use surface gap plugs until the cooling problem is corrected. The center electrode usually ends up in the combustion chamber instead of in the plug body. Don't know why you chose the lost foam block instead of permanent cast one. The lost foam does not hold shape as well as the permanent. Also the permanent has better cylinder sleeve support and higher crankcase pressure. There are several versions of the lost foam. Depending on which one you are using it may be dumping too much water from the bottom causing lack of water pressure at top. Do you monitor water temp, water pressure and CHT ? That would help you find problem and stop before damage occurs. Good luck.
    Whew! That's the best reason ever not to use the surface gap plugs, at least during development. Answers to your questions: 1) The lost foam oval exh port powerhead was available complete with relatively low time. The turbo likewise was a low time dyno piece. I didn't want to invest in high $$$ parts not knowing if the engine would even work - Boy was I surprised! 2) The turbo uses factory water routing (less t-stat) from bottom to top around the cylinders first, then into the head through the t-stat housing, top to bottom, exiting after the head. There's no reason to believe any steam pockets or starvation are occuring. 3) There is no instrumantation except for EGT and boost pressure. The stock 45SS pump has proven robust in all applications and have not measured press or temp. Also, have never run cylinder head (spark plug) temp sensors, but now's a good time - good thinking.

    As the #2 & #3 seem stable, it makes sense the #1 might be failing due to pre-heated cooling water. Thoughts are to revise the cooling system entirely using cross-flow for cylinders, and build a stiffer gasketed or O-ring head this winter.

    Thanks to all for your thoughts and tips.

    Tim

  2. #22
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    Tim:

    Does the switch box on your turbo have a knock sensor? Just curious.

    Jeff

    PS: Did you know htat Buick came up with these now common knock sensors when they introduced their V-6 Turbo Grand National way back in hte 80s? They also pioneered distributor-less ignition at roughly the same time.

  3. #23
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    Quote Originally Posted by Fastjeff57 View Post
    Tim:

    Does the switch box on your turbo have a knock sensor? Just curious.

    Jeff

    PS: Did you know htat Buick came up with these now common knock sensors when they introduced their V-6 Turbo Grand National way back in hte 80s? They also pioneered distributor-less ignition at roughly the same time.
    Sorry for the delay...... The turbo uses the standard CD-3 with no rev limiter, no knock sensor. In this case detonation is not the problem (pistons/spark plug electrodes are fine). Closer scrutiny of the whacked head gasket indicates hydraulic crushing and splitting of the stainless steel fire ring, followed by lateral breach and destruction. There does not appear to be a clamping problem. That the failure occurred twice in the #1 tends to indicate the hotter, leaner cylinder might be contributing to the failure.

    The Pro-Marine aftermarket gasket has a wider, possibly stronger fire ring. It is photographed with the damaged OMC gasket and a new OMC gasket. Note the crushed fire ring in the used gasket (yet to split). The deformation is the same on both sides of the gasket. It would be interesting to learn the cylinder pressure but alas, I don't have that type of test apparatus available.

    Tim
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  4. #24
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    I thinks its very difficult to get a knock sensor to work on a 2 stroke outboard, lots of noise going on there...
    With open deck blocks the cylinders might be moving under high load as well which causes the gaskets to blow.
    One of my mates at OMC said this was a problem with the old racing v4 and v6's back when he worked on them

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