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Thread: Crank case compression bypass on 2 cylender motor?

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    Team Member JohnsonM50's Avatar
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    Default Crank case compression bypass on 2 cylender motor?

    Question about an OMC 22ci 25hp I'm looking into adding the reed plate and intake from a 31.8 OMC. The bolt pattern fits so it would seem no problem but there is. Why would there be a bypass on the crank case side of the reed plate? Apparently it isn't on all of them but is on the one I'm working on. Might fill it as the 31.8 reed plate leaves it exposed to outside air. Or, would it be better to fill in a reed plate to cover it like the 22ci one does? Would this bypass be drawing crankcase compression from a decompressing cylinder or forcing compression into a compressing cylinder? Or, just balancing crank case compression? Hell if I know lol.

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    Quote Originally Posted by JohnsonM50 View Post
    Question about an OMC 22ci 25hp I'm looking into adding the reed plate and intake from a 31.8 OMC. The bolt pattern fits so it would seem no problem but there is. Why would there be a bypass on the crank case side of the reed plate? Apparently it isn't on all of them but is on the one I'm working on. Might fill it as the 31.8 reed plate leaves it exposed to outside air. Or, would it be better to fill in a reed plate to cover it like the 22ci one does? Would this bypass be drawing crankcase compression from a decompressing cylinder or forcing compression into a compressing cylinder? Or, just balancing crank case compression? Hell if I know lol.
    Well, anyhow, Probably something like easier starts, smoother idling, but most probably not enhanced performance. I'm just going with the reed plate that fits for now. I did chamfer the reed openings to near the reed side but not past. I'll do something with the 31.8 reeds on another without the bypass channel. Thinking the larger reeds with composites, the larger fuel pump and carb might liven it up a bit.

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    Pictures are a huge help with threads like this.
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    Team Member JohnsonM50's Avatar
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    Quote Originally Posted by RaisedByWolves View Post
    Pictures are a huge help with threads like this.
    True, just went into putting it together tho, it's at least sounding good pending boat trial.

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    On my homemade Merc triples, adding a by pass (1 to 3 and 2 to both) greatly improved idle.

    On the 90 hp Merc triples those bypass passages are HUGE.

    Jeff
    "We live at the bottom of an ocean of air." - General Marvage Slatington
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    Quote Originally Posted by Fastjeff57 View Post
    On my homemade Merc triples, adding a by pass (1 to 3 and 2 to both) greatly improved idle.

    On the 90 hp Merc triples those bypass passages are HUGE.

    Jeff
    The 22ci has a single carb so balancing that is moot but at the crankcase inside the reed wall makes sense as to idling. Thanks.

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