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Thread: 56" omc cooling

  1. #1
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    Question 56" omc cooling

    Got a stock rebuild to do on a 1986, 70 hp, 56" rude.

    need any additional info on cooling upgrades for the middle cylinder.

    Have already "backed out" the bridge on all the exhaust ports and have drilled piston for bridge cooling.

    Any more suggestions ?

    LT

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    There was a kit available at one time, some fatter main jets. The remedy at the time was to "cool it with fuel". Most customers were not happy....lost 50-100 Rpm. I think some still stuck with the kit.

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    BRF Team Europe Member Per's Avatar
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    I'm not 100% sure this applies to the -86 engine but I know it was recommended to my -91 56CI.

    Relocate tell tale outlet to top of water jacket.
    Rejet, as mentioned before
    Reduce timing to 17degree, think 19 is std.
    I think there is some kind of mod to be done to the thermostat and /or seat as well.
    There is still an upgrade kit available but I don't remember the part# (bought one myself for a couple of years ago)
    Waterpump?


    There's lot of information on this topic on Iboats OMC repair forum. Think most of the mods / part# above are described in detail there.
    Also if not already done search for service bulletins on the topic, there is several...

    Most important, don't lug the engine!

    I bought my engine with seized middle (and scuffed upper) cylinder, the previous owner told me that it happened while he was towing another boat, I'm sure you will find other stories just like that if you google...

    Good luck

    Edit: found what I was looking for...

    Seahorse5 over at Iboats wrote:


    60 & 70 hp service bulletins for cooling and overheating

    SB 2221 Temp sensor new sensor pn 584166, tan/blue stripe wire.

    SB 2225 thermostat seat new seat pn 336416, may not need this in fresh water.

    SB 2271 jet and timing kits ds

    SB 2276R1 relocate tattle tale nipple to top of block.

    SB 2276R1 and new pressure relief springs comes in waterpump kit pn 432955.
    Last edited by Per; 09-20-2011 at 01:19 AM. Reason: found info...

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    do you have a copy of 2271
    the rest we can work out
    thanks

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    BRF Team Europe Member Per's Avatar
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    Quote Originally Posted by Powerabout View Post
    do you have a copy of 2271
    the rest we can work out
    thanks
    I will go to my workshop tomorrow, maybe the paper is still in the box the kit came in...

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    Team Member Bill Gohr's Avatar
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    There were no mods for the 1986 motor, the issues were mainly with 1991 thru 1993, we changed the block for the fall of 1993 which the 94 build, that's when it went to a single exhaust port. If you read those bulletins they should not pertain to an 86' what the 86' did have was a tighter head, and would take out the middle cyl, but if it lived this long its probably OK, if you're worried go up 1 on the main in the middle carb.

    For your engine as far as cooling, buy the 432955 water pump kit and follow the instructions

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    Default cooling

    Thanks Bill,

    This engine definately took out the center cylinder & head.

    Got a later model head for the rebuild.

    Should I still drill the pistons (1/16" hole) to oil the bridge ?

    Lawrence Thornton

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    Team Member Bill Gohr's Avatar
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    Well I have to recommend the factory oversize piston for that repair, I had the cam shape changed on the piston for the service part as well as the holes added

  9. #9
    BRF Team Europe Member Per's Avatar
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    Sorry to ramble in this thread[

    B]Powerabout:[/B]

    Went to the workshop but the box with the kit was not really what I was looking for, it was the waterpump kit...

    I did find some of my own notes in my workshop manual for my -91 56CI stating that a ignition should be reduced to 17degrees like i previously stated the notes also stated that the info was from a SB but not wich number
    In the end I didn't bother to rejet or reduce timing since I figured it would work anyway with my light boat and cold waters
    Also the fuel consumption was already ridiculous compared to my old Volvo Penta VP700

    PS: Powerabout, your PM inbox is full...

  10. #10
    Team Member Bill Gohr's Avatar
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    If the head you are using has a "G" stamped after the part number that would be the later one,

    As far as those service bulletins from 90, 91 92, and early 93, most of them can be disregarded, lots of those were quick fixes trying to cover engines that were failing like popcorn so we really don't need to do all of them and remember if you have a 90-93 with a replacement oval port powerhead and the correct water pump you need to disregard them all.

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