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Thread: Building a Super Mod 2 cylinder Mariner/Yamaha

  1. #81
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    Quote Originally Posted by hydrospeed77 View Post
    To clarify and correct for historical purposes, the 60D (6F1) came with 1.85 gears from the factory (13:24). I'm guessing some racers lobbied to have the 13:26 gears from the 2cyl 40hp (679) officially homologated in via supplemental homologation.

    No the 6f1 was homoglated with 13t 26t

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    Bit more progress

    Dry fit of the parts to see what it would look like

    Still fettling away at the gearbox making the nose cone look a little more oem, tweeked the water definition plate to blend into the cone and tweeked the anti ventilation plate a little just straightened it up and blended it in lost a little bit of material off each side
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    Team Member Dvdracing's Avatar
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    Not a super mod but she run 74mph, mariner 30hp 689 modelName:  ENJIN.JPG
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    Latest updates
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    Team Member hydrospeed77's Avatar
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    Quote Originally Posted by Supremesoundzuk View Post
    No the 6f1 was homoglated with 13t 26t
    Yes, but only at a later date. It never came with 2:1 gears from the factory. The RYA homologation that includes the 2:1 gears clearly states those gears are from the 40F "679" model, and in fact shows the "675" part number as the factory gears (same part number as the 70CES 6J2 factory gears).

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    Quote Originally Posted by hydrospeed77 View Post
    Yes, but only at a later date. It never came with 2:1 gears from the factory. The RYA homologation that includes the 2:1 gears clearly states those gears are from the 40F "679" model, and in fact shows the "675" part number as the factory gears (same part number as the 70CES 6J2 factory gears).
    Yes indeed it does show the forward and reverse gears being replaced with 26t Which is how it was inspected for racing
    the pinion was always 13t though so originally is was 1.85 then changed to 2.1
    the ces was 14t 24t making 1.71 was it not

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    Team Member hydrospeed77's Avatar
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    Quote Originally Posted by Supremesoundzuk View Post
    Yes indeed it does show the forward and reverse gears being replaced with 26t Which is how it was inspected for racing
    the pinion was always 13t though so originally is was 1.85 then changed to 2.1
    the ces was 14t 24t making 1.71 was it not
    All the 60hp models from around 1980/1981 came with the 1.71 "675" gears. 60A "675" and 60C "6F0" (the two I own, all original) as well as the 60D "6F1".

    Racers probably saw that due to the power output and props available, they wanted more appropriate gear ratios and started using the 55B and 40F gears, and requested to have those gears homologated. So in the end you can run factory gears, or whatever the rules allowed/homologated.

    The only place I see the 60D showing 1.85 ratio is on race brochure where it is listed side by side with the 70CES in the same document. So at minimum 1984. I'm guessing it is either a typo or Yamaha changed the included gears based on recommendations from racers. Yamaha likely saw that the 1.71 gears worked well on the 70CES, and since it made more power than the 60D, changed the 60D factory gears so that props can be shared between the two motors (if you are running both classes, for example). 60D product development was highly influenced by racers in the UK back in the early 80's.

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    Team Member hydrospeed77's Avatar
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    Default Super Stock

    Here are some pics from assembling a short shaft from a long shaft. This was a few years ago. I'm adhering to our "Super Stock" racing rules. Basically the powerhead has to be stock, and/or built to a specific spec. We use UIM/RYA/APBA homologation mostly, but limit cranking cyl pressure to 160psi. The other allowances are fibre reeds, exhaust tuner is open to modding, and we can add power trim, adjust jetting and timing. No porting other than casting cleanup, no low water pickups or nose cones. I've since rebuilt my powerhead with oversize pistons and a bit more chopped off the exhaust, but no cyl head shaving yet, so still at like factory compression 140psi. The block in this photo is from a 1979 Mariner 60hp "675" model, the cyl head is blue - from a Yamaha 1989 55hp, but stamped "675" just like the older 60hp Mariner. I've also since installed the more modern flywheel which is also about 50g or 80g lighter I think.

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    The guys and gals in my class running OMC have the SST45 APBA specs as their limits - they are revving fairly easily over 7000rpm. My "55hp" Yamaha does not rev easily past 6500. Well, that entirely depends on how it is propped. But the OMC folks have a small power advantage - I have to gain 2mph or maybe like 300rpm running my current prop and gears if I want to catch the fastest OMC boats.

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