Yamaha 60DES S750 UIM Speed Record 1986

[hydrospeed77]

found this in an old Yamaha publication.

69826

[hydrospeed77]

69830

[hydrospeed77]

1981
69831

[Powerabout]

same engine as the Mariner 55/60?
I think that launched the Merc Yam partnership

[hydrospeed77]

Very similar, yes. not Exactly the same. Likely more differences between the 60D/60DE (6F1) and the regular 48/55/60 2Cyl than the differences between the 70CES (6J2) and the regular 70hp (6H3).

See the discussion regarding these motors in this thread:
http://www.boatracingfacts.com/forums/showthread.php?13663-Building-a-Super-Mod-2-cylinder-Mariner-Yamaha&p=156090&viewfull=1#post156090

[hydrospeed77]

I had a great person help out and measure a new old stock 6F1 piston, and as per speculation, the 60DES bores were 81.30mm for a displacement closer to 747 or 750cc..
Stroke and rods are the same as the 3cyl 85/90, but ports are slightly different. 55B is also slightly different from the 85/90hp. Not sure yet on the 55B/60DES port differences - might be none.

[hydrospeed77]

Some more history regarding the 60D (6F1):
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.

update:
Original 60D came with "675" gears. This is 1.71:1, and as a side note the 70CES parts book also lists "675" gears. I also have a document that states the 60D came with 1.85 gears. So perhaps there is an error in that doc, or later model years came with 1.85 from the factory. The "679" gears from the 2cyl 40F also fit and were used officially for racing back in the early 80's in the UK.

[hydrospeed77]

This is the boat, motor, and driver that set the record shown in the first post in this thread:

https://www.youtube.com/watch?v=hFUgbrZRakE

Amazing that this video exists.

[hydrospeed77]

Some more history related to this motor, and two racers I wish I was able to speak to.

75652