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This if for a project to assemble a short shaft 70.. I haven't ran these parts yet to fully confirm fitment, but I took the chance and ordered them after a tonne of research, and studying parts catalogs and photos found online.































Matt

Cool

Very Cool.

Just measured the donor standard/long "20 inch" 70 mid I got from Doc and it is 442mm, so exactly 122mm longer. Same as the difference between the long and short driveshafts in the above photos.

I can't find a shortie muffler, so if anyone has tips on how to shorten a long muffler, please let me know.

For the tuner, I was going to copy the HydroTec tuner since they have pics of on their site, but also looking for suggestions there too.


cheers,
M

Just cut the inner liner (muffler) just above where it narrows

Build a 70ces tuner

The 70CES has a different powerhead base compared to the stock one. The CES does not run any muffler. Cutting a long shaft muffler works fine. I would get a OMC exhaust pipe from Kevi and rework it. It your not going the full CES root with a CES cylinder head and CES pistons then just shortening the stock tuner is a less costly option.
This build can get very costly!

I've had a couple of people ask about the availability of NEW short shaft parts for the 70 HP [triple] and 55/60 [twin].
Matt is working on BOTH models.
AND YES you can build a NEW motor .
Matt has posted the 70 hp parts on this thread.
The 70 hp 6H3 short drive shaft is no longer available...I can't find one!
The twin cylinder short drive shaft works in the triple as well. So the complete lower unit will fit either motor.
The Pro 50 trim assembly and clamp bracket fit both as well. The trim is a 6H3 part.
The long shaft trim is a 6H1 part [90 hp] and that trim unit will NOT fit in the Pro 50 clamp brackets.
Both the triples 50G and 70CES came with the small 55/60 nitro style foot.
And yes ALL parts were available thru Yamaha Canada in the 1990s to make a 70B short shaft canadian version.
It was not sold as complete motor in Canada...the 70CES and 70CES parts were available thru Hydro Tec...similar arrangement
OMC did with the last Formula E motor last produced in 1986 and only sold thru Second Effort until stock ran out in 1989.
Sea Way now sells SST45 and SST60 replacement parts....yamaha 70CES parts are sold out and no longer available.
The short shaft muffler for the triple is difficult to locate....it is online under part 6H3-14711-01-CA....$135.00 US.
IF you get the muffler order the 2 small rubber damper pads part 6H3-14737-00-00 for $5.08 US each.

HERE IS THE PARTS BOOK FOR THE TRIPLE:
https://www.megazip.net/zapchasti-dlya- ... eto-753836

HERE IS "A" PARTS BOOK FOR THE TWIN:
https://www.megazip.net/zapchasti-dlya- ... mhs-754641
There are several twin powerheads and TWO different short shaft mid sections .
You can purchase a complete short shaft lower unit but at $2600.00 US you would be better off buying the complete long shaft lower unit and the short drive shaft or just cut down and weld the long drive shaft.
https://www.megazip.net/zapchasti-dlya- ... 2-12842020

Matt, I got the custom Yamaha T750 exhaust system completed and I made the trade to get that original stock [part# 663-14711-02-5B] Yamaha T750 15 inch exhaust you need included in the 59 cubic inch Mercury short shaft deal. I will let you know when I have it. I got the Mercury now and I held back an SST60 part until I receive the 15 inch yamaha exhaust.
Maybe we can close the OMC performance gap a little with your Delta/15 inch Yamaha T750!

I managed to find a real 6J2 driveshaft. It is longer than the short 663 driveshaft pictured above by approx 18 to 20mm.

So I decided to investigate some more and compare a factory 2Cyl 55hp long shaft (675 Mariner 60) to a 3Cyl 70hp long shaft (70TLRV). The difference is again approx 19mm in length in the driveshaft - the factory 70hp driveshaft being longer.

Tried to test fit a stock/large 70 long driveshaft gearbox on a 55 2Cyl 20" motor: The stock 70 lower long driveshaft is about 9 or 10mm too long for the large lower to bolt up properly to the long 55hp 2Cyl motor.

So I'm wondering now how much driveshaft to crank engagement I get running the Mariner 2Cyl 60 lower on my Yamaha 70.. No issues so far and it has been under a lot of load a few times.

Another note when running the smaller 2Cyl gearbox on a 3Cyl 70: the back of the exhaust exit on the 70 mid does not fully line up with the smaller lower exhaust guide/walls, so some of the exhaust goes out the relief vents at the back of the lower casing instead of through the prop. I was wondering why my 70 got loud when I trimmed it up. So that's likely the reason.

It'd be interesting to see if a real 70CES (6J2) lower gearcase has the exhaust guide/walls in the proper location. Or it doesn't - the relief is beneficial?



M