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Author Topic:   Transom motor mounting holes
bigbillyfish2002 posted 02-22-2002 09:42 PM ET (US)   Profile for bigbillyfish2002   Send Email to bigbillyfish2002  
I am repowering a 1978 17-Sport (that originally had a 70-HP Evinrude) with a 2001 70-HP Yamaha. I am wondering if the holes made to mount the Evinrude will be the same as for the Yamaha, or will I have to drill new holes? I thought they were universal, but after reading some forum posts I am now not sure. Thanks, Bill
Tom W Clark posted 02-22-2002 09:55 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
While I am not 100% sure, I suspect the holes will be the same in your case. The mounting holes were standardized some years ago and in even if not, Yamaha outboards are, after all, great knock-offs of OMC outboards.

This reminds me of a story my Uncle (John S. Carey) told me. He was the owner of Wright Outboard, the Johnson Outboard distributor for Washington and Alaska from 1960 to the early 1990's when OMC yanked all the distributorships.

In the early 1970's Yamaha invited John over to Japan to talk about distributing their line of outboard motors. He toured the factory and saw Yamaha castings with OMC part numbers cast into them! Talk about a blatant ripoff...

jimh posted 02-23-2002 10:00 AM ET (US)     Profile for jimh  Send Email to jimh     
[This post has been edited to improve readability--jimh.]
jimh posted 02-23-2002 10:06 AM ET (US)     Profile for jimh  Send Email to jimh     
I am not a Yamaha outboard historian, but I thought I had read that the c.1980 Yamaha outboards used lower units from Mercury.

Even today, Yamaha and Mercury seem closedly partnered in some outboard products. Mercury has been selling some 4-stroke models that reportedly have Yamaha powerheads mated to Mercury lower units.

bigbillyfish2002 posted 03-12-2002 11:11 AM ET (US)     Profile for bigbillyfish2002  Send Email to bigbillyfish2002     
i just hung the motor yesterday and all the holes line up.however the bolts yamaha supplied are too long for the 2 lower[blind]holes and i am going to have to grind them down or get shorter ones.when i called the dealer he said they didn't use the blind holes,but lag bolted thru the 2 lower"thru" holes right into the transom. i don't like making extra holes in my boat so i don't want to do this. anybody have any comments?p.s. thanks for all the great input.bill
Wild Turkey posted 03-12-2002 11:50 AM ET (US)     Profile for Wild Turkey  Send Email to Wild Turkey     

I don't think lag bolts are the answer.
Check out this thread:


DanT posted 03-12-2002 05:07 PM ET (US)     Profile for DanT  Send Email to DanT     
I replaced an old Evinrude with a 90hp Yamaha which bolted right up using the blind holes in the Yamaha bracket. The only down side to this method is you give up the ability to adjust the height of the motor on the transom.
Tom W Clark posted 03-13-2002 09:13 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

OK, your holes line up. That's good news. If the supplied bolts are too long then just go buy the correct sized ones or cut them down. That's easy enough and it's what I would do IF you are happy with the vertical position of the motor on the transom.

As DanT points out, using the blind holes eliminates the chance to adjust the motor height. If you want to preserve the adjustability of the motor's height then go ahead and use lag bolts. As I've said in the thread referenced above, lag bolts are what Boston Whaler always recommended in this situation if the motor's mounting bracket would not accept bolts from the splash well area.

I think lag bolts will be fine. The lower bolts are mostly there for shear strength not withdraw strength. I challenge anybody to sight an example of a lag bolt failing on a 17' Whaler motor installation.

It's nice not to have to drill two more holes in your transom but I don't think it's really a big deal if you do. Just be sure to do a good job of patching the former holes, i.e. don't use a dowel (see: )

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