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Hole Pattern on Evinrude

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matta0413

Contributing Member
I picked up a 17' center console that had a 50HP Evinrude on it. The 50 was too small so I picked up a 90HP Evinrude of the same vintage. The foot print of the mounting bracket is identical but the holes that were midway down the bracket on the old 50HP are not present on the 90HP and the slotted holes are below the floor and there is no bilge on this boat so there is no access. The 90HP does have holes that are molded in the aluminum but they are not threaded. Has anyone ever dealt with this before?
 
That doesn't make sense. The BIA bolt pattern as been used since the early 80's. I think 35HP and below probably is different but a 50HP should use the BIA pattern.

The BIA pattern follows this outline:
All holes are 1/2" diameter
Top holes
-- 12 7/8" on center
-- 6 7/16" from the center line.
-- 2" down from the cap of the transom.

Bottom holes
-- 9 7/8" on center
-- 4 15/16" from the center line
-- 8" down from top holes

The attachment is a CAD drawing of the pattern. If your holes don't fit this dimension then something really odd was done with your boat.

Evinrude_Transom_Bracket_Bolt_Pattern.jpg
 
The holes are there but they are cast in the aluminum almost as if they should be threaded and bolted from inside. I'll try to get some pictures.
 
If you compare these two photos you will see in one photo there is a bolt hole just above the slotted holes. And in the other photo that hole is not there. envirude new.jpgevinrude old.jpg
 
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The older transom drilling template. Maybe they've eliminated the alternate location????
 

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fdrgator said:
The older transom drilling template. Maybe they've eliminated the alternate location????
Click to expand...
Curious, I've never seen the alternate location but you're right, those lower holes look like they match that pattern. I can see how the 90HP definitely wouldn't use that mounting point.
 
matta0413 said:
I picked up a 17' center console that had a 50HP Evinrude on it. The 50 was too small so I picked up a 90HP Evinrude of the same vintage. The foot print of the mounting bracket is identical but the holes that were midway down the bracket on the old 50HP are not present on the 90HP and the slotted holes are below the floor and there is no bilge on this boat so there is no access. The 90HP does have holes that are molded in the aluminum but they are not threaded. Has anyone ever dealt with this before?
Click to expand...
I see from the pics what you mean now. Really interesting. Is there a bilge pump anywhere on the boat? If not, this might be you chance to make some useful modifications. It looks like you'll have to cut in the floor and create a bilge well to gain access to those lower bolt holes. This will be okay, just be sure to fiberglass in the area to strengthen it and then you can install a bilge pump in the bottom.

How about you post some pics of the are under the motor well so we can get an idea of what it looks like. If the area is open, you can get a piece of 1/2" thick poly board like King Starboard and create a lid for the hole you created. That will keep stuff from falling down there and will also give you access to the bilge pump when needed.

Here is a link to starboard. You might be able to find something similar at a local hardware but if not this is a place to look.

http://www.kingplastic.com/products/king-starboard-xl/
 
It's raining right now, I will try to get some better pics. But as you can see from the style of boat cutting into the floor is really not something I want to do. And I will have to call the manufacturer just so see if there is any room under the floor or if it is full of flotation.little boat.jpg
 
What brand of boat is this?

I'm really surprised the 50HP doesn't push that boat well enough. You won't win any races but should be able to go about 30MPH.

A picture from inside the boat toward the engine would be great. Also, can you measure the transom height, that seems awful short unless the picture is deceiving my eyes.

It could be full floatation under the deck, but in one of the pictures I definitely see a drain plug in the transom. Unless there is some odd structural thing with the floor and foam I really think a bilge well in the back would be a great addition. It would give you access to the lower mounting bolts and you could install a bilge pump (a must on every boat in my mind).
 
I will get some more pics when the rain lets up. The boat is custom, it is Rosbo. I just picked it up in the fall. I did some research on the company, it was two brothers. This one was built by one of them and he has passed away but the other brother is still making them. Now they are called ROS and are built by Coastal Boatworks in RI. If you google ROS Boats you will find them. It is really a neat little boat. It is very beamy and heavy for a 17'. The 50 was OK but with three guys going blackfishing it would barely get on plane. It is rated for up to a 115HP.
 
What size is the hole in the motor ?----Can you put a 1/2-13 NC thread in them.-----Those holes may have been there for the shipping crate / box that they used to use.----And yes you can thread a bolt in from the inside.
 
racerone said:
What size is the hole in the motor ?----Can you put a 1/2-13 NC thread in them.-----Those holes may have been there for the shipping crate / box that they used to use.----And yes you can thread a bolt in from the inside.
Click to expand...
Good catch. That may be the OP's best choice.
 
Okay, I see how the deck is made. So are those drains on either side of the motor? That's pretty interesting, do you get water coming in there?

I got it on the bigger motor. If you're rated for 115HP, the 50HP is waayyyyy under powered. I like to run a boat at or near max rated HP so the 90HP should perform much better for you.
 
No water. They have the "Ping pong ball" scuppers that stop and water pressure from the outside. As for the 1/2-13 NC Thread, I am considering either tapping those two holes so I can use them or using some JB Weld and putting some studs in those holes so I can fasten from the inside with a nut and washer. Just not sure if the JB Weld will hold.
 
Not that much. Think about the tremendous yank on those bolts when you hit an underwater object at 40 MPH. Tap them and bolt them if it is feasible.
 
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