Four stroke outboard mounting

[JohnG]

I am preparing to mount a new four stroke motor mount on the back of my Hunter 25.5 I have constructed a new pad for the outside of the transom and a new pad for the inside of the transom I plan on using 8 bolts to bolt through the transom do I need 8 bolts or is this just overkill

the motor is a Tohatsu 9.8 four stroke and is considerably heavier than the two stroke it replaced, ( hence the new bracket) I bought a garelick 71090 mount
which appears to be well made and much heavier than the old mount..

I believe that I am going to have to fill or patch 2 holes of the existing fourh holes when I swap out the motor mounts so my question is this..

can I just fill the old holes with Marine Epoxy..with fiberglass cutting mixed in

Also if you don't think I need the pad on the back then please let me know
my thought was that a pad under the motor mount in the shape of a trapezoid that is 5.5 inches longer than the bracket and 4 inches wider would help to distribute the load over a wider area again I plan on using 8 carriage bolts through the transom to more or less sandwich the transom between the two pads I made...

Thanks in advance for any information and your time


Respectfully
John

 

[Benny]

John, you seem to have a sound idea and since

you have fabricated the pads go for it. I looked at the specs for the motor bracket and its more than adequate for the intended application. I just wanted to make some comments; if you want to avoid drilling to many holes rest assured that four bolts will hold the bracket and the engine. I like using pads as they help protect the bolt holes and the gelcoat around the motor bracket. I don't know what kind of wood or material you have made your pads out off but make sure it is strong, water resitant and long lasting. The motor bracket should be mounted as vertical as possible to facilitate trimming of the engine. An angled pad can compensate for a transom that angles inward or outward. Before drilling make sure of the desired position of the bracket. I always like to measure with the mount travel at its lowest to make sure the powerhead will be kept out of the water. To cover old holes you can use epoxy and fiberglass and finish with a gelcoat. To drill holes into fiberglass I place a piece of masking tape to the area and drill through it as it is recommended to prevent cracks. A sealer for the bolts and pads is a must. Good luck.

 

[Mike Whalen]

Watch the clearance on mount

John,
I changed to the four stroke and new bracket. The only real problem I have is that the bracket requires a bit more clearance. In the up position the handle is too close tot he transom. Your block may take care of that. I really should have put one on. If you haven't installed it yet here's a bit of advice. When you mount it and then try the action of the lift you'll swear you've screwed something up. I was looking for a retaining bolt or something. Once the weight of the motor was on it worked fine. That sucker is wound tight.

Enjoy.

Mike

 

[BobM]

Re: Watch the clearance on mount

From what I found, the 9.8 isn't heavier than the Johnson 9.9 sailmaster, which I had on a previous boat. I had no pad on that boat and, unless for some reason you think your transom is suspect, I wouldn't bother. What I would bother with is ensuring that you use good backing on the inside of the transom. When I bought my boat it just had washers and I replaced them with much more significant washers as the originals were distorting. If I was going to do the job from scratch on a boat I meant to keep I'd probably build a good backing plate for inside the transom, because I believe that the most significant forces are at the most distant points, the ends of the bolts.

Also, it sounds like you are replacing an existing mount, so you know where that mount was, but in my experience with a 25 foot boat, it is worth some extra time thinking about where you should place the mount. The new mount might have different extremes of adjustment and a 25 foot boats trim can be very sensitive to weight distribution. The new motor might alter things a bit too, because it is 100lbs, but it is 100lbs at the extreme end of the boat hanging off a bracket giving it greater significance. How heavy was your old outboard?

 

[tommays]

Just remenber there are only 4 BOLTS holding on that GIANT 300 HP outboard that just splashed you


I cant believe that (4) 5/16 or 3/8 bolts with a backing plate would ever have a problem

 

[JohnG]

Thanks

Guys/ Gals


Thanks so much for the replies, I have read the the advice and it all seems sound, so it looks like 4 5/16 bolts will do the job (I tend to build with overkill)

I do know where the old mount was mounted and used the suggestion for the math to properly set the height for the new mount the old mount had about 12 inches of travel and the new one only has nine , so I do have to mount lower but have cut a stick like the installation directions suggest to give me a good idea of where I need to mount the motor with the bracket in the up position as it comes from the factory so it should be straight forward and thanks to all of you for the input the less holes I need to dril the happy the wife will be and therefore the happier I will be..

The old motor weighed in at around 60 pounds give or take two pounds the new one says it weighs 80 pounds dry but it feel like more and certainly looks like more...

The pad I build does give an extra 1.5 inches of clearance so it should make movement of the motor more user friendly when in the upright position...

I will also be using a one inch glass covered backing plate in the inside just to be sure as well as large washers and so on..

at any rate thanks again for the replies..

Respectfully
John

 

[JohnG]

Motor Mounted and working well

Just wanted to give and update on the motor mounting situation

I mounted the bracket on Four Sail on saturday and was able to use the existing holes by just enlarging them a bit and filling in the voids with epoxy
I only used four 5/16 bolts to bolt through the hull as most suggested

the motor functions great and is so much easier to pull up and down
just wanted to mention that had I not used the wooden pad between the transom and the bracket the motor would have been unusable as it would have set right at the transom...

The pad I constructed was 1.5 inches thick made of doug fir marine ply
then covered in a thin layer of glass and then about 6 layers of epoxy paint
I used marine sealer around the outside edges of the pad and at this point anyway all seems to be well...


Thanks again to all of you for your input and suggestions


Respectfully
John G