mounting 70 on jackplate

I have a 1979 Merc 70 that I am going to mount on a SlideMaster jack plate. The SlideMaster has a 10' setback but instead of two bolts on each side that are able to slide up or down, it has 2 bolts on each side that do not allow for adjustment(unless new holes were drilled), is this still considered a jack plate? the back of the "jack plate" has holes already drilled in it for mounting the motor. Which holes on the motor do I use for mounting the motor to this plate? The motor has 2 clamps for mounting, in my application are these still used? If so do I need a spacer of some sort to clamp to because it seems the jack plate is too thin to screw the clamps down on. If I didn't explain myself well enough, let me know, and I'll try and take better pics.

Re: mounting 70 on jackplate

I'm new to these forums, any help is greatly appreciated

Re: mounting 70 on jackplate

That looks like a setback plate not a jack plate, how about picture of the side of it.

Re: mounting 70 on jackplate

You need to bolt transom clamps to jackplate. You need two 3/8" carriage bolts, unless you have PTT, in which case you need 4 or 6 -3/8" carriage bolts. Use SS for saltwater.
Use a spacer (likely 1X6 wood), under the transom thumb screws.

Re: mounting 70 on jackplate

It does have tilt & trim. Obviously I'm new to motor mounting, could you explain more about the spacer you mentioned please? I take it I make it out of a 1"x6", is it so the clamps on the motor have something thicker to clamp to?

So I use the clamps on top to mount the motor, on the bottom of the second photo I'm pointing to the lowest mounting holes, should I use them to secure the motor? or?

Re: mounting 70 on jackplate

That is a jack plate,,,

Re: mounting 70 on jackplate

OK, It looks like your bolt holes on the bottom of the transom clamp do not mate with the jackplate. That is a weakpoint.

See if you can place a 2X8 (or whatever width you need), grain going vertical, under the clamp screws, so you can bolt the lower transom bracket as well as the PTT Brackets to the 2X8. If a 2X8 is too thick, use pressure treated plywood, as thick as possible.

Re: mounting 70 on jackplate

Ok thanks! What would be the best way to go about the mount holes not matching up with the jack plate? It's been drilled a few times, sell it and buy a new one? or? Also when mounting the jack plate to the transom, should the bolt heads be facing the boat? the motor? or does it matter as long as all washers are used correctly?

Re: mounting 70 on jackplate

I mounted the jack plate to the transom. I was anxious to finally see what the boat looked like with a motor on it, it's not mounted, just resting on there. I realize the hp is aggressive, but i'm happy with the physical size of the motor in relation to the boat.