50 hp mounting bracket holes/slots

[waterdoggy]

If the Yamaha 50 is mounted higher by 1 set(2 holes) of its 8 bracket holes, will 20 mm timber packing between bracket and transom be OK to support the small rise?
Thanks.

[boscoe99]

A shim or packing between the top of the transom and the bottom of the clamp bracket is not needed at all. Many motors (I daresay most) are mounted such that they don't rest on the top of the transom. The bolts will support the entire weight of the motor.

[DennisG01]

You're talking about the bracket now having a "space" between the top of the transom and the underside of the bracket? I don't know what the "official" answer is, but I've had numerous small outboards that I (and family) have done that with over the years. 20mm is not much, at all. As long as your transom is sturdy enough, from my experience (again, not an official answer) it should be just fine. To be honest, I've always wondered if it's even necessary.

[waterdoggy]

You're talking about the bracket now having a "space" between the top of the transom and the underside of the bracket?

Yes, you've exactly defined the space that concerned me, because I thought the bolts could be stressed.
The top 2 bolts are new M12 x 140 mm, and the threads of one of them already are damaged, possibly by self tapping through the existing holes in an aluminum beam brace 100 mm below the transom top edge...or maybe that bolt and nut just seized. The previous 100 mm bolts all seem OK, after being removed and replaced a couple of times by me(and an unknown number of times by previous owners).
I was having some trouble with the engine hoist losing height, and had to keep cranking it up, while aiming the bolts.

[DennisG01]

Sounds like your hydraulic engine hoist is either low on fluid or maybe the release knob wasn't turned tight enough - unless it's actually leaking.

With what Boscoe said, it sounds like it's not imperative that you use a spacer. But, you know, it certainly can't hurt, either. Starboard (plastic cutting board material) would be a better choice than wood, though. Or even aluminum plate stacked up - or maybe in conjunction with the starboard to get the exact height needed so that the top of the transom takes some of the weight.

Large motors are typically suspended just on the bolts - and as long as your transom is strong enough, it shouldn't be a problem to do it that way, though.

[boscoe99]

Trust me, the strength of those bolts is more than sufficient to hold the weight of the motor. Even with some knock down drag out pounding in ruff seas.

A number of people raise their engine heights to optimize performance with nary a thought of installing a shim between the clamp bracket and the transom. Yamaha makes no mention of the need for such a shim.

[DennisG01]

Boscoe, I believe you and agree that the bolts are strong enough. My concern centered around the strength of the transom... that maybe it is not designed for the load in that manner and should have weight vertically on the transom cap. But that could be me just being overly cautious.

[waterdoggy]

Pumping/releasing pressure several times this morning seemed to stabilize the engine hoist ram. And I don't have the Starboard plastic material, but will use 20 mm thick pine for now.
The pine will be on top of a thin prism shaped wedge of aluminum, riveted to the existing aluminum surface, because 5 degree wedges will be added behind the transom to trim the Yamaha 50 deeper...this old aluminum hull's transom angle seems steep.
The prism shaped wedge, cut from an old credit card printing machine, will help to keep the pine mounting surface square with the new wedges behind it.
Thanks for all of your advice.

[rodbolt17]

waste of time and pine.
but its your time and pine .