How to properly mount an outboard

[coolguy147]

How do I properly mount an outboard to a newly refurbished transom?

4 or 4.5 inch stainless bolts?

 

[Bob_VT]

Re: How to properly mount an outboard

Just go with the length you need. Extra length will only give you more turns of the wrench and no other benefit. Be sure to use washers on both sides and I prefer lock nuts.

 

[EddiePetty]

Re: How to properly mount an outboard

.....whatever length allows for flat washers on both the bolt head and nut sides with at least 1-1/2 to 2 thread protrusion thru stainless steel Nylok nuts.

 

[Silvertip]

Re: How to properly mount an outboard

There is just a little more to consider when mounting an outboard than just bolting it in place. Engine height is an important consideration fro proper performance. Start with the AV plate about flush to an inch above the keel. Rarely does an engine sit full down on the transom brackets.

 

[pdgs]

Re: How to properly mount an outboard

The first thing you need to do is get yourself a mounting template for the motor you're mounting. Today, the mounting holes are ABYC standard and only vary by engine size. Most Shop manuals have instructions for making the template in the rigging portion.

Once you have your template you can position it on the transom so that when the engine is mounted there is enough adjustment so that the bottom of the lower cavitation plate on the motor can be made to sit 1" above the bottom edge of the hull.

Clamp the template in place and then using a drill guide, drill 4 pilot holes using a 1/4" drill bit. Finish drilling the holes with a 1/2" drill bit. Make sure you use a drill guide so that the holes are drilled square in all directions to the surface of the transom. It's difficult to guess and if you don't drill them correctly they will cause excessive stress on the transom.

Once the holes are drilled, positon the motor over the holes and insert the (4) 1/2" x 4-1/2" fine thread 1/2" dia stainless steel bolts with stainless steel washers. The two lower bolts are inserted from the engine side with the nuts in the inside of the transom and the two uppers are inserted from the inside of the transom with the nuts on the outside. The nuts should be 1/2" fine thread bronze nylock nuts.

Most boat dealers will sell you a set of the proper bolts, nuts and washers. Fine thread nuts and bolts must be used to prevent overtightening and cracking of the motor mount. It's important to use a torque wrench and torque the nuts to spec.

 

[coolguy147]

Re: How to properly mount an outboard

The first thing you need to do is get yourself a mounting template for the motor you're mounting. Today, the mounting holes are ABYC standard and only vary by engine size. Most Shop manuals have instructions for making the template in the rigging portion.

Once you have your template you can position it on the transom so that when the engine is mounted there is enough adjustment so that the bottom of the lower cavitation plate on the motor can be made to sit 1" above the bottom edge of the hull.

Clamp the template in place and then using a drill guide, drill 4 pilot holes using a 1/4" drill bit. Finish drilling the holes with a 1/2" drill bit. Make sure you use a drill guide so that the holes are drilled square in all directions to the surface of the transom. It's difficult to guess and if you don't drill them correctly they will cause excessive stress on the transom.

Once the holes are drilled, positon the motor over the holes and insert the (4) 1/2" x 4-1/2" fine thread 1/2" dia stainless steel bolts with stainless steel washers. The two lower bolts are inserted from the engine side with the nuts in the inside of the transom and the two uppers are inserted from the inside of the transom with the nuts on the outside. The nuts should be 1/2" fine thread bronze nylock nuts.

Most boat dealers will sell you a set of the proper bolts, nuts and washers. Fine thread nuts and bolts must be used to prevent overtightening and cracking of the motor mount. It's important to use a torque wrench and torque the nuts to spec.

My biggest problem is actually drilling orthogonal with the transom.

I'll be going to the local hardware store for stainless bolts because home depot's stainless bolt selection sucks.

 

[Frank Acampora]

Re: How to properly mount an outboard

The hardware store will most likely be like Home depot: Will not have what you need. Try a company called Fastenal, and even there you probably will need to special order. Or spend the big bucks and go to the dealer or marine store.

While regular coarse thread 1/2 inch stainless bolts may work for smaller horsepower engines, if it is anything over 30 don't be tempted: Buy the fine thread 1/2 inch bolts. Fine threads are about twice as strong and take a higher torque. They are the correct bolt for this application.

If you decide to buy stainless nuts beware: Sometimes upon installation or removal stainless on stainless will gall and cold weld, ruining both the nut and bolt. In this applicatrion, the only correct nuts are bronze nylock.

For inside the transom, buy stainless steel extra thick fender washers.

Do it slow, or do it fast, but don't do it half fast. It is worth spending a couple of bucks extra to do it correctly.

 

[coolguy147]

Re: How to properly mount an outboard

The hardware store will most likely be like Home depot: Will not have what you need. Try a company called Fastenal, and even there you probably will need to special order. Or spend the big bucks and go to the dealer or marine store.

While regular coarse thread 1/2 inch stainless bolts may work for smaller horsepower engines, if it is anything over 30 don't be tempted: Buy the fine thread 1/2 inch bolts. Fine threads are about twice as strong and take a higher torque. They are the correct bolt for this application.

If you decide to buy stainless nuts beware: Sometimes upon installation or removal stainless on stainless will gall and cold weld, ruining both the nut and bolt. In this applicatrion, the only correct nuts are bronze nylock.

For inside the transom, buy stainless steel extra thick fender washers.

Do it slow, or do it fast, but don't do it half fast. It is worth spending a couple of bucks extra to do it correctly.

Oh geez...I bought 4 3.5 inch SS bolts, 8 SS 1/2 washers, 4 SS 1/2 lock nuts...the bolts are of 13 threads so coarse....

I got these at a local hardware store since HD sucks lol. I'll be using anti-seize.