---

First of all, on most Classic whaler transoms, a 4" hex head bolt is the length you want to use, 1/2" diameter. Stainless steel is mandatory.

If you really want to mount engine according to B.I.A. standards, here are the parts needed. This is the same system and parts that Mercury has been supplying with new engines for 40 years.

1. the four bolts mentioned above, in FINE thread.

2. four 12MM METRIC SS washers which go against the engine side. These are same hole size as regular 1/2 " washers, but smaller outside diameter to fit the engine bracket. You can get them here:

https://www.zieglerbolt.com/flat-wash...558;21!114

3. Four extra thick regular 1/2" washers for the boat side of the installation. West Marine, or online source has these. You can get them here:

https://www.boltdepot.com/Product-Det...duct=15890

4. four BRASS locknuts in fine thread. Brass locknuts are used because they will not gall (seize up) on 1/2" size bolts as a Stainless locknut can do. You can get them here:

https://www.zieglerbolt.com/12-20-nyl...ine-thrd-2

The installation procedure requires the top bolts to go in from the inside, and the bottom bolts from the outside. If anybody tells you anything else, they don't know what they are talking about! This is so the transom can be properly caulked, to avoid later rot-out, a common problem usually caused by improper engine installation caulking. If you look at any Boston Whaler with a factory installed engine, you will see that this is how they do it.

Use clear "LifeCaulk" brand sealant, which is much better than regular silicone. NEVER use the 3M 4200 and 5200 adhesive product!

With the engine on the hoist, at approximately the right height (mount engine in second set of holes from top), and back a few inches from the transom, slide large washer onto bolt, put a circle of caulking around bolt at back side of washer, and slide bolt all the way through the transom. Where it comes out on the outside, put another circle of caulking around bolt-boat junction. Don't get caulking on the threads. These bolts will need to be held in place as the engine is moved into position and the small washer and nut are installed. Two people recommend for this work.

Also before moving the engine into position, the lower bolts, with small washer installed against bolt head, are then pushed all the way through the engine bracket, and while held in place, caulking is applied to the bolt shank for about an inch. THIS IS EXTREMELY IMPORTANT, as this becomes the sealant preventing water into the hull, particularly if the bottom hole is a SLOT. As the engine is moved up tight to the transom, only the excess will be forced out of hole and form a seal. The bolt now sits in a caulking surround making a tight seal, yet no caulking gets onto the bolt threads. Then a ring of caulking can be applied around the bolt on the inside, and the large washer pressed into it along with the locknut.

If done right, this will give you a net, clean installation, with all four holes being totally watertight.