Engine Mounting Questions

[Fletch170]

Hey guys, wrapping up the rebuild of my 170. I will be mounting my 115 Yamaha next week, I have a few questions.

1. The Cavitation plate should be level with the bottom (keel) of the boat, right? I see some pictures slightly above, and some slightly below. Any suggestions?

2. My lower motor mount bolts will be below the waterline. What is the best practice for installing the bolts, to be sure no water leaks into the transom?

Kind Regards,

-Christian

[Blue Agave]

1) You definitely don't want the cavitation plate below the bottom of the boat. If the cavitation plate is half an inch above the bottom of the boat you will be golden.

2) Use 4200 to seal all 4 mounting holes.

[Fletch170]

I'm assuming that 1/2 inch above the bottom, assuming the plate is level with the bottom, right?

So, I'll caulk the crap out of the bolts then caulk up the mounting holes in the engine bracket.

Another thing.....she will be left in the water. Should I paint the portion of the motor bracket that will remain in the water?

[louiefl]

I've seen people bore oversize holes in the transom, fill with epoxy, and then go back and drill the desired bolt hole. This way, even if there is some seepage intot the hole in the transom, it won't be able to get into the transom core. If you were using 1/2" bolts for the motor, you could drill 3/4" or 7/8" holes, fill with epoxy, and then go back and drill 9/16" holes for the bolts. Overkill, but you asked.

At a minimum, I would coat the inside of the drilled holes with 4200, put some under the head of the bolt (I would suggest using a larger fender washer under the bolt head and putting 4200 between the washer and transom), and then some where the bolt sticks out of the transom.

The motor mounting height may need to be tweaked after you get it all together and run it on the water. Make sure you consider that when drilling the mounting holes - you might need to raise or lower it a couple holes and don't want to run out of holes. If it is too high, the motor will cavitate (worse when turning), or you might reduce water flow to the engine. Too low and you will have a lot of excess drag from the foot.

[kraw2]

Fletch,

My Evinrude is mounted about 1" above the keel. The lower mounting bolts will be underwater. I epoxied the inside of the holes before mounting. I cleaned the engine mounting bracket and back of the boat with acetone. I coated the back of the engine bracket entirely with 4200. Even went around all the holes in the bracket. The 1/2" bolts and holes were coated with 4200. The lower bolts won't accept a fender washer. Not enough room. After mounted I filled all the openings on the bracket with 4200. After it's all cleaned up it will be compltetely sealed.

[fitz73222]

Hey guys, wrapping up the rebuild of my 170. I will be mounting my 115 Yamaha next week, I have a few questions.

1. The Cavitation plate should be level with the bottom (keel) of the boat, right? I see some pictures slightly above, and some slightly below. Any suggestions?

2. My lower motor mount bolts will be below the waterline. What is the best practice for installing the bolts, to be sure no water leaks into the transom?

Kind Regards,

-Christian

Drill 17/32 holes. This allows you to coat the bolts with sealer and allow enough room for a 1/2 bolt to pass through the transom without wiping it off the bolt as you install and allows you enough clearance to finesse the bolt through the transom without having to drive the bolt with a hammer This is standard installation practice. This will keep the core dry. What I like to do is establish the engine height after all the holes are drilled by dropping her down on the transom and bolt her up temporarily with the two top bolts with standard nuts to make it easy (NO SEALER) and check the engine height. Move the engine up to the desired height by moving up to the next bolt hole in the bracket casting until you obtain the height you want. Each bolt hole is about 3/4" in height change ( at least for Mercs it is). I like the anti cavitation plate about an inch or so up from the bottom if you are running a decent cupped stainless prop. Mark the hole on the bracket that you want the bolt to pass through; remove the engine with the hoist and now do your sealing. Top bolts nuts outside, bottom bolts nuts inside. Now you can seal the bolts and shoulders one time and have a good permanent seal, without having to disrupt it to move the engine up. You never seem to get as good a bond if you have to redo the sealing. Just some little tricks to make life easier!