Drilling to mount outboard, hole size?

[willvincent]

I've got a '64 johnson to mount on my boat. The previous outboard had a different bolt pattern, so I'm going to fill those holes with some westsystem six10, and drill new holes for the brackets for the new (to me) outboard.

It uses the now standard bolt pattern, with 1/2" bolts. I've read that I should drill the holes with a 17/32" bit and use 4200/5200 to seal around the shaft of the bolt.. I am having a hard time locating a 17/32" bit though. Would I be alright to drill the holes with a 9/16" or is that too much to worry about sealing with 5200?

 

[willvincent]

I've got the bolt pattern on paper, going to transfer that to some plywood so that I can clamp it on the transom and the holes in the plywood will help guide the bit to keep them perpendicular to the transom. Want to be sure I use the right size bit to make that jig though.

 

[emdsapmgr]

5200 is not required. That caulk is way to aggressive. It will glue the bolt to the fiberglass on the boat so strongly, that you'll rip something apart if you ever try to remove the engine bolts. 4200 is still way aggressive, but better than 5200.

 

[willvincent]

Well.. .what I have is 5200.. what would you suggest? Not a lot of options near me, and want to get this done. Just talked to an installer at a marine shop, he said just drill the holes 1/2", that's what they do. Guess I better be _REALLY_ sure about my measurements that way

 

[racerone]

Those brackets stay on the boat when you slide the motor up and out.----Use the 5200 on the 1/2" stainless bolts.

 

[willvincent]

Thank you. Seems to be a LOT of differing opinions about what to seal with. Including lots of differing opinions about how difficult it is to remove bolts that have been sealed with 5200.

 

[racerone]

We used to clamp the motor in position.---Slide one bracket up in position.---Drill 1/2" hole using bracket as a guide and bolt the bracket on.----Then do the other bracket.---This is not rocket science by any means.----Then later factory offered a drilling fixture that really made it easy.

 

[F_R]

I always used the drilling fixture with 1/2" drill and plain ol' marine caulk, whatever I had on hand.

 

[dthx]

I've done that on a boat on which I rebuilt the transom.....being in a small town and knowing the boat mechanic that worked in our only boat dealership (now out of business and gone)....I was able to borrow the factory fixture that raceone mentioned.
I mounted a 200 hp Ocean Pro Evinrude.....big block and was very heavy.....I used a transom bracket and the holes had to be perfectly perpendicular, etc......
Used 4200....never had a problem.....had the boat in the Gulf of Mexico for 6 years. It's messy stuff, though....try to keep the stuff off the threads of your bolts.

 

[willvincent]

I was mistaken, I had PL marine sealant, not 5200.. I know I was holding 5200 in my hand the other day, not sure how I ended up with the PL instead, maybe it was cheaper.. anyway, it's on and should be sealed well. Thanks guys

 

[interalian]

I spent two summers hanging outboards in the '80s. Used the fancy OMC jig with a 1/2" bit. Sealed everything with clear marine silicone RTV. Never had a comeback. Re-installed my recent project with the same sealant. It had been installed with RTV back in '83 and everything was nicely sealed.