1998 35 hp 3 cylinder johnson mounting bracket question

[JoshKeller84]

hey guys, got the motor running great, and decided to convert to short shaft because i didnt like the way the vertical extension torque'd on the transom. ive run into a problem. I need to drop the motor another hole, but the bottom holes werent drilled to line up with the top, presumably because of a rib being in the way.

will there be any ill effects to dropping the motor down a hole, tightening the top bolts, and drilling a hole into the meat of the transom bracket on the motor, using the holes in the transom as a template? the slide hole in the bracket is at the max adjustment with the top bolts being on the 3rd highest hole.

here is a pic to show what i'm asking.. thanks! i'm talking about drilling a 1/2" hole between the slide adjustment hole and the lone hole in the middle. basically, was the entire unit cast with the holes built in, or were they drilled/milled after. thanks!

 

[boobie]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

If it was my boat I'd get the motor where I wanted it and then modify the transom to fit it with plugs and a lot of sealer 5200. Drilling into the motor brackets weakens them.

 

[JoshKeller84]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

only problem is, the bottom bolt cant be moved any lower - theres a rib on the inside.

 

[boobie]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

Then I guess you're going to have to drill. Just keep the lower hole in sync with the upper holes incase you have to change the motor height again.

 

[JoshKeller84]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

do you foresee drilling causing any problems? i would just go get two new 1/2" bits (one for each side so they are sharp), pull out the bottom bolts, lower the motor, bolt the two top bolts, and just drill the new lower holes from inside the transom using the current holes as a guide.

will the bracket drill easily? it wont shatter or break apart will it? or would you recommend elongating the slotted holes with a dremel/grinder?

 

[oldboat1]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

I've drilled only one, but it was an 85 (older model). had no issues -- had just rebuilt the transom so very secure (looks like your hull might be pretty new, so transom probably not an issue). I think you would have a devil of a time elongating the slot with a Dremel, as you describe, and got to believe that would be less secure than drilling -- think it would remove more metal. I think I would try to drill it a little inboard and a tad higher than you show, but hard to tell with a picture. Just opinion.

 

[JoshKeller84]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

yessir, the hull is a 2013. transom is rock solid - want to keep it that way and avoid drilling anymore holes into it itself. i certainly am willing to drill the bracket if its a general agreement that the bracket wont crack in half or break. just went out and measured, and moving the motor down one hole would be 3/4" which will put the cav plate perfectly along the bottom of the hull. as for where id be drilling, i'd simply move the motor down a hole, rebolt the top, and use the bottom transom holes as a guide to drill the bracket (put drill bit through the transom from the inside, and drill through the bracket)

 

[oldboat1]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

If the location (relocation) of the anti-vent plate is just a happy result of remounting, that's one thing. But if you are using that as criterion for where to locate on the transom, be aware that you have a little latitude -- inch up or down from the bottom of the hull is fine. You probably already know that. (An inch lower probably better than higher, if choosing). I don't see the bracket cracking or distorting, but maybe there is some additional opinion. Boobie wanted to keep an alignment with the existing holes, I think. You would lose options drilling another hole, as I see it, as the adjustment slot would be gone. I think I would just drill through that new transom again if I had to adjust. That's what god made epoxy (or 5200) for.

 

[JoshKeller84]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

i had this motor on the boat as a 20" shaft with a transom riser, and ran into the same problem now- the prop slips as soon as the trim is touched. dropped it down 1 hole and it was perfect - i took measurements, and when i converted to a short shaft, im in the same exact position - slip where the motor is mounted now, with the cav plate the exact same height. i cant drill anymore holes in the transom, because if i go any lower at all, my bottom bolts will have to go through a rib on the inner side of the transom. you can see where the rib is by looking at the rivets on the outside in the picture i posted. im okay with losing the adjustment of the slot, as once i drop it down another hole, its staying there permanently, because i believe it will run the same as it did on the transom riser - the cav plate will be dead on where it was when i got much better results as before.

 

[JoshKeller84]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

picture to show why i cant move the bolts down anymore by redrilling.

 

[oldboat1]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

yes, think you're saying again that you need to drill a hole higher in the mounting plate, as indicated in the earlier pic. That moves the lower bolts higher up on the transom, above that transom rib you refer to (and picture in #10). The other option would probably be a jack plate, which it sounds like you've tried with the longer shaft. Maybe another lister will see it differently.

 

[racerone]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

Look at the forces on the lower bolt !!-----They are not huge by any means.--Drill a new hole for a 5/16" bolt and be done with it !

 

[JoshKeller84]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

Are you talking in the transom or the mounting bracket? I can't drill any lower in the transom. Not an options with the rib there

 

[racerone]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

In the old days the lower bolts on the big 6 cylinder motors used to be 3/8"-----So as far as I am concerned you can use 5/16" bolts for the wee 3 cylinder motor.-Drill where you see the red arrow !

 

[boobie]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

Racer, what 6 cylinder motor used 3/8" bolts ??

 

[racerone]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

?????-------In the old days the inline 6 cylinder Mercury outboards just used a 3/8" lower bolt and transom clamps to hold them on.---Not sure why all this is so puzzling here.--Remember the 40 HP Johnson motor of the 1960's ??--They only used 2 transom clamps up top.

 

[boobie]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

I never was a Mercury man so I guess I wouldn't remember that. And glad I wasn't.

 

[oldboat1]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

Josh -- took another look at your desriptions and pictiures. Think maybe you are saying you want to use the same transom holes if you can. That is, stick the motor on the transom where you want it, using the top transom bolts. Then see where the existing lower bolts would go through the bracket, and drill the bracket at that point from/through the existing holes on the inside of the transom -- probably through the bracket at the location of the arrow. That should work fine, in my opinion. And the above discussion on bolt size can be useful for you too. You MIGHT want to initially drill 1/4 inch holes through the bracket, and consider using 1/4 inch lower bolts if the location on the bracket looks good to you -- or use the 1/4 hole as pre-drilling for the larger 5/16. 1/4 inch holes and bolts will give you a little more clearance, and it's a good idea to pre-drill holes anyway if you want to use the larger bolts. Think you just gotta take a deep breath and get after it....

 

[JoshKeller84]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

Thats exactly what I was wanting to do. i went out and get a new drill bit set, used the motor lift to position the motor, and went ahead and drilled through - it drilled extremely easy with the 1/2" bit that matched the holes already in the transom, and without a problem, so easy, in fact, that i went ahead and lowered it another hole and drilled for those as well in case I ever need them. rebolted and torqued down, and gave the jump test - stood on the cavitation plate and bounced, and no flex, noise, or movement at all, so i think its a go. thanks guys!

 

[oldboat1]

Re: 1998 35 hp 3 cylinder johnson mounting bracket question

wow! nice job! (cringing a little at jumping on the plate)

looks like you are good to go. Happy boating!