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Author Topic:   Transom/motor mount problem: advice needed
beachedwhale posted 08-03-2001 11:55 PM ET (US)   Profile for beachedwhale   Send Email to beachedwhale  
I have a 1968 Naucet that I am restoring. I was at the last step, installation of a new 50 hp Merc 4 stroke. The problem is the mounting holes. They go down approx 12" versus 8 in the old motor. To bolt the lower holes, the transom is not accessable due to the water well in the back. What to do. I have thought of the following options and want to know if anyone has any better ideas.
1. Cut an access hole in the well, tighten the bolts, then patch the fiberglass.
2. Cut an access hole in well, weld up a stainless steel bracket the holds two studs that then sticks out of transom. Patch, then install the motor using external nuts. The advantage over plan 1 is the motor can be changed out without recutting the fiberglass.
My question is simple, any better ideas out there? Thanks in advance.
Tom W Clark posted 08-04-2001 12:20 AM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
This is a very old problem. I can think of three possible ways of dealing with this.

1) If you had the Boston Whaler Owners Manual that came with that boat originally, you would find a paragraph in there about this situation. Whaler suggests that you may have to use lag bolts that would screw into the transom (actually the plywood in the transom).

2) I don't know about the Mercs, but the OMC motors had an extra set of holes in the bracket that could be used in this situation. They are blind holes, i.e. they do not come out the back side but rather are simply tapped to accept a bolt without a nut. they are up higher than the lower slot and thus come out into the splash well where you can get at them.

3) you could explore the possibility of using an aftermarket set back bracket which may allow a greater flexibility in the location of the mounting holes.

Although others here are sure to disagree, I would use option 1 if option 2 were not available. It is what Whaler recommended (not sure what they say now) and it will be strong enough especially for a 50 hp motor. Remember, in the old days outboards simply mounted with two hand tightened clamps! Also, the lower bracket where the lower bolts are are in compression (except when in reverse) and don't do that much "work" except to hold the bracket straight up and down when the boat is turning.

If you choose option 1 be sure to use stainless steel lag bolts and seal them very well with a polyurethane caulk.

LarrySherman posted 08-04-2001 08:53 AM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
check the condition of the wood when you predrill the holes. If it discolored, and/or very soft/mushy, then the lag bolts will not have much purchase. Some transom epoxy work will be in order then.
gunnelgrabber posted 08-04-2001 01:58 PM ET (US)     Profile for gunnelgrabber  Send Email to gunnelgrabber     
tom,..thanks for bringing those points's been hashed at some length prior but still the job wasn't finished in my opinion.i read that about the use of lag bolts in the bw literature myself..tacky as it sounds . i'd like to ask if anyone ever had a failure or heard of one using them..i agree, how much force is on them anyway?....i've got 2 pr.of blind holes now for omc...but remembering clark roberts telling scottfarm to locate it "2 holes up".. ?,then i need to drill "one more pr"...also tacky looking..but if it'll make her run like clark's mercurys it'll be worth it!...lm
Bigshot posted 08-04-2001 02:45 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
I personally would NOT use lags. I would either raise the engine up so you can get into the well(Mine is done that way) or I would get a jack plate and mount that. Lags will work but is kinda shongo in my opinion, which is just that, an opinion.
JimU posted 08-06-2001 10:37 AM ET (US)     Profile for JimU  Send Email to JimU     
I solved the problem mounting my 90 Yam by drilling two auxillory holes in the mounting bracket and angleing the bolts upward to clear bottom of the splash well. worked like a charm. JIM
beachedwhale posted 08-08-2001 05:28 PM ET (US)     Profile for beachedwhale  Send Email to beachedwhale     
Thanks for all the advice. I went ahead and made a SS bracket out of 2 by 2 L material. drilled holes at 9 7/8 " center and top welded SS 1/2 bolts heads to the EL after inserted them. Cut an access hole in the fiberglass well, dug out the foam, installed the bracket and glassed it down, refoamed, and we are now patching the fiberglass. The bolts stick out the back and will fit the motor perfectly. Will post some pictures of this project, including the teak front deck when I finish this weekend.
LarrySherman posted 08-08-2001 05:40 PM ET (US)     Profile for LarrySherman  Send Email to LarrySherman     
How will you inspect this for corrosion?


Chesapeake posted 08-08-2001 05:56 PM ET (US)     Profile for Chesapeake  Send Email to Chesapeake     
Just had the same problem with my new Yamaha. Tom Clark had pointed out what he had done and I let the dealer know this.

Also called Twin Cities Marine - a huge vintage whaler dealer (and Yamaha) in Green Bay,Wisconsin. He immediately knew the problem and said to blind screw from the inside and there are threaded holes in the mounting plate to accept the screw head. He spoke with my local dealer and that is exactly what my dealer told me he did. It even used the existing mounting holes from my old Johnson - amazing to me.

I haven't seen it yet, but am anxious to pick it up - and a little nervous that it is done right. Hind sight being 20/20, I would probably have gone up to Twin Cities in the first place.

Tom Clark: Thought you might appreciate this.

Bob (Chesapeake)

Chesapeake posted 08-08-2001 06:01 PM ET (US)     Profile for Chesapeake  Send Email to Chesapeake     
Tom Clark: Was thinking of an e-mail that I had gotten from Jim U, who had suggested drrilling right through the mounting bracket on an upward angle to catch a nut above the motor well. He said it was only a two beer job.

Kinda glad my dealer didn't have to do that. I will report back when I get a look at her.


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