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Author Topic:   mounting new motor
captbobb posted 01-18-2002 06:28 PM ET (US)   Profile for captbobb   Send Email to captbobb  
i am repowering from an old johnson to a new mercury. upon inspection it looks like bolt pattern is not lineing up. anotherwords i need to fill the old holes and re-drill new ones. i could use advise on:
1. filling old holes
2. drilling into fiberglass
thanks in advance.
JBCornwell posted 01-18-2002 08:04 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Howdy Capt. Bobb. I suggest that you do neither.

Get a fixed jack plate, about 4" set back, and use that. Bolt the front half to the transom, the back half to the engine then bolt the two halves together at the sides. That way you wont compromize the integrity of your transom and you will get improved ride and speed.

I really didn't like the idea when I ran into the same issue when installing my Suzi where an OMC had been, but the dealer talked me into it and I am very glad I did it.

My Suzi DF70 powered Montauk is now almost as fast as my son's Merc 90 2 stroke powered Montauk, and it rides a lot better.

Red sky at night. . .
JB :)

dfmcintyre posted 01-19-2002 06:22 PM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Bobb -

I'll have to agree and disagree with JB. I too have been really happy with the CMC Transom Jack ML65 powerlift unit I purchased and installed last year. It has made a significant difference in steering torque (200 Yama on a 21' Outrage hull) and speed.

I went with the manual lift, as I wasn't planning on constantly tuning the height, but got the unit that makes adjusting it pretty easy. It doesn't require a chainfall. Four bolts are loosened and a manual screw jack type bolt either raises or lowers the motor.

What I disagree with JB on (and it may be a misunderstanding on my part....) is that your still going to have to penetrate the transom (at least I had to with mine, your mileage may vary...), unless the existing bolt holes line up with the jackplate.

If you have not worked with fiberglass, I highly recommend stopping by your local West Marine store (or _any_ marine store for that matter) and pickup all the West system reading material you can fine. It's a very complete and high quality "system". The system consists of the resin and various hardners, and various additives. These additives are in my opinion, what really makes it a system. You will get some good tips in their reading material.

If you have to drill and mount, a epoxy coated wooden dowel will work fine for filling up the core area. Then finish it off with the proper epoxy compound.

Proper drilling and sealing the new holes is something that I learned the hard way, when the shop where my 21 was undergoing a renovation a few years ago. They discovered that the transom had rotted. Pretty much nothing but black wood, due to improper sealing of holes and/or degradation of the bedding compound. Here's how the repair shop mounts the engines on a recently repaired transom:

They drill a significantly oversized hole through the transom, i.e. if the shank of the bolt is 1/2", they will drill a 3/4" hole. They tilt the hull as much as possible and seal the lower hole with masking tape.

Around the upper hole, a "dam" for lack of a better word is made with masking tape. Epoxy is mixed and poured in the upper hole. The epoxy is allowed to setup overnight.

The next day, the proper sized hole is drilled, and the motor is mounted.

By creating a solid epoxy plug (I think West calls the plug an "annealus"), you've created a watertight seal.

Sure, it takes an extra 24 hours to rig a boat (which may be why dealers don't do this), but it's also something that your gonna keep around for a while.

I've also mounted my console and other items on the deck where I know that water could enter, the same way.

Best - Don

JBCornwell posted 01-19-2002 07:50 PM ET (US)     Profile for JBCornwell  Send Email to JBCornwell     
Howdy DF.

We don't disagree. My dealer drilled the plate to fit the old style OMC pattern on the transom and the new standard pattern on the Suzi. If Capt. Bobb would still have to insult the integrity of his transom, I wouldn't have recommended it.

My plate is a T&H Fixed Jack Plate. It cost under $90.

Red sky at night. . .
JB :)

Dr T posted 01-20-2002 12:39 AM ET (US)     Profile for Dr T  Send Email to Dr T     
Interesting approach, JB.

I am thinking hard about using a CMC PT-35 on my little 13 with the 35 hp Johnson. With luck, your approach will work. Otherwise, I will be doing what Don suggests.

BTW, Bobb, a number of forum members have made some significant posts on this general subject. In particular, I remember threads started by Tom C. Clark and Larry Sherman (among others).

SuburbanBoy posted 01-20-2002 09:47 AM ET (US)     Profile for SuburbanBoy  Send Email to SuburbanBoy     
I also have a manual jackplate; it might even be the same T&H brand that JB refers to. I purchased mine from Cabella’s. You did not say what hull and what HP you have. My T&H is not the solution for larger, more powerful motors.

If you choose this solution, it is easy to use a drill press to drill (1/2" holes if I remember correctly) the transom half of the plates to fit your transom. I disassembled the plates. I then measured and determined that I could use one of the existing transom holes with one of the existing jack plate mounting holes. I then fit each half of the plate to the transom using only the one bolthole that matched up. I marked the second hole one each plate, then used a drill press to drill the two holes. Next, loosely bolt the transom half of the plates, then loosely assemble the second half (motor side) of the jack plate. Finally mate the motor up with the jack plate, which is assembled and mounted on the transom. For my 250 lb 70HP, it required four adult males and two strong young women to gently position the motor in place and loosely bolt it to the jackplate. Watch your fingers and use a small pinch bar to help with hole alignment. Also, measure twice and drill once.

Other miscellaneous jackplate comments:
There is a very useful write-up in the reference section
I use mine in freshwater, it is aluminum, and not anodized or corrosion protected.
I used a file to break all of the many sharp edges and corners on the jackplates.
My engine (2001 Tohatsu 70HP) could have bolted directly to the transom hole pattern. It would have required that I used a blind drilled and tapped hole in the motor mount. While this hole was drilled and tapped into my motor mounts by the Tohatsu factory, I did not want to use this solution. I wanted to have all of my fittings thru bolted.
I used all stainless steel bolts, locknuts and washers. I had much trouble with the stainless steel bolts galling to the stainless steel locknuts. They would seize together as I began to tighten them up. I had to cut each bolt and locknut assembly off, using a cutoff wheel on my Moto tool. As I recall, I replaced the stainless locking nuts with brass locking nuts and finished the install.
I am able to raise and lower my motor without a chainfall (as one member has suggested), but my motor is quite possibly lighter than his.
You did not mention control swapping, and this is another issue to research and plan.
Finally, measure twice and drill once. Try to approximate the final motor height in relation to the transom holes, and base your measurements on this position.


dfmcintyre posted 01-21-2002 08:11 AM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Bob / JB
dfmcintyre posted 01-21-2002 08:18 AM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Bob / JB -

A couple of additional points -

JB - Mine came pre-drilled, so I hadn't thought about just using the old holes.

Bob - If you are able to line up or use the existing holes, be sure to check the integrity of those holes. Make sure there is no rot inside them. And consider the use of the plug system, previously mentioned.

I took my bracket apart and sprayed it the same color as the hull, using some epoxy (others have painted it the color of the motor). I _thought_ I had prepped it well, but by mid-season the paint sarted to flake off. The early spring project, besides another coat of varnish on the teak, is to remove the unit, and have it powder coated for a little more durability.

We learn.....


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