Plugging old motor mount holes?

[whistler66]

Removed old motor from my boat and am putting on another smaller unit. I will not be using all the same mounting holes of the original motor. My plan is to use the original washers, 1 on each side of the transom and the original bolt and nut in the unused holes. I plan on using 100% silicone on both sides of the transom under the washers and also make sure the bolt and the holes are covered. My main question, is the silicone product OK for this! It appears a product similiar to this was used originally and all is well as I can tell! Thanks in advance,

 

[Mark42]

Re: Plugging old motor mount holes?

You are right on wanting to seal the bolt holes. BUT DO NOT USE SILICONE!!!

Use a marine grade sealer like 3M 4200 or Boatlife. Silicone will not hold up well at all.

As far as filling the old bolt holes, pick up a length of wood dowel that matches the hole size and cut dowel about 1/4 or 3/8" shorter than the hole is deep. Using Marine Tex epoxy (The marine grade epoxy sold in the home center will work too), cover the dowel and insert in bolt hole so it is slightly recessed on each side of the transom. Then using more epoxy, fill the ends of the holes flush to the transom.

When inserting the new motor mount bolts, coat the inside of the bolt hole with sealer. Then insert the bolt with about 1 or 2 inches of the bolt protruding, then cover with sealer, and drive all the way in. Put sealer under the washer and tighten.

That will be a very well sealed transom.

 

[gcboat]

Re: Plugging old motor mount holes?

Not knowing your transom configuration I'm guessing it's glass over wood. Pretty normal. What your main concern should be is to keep any water from migrating into the wood from the bolt holes. Mark42 has pretty much hit the nail on the head but there is an alternative. Not easier - but an alternative.
Let's say you have a 3/8" bolt with the same hole diameter. You drill it out to 5/8". Pack that hole full of Marine Tex. Let it cure. Then you drill your 3/8" hole and apply the 4200 ( or whatever ) and slam your bolt through it. What the Marine Tex does is literally seal the wood and you'd be drilling through that. So that leaves zero chances that you applied enough sealant.
It is a pain to do but leaves little doubt that there will be any water entering the wood.
Sort of overkill - .
Oh yea - do as Mark42 sez' - don't use silicone !!! Silicone has no place or business on a boat. My $.02

 

[kbkindle]

Re: Plugging old motor mount holes?

those guys have got it right imo i allways would use the waterproof fiberglass it will work great and dries in about ten minuets

 

[whistler66]

Re: Plugging old motor mount holes?

This is an aluminum boat (aluminum over wood). Would the fix you suggested still be better that the one I originally suggested if I didn't use silicone and used one of the products you suggested. Use the SS bolt, washer (both sides of the transom) SS nut. I'm not worried about the appearance as you might on a glass boat. The bolts will hidden on the inside and on the outside mostly unnoticable. Thanks again

 

[whistler66]

Re: Plugging old motor mount holes?

No response to question #5 in this thread so I have been searching locally for 3M 4200 with no luck? I have found 5200 which seems to be about the same stuff? Needs to be 40 degrees to use. Right now were only 30+ degrees too low. What is the main difference in 4200 & 5200? I would still like to maybe repair it as mentioned in #5 as this would give me an easier reversal if I found a suitable big motor that possibly might use the same mounting holes. Thoughts anyone! Thanks.

 

[Pascal]

Re: Plugging old motor mount holes?

No response to question #5 in this thread so I have been searching locally for 3M 4200 with no luck? I have found 5200 which seems to be about the same stuff? Needs to be 40 degrees to use. Right now were only 30+ degrees too low. What is the main difference in 4200 & 5200? I would still like to maybe repair it as mentioned in #5 as this would give me an easier reversal if I found a suitable big motor that possibly might use the same mounting holes. Thoughts anyone! Thanks.

3m says that the 5200 is a faster cure than the 4200....

Here....

http://www.3m.com/Product/information/Marine-Fast-Cure-5200-Adhesive-Sealant.html

Unless you find the same make and model line of motor, you are most likely going to need new holes anyway. I'd go with the dowel plug + the epoxy to fix the old holes in the transom board and a patch over the holes in the aluminum using the 4200 to seal it and then drill and seal the new holes to install the new motor.

 

[sturdavj]

Re: Plugging old motor mount holes?

?66?

I just completed a motor swap from a Johnson SPL 28 to a Suzuki DT 50 on my aluminum hauled boat as detailed in the above posts. My boat is 20 years old so I used a gray color. If yours is still shiny you may want to use silver/aluminum color. (or maybe it's painted, I hear they do that...)

I happen to have access to 1/8 SS steel plate so I placed it on the inside top half of the transom using the upper mounting bolts sandwiching the plywood between the hull and the SS plate, then sealed around the edges of the plate. Probably overkill.

As for a later remount, this can be handled by taking your time now (as described) using a quality wooden dowel and a high grade marine epoxy. If at a later time you need to drill into the same location, you would then follow the same procedures and you?ll the boat on the water in no time at all.

I am not sure why/what silicone was invented to be used for, but in my opinion if heat/ cold, sun light, moisture and contaminates can reach this stuff you might as well save yourself time and labor and dump the stuff in the garbage can at the beginning of the project rather then the end. ?.just my .04 cents worth (prices are going up)

 

[kabcpapc]

Re: Plugging old motor mount holes?

The 3M 5200 is considered a permanent bond. The 4200 is not as permanent but not easily removable either. The 4200 and 5200 is available as a fast cure (24 hrs.) or slow cure (like 7 days). I believe both can be used below the waterline.

 

[Mark42]

Re: Plugging old motor mount holes?

The 3M 5200 is considered a permanent bond. The 4200 is not as permanent but not easily removable either. The 4200 and 5200 is available as a fast cure (24 hrs.) or slow cure (like 7 days). I believe both can be used below the waterline.

The local marina complains about 5200 all the time. They claim removing engines mounted with it pull the glass right off the transom. I would avoid it at all costs.

 

[whistler66]

Re: Plugging old motor mount holes?

I will try to find some 4200. I think it also has a 40or above degree usage temp and a 7 day to cure? Does that mean I would need to have it above 40 for the entire 7 days or can I apply it at 40 an maintain this for a day or so then will it go on a cure at whatever the temp it? I don't have access to a heated garage and it's cold here mid teens! Would like to get it going and do a little trapping! A Big Thanks to all that have responded!

 

[jennis9]

Re: Plugging old motor mount holes?

I have tube of 5200 on my desk - just bought it from WM.

Here's what it says about cure:

Use from 40? to 100?F ? cures at 70?F and 50% relative humidity. 1/4" of sealant becomes tacky in 48 hours and has complete cure in approximately 7 days.