silicone for outboard mounting

[Thumpbass]

What is the best brand/product of marine sealant to use for making the mouting holes on the motor/transom water tight?

any tricks of the trade for doing a good sealing job would be appriciated too!

Thanks

 

[Plainsman]

Re: silicone for outboard mounting

3M 4200 is an adhisive and sealant. I think 3M 4000 is a sealant.

 

[Bob_VT]

Re: silicone for outboard mounting

3m 4200 is right. DO NOT use silicone it will not hold up and has no adhesive ability.

Use large washers and put a nice coat of 4200 on the boat side. WHen you tighten the lock nuts (Use stainless steel bolts, washers and nylock nuts)be carefull not to crush the washer into the boat but, tight enough to squeeze out some adhesive.

I usually coat the holes in the transom by coating the bolt to seal the transom core.

 

[Thumpbass]

Re: silicone for outboard mounting

I have some 3M 5200 (slow cure).. how does this product compare to the 4200 for this application?

 

[Bob_VT]

Re: silicone for outboard mounting

I used 5200 and it is really pretty permanent. It will work. The primary thing that I will caution you about is the engine mounting height. I did a bunch of prop experiments and I was moving my engine up a notch down two up again until I settled on the sweet spot. Once I established that then I used 5200.

If I ever have to remove it I will probable be forced to use an impact gun...... but it does not leak.

4200 is easier to take apart than 5200.