Bolts for mounting motor to transom

[brianteel]

I searched here and did not find too much information on this. I found information about sealing the holes but not much else. I figure I would use the largest bolts that fit which is 1/2 bolts. Should I put a renforcing plate on the transom and go through that or just go through the would and fiberglass and bolt on that. I was thinking about putting some kind of bar on the inside so the it has a larger surface area to pull on. Also should I have the bolts go from the inside out or the other way around. My boat is a 14ft Lone Star 15" transom and I am putting a 40hp 1986 evinrude on it. The transom is new and I do not think it ever had a bolt on motor. Bolts I was thinking high strength corrosion resistant from mcmastercar

 

[DargelJohn]

Re: Bolts for mounting motor to transom

If you have access to an ACE or True Value Hardware, I would use stainless 1/2" bolts, washers and nylock nuts. Coat the inside of the holes with 3M 5200 sealant before installation. A transom plate is a good idea. Good Luck

 

[j_k_bisson]

Re: Bolts for mounting motor to transom

There are two grade of stainless bolts on the market. There is regular and hardened. The hardened are called that but are only a very small amount difference between the two. The hardened are actually more for corrosion restistance.

Go with the regular ones. But caution on the the thread type if you can get the fine thread ones it would be better. They are rated for more holding strenght. Also make sure you have the nuts on the outside of the boat. This allows you to adject the hieght of the motor without remove the bolts from the transom. Meeping the original seal with the 3m 5200.

 

[brianteel]

Re: Bolts for mounting motor to transom

ok kind of what i figured. Any suggestions on where to get a plate for the trans or should i just make one. Stainless or aluminum? I will be going in salt water.

 

[wilde1j]

Re: Bolts for mounting motor to transom

Washers should be fine on the inside. The SS's bisson is referring to are not "hardened" or regular. There are different ss alloys. The most corrosion resistant are the 300 series, with 316L being one of the better ones, although for a small motor like yours 304 SS would be fine, as would be bronze (but NOT brass!). The 400 series ss's are much harder, typically used for knives, etc. and are not good for marine environments BC they will discolor a lot. If your boat is metal, you may want to consider using plastic (ptfe) isolating washers to keep the boat metal from direct contact with the bolt washers. For the salt, I would use 316L SS bolts, washers and nuts.

If the transom is flimsy, you may want to fabricate an aluminum plate to distribute the load. Otherwise, washers should be fine.

 

[Oldyellow71]

Re: Bolts for mounting motor to transom

I redid the transom on my 50's starcraft about 3 yrs ago. I got the stainless bolts at ace. As mentioned above get the nylon, lock nuts due vibration. I just made a aluminum plate out of 80 thousands 7075 that was about 3'' tall and extended horizontally about 3'' past the bolts on each side. It may have been overkill, but I had it all apart, so might as well make it strong.

 

[brianteel]

Re: Bolts for mounting motor to transom

If the transom is flimsy, you may want to fabricate an aluminum plate to distribute the load. Otherwise, washers should be fine.

i just replace the transom with 2 3/4 marine ply so it is extra strong at the moment. i will get someone i know to cut aluminum and bend it for me and make a little bracket.

Would bronze be better than stainless?

 

[Oldyellow71]

Re: Bolts for mounting motor to transom

Wow that is thick! Mine was two 3/4 inch pieces laminated together, then I slid it between the aluminum hull that was roughly .060 aluminum. I didn't put a break or bend in my support bar, it was just a flat piece of metal. Putting a break in it will make it a lot stronger though! As far as bronze compared to stainless, I would say your money is better spent on the steel. I don't know if the benefit of bronze would outwiegh the cost. As Jim was staing above you want someting to prevent dissimiliar metal corrosion. My ace didn't have any ptfe washers that size, so i just cut an old bike inner tube to the size of the washer.

 

[brianteel]

Re: Bolts for mounting motor to transom

how do you guys feel about Sleeve Bearings and then epoxy in place to seal the wood?

 

[DargelJohn]

Re: Bolts for mounting motor to transom

ok kind of what i figured. Any suggestions on where to get a plate for the trans or should i just make one. Stainless or aluminum? I will be going in salt water.

This is the plate I used on my saltwater boat.

http://www.overtons.com/modperl/pro..._Support_Plate&str=transom+plate&merchID=4005

 

[Piece715]

Re: Bolts for mounting motor to transom

I just mounted a CMC PT130 and used all SS 1/2" bolts; Also stress plates out of 6061 aluminum; Huron Angler is doing the same with his restore. 3M 5200 is a popular sealant... unfortunately i couldn't find any locally so went with Loctite Marine Epoxy... May make removal a pain in the @$$ but hopefully that won't need to be done for years

EDIT: Plate sizes; (1) 16"x3"x0.25" and (2) 3"x3"

 

[wilde1j]

Re: Bolts for mounting motor to transom

i just replace the transom with 2 3/4 marine ply so it is extra strong at the moment. i will get someone i know to cut aluminum and bend it for me and make a little bracket.

Would bronze be better than stainless?

No.

Also, I would use 3M 4200 or 5200 to seal, not epoxy and a sleeve.