Transom clamps AND bolts or just bolts ?

[Moody Blue]

Have a 1971 Merc 800 80hp that will soon be installed on a refurbished 1970 Wilker fiberglass deep V hull.

The motor has two transom clamps (like you would see on smaller tiller motors) and provision for four bolts. In addition, I have added PTT to the motor, and the PTT brackets have their own mounting holes (4 in total). The PTT brackets bolt directly to the motor midsection. Because of the position of the motor on the transom I can not use the top two bolting points on the motor.

So I have the ability to install two lower bolts on the motor and 4 bolts on the PTT, two lower and two upper. Do I really need the two transom clamps? How can I remove them if I decide to do so?

 

[achris]

Re: Transom clamps AND bolts or just bolts ?

If you are not using the top engine upper bolt holes you DEFINITELY need the clamps.... If it were me, even with all the bolts in, I'd still use the clamps... The reason is that the top of the engine gets the greatest torque under acceleration... You want as much holding that puppy on as you can get....

Chris........

 

[mthieme]

Re: Transom clamps AND bolts or just bolts ?

I agree.
I always use both.

 

[Moody Blue]

Re: Transom clamps AND bolts or just bolts ?

OK, I hear what you are saying. I was hoping to remove the transom screw clamps to gain more space so I could install a 1/8" aluminum plate on the inside of the splashwell to bolt thru.

The transom is 2" thick and I had planned on using a 1/4" aluminum plate on the outside of the transom. That leaves zero space on the inside for the 1/8" aluminum. The bracket JUST fits over the transom with the 1/4" plate in place.

You will probably suggest I use two pieces of 1/8", one on the inside and one on the outside. Truth is I didn't think things thru all the way and already bought the 1/4" plate. Do you think I'm OK to just use the outside 1/4" plate? The transom is original (38 yrs old) but is in "like new" condition throughout. Have removed all the hardware and drain tubes running thru the transom and not a sign of water or rot anywhere.

 

[achris]

Re: Transom clamps AND bolts or just bolts ?

If the engine is at or under the maximum recommended for that hull and the transom is in good nick, then just bolt straight to the transom. I know a lot of people use a piece of sheet, but you run the risk of introducing a new metal and setting up another galvanic corrosion cell.

Chris........

 

[mthieme]

Re: Transom clamps AND bolts or just bolts ?

I always use something to help spread the load - usually sheet aluminum.
I've never had a piece of aluminum give me a problem due to corrosion.
There's always paint if you're worried about it.
I've been know to use wood on smaller tiller motors and for shims.

 

[j_martin]

Re: Transom clamps AND bolts or just bolts ?

Like Achris says.

If a 2 inch transom is in good shape, it doesn't need any metal on it. If it isn't in good shape, no amount of metal will make it safe. (and still float)

In fresh water, galvanic corrosion is not usually much problem. Salt water is another story altogether.

Even on a strong transom, I use a load spreader on the inside of the upper bolts. The engine, or jack plate bracket has plenty of area to spread the load on the outside of the transom.

hope it helps
John

 

[Chris1956]

Re: Transom clamps AND bolts or just bolts ?

Moody, That motor (with PTT) is designed to use six bolts plus the transom clamps. I used four bolts (transom clamp bolts plus upper PTT bracket bolts) on my '77 Merc 1500 for 20+ years and never had any issue.

I would think the transom clamps are necessary since the PTT brackets bolt on midway up the transom clamp. I would not like to have all that power and no top support on the transom clamp. If it were me, I would use the transom clamp, upper PTT bracket bolts and lower transom clamp bolts, like my 1500 used.

 

[Moody Blue]

Re: Transom clamps AND bolts or just bolts ?

Good advice, thanks for all the comments.

Will do as you suggested and leave the transom clamps in place. Don't want to take any chances of it coming off the back . I found another use for the 1/4" alum plate so I'll buy two pieces of the 1/8" plate instead, one on the inside, the other on the outside.

Even though the transom is perfect, I feel more comfortable having something there to distribute the load.

On a side note, when I removed all the hardware from the transom I found the mfr used some kind of white putty as a sealant on all the fasteners and thru-hull fittings. The stuff was still soft and VERY sticky after all these years. Whatever it was, it worked very well because not a drop of water got inside.

 

[j_martin]

Re: Transom clamps AND bolts or just bolts ?

Good advice, thanks for all the comments.

Will do as you suggested and leave the transom clamps in place. Don't want to take any chances of it coming off the back . I found another use for the 1/4" alum plate so I'll buy two pieces of the 1/8" plate instead, one on the inside, the other on the outside.

Even though the transom is perfect, I feel more comfortable having something there to distribute the load.

On a side note, when I removed all the hardware from the transom I found the mfr used some kind of white putty as a sealant on all the fasteners and thru-hull fittings. The stuff was still soft and VERY sticky after all these years. Whatever it was, it worked very well because not a drop of water got inside.

3M 4200

 

[Moody Blue]

Re: Transom clamps AND bolts or just bolts ?

This stuff is nothing like 3M 4200 or any of the present day silicones or urethanes. It is a putty of some kind, still soft pliable and VERY sticky.

I have used the 4200 and 5200 products in the past but have had poor results when using them on aluminum or stainless steel. When you research the test data on these products, you see the relatively poor performance results when used with stainless and aluminum. It is however the best I have used for fiberglass-fiberglass, fiberglass-plastics, fiberglass-wood. Have actually delaminated the gelcoat from the fiberglass in one case.