Sealant for engine bolts

[TMALEGA]

Ok so after reading a post on mounting engines. I have this question now. I put my motor on the back of my boat and used clear marine silicone i put as much as i could in there while i put the bolts in.

Should i have used 4200 or 5200 instead?? I am worried that the marine silicone wont be good enough in the long run. Am i wrong to be worried? I figure since it is coming on winter i can just back one bolt out and fill it with the right stuff and replace bolt if need be. Thanks guys and gals. It is truely appreciated.

 

[Fireman431]

Re: Sealant for engine bolts

3M 5200 (or even 4200) is the marine standard when sealing bolts and screws. Some have used silicone in the past, but it will breakdone over a couple of years. I recommend replacing it with the 5200. Make sure all of the old silicone is removed completely. I think others here will back me up on this.

 

[DuckHunterJon]

Re: Sealant for engine bolts

Yup, trick is going to be getting rid of the silicone. You may be better off pulling the motor to do it.

 

[smokeonthewater]

Re: Sealant for engine bolts

3M 5200 (or even 4200) is the marine standard when sealing bolts and screws. Some have used silicone in the past, but it will break down over a couple of years. I recommend replacing it with the 5200. Make sure all of the old silicone is removed completely. I think others here will back me up on this.

Consider yourself backed up.


Yup I would definitely pull the engine.... A drill bit helps to clean the 'silly cone' from the holes.

 

[robert graham]

Re: Sealant for engine bolts

My 1999 Yamaha outboard was mounted with blobs of marine silicone at the factory(1999) and it's still there, just like new. But mine's an aluminum jon boat and wouldn't matter if it degraded and leaked some anyway. If I had a boat with a wooden transom I'd strongly consider replacing the silicone with the 3M 5200. What kind of boat and motor do you have?

 

[Home Cookin']

Re: Sealant for engine bolts

I disagree with 5200; that should be used as a permanent fix--sealing empty holes, screws such as a swim ladder you aren't going to remove.
You are more likely to need to remove the engine bolts at some time for a number of reasons (on some boats, to repair steering or the PTT pump).
If you have silicone in the hole and then bolted on, and it's above the water line, you won't have any water intrusion that would make a difference over then next 40 years. If you see the edge of the seal getting ragged, goop some more on.
Below the water line, on a boat that stays moored, I might get 4200 or another non-hardening sealant.

 

[TMALEGA]

Re: Sealant for engine bolts

Yes there are a few good questions i should have addressed to start with. 1 it is a 85 bayliner capri with a 85 hp 85 force on the back. 2 it is trailered when not in the water being used. Dont know how much a difference that makes, but i did run a bead around the inner and outer brackets when we hung the motor to help seal it up and i see no water leaking in the back when we are at rest in the lakes. I used the marine silicone due to it was available and i was thinking if i ever needed to take it back off then i was golden. On the smart tabs i used 5200 and was impressed with it.

Not sure if that changes anyones advice or not but thought i would answer the questions.

 

[Dhadley]

Re: Sealant for engine bolts

Only put 5200 on things that will never be removed. Using 5200 on mounting bolts is never a great idea. We use 4200 or Life Calk or Life Seal. Lots of folks use silicone with no issues.

 

[Texasmark]

Re: Sealant for engine bolts

Only put 5200 on things that will never be removed. Using 5200 on mounting bolts is never a great idea. We use 4200 or Life Calk or Life Seal. Lots of folks use silicone with no issues.

Agree with that. What is there about Silicone to breakdown after a couple of years??????? Besides what is 4200 and 5200 made of?

Mark

 

[zopperman]

Re: Sealant for engine bolts

I'd be using 4200.
I love silicone, but NOTHING beats 42 and 5200... Esp. for below water line use...

 

[smokeonthewater]

Re: Sealant for engine bolts

silicone often cracks or breaks free from one surface or the other.... only takes a pinhole to start wicking water throughout your transom. My advice stays the same btw

robert grahm... are you sure there is no wood in there? I've personally seen an all aluminum transom with a through bolted engine.

4200 and 5200 are polyurethane adhesive sealants BTW

 

[TMALEGA]

Re: Sealant for engine bolts

Well it seems i will be pulling each bolt to redo the sealant. Luckily if i pull a bolt i can get easy access to the hole from each side. So this winter sounds like a plan, one other question about this though. I was told to put a piece of wood behind the inside of the bolts on the back of the transom to help support the pull of the lower bolts. Do i really need this ?? It is just taking up extra room that wont allow the gas tanks to sit in there properly. Thank you all again .


JUST REALIZED I HADNT DESCRIBED THE WOOD PIECE, IT IS ABOUT A 2 X 2 SQUARE PIECE OF WOOD JUST ABOUT 2 INCHES LONGER ON EACH SIDE THEN THE BOLT HOLES ARE WIDE. IT MOUNTS UP ON THE INSIDE OF THE TRANSOM WITH THE BOLTS GOING THROUGH IT AND THE NUTS AND BOLTS TIGHTEN UP ON THAT INSTEAD OF THE TRANSOM ITSELF.

 

[nosticks]

Re: Sealant for engine bolts

52 is forever, 42 is removable when eventually need to remove the engine.

 

[Home Cookin']

Re: Sealant for engine bolts

sounds like a giant wooden washer. Can't hurt, or use big washers. Better to be crunching wood than your transom surface.
Most of the force is pushing the other way when running, and of course the weight is pushing down when sitting or trailering.

That wood may need replacing after 15 years. and if you used 5200....

 

[smokeonthewater]

Re: Sealant for engine bolts

replace the wood with a heavy washer..... even a piece of aluminum plate works well

 

[metriccrescentwrench]

Re: Sealant for engine bolts

If you have silicone in the hole and then bolted on, and it's above the water line, you won't have any water intrusion that would make a difference over then next 40 years.

Sorry, I've gotta' disagree. Here's a photo of an upper engine mount bolt from when I rebuilt my Checkmate, hole was sealed with silicone.

I was told to put a piece of wood behind the inside of the bolts on the back of the transom to help support the pull of the lower bolts.

NO!!!! Not wood. Use an extra large/thick fender washer or else some 1/8 or 1/4 aluminum to spread the load out over a large area.

 

[Home Cookin']

Re: Sealant for engine bolts

Sorry, I've gotta' disagree. Here's a photo of an upper engine mount bolt from when I rebuilt my Checkmate, hole was sealed with silicone.

you mean the hole was NOT sealed with silicone

 

[TMALEGA]

Re: Sealant for engine bolts

Yea i thought the wood was a good idea for spreading out the forces. However it did seem odd to me that i was told that since the forces are coming outside/in when in forward. On the lower half of the mount where the wood block is. The upper part of the mount has a couple screws with pads on them which i did use roughly 1/4 inch steel between the pads and transom as opposed to the aluminum plate i saw at bass pro. Being that i had the steel laying in the back yard figured it couldnt hurt to keep them from "digging" in.

I do have large fender washers on the inside of the boat where the block is at, i think the guy with the idea had a bad transom and was trying to save it from any extra stress, since my transom is very solid i was thinking if nothing else cut the wood in half the thickness and there for still spreading the stress out and allows me the room in the tank compartment for the tanks to rest in correctly. Thanks for the ideas and suggestions. Now to get the time between the baby and two jobs to do more then sleep and look at the boat.

 

[metriccrescentwrench]

Re: Sealant for engine bolts

Sorry, I've gotta' disagree. Here's a photo of an upper engine mount bolt from when I rebuilt my Checkmate, hole was sealed with silicone.

you mean the hole was NOT sealed with silicone

Well, the previous owner had installed it and used silicone. The silicone obviously didn't seal the hole adequately. Oh, while on the subject of silicone - many silicone sealers release acetic acid as they cure, which over time can be quite corrosive. I personally know of one young EE who thought it would be a good idea to seal some soldered electrical connectors with silicone, only to discover a year later that several of the copper wires in the connector had been corroded away.

And as far as why it's a bad idea to use wood crush plates - wood expands and contracts as it's moisture content changes (that's why wooden airplane prop mounting bolts have to be re-torqued frequently). After enough time you're liable to find that the engine mounting bolts are loose, plus there's always the possibility that water will get into the wood and start rotting it.

 

[Texasmark]

Re: Sealant for engine bolts

Well, the previous owner had installed it and used silicone. The silicone obviously didn't seal the hole adequately. Oh, while on the subject of silicone - many silicone sealers release acetic acid as they cure, which over time can be quite corrosive. I personally know of one young EE who thought it would be a good idea to seal some soldered electrical connectors with silicone, only to discover a year later that several of the copper wires in the connector had been corroded away.

And as far as why it's a bad idea to use wood crush plates - wood expands and contracts as it's moisture content changes (that's why wooden airplane prop mounting bolts have to be re-torqued frequently). After enough time you're liable to find that the engine mounting bolts are loose, plus there's always the possibility that water will get into the wood and start rotting it.

The gray is made for things sensitive to Acetic Acid Corrosion and has none. It is what is used in electronic equipment. As far as the release of Acetic Acid in mechanical applications I have never had to be corrosion sensitive in applying Silicon. Maybe it may have occurred but the seal held, and therefore I had no reason to revisit it and discover the corrosion characteristics that may have lead to the failure of the seal.

Mark