My idea for making stronger motor mounts... Tell me what you think. (drawing)

[fabrimacator21]

The motor (305 chevy small block/ OMC 200hp) is currently mounted to the stringers by six bolts in the front and six bolts in the back. (3 on each corner of the motor). It has studs that screw into the stringers but they are pulling out and won't tighten down so here is what I came up with. Keep in mind that the plate will be an "L" bracket that will tie into the stringer on the side and top. The black holes would be the top and the blue holes would be the side(of the stringer). Sorry for the crude paint drawing.

Any thoughts?

I don't think the stringers are bad... the wood isn't moist or rotted, just old and the holes are stripped out. I just put a new floor and carpet in the boat so I REALLY don't want to put new stringers in it.

 

[fabrimacator21]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

On second thought.....


Would stuffing the holes with marine-tex and shoving studs in (no plate) be enough strenth?

 

[Lightnig]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

I like the plate idea, properly built and installed it would last forever. (corrosion issues aside...)

If you decide to go this route the bracket would need to be a bit beefier than 1/4". The depth of the threads need to be at least as deep as the bolt being threaded into them - in steel. 1/4" plate means 1/4" bolt maximum, and I seriously doubt that anyone would want something that small for bolting up a SBC. I would recommend at least a 3/8" bolt, which of course means a 3/8" steel plate to build the mounts out of. Aluminum, add 50% to the thickness.

 

[fishrdan]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

My old boat had rotted stringers and I fixed the motor mounts like this,,, didn't know any better at the time...

Over size drilled the bolt holes big enough to accept a lead lag bolt anchor, the type for cement. Fill hole 1/2 way with JB weld, insert lag anchor, spray lag bolt with WD40 and run the lag bolt into anchor. Next day, remove lag bolt and reinstall motor mount.

The fix was a HACK, but lasted for 10 years when I got rid of the boat,,, land-fill.

 

[fabrimacator21]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

I like the plate idea, properly built and installed it would last forever. (corrosion issues aside...)

If you decide to go this route the bracket would need to be a bit beefier than 1/4". The depth of the threads need to be at least as deep as the bolt being threaded into them - in steel. 1/4" plate means 1/4" bolt maximum, and I seriously doubt that anyone would want something that small for bolting up a SBC. I would recommend at least a 3/8" bolt, which of course means a 3/8" steel plate to build the mounts out of. Aluminum, add 50% to the thickness.

Well, see... the plates being tapped is just added insurance. Theres still gonna be about 2-3" of marine-tex below them that I would also tap. So basically, when comparing to how it came from the factory it'll have the same length of threads but 1/4" of them will be aluminum instead of wood/marine-tex.

The rule that your going off of applies to structural stuff and is a great rule to know but when it comes to stuff like this I don't think it's applicable. a 3/4 inch thick plate would be rediculously overbuilt. I think the stringer would give out or a bolt would bend before one of those plates gave up. Might go 5/16" or 3/8" though... need to price it out.

 

[henrye718]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

I dont know if I would trust the marinetex over time, do you know how it holds up under long periods of stress and exposure to any number of things.

Seems like you are depending in the marinetex to much. We know the aluminum plate wont break down in any funny ways for a long long time. I would go with the suggestions above and lean in the plate more unless you know the other stuff will hold up pretty much for the life of it.

 

[erikgreen]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

I don't think the stringers are bad... the wood isn't moist or rotted, just old and the holes are stripped out. I just put a new floor and carpet in the boat so I REALLY don't want to put new stringers in it.

Sounds like dry rot. 200 or 300 year old wood is just as sound as "new" wood unless it's decayed. Wood doesn't go bad with age. If your bolts are pulling out of the wood, it's rotted.

If it's rotted, following this complex plan to reinforce the motor mounts might buy you a season, but you'll still need to fix the problem.

If you really want waterproof, strong motor mounts, build them out of angle iron

I feel for you, if you've put work into making the interior look nice, it's very hard to pull part of it back out to fix something else. But you can do all the fancy reinforcing you want and it's still not as strong and safe as just fixing the problem in the first place.

I recommend you drill out cores from those motor mounts and post pics of the wood. Folks here can tell you if it's ok or not. If you have to replace them it's possible to do so without a ton of fuss and without replacing all the stringer parts (unless they're all rotted).

If all you want is to get another season, don't bother with the marine tex... it's got nothing to attach to anyway. Sister some supporting wood on the sides of the motor mounts and bolt it through all the way, then if you like run a C-shaped piece of metal plate over the top and bolt it to the sistered wood (from the sides) and re-mount the motor.

Erik

 

[fabrimacator21]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

I don't really see the point in doing part of the stringers (bilge/motor mount area). If I'm gonna do it then I'll do the whole thing, but first things first. Need to see if the wood is ok.

I have a bad feeling that the stringers are gonna need to be replaced.

 

[fabrimacator21]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

Ok... decided that I'm not gonna mess with the plates right now... might do it when I put new stringers in but I think I'm just going to put some marine tex or git rot in it for now and see how long it lasts.

My only question is what would be better.... marine tex or git rot? Both say that they can be drilled and tapped but which would be stronger?

Sort of on the fence between the two... git rot says you don't need to remove the rotted fibers of the wood...

heres a link to git rot.

Tell me what you think.... need to make a purchase by tomorrow.

http://www.discountmarinesupplies.com/configure.cgi

I don't mind spending 30 bucks on git rot or marine tex to see if it works... if it doesn't then I'll restringer the whole boat but I don't have the money right now and I want to go boating few times this summer, so marine tex/git rot it is.

 

[bigbad 4cyl x2]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

i wouldnt use marine tex , use some epoxy thickened with some cut up pieces of fiberglass cloth and the hard additive mix,and instead of aluminum use a piece of stainless, but that might transfer vibrations to your hull . id say sink some stainless rod studs in there with west systems epoxy

 

[fabrimacator21]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

Do you have a link to west systems epoxy? Is that West Marine?



How does that stuff stack up to fiberglass resign with pieces of cloth as you suggested?

 

[bigbad 4cyl x2]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

yes it is west marine , it was all i used and would use . im a simpleton ,and dont want to mess around with other aftermarket brands , but system 3 has good reviews by my boat yard, i go crazy dealing with epoxy blushing

 

[bigbad 4cyl x2]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

i think your talking about polyester resin vs epoxy , epoxy is a state of the art glue ,relying on chemical cross linking. where poly resin is based on adhesion to the substrate and shrinking to hold in place . you definitely need epoxy in this situation

 

[fabrimacator21]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

So system 3 is what you would use if you were me?

I think marine tex is hard to beat strenght wise but I don't know if it'd bond to the wood as good.

 

[bigbad 4cyl x2]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

well actually id go with west systems from west marine in your case cause your not going to need that much . west cost a lot now a days and i was making some statements and for a large project id try system 3 ,just for the cost savings . i probably used over 15 gallons of epoxy on my project , west is top tier quality

 

[bigbad 4cyl x2]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

i think marine tex is easy to sand ,were epoxy thickened with the right stuff sands like steel , which lends me to think marine tex is weak , i had some of that epoxy stick stuff crack dont get that , get the full system with the pumps . it'l be worth it , pre soak the holes first [wet out] then set the stainless rod ;

; here is a pic of a crack using that epoxy stick ,

 

[fabrimacator21]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

Great info man...

I still have a few questions though...

i think marine tex is easy to sand ,were epoxy thickened with the right stuff sands like steel , which lends me to think marine tex is weak , i had some of that epoxy stick stuff crack dont get that , get the full system with the pumps . it'l be worth it , pre soak the holes first [wet out] then set the stainless

What do mean by the "right stuff"? Shouldn't the epoxy come with hardener?

Also when you say "wet out" what exactly do you mean.

Thanks for the great info.

 

[bigbad 4cyl x2]

Re: My idea for making stronger motor mounts... Tell me what you think. (drawing)

im trying to get you to do your own leg work here and go get involved with the west systems product . it is a system of 2 part epoxy hardener and epoxy base . part 'a' and part 'b' with various mixtures you mix in with the epoxy to make a paste of various thickness is or viscosity's to accomplish various tasks, sense it is late and i haven't had to use the epoxy for about 3 years or so since i was in that stage of my project , i have forgotten the terms used for there additives but it is a well thought out system and once you go to west marine you will see it all . Ive Evan used some saw dust for an additive , they have microbaloons,silica,cabosil etc . it makes for an interesting read. and wetting out is done because your wood will soak up the moisture in the epoxy the first time it comes into contact and dries for this reson you want a thinned epoxy to wet it out for capilary action into the wood let it dry then your next application will cross link to the epoxy and wont go dry while curing . you will see