how big should i drill the motor mount hole

[noserider]

Guys

Getting ready to drill my newly rebuilt motor mount boxes and fill with epoxy resin using an oversize hole then redrill. How big should this hole be? My lag bolts are 3 inch by 1/2.


Thanks

 

[Woodonglass]

Re: how big should i drill the motor mount hole

I'd drill em 1 to 1 1/4 " and fill em with epoxy.

I'm just sayin...

 

[noserider]

Re: how big should i drill the motor mount hole

After the epoxy is dry is there any problem drilling the new pilot holes for the lag bolts. I understand the epoxy resin like west system gets very hard. Also should I be concerned about it being brittle when i go back in with the lag bolts. It would be nice if I could somehow tap some new threads but i'm not sure I have ever seen a tap with threads for lag bolts

 

[noserider]

Re: how big should i drill the motor mount hole

Guys

Going to do this tonight if anyone else has anything to contribute.

Thanks

 

[Woodonglass]

Re: how big should i drill the motor mount hole

UH, if a drill bit will drill through steel I don't think it will have any problem drilling through the hardened epoxy, and you are correct there is no tap for lab bolt threads.

I'm just sayin...

 

[noserider]

Re: how big should i drill the motor mount hole

UH, if a drill bit will drill through steel I don't think it will have any problem drilling through the hardened epoxy, and you are correct there is no tap for lab bolt threads.

I'm just sayin...

Understood. What about the issue of screwing the lag bolt into a smaller predrilled hole in hardened epoxy. Any concern with the epoxy being brittle and not making a good base to cut threads?

 

[Woodonglass]

Re: how big should i drill the motor mount hole

OK now you got my attention. I was WAY off base and thinking wrong in what you were doing. If I were you I would investiage Threaded inserts and epoxy them into my motor mounts and then use Bolts to mount my motor. You can get the inserts at ace hardware. I would NOT use lag bolts. This way you could ensure that your motor mounts would be sealed and not have to worry about water intrusion from the lag bolts. Hope this makes sense.

 

[noserider]

Re: how big should i drill the motor mount hole

OK now you got my attention. I was WAY off base and thinking wrong in what you were doing. If I were you I would investiage Threaded inserts and epoxy them into my motor mounts and then use Bolts to mount my motor. You can get the inserts at ace hardware. I would NOT use lag bolts. This way you could ensure that your motor mounts would be sealed and not have to worry about water intrusion from the lag bolts. Hope this makes sense.

Ooops...Hmm...I like the threaded insert plan but chances are the holes will not line up after I drill that size hole and reinsert. Any other good options?

 

[howlnmad]

Re: how big should i drill the motor mount hole

Just out of curiousity but why do you want to drill the holes oversized? Are you concerned with sealing the threads from moisture? If that's the case, I'd drill them undersize as they should be and then fill them with epoxy anf run the lags home. I'm no expert and that's just my .02 worth.

 

[Woodonglass]

Re: how big should i drill the motor mount hole

On your motor do you have ANY leeway for your mounting holes? You should be able to measure accurately enough the drill your holes in your wood and still have some adjusment. Another method would be to just epoxy some pipe into your mounts and then tap the pipe with some threads. Measure twice - Drill Once.

I'm just sayin...

 

[noserider]

Re: how big should i drill the motor mount hole

Just out of curiousity but why do you want to drill the holes oversized? Are you concerned with sealing the threads from moisture? If that's the case, I'd drill them undersize as they should be and then fill them with epoxy anf run the lags home. I'm no expert and that's just my .02 worth.

Yes. The idea of overdrilling and filling with epoxy was to seal the wood against future water intrusion and to hopefully provide a harder core material for the lags to bite in to. Not my idea just one i read about on this forum. I hope it's the right way to go. Just trying to find the best and easiest way to use the epoxy resin and mounting harware to work together. Even after the motor mount boxes and stringer was rebuilt with new glass and wood i did not like the feel of the lag bolts alone going into the wood core. I was able to tighten all of them but one was already not tightening and that was with new wood and glass core. Possibly I predrilled them a little to big. It would be very simple for me to oversize drill the holes (already drilled one 1 1/8") and fill with epoxy resin and redrill and screw the lag bolts back in but I was hoping someone would confirm the hardened epoxy would not be to brittle to accept the predrilled lag holes and lag bolts. Anyone done this method with sucess??

 

[Woodonglass]

Re: how big should i drill the motor mount hole

Noserider,

I got your stuff

http://shop.advanceautoparts.com/we...ALUE3-_-VALUE4&ci_src=14110944&ci_sku=7101112

Fill up your 1 1/8 inch hole with this stuff. Let it dry. then drill an Undersized hole for the lag bolt and drive it home. It WILL hold. This stuff is SUPER Strong and is for MARINE Use.

I'm just sayin...

 

[noserider]

Re: how big should i drill the motor mount hole

Noserider,

I got your stuff

http://shop.advanceautoparts.com/we...ALUE3-_-VALUE4&ci_src=14110944&ci_sku=7101112

Fill up your 1 1/8 inch hole with this stuff. Let it dry. then drill an Undersized hole for the lag bolt and drive it home. It WILL hold. This stuff is SUPER Strong and is for MARINE Use.

I'm just sayin...

Thanks for that info and link!

 

[Bob_VT]

Re: how big should i drill the motor mount hole

In my opinion I would use marine tex or west system 105 epoxy.

If you place the lag with a waser at the bottom and pour in the epoxy .....you can let it set up.

Regardless of the method I would use stainless steel.

If I was doing it I would get the proper thread SS bolt extra long........ place a washer on the bolt and epoxy that it with the threads sticking up far enough........ it will never separate......... some people have used the west system epoxy and even laid fiberglass cloth to make it extra strong.

I am not fond of using the fiberglass that was linked to as an adhesive and that is why I suggested west system 105 or marine tex........ both are much stronger.

 

[noserider]

Re: how big should i drill the motor mount hole

In my opinion I would use marine tex or west system 105 epoxy.

If you place the lag with a waser at the bottom and pour in the epoxy .....you can let it set up.

Regardless of the method I would use stainless steel.

If I was doing it I would get the proper thread SS bolt extra long........ place a washer on the bolt and epoxy that it with the threads sticking up far enough........ it will never separate......... some people have used the west system epoxy and even laid fiberglass cloth to make it extra strong.

I am not fond of using the fiberglass that was linked to as an adhesive and that is why I suggested west system 105 or marine tex........ both are much stronger.

Bob

Sorry but I'm not sure I'm following you. Are you suggesting filling the hole with epoxy and simply inserting a ss extra long lag thru the motor mount with a washer as in the original setup and letting it harden? If so I'm quite sure it would never separate. Is that what your suggesting? What about not being able to remove the lags if the engine needed to come out? Maybe I'm missing something.

 

[Bob_VT]

Re: how big should i drill the motor mount hole

I have modified motor mounts before and used nuts on the top instead of a lag straight down. ......... you remove the nut and lift off and leave the "epoxied" studs in place.

I will warn you that if you fill the hole with epoxy and drill it ......it will dull a drill bit pretty quickly.

 

[TJS]

Re: how big should i drill the motor mount hole

I am new here but not new to mounting systems and boats. I am not going to use lag bolts when I remount my engine in my Baja project. I am going to use 3/4 or 1" round stock with drilled and tapped holes perpendicular to the stingers and use sandwhich plates on either side of the stringers. One side of the plates will be welded to the round stock. The other side will have threads on the round stock protruding out and allow the stringer plate to tie into the round stock with a large nut.
T.J.

 

[JetBote]

Re: how big should i drill the motor mount hole

I am new here but not new to mounting systems and boats. I am not going to use lag bolts when I remount my engine in my Baja project. I am going to use 3/4 or 1" round stock with drilled and tapped holes perpendicular to the stingers and use sandwhich plates on either side of the stringers. One side of the plates will be welded to the round stock. The other side will have threads on the round stock protruding out and allow the stringer plate to tie into the round stock with a large nut.
T.J.

Did you really take the time to draw that out? Anal.

 

[Kiwifisher]

Re: how big should i drill the motor mount hole

Did you really take the time to draw that out? Anal.

This is a very helpful post..

As can be seen from all the various ideas, there's many ways to skin a cat and none of them is wrong. Personally I'd go with Bob or TJS's plan on this one.

 

[noserider]

Re: how big should i drill the motor mount hole

Well the deed is done. My West System Epoxy Resin is hardening while I type. Went with Bob's suggestion and inserted 4 ss studs with a washer and nut on the bottom then filled the holes with west system epoxy resin. Looks really nice and I'm happy with the outcome. Thanks to all that gave help. I'm very good at taking that engine in and out now