best way to fasten motor mounts

[falcon]

I will be installing a Beta diesel in my Cheoy Lee Frisco as soon as the weather warms up. I drilled oversize holes for the engine mounts into the fiberglassed teak stringers and filled the holes with West System epoxy and then inserted stainless lag bolts. I coated the lag bolts with a car past wax to prevent the epoxy from bonding to the bolts so that I could remove them. Later, when dry fitting, I noticed that a couple of the lag bolts did not feel like they would tighten down with any authority, and were perhaps stripped. I noticed on the recent thread regarding excessive vibration in an Atomic 4, that Tim had used threaded inserts and cap screws to fasten the mounts to the engine bed. Question: Is this a better way of doing this? and if so where can I purchase them?

[Quetzalsailor]

There's a great long string on this problem in Sails, Rigging, and Systems: Engine Vibrating Excessively. Thoughts on your observation: did you coat the lag bolts neatly - that is, no excess wax? did you use reinforced epoxy - that is microfiber additive or similar? did you ensure that the lag went back down into the same threads you cast - or did you chew some new threads?

[falcon]

Quetzalsailor, thanks for your responce. I fashoned the motor mounts some time ago and it was the recent thread that you mentioned that prompted my question. Regarding the pastwax coating on the lag bolts, I don't think that I applied more than a thin film. I used neat west systems without an additive and I dont think that I chewed the threads up, atleast untuil I tried to tighten the lags completly. I know that at least one bolt did feel like it was stripped so I may well have done that. I supose contamination is now a concern and I was thinking that I may want to drill out the epoxy and re-install those threaded female recepticals for a cap screw that Tim used. Do you know where Tim got them?

[Tim]

Pete,

The inserts I used are by E-Z Lok, 3/8" internal thread size, # 303-6 (9/16-12 external thread [note: originally this read 9/16-24, which was incorrect]). They have become harder to come by in this size--the last time I used them, I actually was using stock that I purchased in 2005--but here's one hit I got just now:

E-Z Lok threaded inserts at MSC

Also check out http://www.ezlok.com for other potential sources.

[falcon]

Thanks Tim.
Pete

[Triton106]

My problem is that I cannot seem to find any threaded inserts longer than 1". Given that Atomic 4 are bolted directly to the engine stringer (i.e. only four bolts will be holding it down) I would like to use a 3/8" to 1/2" thread size and ideally 2" long threaded inserts. It does not appear that anyone makes them.

Regards,

Ray

[Tim]

That's because such a long threaded insert is unnecessary.

[Quetzalsailor]

Contamination was not my concern with the waxing. Filling the threads overmuch with paste wax was. The idea is to have enough mold release to get the thing apart but also to have the benefit of the full depth of the thread.

I'd like Tim or someone else with adequate experience installing inserts tell us how best to do it. My experience is that they are quite likely to split the work as they're driven in and the horsepower required is quite excessive. I have recently (November) installed 24 of these things for four my interior removable storm windows. I bought stainless steel inserts for 10-24 machine screws which get installed in 5/16" bores (McMaster Carr, of course). They go in near the edge of 1" thick window jamb members and inevitably need to go where window treatments have been installed over the last 150 years. Previous experiences were as difficult. I turned the window's inserts in with a drill and a length of hex wrench; the older project's ones were to be turned in with a screwdriver and proved impossible to do neatly.

[Tim]

The inserts I've used have a 9/16-12 (note: originally this read 9/16-24, which was incorrect) external thread, for which I tap the hole in the wood using the appropriate tool. I set them in epoxy during final installation.

[falcon]

Tim, Thanks for giving me the source for the threaded inserts but had a few questions. The external threads are 9/16 -12 but I noticed that you used 9/16-24 thread. Is that ok? I too was surprised that they were only half an inch long. Would you then use cap scews that are only say 1.5 inces long or would you use longer ones and continue the tap down past the inserts into the epoxy? Final question, what is the best epoxy recipee and how much larger than the insert should the hole be (thickness of epoxy plug)?
Pete

[Tim]

My error: I typed the wrong thing. (note: I've corrected this error in the previous posts as required)

9/16-12 is the correct external thread, not 9/16-24. The external thread is tapped into the wood, not into an epoxy plug. I just used slightly thickened epoxy on the threads when I drove the inserts in the final time.

[Triton106]

After going through the different options I decided to use 1/2" internal diameter coupling nuts in lieu of threaded inserts. The advantage is that they offer 1/2" - 13 internal thread size and 1 - 1/8" length. I placed the order today from McMaster Carrs for four stainless steel coupling nuts and matching bolts.





The specs are -

Type 316 Stainless Steel Coupling Nut 1/2"-13 Thread Size, 1-1/4" Length, 5/8" Width.
Type 316 Stainless Steel Hex Head Cap Screw 1/2"-13 Thread, 2" Length, Packs of 5

The difference in length between the coupling nut and bolts is to account for the thickness of the engine flange and the locking and fender washers. I will rough up the outside the coupling nuts in order to achieve better bonding with epoxy.

[One Way David]

If there was a way, I'd chuck them in a lathe and cut several groves for better bonding. It is an easy operation.

[Triton106]

Great idea David. I don't have a lathe but my friend Rob does. I am sure he will be happy to help.

[Quetzalsailor]

I think I'd test your embedment idea before you wax too enthusiastic, or install 'em. You're trading the strength of epoxy-cast threads for the bond with steel + whatever keying you arrange by grooving the outside of those connectors. Epoxy is dandy stuff but does not really bond to steel; it bonds to the unevennesses on the steel. Also, the steel will expand and contract with temperature, a cyclical source of which is bolted thereto; the wood and epoxy beds will be expanding and contracting with moisture.

Otherwise, those connectors have all sorts of uses beyond joining lengths of threaded rod. I have, for example, welded them endwise onto scraps of flat stock, drilled the flat stock for screws or lag bolts, bolted the assemblies to ceiling joists and patched the plaster ceiling. The connectors ended up eccentric with the joists. The result was four threaded holes, where I needed them, in the painted plaster from which I suspended a serious pot rack and I don't worry about how many cast iron pots Sue hangs.

[Triton106]

Quetzalsailor,

Good point on epoxy not bonding well to metal. I thought of two ways to deal with this issue.

1. Coat the roughed up coupling nuts with JB Weld which bonds well to metal. When JB Weld is cured then bond the coupling nuts (now coated with JB Weld) in the pre-drilled holes with regular thickened epoxy.

2. Bond coupling nuts with System Three MetlWeld Epoxy Adhesive which is designed to bond metal to other material such as fiberglass and wood.

Here is what Systems Three says about MetlWeld:

MetlWeld Epoxy Adhesive

MetlWeld is a super tough epoxy adhesive designed to bond metal and other dissimilar materials such as stainless steel, galvanized steel, aluminum, copper, glass, ceramic neoprene rubber and most porous services.

Features:

It will cure at temperatures as low as 50°F
MetlWeld is pre-thickened so no additional fillers or bulking agents are needed to make it a non-sagging adhesive
MetlWeld will bond metals to metal, wood, stone, concrete, and even glass