setscrews, schmetscrews!

Figment · Post by **Figment** » Mon Apr 07, 2008 9:23 am

Do I really need to use setscrews to hold my cutless bearing in place? Would I be insane to just "gently" epoxy it?

My setscrews are stripped, AGAIN, and I really don't think that upsizing (again) and cutting new threads is the solution. Definition of insanity, etc.

I think (THINK) that if I just bag the setscrews altogether and inject some epoxy into the screwholes, the bearing should be adequately set, but not so well-set that I couldn't break it loose with a pipewrench a few years down the road.

Has anyone else tried this?

Quetzalsailor · Post by **Quetzalsailor** » Tue Apr 08, 2008 8:51 am

Setscrews in fiberglass? Or in a bronze sterntube? Easy enough to clean out the fiberglass bore, paste it full of epoxy filled with microfibers, drill and tap. Easy enough to go one size up in the bronze.

I've enjoyed epoxying things together (inadvertently); holds entirely too well! And just a smidge, too.

The cutless bearing in our old Morgan 27 was pressed into a bronze strut, no setscrews, and absolutely no inclination to come out, either. Had to saw a strip out.

Ceasar Choppy · Post by **Ceasar Choppy** » Tue Apr 08, 2008 8:55 am

Why (WHY?) are you having so much trouble with set screws? :)
What about using epoxy to fill the old holes and RE-TAP the epoxy?

Figment · Post by **Figment** » Tue Apr 08, 2008 9:06 am

Yes, fiberglass tube.

Quetzalsailor wrote:Setscrews in fiberglass? .... Easy enough to clean out the fiberglass bore, paste it full of epoxy filled with microfibers, drill and tap.

Yes, easy enough. I've done it twice already in the five years I've owned the boat. The threads simply don't last. I imagine that vibration has something to do with it, but there's only so much (not a damn thing) I can do about that with an A4.

bcooke · Post by **bcooke** » Tue Apr 08, 2008 9:53 am

You should have the pistons and crankshaft balanced...

Figment · Post by **Figment** » Tue Apr 08, 2008 10:35 am

You volunteering the loan of your engine while you do the work?

Rachel · Post by **Rachel** » Tue Apr 08, 2008 1:02 pm

You're probably way ahead of me on this, but have you used the appropriate Locktite-type product to help keep the vibration from affecting it?

(Or is this a silly idea for some reason; entirely possible.)

bcooke · Post by **bcooke** » Tue Apr 08, 2008 1:02 pm

All high end shops offer loaners.

It goes with the high invoices...

Zach · Post by **Zach** » Tue Apr 08, 2008 1:47 pm

Hmm...

Am I hearing this right that you are bedding the set screw into epoxy to make the thread? That is probably your problem. Basically what has happened, is both threads are the same. If you were tapping metal, you'd have threads that fit so tight, that putting them in by hand they'd hit a point and bind. This bind would be so tight, that for all intents they become welded together and you have to drill them out. Study a tap vs the bolt that goes in the hole... any trash ends up at those points, any irregularities have somewhere to go.

This is especially important on plastics, because when you run a cutter through they deform ever so slightly, making the hole, or in this case the threads slightly smaller than the form. In your case theres a touch of shrinkage to from the volatiles in the epoxy leaving as the reaction cures. (Mix hot, volume expands... slight reduction as the solvents leave, when it cures its volume is smaller.)

When you tighten a screw, what is happening is the length is changing. You are stretching it, its resistance is the torque. The more pressure, the longer it gets. The harder (higher durometer) the plastic the less they like to be stretched, but the more pressure they will take before deforming. Basically the denser the molecular chains are packed, the better it threads. You hit a point where it takes no more tension before shearing the threads right out. Lower durometers will just deform before the fastener even thinks about stretching.

Personally I would goo in a threaded insert bedded into the fiberglass with thickened epoxy 2 or 3 times the diameter of the screw to give a greater surface area for the bond.

As far as what fillers to use when trying to mold a thread, or cut a thread into epoxy I haven't a clue... I know the thermoplastics, but this two part stuff is a whole different ball of wax. Works the same, but the chemistry sure is different!

Quetzalsailor · Post by **Quetzalsailor** » Wed Apr 09, 2008 8:47 am

I've done the tap fiberglass trick several times with success: a layup of polyester-glass, a plug of filled epoxy in an outsized bore in wood or polyester, tapped neat epoxy too - but that was for the adjusting screws when I made a set of wood harpsichord jacks. I've used the cast around method once or twice, successfully using Teflon slip spray for the release, but given my record of inadvertent bonding and the concern about how to reliably get lots of fiber into the threads, it's my last choice.

Clearly, you'd need more thread, a thicker nut, than you would with metal, and a gentler hand to keep from stripping the threads.

I'm surprised that the cutless or its setscrew would vibrate out. Is the fiberglass tube bore a little too big? Or has the fiberglass crept a bit bigger? Perhaps a micro-mini dab of 5200 is appropriate; pretty much where you were when you started this thread.

bcooke · Post by **bcooke** » Wed Apr 09, 2008 8:56 am

If you are thinking 5200 then 4200 might be more appropriate since it is the 'lesser brother' of 5200 and is designed to be removed if necessary.

-Britton

Hirilondë · Post by **Hirilondë** » Wed Apr 09, 2008 9:14 pm

The Jamestown Distributors catalog has a chart showing the tensile strengths of the 3M and Sika lines of adhesives and beddings. I can't find this chart on-line. I do remember a few of the stats as I use the products. 3M 5200 = 700 psi, 3M 5200 fast cure = 600 psi, 3M 101 = 139 psi, and Sikaflex 291-LOT = 250 psi. The numbers themselves probably mean little to most of us (myself included). Being very familiar with Sikaflex 291-LOT though, having used it and removed stuff bedded in it, the numbers give me a fair relative comparison between products. I find Sikaflex 291-LOT to be the best all round bedding adhesive. It has enough adhesive hold to assist in mechanical fastening, cleans easily, the white stays white and with a little care you can get stuff apart later. Because it is a polyurethane (as are 4200 and 5200) and not a polysulfide like Lifecaulk or 3M 101 it can be used safely with plastics (ex. polycarbonate ports lights and PVC inspection ports). The only real down sides to it is that it comes only in cartridges, and not small tubes, and it has a shelf life, which shortens drastically once opened.

Zach · Post by **Zach** » Wed Apr 09, 2008 10:03 pm

Thanks for the suggestions Hirilonde.

Bostik Marine 920 is another one to add to the list. PSI on it is 180. Its tough as nails, flexible, and does everything well. Used quite a bit on the wood boats.

Never hear it talked about on anywhere on the web. Its some of the most tenacious stuff I've come across. It stretches, a lot. Whereas 5200 just grabs on for dear life... this stuff is softer. I've pulled out some floors that were gooped in with that, after the nails were gone it took a sledge to get them loose.

Probably wouldn't want it on the cutlass bearing though, the stretch would get ya ever trying to take it apart, but for a caulk that doesn't pull loose and is UV stable...