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Old 13-05-2008, 14:21   #1
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Unhappy Underwater Loc Tite??

I'm having a problem with machine screws that attach zincs to my volvo penta sail drives. The phillips head machine screws (about 3/16" dia) back out after many hours of running. The last time I changed zinc in the water, I put blue Loc tite on the threads and put them in. That didn't work since they are loose again. I thought about something more aggressive, but don't want the screws to lock in permanently. Any ideas? Will red Loc Tite be too strong?

I have to remove folding props composed of many parts so it isn't a simple fix to tighten the screws periodically.
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Old 13-05-2008, 14:38   #2
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How about the loctite, and double nuts on the bolt? I use double nuts all the time on exhaust systems.
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Old 13-05-2008, 15:07   #3
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Red lock-tite is pretty tough stuff. Its a difficult call on whether or not that would make it impossible to remove it. I would hate to see you strip the head or shear one off. Have you called a boatyard to see what they do?

Do the machine screws thread into the unit or do they thread onto nuts? If thats the case, would nylocks work?
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Old 13-05-2008, 15:54   #4
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You could try Nord-lock washers if you have the room under the heads of the screws.
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Old 13-05-2008, 16:07   #5
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I just had another idea. Wrap the machine screw with Teflon tape. Yes its slippery, but it sure creates more resistance than nothing. Put enough on so you really have to crank down on it to get it in there.
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Old 13-05-2008, 19:19   #6
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The threads on the fasteners used to hold the zinc on the end of my prop come with what appears to be a solidified blue plastic on the last 3/16" of the threads. I don't know what goop the supplier used but it acts similarly to some military fasteners that have a slot and actual piece of plastic installed on the ends to make a vibration-resistant mating.

One needs this especially if the zinc erodes away from beneath the head of the fastener. Perhaps this is what is happening to you.
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Old 13-05-2008, 19:45   #7
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Volvo Saildrive

I just replaced my zincs on my saildrive with no problem (knock on wood). My boat was on the hard so it's a lot easier to work on it than in the water. Is your saildrive similar to mine (see photo)? How can those two bolts back out when the prop also helps keep it in place??? I forgot if I used locktite on the zinc bolts but I definitely used the Red Locktite on the ends of the bolt that holds the prop on. I've never had a problem removing the bolt - just sprayed a lot with P.B. Blaster, tap it periodically and make sure you have a properly fit Phillips head to grab the head of the bolt when removing the prop. I have a feeling your sail drive may be different than mine if those two bolts that are holding the zinc on are loosening.., Hmmm..,
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Old 13-05-2008, 21:22   #8
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Sand and replace that paint on your saildrive, you'll go faster.
BTW don't be afraid of red Loctite.
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Old 13-05-2008, 23:27   #9
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Quote:
Originally Posted by svcattales View Post
Any ideas? Will red Loc Tite be too strong?
Use the red Loctite. Some prop manufacturers include it with their installation kits (Gori comes to mind).
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Old 14-05-2008, 00:22   #10
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I think the issue would be that you tried to use liquid locktite underwater. Locktite have another product that is in a small container like a lipstick. It is more a solid and you will have better luck with having it stay on the thread. Red or Blue will be fine.
Rick, the hard blue stuff on the thread is another loctite type product. It sets once the thread has screwed home.
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Old 14-05-2008, 00:36   #11
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There is also a Locktite Hydraulic Sealant which is purple in color. This is the best sealant I have seen for Hydraulic pipe fittings. It also works good on bolts.
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Old 14-05-2008, 06:47   #12
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Thanks for all the suggestions. My saildrive is identical to SurfNRG's in the picture above. The machine screws countersink into the zinc and thread into blind holes in the sail drive so I can't use nuts or washers. The zinc can't come off because of the prop, but it is loose so I'm worried about proper contact and protection for the sail drive. I think I'll do an experiment in a bucket of water with the red loctite and see how difficult it will be to remove it after it sets up. Fsstbttms & Wheels have very good suggestions. My Flex-O-Fold props come with a red thread lock on the bolts for installing under water and I think it sets after the bolt is screwed in. I just don't know what they are using. I scraped some off a spare bolt and it has a waxy appearance. Wish me luck that I don't screw this up!
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Old 14-05-2008, 17:59   #13
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I found the Loctite product that Rick & Wheels mentioned in their posts. I called the company and the stuff is called Loctite Stick and it comes in a tube like Chapstick. The blue stuff is medium hold and called Loctite 248 and the red is high hold and that's Loctite 268. The technical rep at Loctite said I could use the red because it isn't quite as strong as the red liquid and the machine screws are small diameter. This type of Loctite is sold to automotive stores, but I couldn't find it in my local area. I ordered one blue & one red from www.mro2go.co and plan to experiment in a bucket of water before I decide which one to use. OBTW, they cost $9.84 each.
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Old 14-05-2008, 19:58   #14
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I would use 5200. Coat threads and bottom of head. Wipe threads so that the threads are visible with 5200 in the thread groves. Let the 5200 set but not cure before inserting and tightening down.

For easy removal use a small torch to heat the screw head.

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Old 14-05-2008, 21:56   #15
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Loctite products are generally useless--even the red stuff--unless they are applied to perfectly clean and dry surfaces. Can you put the screws in, and then dimple the threads, or the heads, with a nail punch or chisel so that they simply can't be backed out?
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