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Loctite 515 for case sealant
The Lycoming tech bulletin for case sealants allows Loctite 515 for sealing case halves. I have it on hand, and was planning on using it.
Has anyone had a problem with this route? BTW, my engine came from the Lycoming factory, new, with what I have to assume to be RTV-102, also allowed by Lycoming. Thanks, Rick 90432 gathering up engine parts 'cause my paint issue is still not solved. |
Use Loctite 518 instead!
If you look at the Loctite spec sheets, you'll see that 515 is specifically not recommended for aluminum. So, why does Lyc allow it then? Who knows. I believe Mr. Barrett responded here the last time this question came up and said that he'd had poor success with 515.
However, what Loctite DOES recommend for this application is 518. I also spent a fair amount of time checking the Porsche boards and found the majority of them are using 518 now too (they have the same case sealing situation as we do). So 518 is what I used on my IO-360 earlier this year. FWIW, 80 hours so far and it's completely dry. If you go this route, some foresight is necessary: have all hardware at the ready, clean the sealing flanges with acetone/MEK/lacquer thinner and get all lint from the paper towel off. Speed is of the essence during assembly. Assemble all the case split line bolts first and preliminarily tighten. Then, hurry up and install the thru-bolts and tighten them with washer stacks as shims (since you won't have the cylinders installed yet). Then, final torque the case split line bolts. Remember that the Loctite starts curing immediately when the case halves come together. One more thing: when applying the Loctite, just put a small bead (1/16" or so) on the center of one flange and assemble the case halves. Don't use your finger to smooth the bead down to nothing as it tells you to do in the Service Bulletin. That will just lead to air bubbles being trapped in the sealant and cause future leaks. Any squeeze-out in an inaccessible place inside the engine will just get washed away with motor oil eventually. Remember, this stuff is anaerobic and will only harden in the absence of air, which is in the flange itself. The squeeze-out will not cure inside the engine and will not plug anything it isn't supposed to. And, absolutely DO NOT use silk thread with this method. Heinrich Gerhardt RV-6, flying |
The problem with the other two sealants mentioned in the SB is they set up quickly, and you have to be fairly quick to get everything together. POB #4 is cheap, easy, and gives you a bit of time to work. The downside is you have to use silk thread. The factory uses this stuff for a reason...
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518
Loctite 518 is now the benchmark for sealing flanged aluminum parts. I have never used it on a Lyco, but I have extensive experience with it in the automotive trade. It has been 100 percent reliable in my experience. The key, as mentioned above, is cleanliness of the flanges on assy, and resisting the urge to use too much. Amazingly, it withstands even pressure fed parts such as external oil pump castings, and transmission case halves. I am interested to hear if any of the aviation shops are indeed using it. I would not hesitate to use it on my Lyco.
2 cents....Chris |
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I suggest using Hylomar (developed by Rolls Royce Aerospace) with the silk thread. Permatex sells Hylomar here in the USA. You can find it at any auto parts store. It is a sticky blue paste, which never dries. Therefore, there is no rush to mate the crankcases. It also holds the silk thread firmly in place. Since it never dries, any excess will be flushed away by the oil and trapped in the oil filter. Charlie Kuss |
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OEM's are using this stuff. With warranty costs what they are, they'd never use it if brittleness were a factor. When I took my 28-year-old IO-360 apart, the little bit of factory sealer that was left was pretty much brown chalk. Oh, the case leaked profusely, too. Hylomar might be better than the original brown goo, not sure. Didn't they use Hylomar on British cars? Didn't they leak too? Heinrich Gerhardt |
America's Aircraft engines built my O360 with Hylomar and tread, so far no leaks at all :D
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factory info
I attended the Lycoming engine assembly seminar at OSH. There was a lot of discussion on case sealing. The expert there (I forget his name, he's been at Lycoming for many many years) said that the factory uses the recommended sealant (Hylomar?) and silk thread. He stated that if you re-torque in 100 hours or at at the first faint sign of wetness, it will stay dry until TBO. He also said that the silk thread doesn't do anything for sealing - it provides a dam for the Hylomar, which he called an adhesive, not a sealant.
I'm thinking of having my case O-ringed by Lycon next year. |
518 it is then . . .
In that I already had the 515 on hand, I was going that way. I'll get a tube of the 518 and go that way, I think. The thread thing is a little 1930's for me, although I recognize that it works.
Thanks, all. Rick 90432. |
silk thread
I really like the idea of O ringing the case. Issue solved I do believe, provided the O ring is made of the right compound. Us car guys have had our share of early O ring failures, and resulting severe leaks. The latest O ring compounds have been very dependable. In old school automotive applications, the sealer and thread method was effective, if done carefully. The thread served as reinforcement for the sealer. Like rebar in a concrete slab. It also served to keep the sealer from being completely squeezed out when the case halves were torqued. Scuffing the case halves lightly in the direction of the sealer bead was recommended by the Brits. Gave the sealer bead some tooth to resist blowout. If the planets were aligned just right, it lasted a long time. All that said, the industry has switched to Hi performance anerobic compounds to do the job. Smooth flange leaks are really a thing of the past since then.
2 cents, Chris |
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