Loctite 515 for case sealant

[rocketbob]

Some food for thought... on most Mustangs nowadays the guys I know maintaining them use proseal as a sealing compound between the heads and banks. In our application there's no reason why it couldn't be used similarly.

[carguy614]

Thats interesting....Proseal is good stuff, but I have never heard of using it for such an application.

Regards,
Chris

[chaskuss]

Originally Posted by hgerhardt

Not according to Henkel, the manufacturer: "Loctite? 518? Gasket Eliminator? Flange Sealant forms a flexible, solvent-resistant seal that will not tear or decay. Seals to 300?F and fills gaps to 0.050". Can be used on flexible metal assemblies, including aluminum surfaces."

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

Heinrich,
I'll defer to your experience with 518. I've never used it myself. My comments were directed towards 515, which I HAVE used, and don't like.
Charlie Kuss

[svennijo]

I have always used PRC for the case halves and had no leaks. The PRC gives you a couple of hours to get everything set. I do not use thread, since I have not had a need for it. On the accessory case I like to use hylamar since it stays more flexible and it is easier to remove the accessory case if you need to for a maintenance issue.
I also like the o-ring cases. A lot less of a leak chance. Another good idea is to have dowels put into the case. To the best of my knowledge Lycoming still does not have dowels in their new engines, but I have seen many cases starting to fret. The dowels will eliminate the fretting possibility.
I learned these techniques from a friend who mentored me through my A&P and has been overhauling engines for 20+ years. He has never had a problem either. Just my two cents.

[rocketbob]

I'm finishing up overhauling a 300hp IO540 right now for a certified airplane, and I used POB #4 and silk thread. I really don't like that stuff, its too thin. The thing that I don't like about the anerobic sealants is that little guy called Murphy, and he makes it a little difficult sometimes to put things back together in a timely fashion, which the other approved sealants require. When I OH the 540 in my rocket I'll use PRC. If its good enough to put a Merlin together with, its good enough for a Lyc. I suspect Nixon and Roush know a thing or two and I understand that's what they use. Many mustang mechanics have fought leaks around the heads until they started using PRC, and I have a friend that's used it on the Merlin he maintains and now he swears by it for Merlins and Lyc's.

[rongawer]

This is an old thread, but want to make sure folks have all the information. According to Loctite 515 Technical Documentation Sheet, the cure time is 24 hours on aluminum, with full strength at 72 hours.

So I do not agree with the "gotta rush" aspect posed here.

Also, the only material listed to not use this sealant with is plastics. As for aluminum, not only is it listed for use with aluminum, it shows a curing time curve for aluminum. So there is no need to go with 518, but rather stick with the Lycoming approved 515.

When applied by the directions, it works very well.

[Sue]

I have used hylomar? For 40+yrs on aircraft
Powerplants, and have used prc (1422,8802)
For a few aircraft and a bunch auto engines.
Opposed engine cases, my vote hylomar, next
Prc 1422, 8802.... 1422 can be had 1/2hour
All the way up to 30 day cure time.

[mahlon_r]

My 2 cents;
Anything that prevents metal to metal contact between the case halves isn't good. You want as much rigidity there that is possible. Metal to metal there with nothing in between would be the best if it would seal. The thread and POB sealant provides good rigidity. A film of flexible sealant doesn't. The POB is not acting as a seal, the thread is. the POB should be applied as thin as possible and squeezed out on assembly. Once the case halves are torqued the POB is squeezed out and the thread is flattened between the case halves. Although the thread is there it still allows metal to metal around the squeezed thread area. Thus providing a more rigid assembly. That is why you must use silk thread it will flatten and allow metal to metal. The reason case halves leak at the seam is because the thread breaks or distorts due to case movement between the halves. That movement is the enemy as it allows the start of case fretting, which as we all know is a major problem with these engines. So anything that provides a flexible film will probably seal OK as there is no thread to break but that seal flexibility will also allow movement between the surfaces. And to me that isn't good for the long term. anything that allows movement of the case halves against each other, anywhere they meet, can help induce fretting, even if the sealant is flexible enough to prevent a leak with the movement. I always used thread and POB for that reason. Yes, the factory listed and used alternatives but to me the most rigid solution was the best to use and in my opinion thread and POB provided that.
Good Luck,
Mahlon

[deek]

^^^^ When Mahlon speaks I listen ^^^
I've had Mattituck build 3 engines for me, and had two of the three were overhauled after the initial Red/Gold overhauls. None ever had case split leaks, and none had shown any evidence of case fretting despite a fair mount of "abuse" and high ( >than 2900) RPM.

I've watched the techs at Matttituck lay down the silk thread on my engines, and questioned how such an archaic process could possibly work. But it does.

[lr172]

Originally Posted by carguy614

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

+1

I learned this from the Porsche world (alum boxer engines structurally similar to lyco's). I used permatex anaerobic flange sealant (similar to the loctite 515) on my 320. 640 hours and not a seep or drip to be found. Case bolts will need to be snugged up a time or two early in it's life, from my experience.

Cleanliness is key with these products. Surfaces MUST be clean.

The permatex is NOT a flexible sealant. It cures hard and will even crack when you peel it off a surface after cure. To Mahlon's point, metal flanges are just like our case halves, where a flexible sealant is not desired. This stuff was engineered for large metal flanges and fits the bill well in our application.

Larry