Engine Case Sealants

by Jim Thompson, John Anderson, and Richard T. Perry


Jim Thompson recommends:

Curil K2 $9.99 for a 175G Tin w/o handpump (With the neat pump it's $17.94)
Curil T $7.25 for a 100G Tube

A few machine shops in the area and most of our wholesale customers back East buy the stuff a lot because they say it's hard to find and won't use any other types of compounds. Guess they want the original stuff.

Been using the K2 on case halves for an untold amount of years - no leaks ever. Also used Permatex 3H (Aviation Form-a-Gasket) with equal results when I couldn't find the K2 - probably better priced too, even from the "Fast-Food" FLAPS, such as Chief, Kragen, Checker, Pep Boys, etc.

Also carry another Curil product (actually Elring-Germany makes them all) called Dirko, which is an elastic sealing and filling compound. $8.95 for 100G tube. Works great sealing the gear reduction boxes.


John Anderson says:

Might want to consider the Loctite 574 (orange), supposed to be a bit thicker (but not at all thick) and offer a more reasonable crush. Also most Porsche racers around me recommend it as the best stuff hands down ($13 for a 50 ml tube locally--note: Automotion wants $25 for the same).


Ron Van Ness says:

Be attentive when applying sealer to the case halves. I purchased a bottle of Permatex 3H that had a cap top brush applicator with loose hairs. Every few brush strokes a hair would leave the brush, depositing itself on the case seam surface. Examine the cap brush for loose hairs and have a reliable applicator on hand if necessary.


"This weekend I hope to assemble the bottom end of my stock 2 liter engine. I'm planning on using Permatex Aviation Form A Gasket on the split-line, but I've got the " thread in the sealant " method on my mind. Have any of you ever done this, and what where your experiences ? I know that method is used on aircraft engines, but there it is expected. What good is it to measure bearing journals to the ten thousandths and then do something that will have a measurable, even if small, effect?"
Richard T. Perry offers:

String in the Permatex Method

As an A&P mechanic, I've done this a few times. Frankly, I don't have all that much experience in engine overhaul, and I don't have a manual handy, but here goes. First, you use the Permatex you mentioned, and a (I'm dredging this up from DEEP memory) "00" silk thread. The procedure goes something like this:

  1. Clean everything carefully. This method will only work with perfectly clean flanges. When cleaning, ensure that you're using a scraper that's softer than the flange, too...scratch the flanges up and you're done.

  2. Put down a small layer of Permatex, and smear to cover flanges evenly with a finger. This is not a case of more is better. Put on too much, and the SOB will leak forever. Try not to get much into the case-half-bolt-holes. You know you've got the right thickness of permatex when it looks like you've just colored the surface, but can still see the surface through the permatex.

  3. Let the permatex get a little tacky (5-10 minutes? It's been a WHILE), then carefully lay down the thread on one flange. Use a double thread, (i.e. two different threads or lay it in once , then bring it back through) and ensure that they NEVER cross over each other. That, too, will make it leak. Ensure that the string doesn't interfere with the bolt-holes, btw. I usually try to put both layers on the inside of the holes all the way around.

  4. Assemble the engine and tighten the case half bolts to the spec torque.

  5. Take a sharp knife and trim the string off flush where it comes out of the case parting surface.

  6. Let sit for 24 hours before introducing fluids (oil, specifically) to the crankcase.
When this is done right, it won't leak in a standard overhaul period.

Now - big disclaimers are in order here. I haven't done this in a while, and I'm not looking at a manual, and (MOST IMPORTANT) this is the procedure for a Lycoming (I think it was a O-320-A4K, last) not a VW. Your Milage WILL vary. I've never torn a VW apart, (I'm a wannabusser right now), and I don't know what kind of standards they had for those surfaces. For instance, in an aircraft engine (with a few exceptions), the case halves are cast as a unit. Cannot be individually replaced [editor's note: VW case halves are also matched pairs].



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