Permatex Aviation Form-A-Gasket #3

[rongawer]

I had a conversation with Lycoming tech support today, mostly about my engine case which started life as a TIO-540, but will now live on as a 540-X. But while talking, I learned that they're coming out with an updated SI 1125 (should be revision E, but not certain) that will replace the no-longer-available Perfect Seal POB #4 with Permatex 80017, making it official.

My guess is that is what folks have been using for years already, (that and Hylomar blue), but thought I'd pass that on for anyone who may be searching on the topic.

 

[jliltd]

We always use Loctite 515 (aka Grape Jelly) with silk thread for case halves. Also use it as a non-permanent gasket holder. It's the approved product for Continentals and it used to be repackaged with a Continental part number on it at three times the price, until they gave up a few years ago and just send the Loctite packaging when ordering. It works great on Lycoming cases and we have never had a leak since using it.

 

[lr172]

I did both of my cases with loctite anaerobic sealant & no silk thread (think it was 515 or 517)) and both have been leak free.

Larry

 

[rongawer]

I think you guys missed the point...for those that want to use silk thread, the proper sealant to bed the thread in is now officially Permatex #3. Updated SI pending.

While Loctite 515 and RTV-102 are approved alternate sealants, SI 1125D specifically highlights, in bold words, to NOT use silk thread with either alternate sealants. The two alternates are anaerobic sealants, which are flexible - yet cure in the absence of oxygen (anaerobic), whereas permatex #3 is non-hardening.

 

[rcharris]

For people that find this thread later - the SI-1125E has updated guidance regarding silk thread and 515.

 

[jliltd]

So. Lycoming missed the point but finally came around with a big change in their Service Bulletin that matches years of field experience of using 00 silk thread with grape jelly (Loctite 515). They even added the option of the newer pomegranate jelly (Loctite 518). The Service Bulletin now specifically states, "Lycoming has found the use of LOCTITE® 515 or 518 and silk thread to be the preferred method, but field service facilities may choose to use any of the approved methods contained in this instruction."

My experience has been with Loctite 515 with perfect results. But Loctite 518 is described to be designed more for Aluminum surfaces. "Loctite 518 is a flexible, red gel-like material that adapts to minor flange movements. Loctite 515 is a thicker, dark purple paste that creates a much stronger bond, which can sometimes make separating the cases difficult. 518 features updated chemistry that cures significantly faster and more reliably on aluminum than 515." While having great results with 515 grape jelly we did have to buy a case splitter to release it's over-achieving bond during teardown. I would like to hear from anyone who has field expereice with Loctite 518. Few things as unforgiveably disheartening as leaky case halves in a low-time engine.