crankcase joint seal

[eric_marsh]

Right now the recommended case sealant in the motorcycling world is Hondabond HT. I used it the last time I assembled my Busa motor and it's working fine. Say what you like about Honda, the do know engines. I don't know why it wouldn't work on an aircraft engine.

[rocketbob]

I've got a great running O-360 that someone sealed the case halves with silk thread and I'm sure they also did it correctly and found it not a hard process to do. Leaks like a sieve however.

There is no engine produced today that I'm aware of, other than Lycomings and Lycoming clones, that use this antiquated method to seal mating surfaces.

[rocketbob]

Case on my O-360 leaks just aft of the front seal on the bottom. With UV dye I've verified its not the nose seal leaking. Essentially just below the main bearing.

On the 540 I did last year it leaks slightly just below the flow divider on top of the case. I sealed that one with two strings of silk thread inside and outside of the bolts, POB #4, torqued the case bolts to 100in/lbs.

[Frank Smidler]

Hey Bob, my 0-360-A1A is starting to leak at the crank case halves just behind the starter mount. I haven't pinpointed the leak yet and it may be the through bolt. What did you do to stop/reduce the leaking?

[Ironflight]

Originally Posted by eric_marsh

Right now the recommended case sealant in the motorcycling world is Hondabond HT. I used it the last time I assembled my Busa motor and it's working fine. Say what you like about Honda, the do know engines. I don't know why it wouldn't work on an aircraft engine.

Hi Eric,

I know that you have said in another thread that you are new to aircraft engines - one of the things you'll probably figure out tis that we are dealing antique designs here - not the latest stuff coming out today. The case halves on a Lycoming are machined so that they match exactly - no O-rings or gaskets (other than the specified silk thread). The camshaft rides directly in the machined bore of the crankcase, so if you change the fit between the case halves, you change the clearances of the camshaft bearing.

Which is not to say that alternative sealing machines can't work (many do) - it is just to be careful about using anything that changes the fit (adding space) between the case halves.

Paul (not an engine expert, but have learned a lot from folks that are...)

[rocketbob]

Originally Posted by Frank Smidler

Hey Bob, my 0-360-A1A is starting to leak at the crank case halves just behind the starter mount. I haven't pinpointed the leak yet and it may be the through bolt. What did you do to stop/reduce the leaking?

Hey Frank! Likely its because the thru-bolt is not o-ringed. You can just goop up some proseal and cover up the bushing and thru bolt nut.

[eric_marsh]

Originally Posted by Ironflight

Hi Eric,

Which is not to say that alternative sealing machines can't work (many do) - it is just to be careful about using anything that changes the fit (adding space) between the case halves.

Hi Paul,

The Hondabond HT is similar to Permatex. A thin coat is applied to each of the machined surfaces and when the cases are assembled what doesn't squeeze out cures and seals the cases.

I only mentioned it because it's pretty much considered to be the state of the art product at this time. But I understand that the adoption of new products tends to be slow and for good reason. Better the Devil you know than the Devil you don't.

[The Green Baron]

Do you guys recommend putting Hylomar on both crankcase half surfaces before mating or just one?

Also do you think two strands of silk thread is overkill?

I have read different combos, just wondering what method is more common.

Thanks
John

[apkp777]

I have decided to use Hylomar (Hylomar? AeroGrade Ultra) http://www.hylomar-usa.com/_resource.../products.html

I think it is the "cat's meow" of crankcase sealants. We'll see.

[9GT]

Originally Posted by apkp777

I have decided to use Hylomar (Hylomar? AeroGrade Ultra) http://www.hylomar-usa.com/_resource.../products.html

I think it is the "cat's meow" of crankcase sealants. We'll see.

That's what I used.