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A few months ago I read that Lycoming wants Case Studs anchored with a thread locker. I am installing a new cylinder base stud in the case of an 0-320 and can't remember where I read this requirement and now can't find it in Lycoming's tech pubs. Anyone know which Loctite to use? And maybe have a reference from a Service Letter or OH Manual update?
Another thread here references "Loctite Food Grade Anti-Seize" on other case studs, but does not address Cylinder Base Studs in particular, or the type Loctite color/number.
Loctite sells high temperature thread locker which I have used on other crankcase bolts. I can't imagine that it would hurt to use, just keep it out of the engine interior.
My guess would be that it was not to use loctite. Lycoming makes the base studs in oversize where they attach to the case when the thread interference is lost. Add "P" (P=plus) and the oversize ".003" as a suffix to the part number. For example "P3" would be added to the part prefix.
Have you tried taking them out??? Using loctite does not make sense, most times they can be really stuck. Application of heat, jolting them out with a quick snap, and so on. The Snap On stud puller in the overhaul manual works the best. Uses a BIG 1 1/8" wrench about 18" long to supply the torque . Also... you can use the stud puller to capture the removed stud deck height so when you put it all together the new stud does not hit the fins when you try to put the nut on.
All of the torques in the LYC manual are "wet torques". Food grade Anti seize, engine oil, STP etc..... are all used for torquing. I believe that there is no Torque value given for the cylinder base studs (just the threads that go into the case) as deck height is a bigger issue than final torque.
Last edited by Vagabondblues; 08-25-2019 at 09:12 AM.
The overhaul manual calls out Loctite Food Grade Anti-Sieze. Loctite is the brand, it's not a thread locking compound. I used a mix of stp and motor oil on a stud I replaced and heated the case with a heat gun before installation.
The screwed in case studs are Locktited. Had a conversation with Ken at LyCon just last week because on his overhauls they use Divco and Crankcase Services to overhaul crank cases but they don't pull the studs and magnaflux. LyCon does this on their overhauls because they have had issues in the past and he said sometime the studs leak oil as well. I will find out what they use.
The screwed in case studs are Locktited. Had a conversation with Ken at LyCon just last week because on his overhauls they use Divco and Crankcase Services to overhaul crank cases but they don't pull the studs and magnaflux. LyCon does this on their overhauls because they have had issues in the past and he said sometime the studs leak oil as well. I will find out what they use.
Thanks Steve, I'd like to hear their recommendation. I've flown a LyCon engine and really believe they have figured out the formula.
I've seen oil leaking through cyl base studs that are well torqued; and when you heat the stud for removal the oil sometimes boils oil up through the threads and that's when you know to turn it out. Sometimes the studs will come right out of the case with a frozen cyl base nut when pulling a cylinder (as I'm sure many have experienced). It's an art to get a new stud in tight and at the right depth as Vagabondblues pointed out. They act like a pipe thread the way they bind up, but are just a 1/2 NC 13 straight thread. The bolt hole goes all the way through the case but one of our Lycoming engine gurus will have to tell me if it was originally tapped to a certain depth or bottom-tapped ?
Really doesn't matter now with a 1955 case and strange variances in Lycoming QC. Machining errors, rolled threads, coked and obstructed threads, prior overhaul tapping etc. leave each stud hole its own deal. At the least a hi-temp thread locker will fill the gaps like structural epoxy and while it certainly can't take the impact of the firing stroke maybe it can help keep the stud anchored through the heating and cooling. And seal oil leaks.
Can't say enough about the tool Vagabondblues also mentioned. The Snap-On Stud remover with some drive grip on the threads can save the day. Both installing and removing.
LyCon uses Loctite 271 High Strength Adhesive Sealant with Loctite 7471 Primer. When they vat the crankcases it sometimes effects the sealant so they remove the studs when they come back from the case shop, magnaflux them and install with sealant. Same thing Continental uses per SIL-99-2B
LyCon uses Loctite 271 High Strength Adhesive Sealant with Loctite 7471 Primer. When they vat the crankcases it sometimes effects the sealant so they remove the studs when they come back from the case shop, magnaflux them and install with sealant. Same thing Continental uses per SIL-99-2B
Steve,
What are we really talking about? Thread locking or sealing?
The original poster used the word "threadlock" so...I assumed that he was talking about the Lycoming thread interference fit requirement. i.e. inspect, measure and if needed use an oversize part to establish interference fit.
I understand that all of the references you gave, as FAA approved Repair Stations can create processes and have it approved and written into their Repair station manual. So does that mean they have approval to use loctite as a threadlock to restore the fit? Or, is it a "special sauce" they use to stop leaking? Either way it would be approved data, but not to start a pissing contest on the rules.......it may not be approval for our personal responsibilities.
Having worked in a Repair station as an A&P I always signed off using the "entity" certificate number not my own.
I have not been able to find any data from Lycoming on removing the studs and reinstalling them from the crankcase. Ken told me they have had issues with overhauled crankcases leaking oil out of the studs and said that when they are cleaned and vatted at overhaul the sealant originally used when built is compromised. After overhaul of the case they remove the studs and magnaflux them and reinstall using the products I listed. My understanding is they are using it as a sealant, not to restore fit. I would call it a standard practice if I was ever questioned about it. Kind of like putting fuel lube on magneto gaskets prior to installation so that I can rotate the mag to adjust the timing over time.
I have not been able to find any data from Lycoming on removing the studs and reinstalling them from the crankcase. Ken told me they have had issues with overhauled crankcases leaking oil out of the studs and said that when they are cleaned and vatted at overhaul the sealant originally used when built is compromised. After overhaul of the case they remove the studs and magnaflux them and reinstall using the products I listed. My understanding is they are using it as a sealant, not to restore fit. I would call it a standard practice if I was ever questioned about it. Kind of like putting fuel lube on magneto gaskets prior to installation so that I can rotate the mag to adjust the timing over time.
The original poster said it was a replacement stud. Section 3-33 of the lycoming direct drive overhaul manual has the verbage.
Last edited by Vagabondblues; 08-28-2019 at 07:12 PM.
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Cylinder Base Stud Loctite
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Originally Posted by Steve Pierce
....it may not be approval for our personal responsibilities.