AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Lycoming 0-320 Exhaust studs working loose          AirTalk.org Forum Index -> Owning Airplanes View previous topic :: View next topic   Author Message Mike Spera Guest Posted: Fri Apr 27, 2007 3:52 am    Post subject: Lycoming 0-320 Exhaust studs working loose I have had intermittent problems with 0-320 exhaust studs working loose, usually with overhauled cylinders. I understand it if I have a stubborn nut to remove for a gasket change and the stud comes out with it. I figure that if I reuse that stud/nut again I am asking for it to work back loose because it is no longer bottomed in the hole. But I just had another one work loose in flight that was never disturbed from new. I always wondered why we use plain steel studs and nuts for this application anyway. It screams "corrosion". Why not heli-coil the port threads and use a stainless bolt and lock-washer? That way, the threads are protected from the elements to some degree and using stainless hardware gives you a little better resistance to rot. Any engineers know why studs are used on exhaust systems in general? Thanks, Mike Back to top Orval Fairbairn Guest Posted: Fri Apr 27, 2007 6:12 am    Post subject: Re: Lycoming 0-320 Exhaust studs working loose In article <q2aYh.4086$Ut6.331 (AT) newsread1 (DOT) news.pas.earthlink.net>, Mike Spera <mwspera (AT) earthlink (DOT) net> wrote: Quote: I have had intermittent problems with 0-320 exhaust studs working loose, usually with overhauled cylinders. I understand it if I have a stubborn nut to remove for a gasket change and the stud comes out with it. I figure that if I reuse that stud/nut again I am asking for it to work back loose because it is no longer bottomed in the hole. But I just had another one work loose in flight that was never disturbed from new. I always wondered why we use plain steel studs and nuts for this application anyway. It screams "corrosion". Why not heli-coil the port threads and use a stainless bolt and lock-washer? That way, the threads are protected from the elements to some degree and using stainless hardware gives you a little better resistance to rot. Any engineers know why studs are used on exhaust systems in general? Thanks, Mike They are cheaper. Helicoil is the standard repair. Back to top Jay Masino Guest Posted: Fri Apr 27, 2007 6:12 pm    Post subject: Re: Lycoming 0-320 Exhaust studs working loose Orval Fairbairn <orfairbairn (AT) earthlink (DOT) net> wrote: Quote: In article <q2aYh.4086$Ut6.331 (AT) newsread1 (DOT) news.pas.earthlink.net>, Mike Spera <mwspera (AT) earthlink (DOT) net> wrote: I have had intermittent problems with 0-320 exhaust studs working loose, usually with overhauled cylinders. I understand it if I have a stubborn nut to remove for a gasket change and the stud comes out with it. I SNIP Any engineers know why studs are used on exhaust systems in general? They are cheaper. Helicoil is the standard repair. In addition, there are 0.010 oversized studs available to tighten up the loose fit. It would be interesting to hear from someone with metalurgic experience. I wonder if stainless studs may not be as able to withstand the very high heat that these studs experience? --- Jay -- Jay Masino "Home is where My critters are" http://www.JayMasino.com http://www.OceanCityAirport.com http://www.oc-Adolfos.com Back to top nrp Guest Posted: Fri Apr 27, 2007 8:42 pm    Post subject: Re: Lycoming 0-320 Exhaust studs working loose Quote: From a mechanical engineering standpoint (and not necessarily aircraft!) Studs are generally used so that normal disassembly doesn't wear on a non-replaceable soft part (i.e. the cyl head). Studs are stronger for that reason. My personal preference with mechanical machine design is to not use lockwashers as they perform quite poorly (such as breaking) in a severe fatigue environment. The design of a threaded fastener joint really is best if there is no flex in the joint, and the length of the fastener is maximized and tightened to a preload sufficient to keep the assembly locked together - such as in a metal propeller- crankshaft interface. A marginal joint would be a cylinder base (where the flange might flex some) or of course an exhaust flange. Have you tried using high temerature antisieze paste? The stuff I've used for general purpose is called "Neva-Sieze" as I recall. It is good at keeping out corrosion even underwater and at high temperatures. Be careful tightening up a nut with this stuff under it as it is really slippery. I also use it on spark plugs but again be sure to torque it only to the low limit. Stainless has a bad tendency to gall with other metals and particularily with itself. In addition. Anti-seize should be always used with stainless for general work - although I don't know anything about how the turbine stuff is maintained. Helicoils are effective for getting good strong threads in soft materials, but once you wreck it, there is no additional fix without removing an unacceptable amount of parent material. I suspect that (and $) is the reason they are not used in exhaust attachments. Fortunately they do use them effectively in sparkplug holes as you know. Back to top David Lesher Guest Posted: Sun Apr 29, 2007 3:27 pm    Post subject: Re: Lycoming 0-320 Exhaust studs working loose Mike Spera <mwspera (AT) earthlink (DOT) net> writes: Quote: It is common for cylinder overhaulers to weld all the exhaust holes shut and then redrill and tap them as part of the overhaul process. I'm wondering how you fill up a stud hole with a welder. It strikes me as a non-trivial task... -- A host is a host from coast to coast.................wb8foz (AT) nrk (DOT) com & no one will talk to a host that's close........[v].(301) 56-LINUX Unless the host (that isn't close).........................pob 1433 is busy, hung or dead....................................20915-1433 Back to top Mike Spera Guest Posted: Sun Apr 29, 2007 5:52 pm    Post subject: Re: Lycoming 0-320 Exhaust studs working loose nrp wrote: Quote: From a mechanical engineering standpoint (and not necessarily aircraft!) Studs are generally used so that normal disassembly doesn't wear on a non-replaceable soft part (i.e. the cyl head). Studs are stronger for that reason. I figured that was the reason. However, these studs corrode instantly and make future removal difficult or impossible. So it would seem this method is not accomplishing that. Many use various penetrating oils to attempt to break the corroded nuts free. Although once you get the nut off, you may see that the stud has corroded sufficiently that it is unusable anyway. I have used a cutoff wheel on a Dremel to cut the siezed nut off a couple of times. ..stuff snipped Quote: Have you tried using high temerature antisieze paste? . more stuff snipped Never tried anti-sieze because I worry that the nuts would work loose. Never talked to an aircraft wrench who used it and/or reported success. Quote: .still more stuff snipped Helicoils are effective for getting good strong threads in soft materials, but once you wreck it, there is no additional fix without removing an unacceptable amount of parent material. I suspect that (and $) is the reason they are not used in exhaust attachments. Fortunately they do use them effectively in sparkplug holes as you know. It is common for cylinder overhaulers to weld all the exhaust holes shut and then redrill and tap them as part of the overhaul process. Quote: Thanks for the feedback. Mike Back to top Guest Posted: Mon Apr 30, 2007 6:12 am    Post subject: Re: Lycoming 0-320 Exhaust studs working loose The Lycoming studs have a slightly larger thread on the head end and are an interference fit. They must be double-nutted and driven all the way. If your studs are backing out they're likely the wrong studs or the cylinders have been overhauled too many times. We run six Lycs and have no trouble with studs coming out. Of course, these are all factory overhauls and Lycoming won't reuse cylinders. The proper nuts are plated with somethng better than the usual stuff and do not easily corrode. You might have plain AN coarse- thread nuts instead of the Lycoming nuts. Dan Back to top nrp Guest Posted: Thu May 03, 2007 6:12 am    Post subject: Re: Lycoming 0-320 Exhaust studs working loose Mike - I'm not an A&P but always used antiseize on my O-320E2D Lycoming exhaust studs and small muffler bolts for 30 years without any trouble with them loosening or backing out. Never even gave it a thought. I also used it on spark plugs (torquing to the low limit), Once I had a little bit dribble over the end that required the plug to be removed & washed to get it to fire. 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