A sketch would be post here the same as a picture and as discussed here in the past that is not a straight forward procedure. You can do a search on that subject of posting pictures and if you have the necessary computer skills and on line space have at it.
Otherwise if we can't figure this out without a sketch you could email it privately to me and I'll post it for you.
As for your problem I'm trying to picture this from a year ago when I rebuilt my engine.
The first and only thing that comes to mind is that the gasket behind the generator and tach drive is one gasket and should remain one gasket.
Many people have had success cutting them apart including my installation prior to the rebuild but after looking at how close the tack drive gear hole is I can't recommend that.
Are you replacing the whole gasket or just trying to piece it in under just the tach drive? If you trying to piece it in that is your problem.
Oil Leak at Generator
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
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Bruce Fenstermacher
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N73087
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Bruce Fenstermacher
- Posts: 10318
- Joined: Tue Apr 23, 2002 11:24 am
Dave, the area of relief actually occurs in order to prevent the leaking of oil, and that is why it is so important not to ever cut that gen/tach-drive mounting gasket.
A think coating of Permatex number No. 2 should work just fine on that gen/tach-housing mount gasket.
I'm going to gues that the diagnosis is close...but not exactly correct. For one thing, there is no pressure at that point unless your crankcase vent is blocked.
An alternative idea I'm thinking is that one of the thru-studs (if any) of your tach-drive or generator or starter-mount housing is leaking oil up the threads. The normal fix for that sort of leak is to use a collet to remove the stud and either install another stud (several sizes available within the same range) and/or to epoxy the stud back into the case. (Another fix of thru-studs is to clean them thoroughly with electronics cleaner and use Permatex to re-seal the threads and add an o-ring beneath the housing when it's reinstalled, but in this case I don't think that is workable.) But in every case, the stud base should be clean and the surrounding area lightly coated with Permatex before the gasket is also thinly coated and put in place.
Another idea I'm thinking about (but one you've probably eliminated) is the starter-clutch sliding pinion shaft. Those seals are notorious for leaking oil which invisibly soaks downward and appears to leak from the area we're discussing. That seal and gasket (starter/clutch seal/gskt) can leak and look just exactly like you are describing.
In any case, the relief area should remain clear/open and not be filled with sealant. It's actually designed pathway to relieve oil which drains from the tach-housing back to the sump.
A think coating of Permatex number No. 2 should work just fine on that gen/tach-housing mount gasket.
I'm going to gues that the diagnosis is close...but not exactly correct. For one thing, there is no pressure at that point unless your crankcase vent is blocked.
An alternative idea I'm thinking is that one of the thru-studs (if any) of your tach-drive or generator or starter-mount housing is leaking oil up the threads. The normal fix for that sort of leak is to use a collet to remove the stud and either install another stud (several sizes available within the same range) and/or to epoxy the stud back into the case. (Another fix of thru-studs is to clean them thoroughly with electronics cleaner and use Permatex to re-seal the threads and add an o-ring beneath the housing when it's reinstalled, but in this case I don't think that is workable.) But in every case, the stud base should be clean and the surrounding area lightly coated with Permatex before the gasket is also thinly coated and put in place.
Another idea I'm thinking about (but one you've probably eliminated) is the starter-clutch sliding pinion shaft. Those seals are notorious for leaking oil which invisibly soaks downward and appears to leak from the area we're discussing. That seal and gasket (starter/clutch seal/gskt) can leak and look just exactly like you are describing.
In any case, the relief area should remain clear/open and not be filled with sealant. It's actually designed pathway to relieve oil which drains from the tach-housing back to the sump.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
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N73087
It's not the starter, I have a SkyTec.
I have cleaned the case with mineral spirits and air pressure, and allowed it to dry overnight. I sprayed it up with powder, and ran it for just a minute. I am confident that the leak is not coming from anywhere else.
I even went so far as to remove the accessory case withe the tach drive and generator attached. I did a careful disassembly, which is how I found the "unglued" area. None of the studs are faulty.
The glob of permatex is sounding more and more likely. (More is not always better.)
In the back of my head, I am starting to think that maybe the end of the shaft is protruding above the face of the case. That would keep the generator from bottoming. When I get back to the airport, I need to re-examine the old gasket to see if the shaft left a dent.
The next time I take the generator off I will put a straight edge across the shaft end and see what I can feel.
I only want to take the generator off one more time.
I have cleaned the case with mineral spirits and air pressure, and allowed it to dry overnight. I sprayed it up with powder, and ran it for just a minute. I am confident that the leak is not coming from anywhere else.
I even went so far as to remove the accessory case withe the tach drive and generator attached. I did a careful disassembly, which is how I found the "unglued" area. None of the studs are faulty.
The glob of permatex is sounding more and more likely. (More is not always better.)
In the back of my head, I am starting to think that maybe the end of the shaft is protruding above the face of the case. That would keep the generator from bottoming. When I get back to the airport, I need to re-examine the old gasket to see if the shaft left a dent.
The next time I take the generator off I will put a straight edge across the shaft end and see what I can feel.
I only want to take the generator off one more time.
very bad idea. If that stud ever needs to be pulled it'll probably ruin the accessory case.gahorn wrote: ... to epoxy the stud back into the case.
I've had impossible-to-cure access case leaks that were only fixed by pulling the access case and sealing up the (very well cleaned) stud holes w/ RTV. I believe the oil's not leaking past the stud threads but rather thru cracks in the mag case around the threads. These open up from overtorquing the studs or just the stress of multiple mount/unmounts of accessories. No need to pull the studs to put sealant on the threads, that just wears out the case threads and you're one step closer to needing oversize studs.
as for precut gaskets, Permatex should not be necessary to get a good seal if both surfaces are properly prepared. The only thing I use on them is a light coating of DC4 on both sides so it all comes apart cleanly.
The "epoxy" fix was/is recommended by many engine shops. Loctite #242 epoxy does not prevent future removal of studs and is specifically designed for the purpose. They un-thread just fine.
RTV is not compatible with oil and should not be used to assemble engines. Perhaps you meant Hylomar?
(TCM manual X30013 recommends "National Oil Seal Compound" however.)
RTV is not compatible with oil and should not be used to assemble engines. Perhaps you meant Hylomar?
(TCM manual X30013 recommends "National Oil Seal Compound" however.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
Because you question whether any of them have made that recommendation to me? (I don't especially feel compelled to respond to that kind of challenge...and I'd be disappointed if that were the case.) Or for some other purpose? (I haven't asked permission to post their names on the web in association with it ...only been my experience that's how they've repaired leaking studs in my IO-470's on my Baron, the GTSIO 520 in a client's Cessna 414A, and my IO-520 in my 206 (Page-AvJet, a genuine Cessna Service Center did that one.) Two of them are certified repair stations tho', and one is a pretty well-known engine overhauler/ modification center near Waco, TX. )
I repaired the left front engine mount leak on my O-300 with nothing more than Permatex No2 and an O-ring.
I repaired the left front engine mount leak on my O-300 with nothing more than Permatex No2 and an O-ring.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
because I doubt whether anybody that knew what they were doing would epoxy a steel stud into a magnesium case. I can only imagine doing that after exhausting all possibilities of oversize studs and "helicoils". I *would* expect them to use a threadlocking compound on any stud installation, not just as a repair to cure a leak.
because I'd hate to have somebody reading your post epoxy a stud into their accessory case because you confused threadlocker and epoxy.
because you've never had a problem naming shops on this board before.
paul
because I'd hate to have somebody reading your post epoxy a stud into their accessory case because you confused threadlocker and epoxy.
because you've never had a problem naming shops on this board before.
paul
Paul, your perception is incorrect. I usually mention shops by name/number whenever I"ve been asked for a reference and when that provider/shop has been contacted and permission obtained for the reference (such as the Ajax mention I gave earlier. In that instance, I visited with Ajax's owner and queried him as to whether or not they were certified to make certain repairs, and asked if I could give out contact info, before I did so.) Or, in some cases, I have mirrored information which appears in one of two aviation directories I have already promoting a company's products and services. I wouldn't ordinarily refer to a company if their own literature didn't specifically promote a particular product or service, and/or if I wasn't specifically sending you to one of them for the service being discussed. I don't think you were looking for a place to get your studs sealed. (And none of the engine shops I was thinking of advertise their "stud service".)
Epoxy is a term that describes lots of different adhesives, sealants, and coatings. " Most conventional unmodified epoxy resins are produced from epichlorohydrin (chloropropylene oxide) and bisphenol A . The other types of epoxy resins are phenoxy resins, novolac resins, and cycloaliphatic resins." *
Like the term "oil", it is not indicative of any particular brand/type product. (We put oil in engines to lubricate and cool. We also use oil to heat/cook with. We use it to machine steel parts or cut threads also. The point is that one should use the proper product for the specific purpose intended.) Just because an epoxy was used to seal a stud...doesn't imply it was JB-Weld.
Your concern with my use of the term "epoxy" (the stuff many "threadlockers" is made of) didn't cause concern about your use of the term "RTV"? RTV is most commonly used to describe Room Temperature Vulcanizing Silicone-Rubber, which should never be used internally on engines because it will delaminate when in contact with gasoline or oil, and besides resulting in a leak also risks clogging vital oil passages. While threadlocking compounds may be used on studs, I wouldn't "expect" it to be used as it is not prescribed in the engine overhaul/repair manual. By the way, "Helicoil" thread repair schemes are notorious for seeping oil-leaks when used in thru-studs. One can virtually guarantee that the stud will require sealant.) In any case, we shouldn't be picking on each other, because I'll bet you and I are both saying the same thing. Use the proper product for the specific purpose.
PS * Online Dictionary.
More useless info about epoxies:
http://www.dow.com/webapps/lit/litorder ... f&pdf=true
Epoxy is a term that describes lots of different adhesives, sealants, and coatings. " Most conventional unmodified epoxy resins are produced from epichlorohydrin (chloropropylene oxide) and bisphenol A . The other types of epoxy resins are phenoxy resins, novolac resins, and cycloaliphatic resins." *
Like the term "oil", it is not indicative of any particular brand/type product. (We put oil in engines to lubricate and cool. We also use oil to heat/cook with. We use it to machine steel parts or cut threads also. The point is that one should use the proper product for the specific purpose intended.) Just because an epoxy was used to seal a stud...doesn't imply it was JB-Weld.
Your concern with my use of the term "epoxy" (the stuff many "threadlockers" is made of) didn't cause concern about your use of the term "RTV"? RTV is most commonly used to describe Room Temperature Vulcanizing Silicone-Rubber, which should never be used internally on engines because it will delaminate when in contact with gasoline or oil, and besides resulting in a leak also risks clogging vital oil passages. While threadlocking compounds may be used on studs, I wouldn't "expect" it to be used as it is not prescribed in the engine overhaul/repair manual. By the way, "Helicoil" thread repair schemes are notorious for seeping oil-leaks when used in thru-studs. One can virtually guarantee that the stud will require sealant.) In any case, we shouldn't be picking on each other, because I'll bet you and I are both saying the same thing. Use the proper product for the specific purpose.
PS * Online Dictionary.
More useless info about epoxies:
http://www.dow.com/webapps/lit/litorder ... f&pdf=true
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
you said Locktite 242. The term "epoxy" doesn't occur in the Technical Data Sheet for that product, http://tds.loctite.com/tds5/docs/242-EN.PDF, nor for it's high-strength brother 262. Since Loctite is just about synonymous with threadlock, which threadlockers *are* made of epoxy?gahorn wrote:Just because an epoxy was used to seal a stud... my use of the term "epoxy" (the stuff many "threadlockers" is made of)
yep, I meant what I said. In general I would not recommend RTV inside an engine but it works very well for this application. Ever tried to get RTV out of the bottom of a threaded blind hole? The key, as always, is a properly prepared substrate.gahorn wrote:your use of the term "RTV"
huh? By definition a thru-stud doesn't have any threads in the case.gahorn wrote:By the way, "Helicoil" thread repair schemes are notorious for seeping oil-leaks when used in thru-studs
Maybe. I initially commented that your recommendation to epoxy in studs was a bad idea. All the rest of this bickering is you defending that statement instead of just admitting you were thinking of something else.gahorn wrote:In any case, we shouldn't be picking on each other, because I'll bet you and I are both saying the same thing.
Paul, I'm merely trying to help another member repair his leak with what I believe is an acceptable method. I'm neither needful of winning your "bickering" contest nor even wishing to be involved in it. I'm not failing to "admit" anything and your comment to that effect doesn't make it so. I made a recommendation way back in November of 2004 in this same discussion if you care to look. I mentioned the word "epoxy" at that time and you didn't say anything. I also made a specific recommendation as to a particular product to use at that time and my recommendation has not changed.*
If you truly wish to hold my feet to the fire regarding this particular discussion, then you should quite plainly state your postion/concurrance with the mention of Loctite 242...or offer another product name. I used the generic term "epoxy" because that's what many such products are commonly called. I came back with that particular brand-name in order to be more specific following your "bad idea" which I felt was harsh. Without "naming names" I merely used the terminology many shops in my region use to describe the process. (And any mechanic long in the business of twisting wrenches has experience using epoxies to repair oil leaks. But Paul is correct in that most industrial epoxies are pretty permanent and can make future removal of a stud difficult.) It's sounding less and less like that's the problem in this particular situation.
A "thru stud" is any stud which passes completely thru the case and into the next compartment...threaded or not. In some situations, it may be an unthreaded stud...as some of the studs in the accessory-case pass thru it without threading into the accy-case itself.....BUT...(if you wish to be as exacting in terminology as you seem to demand of me in this instance)...if you are speaking of that type of thru-stud (which does not thread into the accy-case) then exactly what do you mean by insisting upon the use of a threadlocker on a non-threaded stud?
I'm sorry to say I think you just mean to be argumentive and confrontational and that's not a friendly thing.
I strongly disagree with ANY use of RTV in engines where it might contact oil or gasoline. (And digging RTV out of a blind hole such as you mention has what to do with this discussion? A blind-stud, since it does not protrude into an oil-filled cavity, will not leak oil along it's threads and will not require sealing.
To All: using sealant of any kind in a blind hole can cause case cracking and/or thread damage because of the hydraulic-lock it can create when the stud is screwed down into the hole and it runs into the resistance of the trapped sealant. This is another case of "if a little is good .. a lot is not necessarily better". Don't use common RTV in places it will contact oil/gasoline unless the product especially advises it's use in such locations. RTV refers to a synthetic rubber type product whose curing process occurs without a catalyst, at "Room Temperature"...as opposed to a product such as "epoxy" which requires two parts (one of which is a catalyst) or an anerobic product (cures in the absence of oxygen) such as many Loctite-branded products. (There may be particular products out there somewhere that go under the moniker of "RTV" that may allow such use in the presence of oil, but I'm not aware of any. I've seen a GE product that claims to be a "gasket maker" but I don't believe it's intended for aviation use and I don't believe it's intended for use in oil or gasoline. There is a product (similar to but not the same as RTV) which comes in a tube and made by/for Rolls-Royce called "Hylomar" which is specifically approved for aircraft engines, but it's not common and it's not commonly called "RTV".
*(Threadlockers do not usually claim to seal threaded fasteners against leaks. Loctite does not make that claim either. Threadlockers are designed to prevent the loss of torque on a fastener, usually due to vibration or corrosion. Permatex No. 2 or National Oil Seal Compound are still my favorite fixes for sealing threaded studs.)
If you truly wish to hold my feet to the fire regarding this particular discussion, then you should quite plainly state your postion/concurrance with the mention of Loctite 242...or offer another product name. I used the generic term "epoxy" because that's what many such products are commonly called. I came back with that particular brand-name in order to be more specific following your "bad idea" which I felt was harsh. Without "naming names" I merely used the terminology many shops in my region use to describe the process. (And any mechanic long in the business of twisting wrenches has experience using epoxies to repair oil leaks. But Paul is correct in that most industrial epoxies are pretty permanent and can make future removal of a stud difficult.) It's sounding less and less like that's the problem in this particular situation.
A "thru stud" is any stud which passes completely thru the case and into the next compartment...threaded or not. In some situations, it may be an unthreaded stud...as some of the studs in the accessory-case pass thru it without threading into the accy-case itself.....BUT...(if you wish to be as exacting in terminology as you seem to demand of me in this instance)...if you are speaking of that type of thru-stud (which does not thread into the accy-case) then exactly what do you mean by insisting upon the use of a threadlocker on a non-threaded stud?
I'm sorry to say I think you just mean to be argumentive and confrontational and that's not a friendly thing.
I strongly disagree with ANY use of RTV in engines where it might contact oil or gasoline. (And digging RTV out of a blind hole such as you mention has what to do with this discussion? A blind-stud, since it does not protrude into an oil-filled cavity, will not leak oil along it's threads and will not require sealing.
To All: using sealant of any kind in a blind hole can cause case cracking and/or thread damage because of the hydraulic-lock it can create when the stud is screwed down into the hole and it runs into the resistance of the trapped sealant. This is another case of "if a little is good .. a lot is not necessarily better". Don't use common RTV in places it will contact oil/gasoline unless the product especially advises it's use in such locations. RTV refers to a synthetic rubber type product whose curing process occurs without a catalyst, at "Room Temperature"...as opposed to a product such as "epoxy" which requires two parts (one of which is a catalyst) or an anerobic product (cures in the absence of oxygen) such as many Loctite-branded products. (There may be particular products out there somewhere that go under the moniker of "RTV" that may allow such use in the presence of oil, but I'm not aware of any. I've seen a GE product that claims to be a "gasket maker" but I don't believe it's intended for aviation use and I don't believe it's intended for use in oil or gasoline. There is a product (similar to but not the same as RTV) which comes in a tube and made by/for Rolls-Royce called "Hylomar" which is specifically approved for aircraft engines, but it's not common and it's not commonly called "RTV".
*(Threadlockers do not usually claim to seal threaded fasteners against leaks. Loctite does not make that claim either. Threadlockers are designed to prevent the loss of torque on a fastener, usually due to vibration or corrosion. Permatex No. 2 or National Oil Seal Compound are still my favorite fixes for sealing threaded studs.)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
there's been a few things you've said on this board that've made me cringe <g>. Mostly I just let them slide, not having the time and energy for one of these tete-a-tete's with you. Sometimes it takes a second mention for me to take the bait.gahorn wrote:I mentioned the word "epoxy" at that time and you didn't say anything.
lest I leave the wrong impression, 95% of what you say here is dead on correct, and I really do appreciate your taking the time to share it.
thought I was clear; I use Loctite 242 on almost every stud I install.gahorn wrote:you should quite plainly state your postion/concurrance with the mention of Loctite 242
however, and BACK ON TOPIC, the point of my original post was that there are "stud leaks" out there that don't appear to be leaking past the threads, but thru microcracks in the stressed case material beyond the threads. *No* type of sealant applied to the threads will cure this. It can be cured by sealing the bottom of the threaded hole the stud's installed in.
but what to use for sealant? Permatex, Nat'l Oil Seal Compound, etc are all meant to be used between mating surfaces - I don't think they'd work nor stay in place. I do know a well-placed dab of RTV will seal it and looks like it'll stay.
the foregoing is only my opinion, and specifically about the magnesium accessory case as found on our C-145/O-300's.
that's pretty silly. Where'd I give you that impression?gahorn wrote:exactly what do you mean by insisting upon the use of a threadlocker on a non-threaded stud?
was my description that bad <g>? It's a through hole but the stud's already installed, "blinding" the hole. You're sealing the bottom of a blind threaded hole.gahorn wrote:digging RTV out of a blind hole such as you mention has what to do with this discussion?
I think this'll be my last post in this thread. You get the last word this time George <g>.
- paul