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Thread: Oil Leak on C85

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    cubman's Avatar
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    Oil Leak on C85

    I am struggling to locate the source of an oil leak on my PA11. It is a C85-12f that was rebuilt last year. It appears the oil is coming from the rear (accessory case) area or perhaps the kidney tank. Push rod tubes, prop seal, etc. look dry. Has anyone ever used one of the UV oil leak detection kits to locate a leak?

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    d.grimm's Avatar
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    I washed mine clean, ran it for a few minutes and dusted baby powder over the suspected areas.
    worked and cleaned off remaining powder with compressed air.
    Dave
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    Does your C85 have an O200 crank? And if so was the case drilled for a through bolt to strengthen it? If so the drilling may have nicked the oil vein in the case and you now have a leak from that through bolt on one side of the case under a cylinder. If that leak is too bad to live with you'll have to replace the case with an O200 case.
    You can't get there from here. You have to go over yonder and start from there.

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    Mine leaked a bit. At 50 hours I re-torqued all case and pan bolts, as well as cylinder nuts. Stopped it. Also watch that plate behind #2 - three nuts. It has pressure oil under it.

    Did not know we needed a through bolt. My STC was from 1996, although I assembled the engine in 2017.

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    Quote Originally Posted by cubman View Post
    I am struggling to locate the source of an oil leak on my PA11. It is a C85-12f that was rebuilt last year. It appears the oil is coming from the rear (accessory case) area or perhaps the kidney tank. Push rod tubes, prop seal, etc. look dry. Has anyone ever used one of the UV oil leak detection kits to locate a leak?
    As previously stated, wash it clean, dust with foot powder, run for a few minutes and check again. The the powder will absorb the oil at the leak to show where it's at. It's not unusual for the oil tank on the C-85 to crack just below the mounting flange. But could also be a gasket under a mag, seal or gasket on the tach drive, gasket on the starter mount, seal or gasket on the generator/alternator or even that gasket under the accessory cover. I've seen people change the generator and cut the gasket that is for the generator and the tach drive so they would only have to replace the generator half of the gasket. The back side of that gasket at the seam between the generator and tach drive covers the end of the counter shaft of the oil pump and will leak like crazy if one tries to split the gasket. Generally speaking, it's not hard to locate the leak, and once found, not hard to fix.

    It's also not unusual to find the tack drive seal or the generator seal to be installed backwards. The inner lip on those two seals should face towards the engine.

    -Cub builder
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    I'd check gaskets if you have any superior airparts. This one is on a valve cover, but have seen several lately that had shrunk and split on different engines and components.All of them had been on recent overhauls. Chasing oil leaks sucks.
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    Quote Originally Posted by Another Cubber View Post
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    I'd check gaskets if you have any superior airparts. This one is on a valve cover, but have seen several lately that had shrunk and split on different engines and components.All of them had been on recent overhauls. Chasing oil leaks sucks.
    I replaced my valve cover gaskets with silicone ones last year, the port side perfect and no leaks, the starboard side still spatters oil over the side cowl........ hmmmmmmmmm


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    The ones i have had trouble with are the red paper type. Have found the trick with the silicone, or any rubber for that matter, to be clean dry surfaces. As in cleaned with mek or acetone. Then precisely torque them and not over them
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    Clean and dry with the silicone ones. If you use cork or paper gaskets, they need to be glued to the valve cover with 3M 1300 before installation. It's a trick I learned years ago, working with valve covers on cars.

    Web
    Life's tough . . . wear a cup.
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    I have some 1/8" thick cork from 1966 that seals perfectly. My latest engine got the red silicones, and they don't leak either. You need a cheapie expander tool to seal the pushrod housings.

    Do the torque recheck first.
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    cubman's Avatar
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    Thanks to all for your suggestions. This is one of the reasons SC.org is so great!

    Here's the latest. Everything forward is dry (prop seal, cylinders, case, etc.) Kidney tank ok too. Source of the leak appears around/near the alternator. I replaced a heavy generator when we rebuilt the engine. Just cleaned FWF again and will run it for a few minutes to try and isolate the exact source. Unfortunately, won't be able to get to work on it for a few day. I'll post the what is found.

    Cubman

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    An old white T-shirt works also. Rip it into 1/2" strips and tie them around suspected areas. The baby powder works but makes a mess and sometimes picks up oil blown around.

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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    When you build up an engine, check torque on every fastener, then re-check the next day! Itís amazing how much the torque will relax overnight after setting the torque the previous day.


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    Quote Originally Posted by cubdriver2 View Post
    An old white T-shirt works also. Rip it into 1/2" strips and tie them around suspected areas. The baby powder works but makes a mess and sometimes picks up oil blown around.

    Glenn
    Sounds like a great idea and Iím going to try it as sounds a lot less messy than the talc! But is there a risk of fire? or is this suggested for shortish ground runs?


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    Wrap it around things and tie it, then go fly

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

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    Quote Originally Posted by dgapilot View Post
    When you build up an engine, check torque on every fastener, then re-check the next day! Itís amazing how much the torque will relax overnight after setting the torque the previous day.


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    I came back today via the bicycle shop and bought a 25 inch/lb torque wrench


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    I think the smallest fasteners need 100 in-lbs. I will check. The cylinders need 35 and 42 foot lbs. a good Snap-On torque wrench is called for there.

    Do the oil kidney by feel - by the time you finish all the case nuts, you will have the "feel" necessary.
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    Checked and retorqued all the valve cover bolts to 20 pound inches, test flew for 3 short flights and greatly reduced spatter


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    Seriously - after an engine rebuild, a retorque is recommended by most good rebuilders after a few hours at operating temperature. Rocker boxes,while prone to leaks, are way down on the list.

    Please don't hammer me with the difference between rebuilt and overhauled. I should have used "assembled".
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    As noted oil free surfaces for silicone gaskets are important (they'll leak). Once they leak cleaning is necessary before retightening. Eventually cork or fiber compresses and metal valve covers can deform and bell out at the fastener holes so check that surface that for flatness.

    Gary
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    Quote Originally Posted by BC12D-4-85 View Post
    As noted oil free surfaces for silicone gaskets are important (they'll leak). Once they leak cleaning is necessary before retightening. Eventually cork or fiber compresses and metal valve covers can deform and bell out at the fastener holes so check that surface that for flatness.

    Gary
    Yes, my plan was to try a retorque with my new torque wrench (which worked beautifully!! - Bike Hut 2-20 NM) and test and if still spattering remove the covers and silicone gaskets and clean and refit, but just tightening to the recommended 20 foot inches has made enough of a difference, so no need to remove and refit, but will continue to monitor and r&r if the spatter increases again


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    I had success finding an oil leak on my c85-12 using the uv leak detector and black light. I had cleaned, ran, cleaned flew, cleaned, retorqued all with no luck. When I used the leak detector I found a small crack at the weld where the oil sump is welded to the mounting flange. I got the detection fluid at the local Chevy dealership and they were kind enough to let me borrow their black light. Good luck
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    Here's the latest on my oil leak. Took the alternator off and replaced it with a plate. Flew it for 15 minutes yesterday. Unfortunately, removing the alternator didn’t resolve the oil leak. Now looks like it might might be coming from up around the tach cable or below the left magneto.


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    theres a washer under the tach cable adapter, people use a brass crush washer there and thats not whats suppose to be there, it uses a solid brass washer, a continental part number. and remember if you mess with that tach adapter the threads are backwards. or maybe just a mag gasket?

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    cubman's Avatar
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    I determined the leak was coming from around the alternator, tach or maybe right mag by using the UV leak detector. Replaced the alternator with a plate - still leaked. Replaced the gasket and added washers to the tach housing (maybe the nut ran out of travel before getting tight against the gasket). Flew for an hour this morning - no leaks.
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    Quote Originally Posted by cubman View Post
    I determined the leak was coming from around the alternator, tach or maybe right mag by using the UV leak detector. Replaced the alternator with a plate - still leaked. Replaced the gasket and added washers to the tach housing (maybe the nut ran out of travel before getting tight against the gasket). Flew for an hour this morning - no leaks.
    HOOOORRRRAAAYYYYYYYY!!!!!! Well done!!!!!!

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    Quote Originally Posted by Philly5G View Post
    Yes, my plan was to try a retorque with my new torque wrench (which worked beautifully!! - Bike Hut 2-20 NM) and test and if still spattering remove the covers and silicone gaskets and clean and refit, but just tightening to the recommended 20 foot inches has made enough of a difference, so no need to remove and refit, but will continue to monitor and r&r if the spatter increases again


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    I did a 90 minute flight on Sunday and when I opened the cowling, there was loads of oil spatter again I checked the torque again and ALL the bolts had loosened off significantly (torqued originally to 20 inch/pounds). I took some advice, got some new star type washers that are supposed to stop bolts coming loose, removed all the bolts, covers and silicon gaskets. Washed and dried the metal parts and silicon with 100LL petrol and then refitted and retorqued the bolts to 25 inch/pounds, using JUST the star washers.......

    Should hopefully be flying this weekend and I can't wait to see the lovely clean cowlings when I've finished

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    I have a J3 on floats in Alaska. I've been using SAE 50. What oil is recommended for C85. Or Where might I find an Owners Manual for a C85. Thanks.

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    You can't get there from here. You have to go over yonder and start from there.

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    Quote Originally Posted by Tadams View Post
    I have a J3 on floats in Alaska. I've been using SAE 50. What oil is recommended for C85. Or Where might I find an Owners Manual for a C85. Thanks.
    Send me a personal mail here with yours attached and I'll directly forward a PDF copy of mine. Not starting an oil thread but what you use is ok but the manual also approves multi-viscosity options. I'd post the 3.8MB manual but he quality that gets posted is often poor and uses up bandwidth.

    Gary

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