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My turn to ask for help.

Discussion in 'XJ Technical Chat' started by k-moe, Nov 22, 2020.

  1. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    So....My oil leak has returned.
    Background:'82 XJ 750 Seca that I refurbished 8 years ago (oil cooler has been fitted), and which developed a leaky base gasket 2 years ago.
    I redid the gaskets on the top end again once the leak became bothersome (including the valve cover doughnuts).
    The leak is not present at in-town speeds, but is very evident at highway/freeway speeds.

    My thoughts are a blocked breather, or that the valve cover is still not sealing properly.
    I do not see evidence of oil leaking from the base gasket, or the cam feeds. It's running along the head gasket line, but the head gasket is new as of 2 years ago (the bike has mostly sat since), and the head nuts are at the specified torque.

    More background: The cases are from a Maxim, and the studs are what came with the cases. It may be that they are beyond their stretch limit, but I"m not convinced of that at this time (could be wrong though).

    She runs strong with no smoke.
    Suggestions are welcome. I'd prefer to not limit my leak-free riding to in-town.
     
  2. Toomanybikes

    Toomanybikes Well-Known Member

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    Had a problem with a 750 maxim a customer dropped off.
    Small crack in cam chain tunnel at front of cylinders just where it meets the main cylinder area at the head gasket. PO had over torqued the 6mm nut at the front to stop a leak.
     
  3. Franz

    Franz Well-Known Member

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    If you clean the oil and put the bike on the side stand and start the engine as oil cannot run uphill is may be easier to locate the source of the leak. Then again if it is only happening at highway speeds that won't work.
     
  4. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Yep. That's the problem. By the time I can see the leak the oil is all over the front of the head.
    Hmm.....maybe. I don't recall overtorquing that nut though. And the leak is above that area. Worth looking into though. Thanks.
     
  5. Franz

    Franz Well-Known Member

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    Perhaps tightening the cam cover bolt nuts slightly will stop it?
     
  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    They are already torqued to spec. Tightening them more will only result in damage.
    I'll be taking the breather apart as soon as weather and time permit (Likely Wednesday).
    It may be that the mating surface for the valve cover gasket is nicked somewhere that I missed.
    One thing at a time.
    The only big change I made prior to the original leak (which was solved) was to fit the correct oil cooler instead of the one from a 650 that I had been running for several years. I did pressure test the cooler before fitting it and found no leaks. I do wish that I had eyes to see the front of the engine while running on the freeway.
     
  7. Franz

    Franz Well-Known Member

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    Yes you don't want them damaged. It will be something simple, when was the last time you checked the breather? I did the breather on my engine but that was because I was rebuilding it.
     
  8. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    I checked it last when I swapped the cases, so about 5 years ago.

    I do wonder about the possability of a crack in the head. If the breather ends up being a dead-end I'll invest in some flouescent dye.
    She was leak-free for a long time. This is so annoying.
     
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  9. Franz

    Franz Well-Known Member

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    Hopefully it is the breather.
     
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  10. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    It would be very nice if it was. I'd hate to have to to pull the head again to have it resurfaced.
    She's been a very reliable machine sine I did the recomissioning, and suits me perfectly.
     
  11. Jetfixer

    Jetfixer Well-Known Member

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    You can try to spread talcum powder around base run engine you might see where the leak is .
     
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  12. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Will do. I haven't had many rides out of the city since getting her back home. I am certian the the leak is not at the base gasket.
     
  13. Franz

    Franz Well-Known Member

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    Yes as you say check the easy things first. I know CB750's SOHC engines can have head gasket problems, I had an oil leak from mine and replaced the gasket. I have not had that problem with my XJ. Hope the head is not cracked.
     
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  14. Toomanybikes

    Toomanybikes Well-Known Member

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    The other way to find leaks is with spray deodorant after cleaning the engine and when it’s dry and cold spray liberally and fire her up and use a fan to keep thinks cool and the deodorant will go black the second oil appears.. it could be an o ring around one of the cylinder head locating dowels.
     
    Last edited: Nov 22, 2020
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  15. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    I first suspect the valve cover gasket
     
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  16. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    I am leaning in that direction. There would be more oil splash off of the cams at higher RPMs. I won't be able to do any checking until Friday. Rain is foreacst for all day tomorrow.
     
    Last edited: Nov 25, 2020
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  17. JCH

    JCH Active Member

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    If the gasket checks out okay and the breather system is clear you may want to to check for too high of crankcase pressure, CLT test for worn engine rings causing too much pressure entering the crankcase, hopefully this isn't the issue and would be the worst case outcome.
     
  18. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    Will do.
    That is unlikely as I measured the rings and bores when I did the refurb, and again when I changed the base gasket. They were still well in-spec, but that doesn't preclude the possability of a failure.
     
  19. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    I finally managed to get other projects out of the way and started to look into things further.
    The breather is clear.
    I pulled the valve cover and found..........nothing out of the norm.
    There may be a spot near the front right where the cover is slightly warped since I found oil under the gasket there as soon a I lifted it up.
    I didn't take the gasket off to check since it's glued to the cover and I don't have a spare on hand (at least I can't find the box it's in if I do have one).
    I cleaned it all up with alcohol and put a light coat of fresh oil on the head mating surface, followed by an extremely thin coat of RTV all around (not my first choice, but it will do for now). She'll sit overnight and I'll go for a ride tomorrow. IF the leak is gone then I know what needs to be done at the next valve clearance check. A glass plate and some grit to level out the valve cover (if it's not warped too badly).
     
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  20. hogfiddles

    hogfiddles XJ-Wizard, Host-Central NY Carb Clinic Moderator Premium Member

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    I would not had put oil on the mating head. If the valve cover is leaking, you’re ALREADY GETTING oil on the mating surface. You’re trying to STOP getting oil on the mating surfaces. I would pull it back off, go over the gasket surface and the metal face and clean it with brake cleaner or some other agent that will quickly degrease and dry. Then put a narrow bead of rtv around the whole mating face. Also use a very fine machinist file and just lightly kiss the corners by the ‘half moon’s to eliminate any sharp burrs right on the corners here the faces drop into the curves.

    I suspect the gasket has gotten some micro cracks in it, or the corners by the ‘half moons’ have cut into the gasket and you’re getting leaks there. That is an all-too-common issue right there,
     

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