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Xj750 seca head gasket

Discussion in 'XJ Technical Chat' started by Jeputera, Dec 29, 2020.

  1. Jeputera

    Jeputera Member

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    So my xj750 head gasket is leaking. Could this be causing an inflated resting RPM by letting additional air into the engine? Also I know on the xj550 you can remove the engine head without taking anything else off the bike, but its tight. Anyone successfully done this with xj750?
     
  2. Franz

    Franz Well-Known Member

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    Have you checked the valve clearances first and did a compression test? What evidence do you have the head gasket has failed? Cracked intake boots and carburettor throttle shaft seals can cause vaccum leaks. To remove the head you need to remove the exhaust system and carburettors. I am sure you can remove the head with the engine in the frame. But check the easy things first. If you check the shim clearances (replace shims as required or swap between cylinders if possible) and do a compression test. Then compare the readings to the Haynes manual or factory manual specs that can save you having to dismantle the top end of the engine when it might not be necessary.

    If you have (oil running down the motor) that is more likely caused by a leaking camshaft cover gasket, and or cam cover bolt rubber seals than the head gasket.
     
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  3. Jetfixer

    Jetfixer Well-Known Member

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    Is the gasket leaking oil? Or is it blowing air which would mean your losing compression. Franz posted at same time , agree with what he says!!!
     
  4. Jeputera

    Jeputera Member

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    So the bike is leaking oil onto the engine on the left side, right it looks exactly the right spot for the head Gasket. There is always oil on my left shoe and buildup on the left side of the engine just below the gasket. When i replaced tthe gasket on the 550, i managed to not take the carbs off, but I don't remember why I didn't need to. What is the reasoning for taking it off? Thanks in advance.
     
  5. Jeputera

    Jeputera Member

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    Ok, I'm still a bit new to all this. What are the camshaft covers?
     
  6. k-moe

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

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    The valve cover. The XJ750 uses a system consisting of a (usually) reuseable rubber gasket and rubber seals/bushings that provide the clamping force to keep the gasket oil-tight. As the rubber in the bushings age they can no longer provide the clamping force necessary to keep the gasket sealed. Oil WILL run down along the spark plug drains and onto the gap between the head and the jugs making it look like the head gasket is leaking.

    You have to check the valve clearnaces anyway (every 5,000 miles), so spring for a new gasket and doughnuts (the bolt seals/bushings).

    DO NOT under ANY curcumtances attempt to solve the problem by tightening the valve cover bolts. That WILL either strip the threads in the head, or crack the head (or if you're lucky it will only break one of the dummy cam caps that hold the inner part of the cover). The bolts are shouldered, and the shoulders contact the head when properly torqued.
     
    Last edited: Dec 29, 2020
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  7. Franz

    Franz Well-Known Member

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    Valve cover.

    Valve Cover.jpg
     
  8. Jeputera

    Jeputera Member

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    Pictures for details. Any thoughts? Looks like it could be the seal on the valve cover. Thanks for the tip, I will not tighten. Those sound like bad problems.
    20201229_185210.jpg 20201229_185158.jpg 20201229_185233.jpg
     
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  9. Franz

    Franz Well-Known Member

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    I think the valve cover gasket and or the bolt seals which hold the valve cover to the head are the most likely causes. Oil is on your cooling fins above the cylinder head cylinder barrel joint. If the head gasket was causing the oil to leak it would not run up towards the valve cover. Photographs 13 and 14 on this valve adjustment thread show the rubber seals and valve cover gasket we are referring too.

    https://xjbikes.com/forums/threads/airhead-valve-adjustment-with-pics.14827/

    The are not bad problems, new gaskets and seals should fix it. You can get the parts you need from Chacal on info@xj4ever if you wish. Taking the head off and replacing the head gasket is more involved and in my experience head gaskets don't fail often. Careful with those valve cover bolts though as k-moe stated. If you do not have a manual for your bike you should get one.
     
    Last edited: Dec 29, 2020
  10. Jeputera

    Jeputera Member

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  11. Minimutly

    Minimutly Well-Known Member

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    Perhaps you didn't get the message, in the US you have the best source of correct parts for your bike:-
    https://www.xjbikes.com/forums/forums/xj4ever-supporting-vendor.23/
    You will get the right bits and any advice needed. Also, as advised, you should check your valve clearances, and the kit of tools for this can be had here too. It could save you some heartache
     
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  12. Jeputera

    Jeputera Member

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    Well that's amazing. Thanks.
     
  13. Jetfixer

    Jetfixer Well-Known Member

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    Xj4ever parts list is extensive, yes a little hard to navigate , but his service is fantastic , to order send him an IM he will send you an order number and it is best thru paypal .
     
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  14. Jeputera

    Jeputera Member

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    Finally finishing today, thanks for all the help.
     
  15. Franz

    Franz Well-Known Member

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    Let us know the outcome when you run the engine hopefully the oil leak will be fixed.
     

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