evo engine, head gasket leak

Discussion in 'Softail Models' started by SE6A, May 16, 2016.

  1. SE6A

    SE6A Member

    my 1999 evo with around 42,000 miles on the clock has developed a leaking head gasket in the front cylinder, while I carry out all my own maintenance, I haven't had any engine issues. Apart from a torque wrench, and something to compress piston rings, how much of a job would this be?..i realise the barrel would have to come off and the gasket below replaced too.
  2. HDDon

    HDDon Experienced Member Contributor Retired Moderators

    If you have the manual and follow the pattern for tightening and you make sure that the surfaces are flat it sounds like you're good to go. Let us know if you have any questions once you start and be sure to let us know how the project goes. Wrench On!
  3. Jack Klarich

    Jack Klarich Expert Member

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  4. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    If you are gonna replace the head gasket, then it is worth doing a top end job anyway. That is a valve job on the heads, new rings, cylinders honed and replacing all the gaskets, o-rings and seals associated with the top end.

    Since one needs some special equipment to do the valve jobs and hone the cylinders (torque plates), I take those (heads and jugs) to an HD shop or good indy to have that stuff done. Everything else is very easy to do. Just make sure you replace ALL the gaskets with new ones. Please don't skimp on these (especially the base gaskets).

    I suspect that the base gasket on the cylinder that blew the head gasket was leaking, and that eventually allowed enough movement to blow the head gasket. That is what happened to my '91 EVO. The lesson I learned from that experience was to make sure I warmed up the engine sufficiently before rolling down the road and hitting the throttle! Makes a big difference.

    Here is my rebuild on the '91 Dyna when I had the rear head gasket blow:

    http://s731.photobucket.com/user/TQuentin1/slideshow/1991 Sturgis Rebuild - 1999


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  5. Jeff Klarich

    Jeff Klarich Well-Known Member Contributor

    +1 on TQ's post, at 42000 miles and as long as you're in there, freshening up the top end would give you many more worry free rides.
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  6. dolt

    dolt Senior Member Contributor

    SE6A, are you sure it is a head gasket that is leaking? If there is any doubt, a compression test will confirm. At 42K miles, I doubt the top end or the heads NEED rebuilding. However, once you replace the head gasket and before you put things back together, run a compression and leak down test; the results will tell you the condition of the top end and, if within service limits, will save you the time and expense of an overhaul that may not be needed.

    If you are careful, you do not have to remove the cylinder and replace the cylinder to case o-ring. If the head gasket is leaking, when you remove the head bolts the head should pop right off. As soon as the head is off, secure the cylinder to the case with some 1/2" PVC couplings to maintain the cylinder to case seal. If the head gasket is OEM, it may be stuck to the cylinder. Once secured, us a plastic gasket scraper to remove any remaining gasket pieces. Clean up the cylinder, blow any gasket pieces out of the cylinder, replace the head and torque to spec.

    Now you can run the compression and leak down test to evaluate whether or not the top end and/or heads need attention which I suspect they don't. Put her all back together and call it good. If the compression and/or leak down test show that top end needs attention, you can address the issues and the only wasted time and cost was the time it took to R/R just the head and the cost of the gasket. JMHO.

    Attached Files:

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  7. HDDon

    HDDon Experienced Member Contributor Retired Moderators

    I wasn't aware that the 1999 EVO had an O ring at the base. I don't doubt that if you're careful and the base gasket isn't leaking you might get away with just the top cyl. gasket but since you are already there and to be on the safe side why not go ahead and replace the base gasket too? JMHO
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  8. Jack Klarich

    Jack Klarich Expert Member

    Check the barrel studs for torque, if in doubt replace them also check the deck area for cracks
  9. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

    Are you sure it is the head gasket as the lower rocker cover gaskets are known to leak on the evo
    If the leak is above the exhaust port it is the lower rocker if it is below then it is the head gasket
    If it is the head gasket you will want to do the cylinder base gasket as well as once disturbed they tend to leak a service manual will give you all the info you need to do the work nothing particularly difficult about the job worst part will be scraping the old lower rocker and cylinder base gaskets off as both are thin paper gaskets and tend to stick to one side or the other
    I do not know about original head gaskets on the 99 but earlier heads required o rings around the cylinder dowels later replacement gaskets require the o rings to be removed
    A Clymer manual will give you more than sufficient info for this job and all measurements in metric and imperial my HD service manuals only have imperial measures so I tend to turn to the Clymer when I am doing any work

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  10. Jack Klarich

    Jack Klarich Expert Member

    Have a look here
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