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  1. #1
    speeder's Avatar
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    head cracking prevention hypotheses

    Our riding group in canada has 4 2014 to 2016 fx svho skis. 3 of them had head cracks. the 4th one is in the dealer now for a diagnosis of water in oil which could be the 4th head cracked. we ride a lot in the fraser river around the vancouver area.

    we sometimes ride in winter when the water can get down to 5 C (40F). summer temps get up to about 20 C (68F).

    One theory is that when the engine is hot and the thermostat opens, the cold water hits the hot cylinder head and after many of these cycles, a crack forms on the exhaust side (all of them have cracked on the exhaust side between the cylinders around the head bolt).

    If this is the case, would a possible solution be to install the riva thermostat delete kit? theory being that the engine would be constantly cooled so there isn't a sudden shock of cold water once the engine is already hot.

    https://www.4-tecperformance.com/ind...oducts_id=3396

    there hasn't been much info/experience here about this kit. is it only for modded skis? racing? Is it ok for rec skier?

    any comments/ideas are appreciated!


  2. #2
    i cant say for sure but i like the ideal...

  3. #3
    big john's Avatar
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    IMO the most likely cause is shutting the motor off after a hard hot run without allowing it to cool off by letting it idle around for a few minutes, or restarting a hot motor and blasting it with cold water. water does circulate thru the head before the thermostat opens, but when it reaches temp it allows maximum water flow to cool the motor. ive always idled/low rpm for a couple minutes to bring the engines down after a hot run, almost 300 hours between two ski and no cracked heads. remember that the motor drains out when its not running and that head is hot af with nothing in it to absorb the heat. everyone know not to pour cold water into a hot engine


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    SplishSplash's Avatar
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    As I stated in the other thread on heads cracking. Are the core plugs between the sparkplugs aluminum or some other metal?
    If they are a dissimilar metal, that may be why they crack with temperature changes.

    Seen it on many automotive 16 valve dohc heads and that was the cause. Changed to aluminum ones and no more heads cracked.


  5. #5
    speeder's Avatar
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    the core plugs (those big ones in the middle of the head between the cylinders) are not steel - checked with a magnet. the head bolts are not aluminum.
    Last edited by speeder; 02-13-2020 at 07:16 PM.

  6. #6
    SplishSplash's Avatar
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    Quote Originally Posted by speeder View Post
    the core plugs (those big ones in the middle of the head between the cylinders) are not steel - checked with a magnet. the head bolts are not aluminum.
    Could be stainless steel, as it's non magnetic and head bolts are not tight in the head and are of far less diameter than the core inserts.

  7. #7
    speeder's Avatar
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    Quote Originally Posted by big john View Post
    IMO the most likely cause is shutting the motor off after a hard hot run without allowing it to cool off by letting it idle around for a few minutes, or restarting a hot motor and blasting it with cold water. water does circulate thru the head before the thermostat opens, but when it reaches temp it allows maximum water flow to cool the motor. ive always idled/low rpm for a couple minutes to bring the engines down after a hot run, almost 300 hours between two ski and no cracked heads. remember that the motor drains out when its not running and that head is hot af with nothing in it to absorb the heat. everyone know not to pour cold water into a hot engine
    for me generally, that is the procedure. warm up 3 to 5 minutes, and after ride, idle around for a few minutes after ride before shutting off...never just ride in hard and shut down or just start up and go.


  8. #8
    dcuhpw's Avatar
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    Quote Originally Posted by big john View Post
    IMO the most likely cause is shutting the motor off after a hard hot run without allowing it to cool off by letting it idle around for a few minutes, or restarting a hot motor and blasting it with cold water. water does circulate thru the head before the thermostat opens, but when it reaches temp it allows maximum water flow to cool the motor. ive always idled/low rpm for a couple minutes to bring the engines down after a hot run, almost 300 hours between two ski and no cracked heads. remember that the motor drains out when its not running and that head is hot af with nothing in it to absorb the heat. everyone know not to pour cold water into a hot engine
    YES, I completely agree. Older kawi ultras have the same issue. Interestingly enough, here on Guam were water temps never dip below about 82 there have been no reports of cracked heads from either the Yami or Kawi dealerships (I know the lead techs).

  9. #9
    Is it well known meth injection cools the temps? Of course. Thing is We can all guess at what we think things are doing engine wise but some of us like real data.

    I suspect they have 2 different head castings, they both have a weak spot but one is ever so slightly different then the other. I had 300hrs on one head before it cracked, my second didnt last 20, third one went on late last summer so we'll see.

  10. #10

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    Allowing these motors to idle for three to four minutes prior to shutting them down is a good idea, especially since all the block/head water drains out after the motor is shut down . I always run my ski two to three min. at idle on the trailer prior to putting it in the water also on a cold motor.

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