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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


  4. #4
    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
    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.


  7. #7
    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.

  8. #8
    TimeBandit's Avatar
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    Quote Originally Posted by speeder View Post

    . . . . . .

    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.

    . . . . . .

    any comments/ideas are appreciated!

    I like this theory, and just trying to get my head around it a little better . . .
    While a thermo delete would promote a cooler engine while actively running, I think the risk of thermo-shock on restarts would be in-fact greater without the added restriction of a thermostat even in an open state.

    Most know this already . . . coolant routing begins in the lower exhaust manifold, flows upward, and then has to pass through 4 small port-holes manufactured into the exhaust manifold gasket. This engineering (I’m sure) attempts to mitigate the over-all thermo-shock risks, by tempering the coolant before reaching the head jacket, and to meter the total/max flow rates into the head - regardless of a thermo open or not.

    Next thing to consider (and I don’t know the ratio of NA - vs - SC ski in the wild) is that we see way way more cracked head issues on super-charged platforms, lending to the culprit possibly being more to do with higher combustion stresses/temps in the head.


  9. #9
    Do seadoos with the cc system crack heads?

  10. #10

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    The problems with Yamaha heads cracking, is that just related to the supercharged engines or both, naturally aspirated and supercharged are having problems with their heads?

    Engines that are detonating will tend to overheat, because the boundary layer of gases gets interrupted against the cylinder head and heat gets transferred from the combustion chamber into the cylinder head. This might be from not using the correct octane level.

    You know what's interesting here is, when Honda had a ski on the market it seemed to be problem free for the most part. They did not have a pattern of heads cracking, clutches breaking down and they ran a turbo chargers on their engines, and for the most part was trouble free with that setup. It looked to be a very reliable platform to build on.

    CJ
    Last edited by cjk6119; 02-16-2020 at 05:13 PM.

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